ScienceWeek

SCIENCE-WEEK

A Weekly Email Digest of the News of Science

A journal devoted to the improvement of communication
between the scientific disciplines, and between scientists,
science educators, and science policy makers.

October 15, 1999 -- Vol. 3 Number 42

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What I am going to tell you about is what we teach
our physics students in the third or fourth year of
graduate school... It is my task to convince you
not to turn away because you don't understand it.
You see my physics students don't understand it...
That is because I don't understand it. Nobody does.
-- Richard P. Feynman (1918-1988)

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Contents of This Issue:

1. Postdoctoral Training: Patterns and Problems
2. On the Black Hole at the Center of Our Galaxy
3. Direct Visualization of the Shapes of Electron Orbitals
4. RNA World: RNA-Phospholipid Membrane Interactions
5. Emerging Marine Diseases: Climatic and Anthropogenic Factors
6. Medical Biology: Anthrax as a Biological Weapon

In Focus: On Women in Physics

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1. POSTDOCTORAL TRAINING: PATTERNS AND PROBLEMS
Recent reports in the US have claimed that increasing numbers of
PhD scientists are holding postdoctoral appointments for longer
periods than ever, and concern about the implications for careers
in the life sciences has prompted warnings of overproduction of
PhDs in the life sciences. The last US postdoctoral survey was
published 15 years ago, so that recent comprehensive data
concerning postdoctoral appointees in general has been
unavailable.
... ... M. Nerad and J. Cerny (University of California Berkeley,
US) now report the highlights of a new study (PhDs -- Ten Years
Later [PTYL]), which collected data on the career paths of
scientists and engineers in biochemistry, computer science,
electrical engineering, and mathematics, including the role of
postdoctoral appointments [*Note #1]. The authors make the
following points:
     1) Postdoctoral appointments can have different functions
and meanings, depending on the field and whether the postdoctoral
fellow is a man or a woman. The PTYL study confirmed that in
biochemistry, the postdoctoral fellowship, not the PhD, has
become the general proving ground for excellence both in academia
and industry. Because they spend a longer time in these
"mandatory" postdoctoral positions, biochemists had the largest
proportion of untenured faculty 10 to 13 years after the PhD.
     2) In mathematics, where substantially fewer postdoctoral
positions are available, PhDs taking postdocs are more likely to
obtain faculty positions, but this is true only for men.
     3) The authors suggest university administrators should be
accountable for monitoring the total time spent in these
positions and should provide administrative assistance for skills
training, career growth, and the job search. The authors also
suggest that creative solutions concerning the dual-career couple
phenomenon are necessary.
-----------
M. Nerad and J. Cerny: Postdoctoral patterns, career advancement,
and problems.
(Science 3 Sep 99 285:1533)
QY: Maresi Nerad, 424 Sproul Hall, Berkeley, CA 94720-5900 US.
... ... *Note #1: The national study was conducted by the authors
and involved 6000 PhDs from 6 disciplines: biochemistry, computer
science, electrical engineering, English, mathematics, and
political science. The PhDs were from 61 doctoral-granting
institutions across the US. The survey population accounted for
57 percent of the PhDs awarded at all US institutions in the 6
selected disciplines between 1 July 1982 and 30 June 1985.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
-------------------
Related Background:
ON THE DUAL-CAREER-COUPLE PROBLEM IN PHYSICS
We are in an age of changing or vanishing gender-based divisions
of labor, with more and more women working side by side with men
as professionals in scientific research. One natural consequence
of this is a substantial increase in the number of dual-research
married couples. Since research productivity depends to a large
extent upon specialization, and since the more specialized one's
field of research the less likely a position in that
specialization will be available in any specific geographical
location, there is a chronic employment problem for many dual-
research couples. It is a considerable irony that society can
commit substantial resources to the training of young scientists,
and then have those same scientists unable to work in science
because the commitment of society ends abruptly with their
training. Such problems are not unique to the physics community,
but the problems in that community are currently highlighted and
a cause of particular concern.
... ... L. McNeil and M. Sher (2 installations, US) present a
review of the problem in the physics community, the authors
making the following points:
     1) The authors conducted a survey via several branches of
the American Physical Society, and received responses from 632
individuals who were members of dual-career couples. The purpose
of the survey was to gather data on the extent of the dual-career
problem in physics and consider possible solutions to the
problem. Of the respondent group, 89 percent were physicists
married to other scientists, and 45 percent were physicists
married to other physicists. The authors queried physicists whose
partners are scientists about their experiences in finding
employment and about the kinds of positions they had accepted,
and the published report consists primarily of anecdotal data.
The primary goal of the study was to obtain information about
possible approaches to the problem, and no attempt was made to
use rigorous statistical sampling techniques or sophisticated
quantitative analysis of the responses to the survey.
     2) The authors report that in the 3 decades since 1966, the
percentage of women earning PhDs in physics each year has grown
from approximately 2 percent to approximately 13 percent. At
present, women constitute only 6 percent of US physicists
overall, but they make up approximately 13 percent of all
physicists under the age of 31. Approximately half of all women
physicists are married, compared to 74 percent of all male
physicists.
     3) The authors report that female physicists are far more
likely to be married to physicists and other scientists than are
male physicists. Thus, the dual-career-couple problem has a
disproportionate effect on women. Although statistics are
difficult to obtain, anecdotal evidence suggests that dual-career
employment problems may cause some women to leave physics
altogether.
     4) As possible solutions to the problem, the authors suggest
and discuss split positions, spousal hiring programs, alternative
academic positions, and long-distance commuting.
     5) The authors conclude: "As women represent a growing
fraction of younger physicists, the number of new hires facing
the two-body problem can be expected to increase. It is in the
interests of institutions to take an active role in addressing
these dual-career situations."
-----------
L. McNeil and M. Sher: The dual-career-couple problem.
(Physics Today July 1999)
QY: Laurie McNeil, Dept. of Physics and Astronomy, University of
North Carolina Chapel Hill 919-966-3621
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 30Jul99
-------------------
Related Background:
ON THE OVERPRODUCTION OF US BIOMEDICAL RESEARCHERS
There are always practical problems concerning the training of
scientists, but two persistent questions are How many? and Where
do they work? Marincola and Solomon (2 installations, US), in a
recent editorial in the journal _Science_, review the current
problems in the training of biomedical research scientists (and
propose a solution), but the ideas are perhaps just as applicable
to physics and chemistry. The authors make the following points: 
1) Although the number of biomedical research trainees in the US
has expanded considerably over the past 20 years, the number of
tenured positions is declining. 2) The average time to obtain a
PhD rose from 4.4 years in the 1970s to 5.6 years in the 1990s.
3) Each principal investigator trains many times the single
scientist required to replace himself or herself. This intrinsic
instability could threaten the profession. 4) Many researchers
perceive that science is thriving at increasing and unacceptable
cost to those being trained. In strictly economic terms, it is in
the interest of senior investigators to maintain the number of
trainees, who work long hours in large numbers for little pay
over many years in return for the chance to develop a satisfying
career. 5) A solution may be to uncouple scientific productivity
from an investigator's ability to attract and employ trainees --
the creation of permanent research positions for scientists who
would neither compete for grants nor train others. They would be
supported through investigators who hold traditional academic
appointments. The authors give as an example the institution of
3-year positions for researchers at the Scripps Institute (US).
The essential idea, then, is the amplification of the number of
already existing non-tenure "research associate" positions, these
positions to be filled by PhDs on a continuing short-term
contract basis. The authors state: "This career track could be
recognized explicitly, legitimized, and nourished to become an
element of the research enterprise." The editorial does not
address the question of how this two-tier structure will satisfy
the career objectives of young scientists who are first-rate, but
because of lack of employment opportunities, are forced into the
second tier.
QY: Elizabeth Marincola 
(Science 31 Jul 98 281:64) (Science-Week 28 Aug 98)


2. ON THE BLACK HOLE AT THE CENTER OF OUR GALAXY
Recent observations have led to the conclusion that at the center
of many galaxies there is an object producing effects
characteristic of a supermassive *black hole. Alexei V.
Filippenko (University of California Berkeley, US) reviews
current research on black holes, the author making the following
points concerning the apparent massive black hole at the center
of our own Galaxy:
     1) Some galaxies are known to have very "active" central
regions from which enormous amounts of energy are emitted each
second. These "active galactic nuclei" are probably powered by
accretion of matter into a supermassive black hole of 10^(6) to
10^(9) solar-masses. The center of our own Galaxy exhibits mild
activity, especially at radio wavelengths: so-called "nonthermal
radiation" characteristic of high-energy electrons spiraling in
magnetic fields is emitted by a compact object at the Galactic
center known as *Sagittarius A*. Does the center harbor a
supermassive black hole? One approach is to determine whether
stars in the central region are moving very rapidly, as would be
expected if a large mass were present. During the past 5 years,
two teams have obtained high-resolution images of our Galactic
center, each team on several occasions, so that temporal changes
in the positions of stars could be detected. The observations
were conducted at infrared wavelengths, which penetrate the gas
and dust between Earth and the Galactic center (a distance of
approximately 25,000 light years) much more readily than optical
light. In summary, the data are in excellent agreement with the
conclusion that the gravitational potential of the central region
of our Galaxy is dominated by a single object. The derived mass
of this object is (2.6 +- 0.2) x 10^(6) solar-masses, and the
mass density within a radius of 0.05 light-years is at least 6 x
10^(9) solar-masses per cubic light-year, effectively eliminating
all possibilities other than a black hole.
     2) Although our Galaxy provides the most convincing case for
the existence of supermassive black holes, observations of the
centers of a few other galaxies bolster the conclusion. For
example, very precise measurements of the galaxy NGC 4258 reveal
a central compact object with a derived mass 3.6 x 10^(7) solar-
masses. On somewhat larger scales, spectra obtained with the
Hubble Space Telescope show gas and stars rapidly moving in a
manner consistent with the presence of a supermassive black hole.
The most massive existing case, that of the giant elliptical
galaxy M87, is approximately 3 x 10^(9) solar-masses. Moreover,
x-ray observations of some active galactic nuclei reveal emission
from a hot disk of gas apparently very close to a black hole,
since extreme relativistic effects are detected. In general, it
now seems that a supermassive black hole is found in nearly every
large galaxy amenable to such observations.
     3) The author concludes: "In the last decade of the 20th
century, black holes have moved firmly from the arena of science
fiction to that of science fact. Their existence in some *binary
star systems, and at the centers of massive galaxies, is nearly
irrefutable. They provide marvelous laboratories in which the
strong-field predictions of Einstein's general theory of
relativity can be tested."
-----------
Alexei V. Filippenko: Black holes in the Milky Way galaxy.
(Proc. Natl. Acad. Sci. US 31 Aug 99 96:9993)
QY: Alexei V. Filippenko [alex@astro.berkeley.edu]
-----------
Text Notes:
... ... *black hole: If the terminal stages of star death leave
a remnant star mass greater than 3 solar masses, the ultimate
gravitational collapse will produce a black hole, a relativistic
singularity. A black hole is a localized region of space from
which neither matter nor radiation can escape. The "trapping"
occurs because the requisite escape velocity, which can be
calculated from the relevant equations, exceeds the velocity of
light and is therefore unattainable. Another view of a black hole
is that it is a mass that has collapsed to such a small volume
that its gravity prevents the escape of all radiation. White
... ... *Sagittarius A*: Sagittarius A is a prominent radio
source in the constellation Sagittarius, coincident with or close
to the center of our Galaxy. It is a highly complex region
consisting of a central core approximately 50 light-years in
diameter. Sagittarius A* is a compact component at the heart of
the central core of Sagittarius A. Sagittarius A* is an intense
source of radio waves, and is apparently unique in our Galaxy:
while everything else in our Galaxy is on the move as they follow
their orbits, Sagittarius A* is absolutely stationary and must
therefore lie exactly at the Galaxy's center. Many astronomers,
in fact, use Sagittarius A* as the "Greenwich Meridian" of the
Galaxy.
... ... *binary star systems: Binary stars are a pair of stars
revolving around a common center of mass under the influence of
their mutual gravitational attraction, and apparently the
majority of stars in the Universe are binaries and not singlets.
In some cases the binary system is resolvable into two
components, and in other cases the presence of a second star is
inferred by perturbations in the motion or emitted radiation of
the first star. If the binaries are close enough, they may share
stellar material, and this results in a particular kind of
stellar evolution. In the black hole-binary systems mentioned in
this report, matter transfers from a relatively normal star
(known as the "secondary star") to a dark compact object (the
"primary"). Recent comparisons of x-ray and optical brightness
suggest that in many cases the dark primary in such a binary
system is a black hole.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
-------------------
Related Background:
ASTROPHYSICS: BLACK HOLES AS EMPIRICAL OBJECTS
During the life of a star, two opposing forces control the
star's equilibrium: the gravitational force, which drives the
collapse of the star's mass inward to the center of gravity, and
the counteracting outward pressure derived from the nuclear
fusion reactions in the star's core. When the nuclear fuel burns
out, the star begins its death and gravitational collapse
occurs. If the terminal stages of star death (during which large
amounts of stellar material are blown away) leave a remnant star
mass greater than 3 solar masses, the ultimate gravitational
collapse will produce a black hole, a relativistic singularity.
A black hole is a localized region of space from which neither
matter nor radiation can escape. The "trapping" occurs because
the requisite escape velocity, which can be calculated from the
relevant equations, exceeds the velocity of light and is
therefore unattainable. Another view of a black hole is that it
is a mass that has collapsed to such a small volume that its
gravity prevents the escape of all radiation. Space and time
essentially have no meaning in a black hole. The boundary of the
black hole is called the "event horizon", because any event
within the boundary is invisible outside, the invisibility
resulting from the fact that no radiation can escape to be
detected. The radius of the black hole depends upon how much
matter has fallen into the region; it is called the
"Schwarzchild radius", and it is usually a few kilometers.
However, massive black holes are possible and are thought to be
the source of quasars (quasi-stellar objects), which are
extremely luminous sources radiating energy over the entire
spectrum from x-rays to radio waves, and which are apparently
the oldest and most distant objects in the universe. If quasars
indeed involve black holes, the radiation is from material just
outside the black hole, and not from anything within it. Nothing
inside a black hole can get out of it. Other massive black
holes, closer to us than quasars, are apparently the centers of
galaxies, both *galaxies with active centers and galaxies with
dormant centers.
... ... R.Blandford and N. Gehrels (2 installations, US) present
a review of current research on black holes, with a focus on
observable phenomena. The authors make the following points:
     1) The term "black hole" was introduced in a lecture by John
Wheeler in 1968, and used to describe a new view of gravitational
collapse, a shift in perspective from that of an observer at
infinity, for whom the black hole is a limiting case and never
forms, to a description of a black hole in terms of the fate of
matter falling into it as the matter crosses the event horizon.
     2) Energy is the key to understanding astrophysical black
holes. For the past three decades, it has become well established
theoretically that black holes can be voracious monsters
devouring all that they encounter. Some black holes are extremely
luminous and easily outshine their stellar and galactic
counterparts that rely on nuclear, as opposed to gravitational,
energy for their power. Since the late 1970s, it has been well
understood that black holes are most likely to be detected in
stellar *binary systems of approximately 10 solar-masses (i.e.,
10 times the mass of the Sun, whose mass is approximately 2 x
10^(30) kilograms), and in galactic nuclei with masses of the
order of 10^(6) to 10^(9) solar masses.
     3) The archetype of the stellar black hole is Cygnus X-1, a
powerful x-ray source varying so rapidly that it must be a
compact star. Only 3 types of compact stars are known: *white
dwarfs, *neutron stars, and black holes. But theory indicates
that of compact stars only black holes can have masses greater
than 3 solar-masses. Since application of Kepler's laws to Cygnus
X-1 in 1971 resulted in an estimated mass of 8 solar-masses, this
object was established as a black hole.
     4) For black holes in active galactic nuclei, dynamical
investigations beginning in the late 1970s, established that
galaxies, such as the giant *elliptical galaxy M87 in the Virgo
Cluster, contain central dark masses (3 x 10^(9) solar-masses in
the case of M87) that appeared to be too compact to be a central
cluster of stars. In 1995, M. Miyoshi et al were able to measure
the orbital speed of the gaseous disk around the nucleus of the
nearby spiral galaxy NGC 4258. The authors demonstrated that the
gas speed obeys Kepler's laws, and that the gaseous disk is
warped. Since the calculated mass and size of the central object
are 4 x 10^(7) solar-masses and half a light year, respectively,
the consensus is that the central object is definitely a black
hole.
     5) Concerning our own Galaxy, measurements of motions and
velocities of individual stars in orbit around the center of the
Galaxy indicate the mass of our own black hole has a value of 2.6
x 10^(6) solar-masses.
     6) The authors suggest that at the present time we have 15
mass estimates for black holes in the nuclei of nearby galaxies
that are quite secure. It appears that the majority of nearby
luminous galaxies now contain dormant black holes. However,
during earlier epochs, when the black holes were supplied with
gaseous fuel at a much higher rate, they were able to outshine
their host galaxies, in some cases by factors of thousands. These
ancient objects are the quasars, which we can spot from distances
so large that many of them emitted the light we see now when the
Universe was less than 10 percent of its present age.
     7) In summary, the authors note: "The past five years have
seen a remarkable gain in the sophistication of black hole
observations with telescopes that span the entire electromagnetic
spectrum. No longer is there any serious debate as to whether
black holes exist. We know that they must be quite common, and we
can now study them in increasing detail."
-----------
R. Blandford and N. Gehrels: Revisiting the black hole.
(Physics Today June 1999)
QY: Roger Blandford, Calif. Institute of Technology 818-395-6811.
-----------
Text Notes:
... ... *galaxies with active centers: Active galactic nuclei are
central regions of galaxies in which considerable energy is
apparently generated by processes other than those operating in
ordinary stars. The energy may result from the accretion of
material into a massive black hole situated at the core of the
galaxy.
... ... *binary systems: See notes in main report.
... ... *white dwarfs: White dwarf stars are extremely dense
and compact stars that have undergone gravitational collapse.
They are the final stage in the evolution of low-mass stars after
they have lost their outer layers. White dwarf stars are
approximately the size of Earth, but with a mass approximately
that of the Sun.
... ... *neutron stars: If, following its terminal stages, the
remnant mass of a star is between 1.4 and 2 to 3 solar masses,
the star will collapse into a neutron star, a body with a radius
of 10 to 15 kilometers, with a core so dense that its component
protons and electrons have merged into neutrons.
... ... *elliptical galaxy: In 1925, the astronomer Edwin Hubble
introduced a classification scheme for galaxies that is now
widely used. The scheme has 3 main types of galaxy: elliptical,
spiral, and barred spiral, and each is further divided into
morphological subtypes. Elliptical galaxies are apparently
composed of old stars, contain little dust, are the central
dominant galaxies in rich clusters, and many are powerful sources
of radio wavelength radiation. The size of elliptic galaxies
ranges from dwarf ellipticals [10^(8) stars] to supergiant
ellipticals [10^(13) stars]. Elliptical galaxies are believed to
be a stage in the evolution of galaxies, and different
cosmological models make specific predictions about the number of
elliptical galaxies as a function of redshift. In principle,
therefore, observations of elliptical galaxies can be used to
discriminate between models.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 10Sep99
-------------------
Related Background:
ON THE EXISTENCE OF BLACK HOLES
... ... Jean-Pierre Lasota (Institute of Astrophysics Paris, FR)
presents a review of current studies of apparent black holes and
the evidence for the existence of black holes, the author making
the following points:
     1) To deduce the existence of black holes, astrophysicists
have had to rely on two indirect lines of argument. a) Near
galactic centers, stars are moving so rapidly that they would fly
off unless the gravity of a huge mass -- as large as the
equivalent of a billion Suns -- held them in. Whatever has this
mass must be extremely dense, and there is no known theoretical
alternative to a black hole. b) Many galactic centers and binary
star systems spew radiation and matter at enormous rates, which
suggests they contain an extraordinarily efficient mechanism for
generating energy. Again, in theory, the most efficient engine
possible is a black hole.
     2) The above lines of argument, however, are indirect, a
deduction by default: Such evidence indicates only the existence
of some kind of compact body, but it does not positively identify
black holes based on any of the unique characteristics of black
holes.
     3) A central problem in the study of black holes has been to
discover how to distinguish them from neutron stars. In recent
years, a method has been developed, a method based on x-ray
emissions from the vicinity of each type of body. This method has
allowed the demonstration that black holes are indeed a reality.
The x-ray emissions of x-ray binary systems have been
particularly revealing.
     4) The inferred temperature of the collapsed entity in
certain x-ray binary systems is of the order of 10^(7) degrees
kelvin, which is consistent with that expected for a black hole.
To generate the observed emission, a black hole would need to
swallow 10^(-9) to 10^(-8) solar mass per year -- which agrees
with estimates of how quickly the ordinary star in the binary
system is losing mass to its companion. Thus, certain x-ray
binaries could be the best proof that stellar-mass black holes
exist.
     5) It is known, however, that in many cases the compact
object in the binary systems is not a black hole. Radio pulsars
found in binaries are thought to be rapidly rotating magnetized
neutron stars. Astronomical black holes cannot have magnetic
fields. They are nearly featureless objects and cannot generate
the regular pulses observed in pulsars. Similarly, x-ray pulsars
cannot be black holes. Any regular stable pulsation rules out the
presence of a black hole. Even irregular x-ray bursts entail a
neutron star, which provides a surface on which matter can
accumulate and explode.
     6) Recently, evidence for the existence of black holes has
come from comparison of the brightness of objects exceeding 3
solar-mass with that of objects of less than 3 solar-mass. The
more massive objects are fainter than the less massive objects,
even under conditions where radiation should be emitted at the
same rate. The discrepancy can be explained if matter and energy
are disappearing, which only a black hole could accomplish.
     7) The theoretical modeling of flows into black holes is an
active field of research. Bodies too massive to be neutron stars
can now be moved from the category of black hole candidate to
confirmed black hole. Only an object with an event horizon can
cause energy to disappear in the manner that is inferred for
certain x-ray binary systems.
-----------
Jean-Pierre Lasota: Unmasking black holes.
(Scientific American May 1999)
QY: Jean-Pierre Lasota, Institute of Astrophysics, Paris FR.
-----------
Text Notes:
... ... *Schwarzchild radius: Named after the astronomer Karl
Schwarzchild (1873-1916). In 1916, he demonstrated that in the
general theory of relativity, a sphere of material approximating
to a star, collapsing under its own gravitational field to less
than a certain radius, would cease to radiate energy. The term
"black hole" was apparently first applied to such an object by
John Archibald Wheeler many years later (1968). The Schwarzchild
calculation yielded what is called a "Schwarzchild black hole",
which is a black hole without charge and without angular
momentum. The current consensus is that real black holes have
little or no charge but are almost certainly rotating, and these
black holes are called "Kerr black holes".
... ... *Chandrasekhar limit: Named after Subrahmanyan
Chandrasekhar (1910-1995), who presented the first theoretical
derivation of the limit in 1939. The limit actually ranges from
1.11 to 1.44 solar-mass, depending on the composition and
structure of the star.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 18Jun99
[For more information: http://scienceweek.com/swfr/search.htm]


3. DIRECT VISUALIZATION OF THE SHAPES OF ELECTRON ORBITALS
     It is an old and often repeated adage that the most
important piece of information possessed by the human species is
that everything is made of atoms. Indeed, much of the physical
sciences of the past 200 years has been devoted to providing the
details concerning atoms, and much of the technology of this
period has been devoted to exploiting these details.
     The idea that matter is made of discrete and further
indivisible building blocks goes back to the Greek philosopher
Democritus of the 5th century BC. The joining of this
philosophical idea with the analytical methods of physics began
in the late 18th and early 19th centuries, with John Dalton
beginning the systematic development of the atomic theory. Then,
in 1897, J.J. Thompson clearly demonstrated that atoms are
electromagnetically constituted, and that from atoms can be
extracted fundamental material units bearing electric charge, the
units called "electrons". The electrons of an atom account for
only a negligible fraction of its mass, so that by virtue of the
electrical neutrality of every atom, most of the mass must reside
in a compensating positively charged component -- the atomic
nucleus.
     In the early years of this century, Niels Bohr and others
constructed "solar system models" of atoms containing planetary
point-like electrons orbiting around a positive core, but these
models were ultimately superseded by modern non-particulate wave
quantum theories of both electrons and atomic nuclei. According
to contemporary quantum mechanics, it is not possible to provide
a definite path for an electron. According to wave quantum
mechanics, the electron has a certain probability of being in a
given element of space, and the probabilities of finding
electrons in different regions can be obtained by solving the
Schrodinger wave equation to give the wave function Psi, and the
probability of location per unit volume is then proportional to
the square of the absolute magnitude of Psi. Thus the idea of
electrons in fixed orbits was replaced by that of a probability
distribution around a nucleus -- an atomic orbital. Essentially,
an atomic orbital (electron orbital) can be thought of as an
electric charge distribution averaged over time, and in
representing orbitals it is convenient to describe a surface
enclosing the space in which the electron is likely to be found
with a high probability.
... ... J.M. Zuo et al (4 authors at Arizona State University,
US) now report what is apparently the first experimental
determination of the shapes of electron orbitals. The authors
used a combination of electron and x-ray diffraction to study the
shape and bonding of copper atoms in copper oxide. The authors
point out that their methods can be used to determine bonding in
high-temperature copper oxide superconductors, a satisfactory
theory for which has eluded researchers for more than a decade.
... ... In a commentary on the work of Zuo et al, Colin J.
Humphreys (University of Cambridge, UK) suggests that the paper
by Zuo et al is remarkable because the quality of their charge-
density maps allows, for the first time, a direct experimental
"picture" to be taken of the complex shape of a higher level
orbital (the d(subz)2 orbital), and that the correspondence
between the experimental charge density map of Zuo et al and the
usual textbook diagram of the d(subz)2 orbital is striking.
Humphreys points out that although in crystals x-ray diffraction
can reveal the main peaks of charge density, x-ray diffraction is
normally unable to provide details concerning the shape of the
charge distribution, in particular the shape of the bonds. The
main reason for this is that crystals contain defects such as
dislocations, and the x-ray scattering from such defects is
greater than the scattering from bonding electrons. What Zuo et
al have done is to use an electron microscope to image a crystal,
select a perfect region between crystal defects, and then form a
diffraction pattern from this perfect region. Using this method,
it is possible to make very accurate charge density maps that
reveal the shapes of electron bonds.
-----------
J.M. Zuo et al: Direct observation of d-orbital holes and Cu-Cu
bonding in Cu(sub2)O.
(Nature 2 Sep 99 401:49)
QY: J.M. Zuo [Zuo@asu.edu]
-----------
Colin J. Humphreys: Electrons seen in orbit.
(Nature 2 Sep 99 401:21)
QY: Colin J. Humphreys [cjh1001@hermes.cam.ac.uk]
-------------------
Summary by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
[For more information: http://scienceweek.com/swfr/search.htm]


4. RNA WORLD: RNA-PHOSPHOLIPID MEMBRANE INTERACTIONS
The term "RNA world hypothesis" refers to the concept that RNA
nucleotide sequences possessing catalytic and self-replicating
capabilities predated catalytic protein systems in prebiologic
times. Another assumption of this hypothesis is that RNA was
competent for varied essential functions such as regulation of
membrane permeability. Biological cells communicate with their
environments across phospholipid bilayer membranes that are
relatively permeable to water but virtually impermeable to polar
molecules, and even impermeable to small ions [*Note #1]. In
order for cells to remain viable, their membrane permeability
must be regulated: facilitated transport of certain molecules
through the membrane is required. The RNA world hypothesis
postulates ancestral cells in which RNA played many of the
membrane-regulating roles of modern proteins.
... ... A. Khvorova et al (5 authors at 2 installations, US) now
present a study of the interaction of RNA with phospholipid
membranes, the authors reporting the following:
     1) The authors approached the question of RNA involvement in
membrane permeability by first using "selection-amplification" to
isolate RNAs that bind to pure phospholipid membranes. In this
technique, novel RNA activities are isolated by selecting
infrequent molecules from large pools of RNAs with randomized
sequences. Repetitive selection (i.e., repetitive purification)
is made possible by nucleic acid amplification applied to the
partially purified pools, so that large cumulative purifications
are possible after multiple cycles of selection-amplification.
Ultimately, the technique produces useful amounts of single pure
active RNAs for study.
     2) Secondly, the authors reintroduced purified membrane-
binding RNAs from selection-amplification into several membrane
systems to measure their effects on permeability, a general
methodology already in use for membrane channel proteins.
     3) The authors report their experiments yielded RNAs that
bound *phosphatidylcholine-cholesterol liposomes. At least 8
distinct RNA sequences of approximately 95 residues bound well to
the outside of the lipid bilayer, though randomized sequences had
no such activity. No distinct sequence motif for lipid binding
was found. However, truncation of one such RNA showed that a
smaller 44-nucleotide irregular RNA *hairpin is an active
membrane binding domain. Bound RNA increases the permeability of
liposomes to (sup22)Na(+). In addition, using *voltage clamp
techniques to measure ion currents, 4 individual RNAs increased
the ion permeability of the plasma membrane of cultured human
*epithelial kidney cells.
     4) The authors suggest that the existence of multiple RNA
sequences that bind membranes and provoke membrane permeability
changes indicates that these may be elementary RNA functions that
could be selected in vivo. The authors conclude: "RNAs may
partially insert and perturb both leaflets of the membrane or,
alternatively, may interfere with membrane structure by
interacting with the proximal phospholipid leaflet. Whether these
RNAs have structure or function comparable to transmembrane
proteins or use of a mechanism unique to RNA is unknown and a
matter for further experimentation. Nevertheless, even the
present data suggest that RNA might have functioned as
rudimentary [membrane] channels and taken other membrane roles
during cellularization in an RNA world."
-----------
A. Khvorova et al: RNAs that bind and change the permeability of
phospholipid membranes.
(Proc. Natl. Acad. Sci. US 14 Sep 99 96:10649)
QY: Michael Yarus [yarus@stripe.colorado.edu]
-----------
Text Notes:
... ... *Note #1: For further information on cell membranes, see
SW Focus Reports Biological Cell Membranes 1 and 2 at
[www.scienceweek.com/swfr.htm].
... ... *phosphatidylcholine-cholesterol liposomes: The lipids
phosphatidylcholine and cholesterol are ubiquitous in animal cell
membranes. "Liposomes" are laboratory-created vesicles
(spherules) in which the lipid molecules are spontaneously
arranged into bilayers with hydrophilic groups exposed to water
molecules both outside the vesicle and in the core.
... ... *hairpin: In this context, the term "hairpin" refers to a
turning of a polymer chain, the turning having the shape of
hairpin.
... ... *voltage clamp techniques: In general, a "voltage clamp"
technique is a method, involving an electrical feedback circuit,
for holding the membrane potential across a cell membrane
constant at an arbitrary value while measuring responding trans-
membrane currents. The technique can be used to separate the
total current into various ion currents, and with certain
simplifying assumptions concerning the electrical properties of
the membrane, the changes in ion currents are taken as changes in
ion permeabilities.
... ... *epithelial kidney cells: In animals, "epithelial cells"
compose the cell layers that form the interface between a tissue
and the external environment, for example, the cells of the skin,
the lining of the intestinal tract, and the lung airway passages.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
-------------------
Related Background:
RNA-CATALYZED NUCLEOTIDE SYNTHESIS
In research concerning the origin of life on Earth, the "RNA
world" hypothesis proposes that early life developed by making
use of RNA molecules, rather than proteins, to catalyze the
synthesis of important biological molecules. It is believed,
however, that the nucleotides constituting RNA were scarce on
early Earth, so that RNA-based life must have acquired the
ability to synthesize RNA nucleotides from simpler and more
readily available precursors such as sugars and bases. Apparently
plausible prebiotic synthesis routes have been proposed for
sugars, sugar phosphates, and the 4 RNA bases, but the coupling
of these molecules into nucleotides, specifically pyrimidine
nucleotides, poses a challenge to the RNA world hypothesis.
... ... P.J. Unrau and D.P. Bartel report the application of in
vitro selection to isolate RNA molecules that catalyze the
synthesis of a pyrimidine nucleotide at their *3' terminus. The
authors suggest the finding that RNA can catalyze this type of
reaction, which is modeled after pyrimidine synthesis in
contemporary metabolism, supports the idea of an RNA world that
included nucleotide synthesis and other metabolic pathways
mediated by *ribozymes.
-----------
P.J. Unrau and D.P. Bartel (Massachusetts Institute of
Technology, US): RNA-catalyzed nucleotide synthesis.
(Nature 17 Sep 98 395:260)
QY: David P. Bartel, Mass. Inst. of Technology 617-253-1000.
-----------
Text Notes:
... ... *3' terminus: Both DNA and RNA are polymers whose
constituent nucleotides are linked by 3',5'-phosphodiester bonds,
and the polymers have polarity, with one end a 5'-end unattached
and the other end a 3'-end unattached. This asymmetry is mirrored
in the differing functional involvement of the 2 ends in various
biochemical events in the living cell.
... ... *ribozymes: First discovered in 1981, ribozymes (not to
be confused with riboSOMES) are a small group of RNA molecules 
that act as enzymes. They are found in the ciliate protozoan
Tetrahymena, and they are intriguing because they defy the usual
rule that enzymes are proteins.
-------------------
Summary & Notes by SCIENCE-WEEK  9Oct98
[For more information: http://scienceweek.com/swfr/search.htm]


5. EMERGING MARINE DISEASES: CLIMATIC AND ANTHROPOGENIC FACTORS
Compared to terrestrial life forms, the oceans harbor enormous
biodiversity, much of which is still poorly described. Even less
well known are the dynamics of intermittent, ephemeral, threshold
phenomena such as disease outbreaks. Despite decades of intense
study of the biological agents affecting natural communities, the
ecological and evolutionary impact of diseases in the ocean
remains unknown, even when these diseases affect species which
are economically and ecologically important.
... ... C.D. Harvell et al (13 authors at 13 installations, US
NL) present a review of current research concerning emerging
marine diseases, the authors making the following points:
     1) In the past few decades, there has occurred an apparent
world-wide increase in reports of diseases affecting marine
organisms. In the Caribbean, mass mortalities among plants,
invertebrates, and vertebrates have resulted in dramatic shifts
in community structure. Recent outbreaks of diseases among
*coralline algae have affected Indo-Pacific communities on
unprecedented scales. In the North Atlantic, frequency of mass
mortalities of marine mammals appears to be increasing,
particularly along heavily polluted coastal areas, suggesting
human activity as a factor in disease dynamics.
     2) A marine disease outbreak is favored by changing
environmental conditions that either increase prevalence and
virulence of existing disease or facilitate new disease. Two
conditions -- climate variability and human activity -- appear to
have played roles in epidemics by undermining host resistance and
facilitating pathogen transmission.
     3) Many potentially pathogenic organisms are naturally
active in estuaries and oceans, and some of these pathogens can
persist in dormant, unculturable, but viable states. Human
activity has also added to the pathogen load in the oceans,
primarily through sewage discharges, and storm waters also carry
human and animal wastes.
     4) Fundamental to the understanding of infectious marine
disease is the identification, isolation, and characterization of
the causative agent. This in turn enables the development of
specific diagnostic methods for epidemiological surveys and
specific methods to measure host resistance. Identification of
marine pathogens has until now been difficult because of
ineffective culturing techniques, but recent advances in
molecular biology are providing approaches to the identification
of pathogen species, strains, and life-cycle stages.
     5) In summary, the authors suggest that reports of diseases
in the oceans are on the rise, as illustrated by reports
concerning shellfish, corals, and marine mammals. But epidemics
must also be affecting less apparent species, many of which may
be disappearing without notice.
     6) The authors suggest that most new marine diseases occur
by host shifts and not by the emergence of new microorganisms.
Contributing to the emergence of new marine diseases would be a
long-term warming trend, coupled with extreme *ENSO (El Nino
Southern Oscillation) events and human activities that have
modified marine communities. The inability to identify most
causative agents, and the lack of standard epidemiological data
for diseased populations, limit our ability to examine host-
pathogen interactions.
     7) The authors conclude: "There is an urgent need for
interdisciplinary studies of marine diseases focusing on the 
development of better molecular and computational tools and on
understanding mechanisms of disease resistance in marine
organisms."
-----------
C.D. Harvell et al: Emerging marine diseases -- Climate links and
anthropogenic factors.
(Science 3 Sep 99 285:1505)
QY: C.D. Harvell, Dept. of Ecology and Evolutionary Biology,
Cornell University, Ithaca, NY 14853 US.
-----------
Text Notes:
... ... *coralline algae: The term "coralline algae" refers to
red algae (Rhodophyta) encased in transparent calcium-containing
shells. Coralline algae are colonial, and like coral polyps build
up hard structures that become reefs. In general, "red algae" are
mostly marine, their characteristic color due to certain
photosynthetic pigments.
... ... *ENSO (El Nino Southern Oscillation): The "El Nino
Southern Oscillation" (ENSO) is a shift in the climate and ocean
currents of the Pacific region that occurs approximately once
every 7 years. ENSO is the strongest source of natural
variability in Earth's climate system. Although ENSO originates
in the tropical latitudes of the Pacific Ocean, its climate
impact is felt globally.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
-------------------
Related Background:
MARINE VIRUSES: BIOGEOCHEMICAL AND ECOLOGICAL EFFECTS
Viruses are small particles, usually 20 to 200 nanometers in
their largest dimension, and their unique properties set them
apart from all living creatures. Heterogeneity among viruses is
ensured by their dependence upon a host for replication. Host-
virus interactions tend to be highly specific, and the biologic
range of viruses mirrors the diversity of potential host cells.
Further diversity of viruses is exhibited by their broad array of
strategies for replication and survival. Essentially, a viral
particle consists of a nucleic acid molecule, either DNA or RNA,
enclosed in a protein coat (capsid). The capsid proteins
determine the specificity of interaction of a virus with its host
cell, the capsid both protecting the nucleic acid and
facilitating attachment and penetration of the host cell by the
virus. Once inside the cell, viral nucleic acid redirects the
enzymatic machinery of the host to functions associated with
replication of the virus. In some cases, genetic information from
the virus is incorporated as DNA into the host genome. In other
cases, viral genetic information outside the host genome serves
as a basis for cellular manufacture and release of copies of the
virus. In both cases, complete replication of a virus is a
process which requires replication of viral nucleic acid and
production of specific viral proteins. Maturation consists of the
assembly of newly synthesized nucleic acid and protein subunits
into mature viral particles which are then liberated into the
extracellular environment. In general, there are two types of
viral release from the host cell: in one type the host cell is
destroyed by the process and all the intracellular viral
particles are released at once; in the second type of release,
viral particles are released over several generations,
translocated through the host cell membrane by extrusion or
budding, the continuing translocation and release leaving the
host cell viable. ... ... Jed A. Fuhrman (University of Southern
California, US) presents an extensive review of marine viruses
and their biogeochemical and ecological effects, the author
making the following points:
     1) Viruses are consistently the most abundant biological
entities in the sea -- nearshore and offshore, tropical to polar,
sea surface to sea floor, and in sea ice and sediment pore water.
Viral abundances are typically 10^(10) per liter in surface
waters (approximately 5 to 25 times the bacterial abundance), and
follow the same general location abundance patterns as bacteria.
     2) One of the reasons biological oceanographers first looked
for abundant viruses was a missing sink apparently associated
with excess bacterial production. In the decade since the
discovery of high viral abundance, several lines of evidence have
converged to the conclusion that viruses are significant agents
in both the mortality of aquatic microbes and in the
restructuring of aquatic communities.
     3) Probably the most uncertain aspect of marine viruses is
their role in genetic exchange among microorganisms, and the
effect of this on short term adaptation, population genetics, and
evolution. Direct effects would involve transduction, in which a
virus picks up DNA from one host and transfers it to another
host. The overall effect over large scales of space and time
would be to homogenize genes among the susceptible host
populations. An indirect effect might involve the release of free
DNA from the host organism by viral lysis (destruction of the
host cell upon release of new replicated viruses), with this free
DNA transferred to other organisms through natural
*transformation. Dissolved DNA is in fact readily found in sea
water, and it has been reported that viral lysis may be a major
source mechanism. These two processes, generalized viral
*horizontal gene transfer and transformation, would have the
effect of mixing genes among a broad variety of species, with
wide-ranging effects on adaptation and evolution. The author
suggests these considerations should be included in the
evaluation of the potential spread of genetically engineered
microbial genes, or of the spread of antibiotic resistance
introduced by the use of antibiotics in intensive fish farming.
     4) The author suggests the principal conclusion concerning
marine viruses is that these viruses can exert significant
control on marine bacterial and *phytoplankton communities, with
respect to both biological production and species composition,
influencing the pathways of matter and energy transfer in the
marine system.
     5) The author concludes: "New molecular methods that enable
the diversity of viruses and their hosts to be studied within
their natural habitats will make it easier to unravel the complex
web of interactions in marine communities."
-----------
Jed A. Fuhrman: Marine viruses and their biogeochemical and
ecological effects.
(Nature 10 Jun 99 399:541)
QY: Jed A. Fuhrman [fuhrman@usc.edu]
-----------
Text Notes:
... ... *transformation: Biologists recognize two types of gene
transfer from one organism to another: vertical and horizontal.
Vertical gene transfer occurs between parents and offspring, and
horizontal gene transfer is the transfer that may occur between
organisms otherwise. It is in bacteria that horizontal gene
transfer has been studied most extensively, particularly in the
last decade. Three types of horizontal gene transfer exist:
conjugation, transduction, and transformation. Conjugation is a
type of sexual reproduction exhibited by some bacteria, the
process involving the exchange of genetic material by means of a
tube or bridge, the transfer of DNA occurring either in one
direction or in both directions. Transduction involves the
transfer of genetic material from one bacterium to another with
the intermediation of a virus. Essentially, when the virus
infects one bacterium, it often carries away pieces of that
bacterium's genome, and those pieces, upon the infection of a new
bacterium, become incorporated into another genome. Finally,
transformation is the process involving the uptake or
incorporation of DNA fragments (or plasmids) by a bacterium,
first observed in 1944 by Oswald Avery. Transformation is a
common laboratory technique used in genetic engineering. One
significant aspect of these modes of horizontal bacterial gene
transfer is that in principle they make possible the horizontal
gene transfer of genetic material from genetically engineered
bacteria to other organisms without predictable results. So if
genetically engineered bacteria are to be widely used in
industry, for example, it is of some importance to have a
thorough understanding of the mechanisms in order to limit any
harmful ecosystem transfer effects.
... ... *horizontal gene transfer: See previous note.
... ... *phytoplankton: (photoplankton) Small, usually
microscopic, aquatic plants capable of photosynthesis; e.g.,
unicellular algae. Phytoplankton and plankton are not equivalent.
The term "plankton" is a general designation for various drifting
microscopic aquatic organisms in the upper regions of the oceans,
both photosynthetic and non-photosynthetic.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 25Jun99
-------------------
Related Background:
ON THE CHEMISTRY AND BIOLOGY OF THE OCEANS
The combination of vast areas of liquid water on its surface
together with a high concentration of free molecular oxygen in
its atmosphere is unique to Earth in this solar system.
Calculations based on *ultraviolet absorption cross sections
indicate that whereas direct photolysis of water could have
produced small amounts of O(sub2), almost all of the gas was
produced by biological systems through the photobiologically
catalyzed oxidation of the liquid. ... ... Falkowski et al (3
authors at 3 installations, US DE) review the controls and
feedbacks between oceanic *phytoplankton and geochemical
processes with an emphasis on factors that cause a deviation from
the steady state. The authors make the following points: 1)
Changes in oceanic primary production, linked to changes in the
network of global biogeochemical cycles, have profoundly
influenced the geochemistry of Earth for over 3 billion years. 2)
In the contemporary ocean, photosynthetic *carbon fixation by
marine phytoplankton leads to the formation of approximately 45
gigatons of organic carbon per year, of which 16 gigatons are
exported to the ocean interior. 3) Changes in the magnitude of
total and export production can strongly influence atmospheric
CO(sub2) levels (and hence climate) on geological time scales, as
well as set upper bounds for sustainable fisheries harvest. 4)
Because the average turnover time of phytoplankton carbon in the
ocean is on the order of a week or less, total and export
production are extremely sensitive to external forcing, and
consequently are seldom in steady state. 5) Elucidating the
biogeochemical controls and feedbacks on primary production is
essential to understanding how oceanic biota responded to and
affected natural climate variability in the geological past, and
to understanding how oceanic biota will respond in the coming
decades to changes influenced by human activities.
QY: Paul G. Falkowski 
(Science 10 Jul 98 281:200) (Science-Week 31 Jul 98)
-------------------
Related Background:
... ... *ultraviolet absorption cross sections: The ratios of the
amount of energy removed from incident UV by absorption to the
total energy of incident UV. In other words, in this context, a
measure of how much energy is (was) actually available for direct
photolysis of liquid water.
... ... *phytoplankton: Also called photoplankton. Small, usually
microscopic, aquatic plants capable of photosynthesis; e.g.,
unicellular algae. Phytoplankton and plankton are not equivalent.
The term "plankton" is a general designation for various drifting
microscopic aquatic organisms in the upper regions of the oceans,
both photosynthetic and non-photosynthetic.
... ... *carbon fixation: Refers to the process of converting the
carbon in a substance into a form usable by an organism. For
example, the conversion of the carbon in CO(sub2) into organic
carbon (the carbon in organic compounds).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 31Jul98
[For more information: http://scienceweek.com/swfr/search.htm]


6. MEDICAL BIOLOGY: ANTHRAX AS A BIOLOGICAL WEAPON
The term "bacillus" (plural: bacilli) is derived from the Latin
word _bacillus_, literally meaning "a stick". Bacilli are rod-
shaped bacteria that come in a variety of forms, some relatively
short and fat, others long and slender. Often the end of the cell
is swollen to accommodate its *spore (endospore). Many bacilli
arrange themselves into specific metaforms. Bacillus anthraci,
the causative agent of anthrax, grows long chains of cells
aligned along the long axis of the cell. The typical anthrax cell
measures 1 x 3 to 4 microns, has square ends, and an endospore
located in the center of the cell. Although anthrax is not a
common disease, it has recently been much in the news because of
its potential use as a biological weapon. 
... ... T.C. Dixon et al (4 authors at 4 installations, US)
present an extensive review of the biological and medical aspects
of anthrax, the authors making the following points:
     1) Anthrax is an often fatal bacterial infection that occurs
when Bacillus anthracis endospores enter the body through
abrasions in the skin or by inhalation or ingestion. The disease
is a "*zoonosis" to which most mammals, especially grazing
*herbivores, are considered susceptible. B. anthracis is a *gram-
positive soil organism. Anthrax endospores do not divide, have no
measurable metabolism, and are resistant to drying, heat,
ultraviolet light, gamma radiation, and many disinfectants. In
some types of soil, anthrax spores can remain dormant for
decades. Their hardiness and dormancy have allowed anthrax spores
to be developed as biological weapons by a number of nations,
although their only known use in war was by the Japanese army in
Manchuria in the 1940s.
     2) The virulence of B. anthracis is essentially caused by
the secretion by the bacterium of two toxins: a) a toxin which
causes *edema (edema factor), and which has been identified as a
*calmodulin-dependent adenylate cyclase; b) a lethal toxin
(lethal factor), which is a *zinc metalloprotease that
inactivates *mitogen-activated protein kinases in vitro. The
lethal anthrax toxin stimulates *macrophages to release certain
entities (*tumor necrosis factor alpha and *interleukin-1beta)
which are partly responsible for sudden death in systemic
anthrax.
     3) Human anthrax infections result from contact with
contaminated animals or animal products, and there are no known
cases of human-to-human transmission. Human anthrax is not
common. Cutaneous anthrax, the usual human form, is ordinarily
curable. However, a small percentage of cutaneous infections
become systemic, and these infections can be fatal. Systemic
infection resulting from inhalation of the organism has a
mortality rate approaching 100 percent, with death usually
occurring within a few days after the onset of symptoms. The
mortality rate among persons with infections resulting from
ingestion is variable, depending on the outbreak, but it may also
approach 100 percent. Whatever the portal of entry, systemic
anthrax involves massive *bacteremia and *toxemia with
nondescript initial symptoms until the onset of *hypotension,
*shock, and sudden death. In the terminal stage of systemic
anthrax, the number of organisms per milliliter of blood is of
the order of 10^(7) to 10^(8).
     4) The authors conclude: "Recent revelations regarding the
development of anthrax weapons by the former Soviet Union and by
Iraq, and of attempts to develop such weapons by the Aum
Shinrikyo cult in Japan, make the potential use of B. anthracis
in biological terrorism a legitimate concern. New strains
resistant to antibiotics or containing additional virulence
factors could be misused with the intent of confounding treatment
or prophylaxis. Whether our medical system would be able to
provide appropriate prophylaxis and therapy in the event of a
large-scale exposure to pathogenic endospores remains uncertain,
even doubtful. It has now become relevant for physicians to re-
familiarize themselves with clinical anthrax."
-----------
T.C. Dixon et al: Anthrax.
(New England J. Med. 9 Sep 99 341:815)
QY: Terry C. Dixon [dixont@umich.edu]
-----------
Text Notes:
... ... *spore: Only certain bacterial species form spores,
which are specialized cell structures that may allow survival in
extreme environments. In general, under conditions of nutritional
depletion, each bacterium forms a single internal spore
(endospore) that is liberated when the mother cell undergoes
destruction (autolysis). The spore is a resting system, highly
resistant to desiccation, heat, and chemical agents; when
returned to favorable nutritional conditions and activated, the
spore germinates to produce a single bacterium.
... ... *zoonosis: In general, the term "zoonosis" refers to a
disease of humans acquired from an animal source.
... ... *herbivores: In general, a "herbivore" is an animal that
eats plant material as a main or sole food source.
... ... *gram-positive: Most bacteria can be classified
into two types, depending on the chemistry of their outer coat,
which chemistry determines whether a bacterium will admit certain
dyes into the interior. The classification, according to the
differential staining technique, is gram-negative vs.
gram-positive, named after the bacteriologist H.C. Gram
(1853-1938). Gram-positive bacteria take up a crystal violet
stain and turn purple, while gram-negative bacteria exclude the
crystal violet and counterstain instead with stains such as
safranin, eosin red, or brilliant green. As might be expected,
since the technique differentiates the outer coats of bacteria,
some antibiotics are effective against one type and not the other
type, and vice versa.
... ... *edema: In general, an accumulation of an excessive
amount of watery fluid in cells and tissues.
... ... *calmodulin-dependent adenylate cyclase: Calmodulin is a
Ca(2+) binding protein that mediates many of the regulatory
effects of calcium ions in eukaryotic cells (cells with nuclei).
Adenylate cyclase (adenylyl cyclase) is an enzyme that catalyzes
the production of cyclic AMP from ATP. Adenosine triphosphate
(ATP) is the most important chemical energy source in all living
cells, intimately involved in various cell functions and cell
metabolism, and an entity in numerous cyclic chemical pathways
involved in the synthesis of components. One of the reaction
products of ATP is cyclic AMP, which acts as an intracellular
hormone responding to signals from extracellular hormones (i.e.,
an intracellular chemical messenger: thus the
name "second messenger" for cAMP).
... ... *zinc metalloprotease: A metalloprotease is a proteolytic
enzyme that requires the presence of a metal ion as a cofactor
for its catalytic activity. In general, "proteolysis" is the
enzyme-catalyzed degradation of protein by hydrolysis of one or
more peptide bonds.
... ... *mitogen-activated protein kinases: A family of protein
kinases that perform a crucial step in relaying signals from the
plasma membrane to the cell nucleus. They are activated by a wide
range of proliferation- or differentiation-inducing signals. (A
"mitogen" is any compound that stimulates mitotic cell division.)
... ... *macrophages: Macrophages are amoeba-like leukocytes
("white blood cells" of the immune system) that are able to
surround and digest foreign entities such as bacteria and
protozoa.
... ... *tumor necrosis factor alpha: A *cytokine produced by
various types of cells, mediating the expression of a variety of
genes, and capable of causing *cytolysis of certain tumor cell
lines.
... ... *cytokine: A cytokine is any substance that promotes cell
growth and cell division. Certain cytokines are endogenous, and
need to be controlled by cell regulatory mechanisms. When these
mechanisms fail, endogenous cytokines may be implicated in
serious human diseases such as rheumatoid arthritis, where
apparently deregulated cytokines cause the inflammatory response
that produces the symptoms. As a promoter of cell growth and
division, a cytokine acts as a messenger to cells, and the
transmission of the message requires a binding of the cytokine
molecule to a cytokine-specific receptor on the cell surface.
This receptor is either a protein or a protein complex or a part
of a protein.
... ... *cytolysis: In general, the breakdown of cells,
especially by destruction of their outer membranes.
... ... *interleukin-1beta:  The interleukins (lymphokines) are
hormones secreted by certain antigen-processing cells of the
immune system, the hormones causing immune cells specific for the
antigen to proliferate. An "antigen" is any chemical entity that
activates an immune response, especially an entity originating
outside the body.
... ... *bacteremia: In general, "bacteremia" is the presence of
viable bacteria in the circulating blood.
... ... *toxemia: In general, a clinical syndrome caused by a
toxic substance in the blood.
... ... *hypotension: Subnormal arterial blood pressure.
... ... *shock: In this context, "shock" is a profound depression
of bodily functions following severe traumatic injury (in this
case, severe toxemia).
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 15Oct99
-------------------
Related Background:
ON BIOLOGICAL TERRORISM
Although political events during the past decade have reduced
fears of biological warfare among the major powers, the pathogens
likely to be used in such warfare have not vanished, and there is
now an apparent growing concern about the use of such pathogens
in acts of biological terrorism ("bioterrorism").
... ... Donald A. Henderson (Johns Hopkins University, US)
presents a review of current views, expectations, and contingency
plans, the author making the following points concerning the
scientific fundamentals: 1) The expected scenario following
release of an aerosol cloud of a biological agent is entirely
different from that following an attack of nuclear or chemical
terrorism. A biological agent aerosol release could be silent and
would almost certainly be undetected. The cloud would be
invisible, odorless, and tasteless. It would behave much like a
gas in penetrating interior areas, and the release would not be
suspected for days or weeks later. 2) The implicit assumption has
frequently been that chemical and biological threats and the
responses to them are so generically similar that they can be
readily handled by a single "chembio" expert, usually a chemist.
This is a serious misapprehension. 3) Any of thousands of
biological agents that are capable of causing human infection
could be considered a potential biological weapon, but
realistically only a few pose serious problems. Only a very small
number of species of these pathogens can be cultivated and
dispersed effectively so as to cause cases and deaths in numbers
that would threaten the functioning of a large community. The
current consensus is that there are 11 pathogens "very likely to
be used." *Smallpox, *plague, *anthrax, and *botulism are
considered the top four candidates. The others are *tularemia,
*glanders, *typhus, *Q fever, *Venezuelan equine encephalitis,
*Marburg virus, and *influenza virus. 4) Any group with
sufficient resources could purchase prepared supplies of
aerosolizable organisms and could transport them easily, because
only small quantities are needed to inflict casualties over a
wide area. No mechanisms currently exist for screening to
intercept such materials at state or national borders. 5) Of the
potential biological weapons, smallpox and anthrax pose by far
the greatest threats, but these pathogens have different clinical
and epidemiological properties. Smallpox poses an unusually
serious threat, in part because virtually everyone is now
susceptible, vaccination having stopped worldwide 20 or more
years ago as a result of the eradication of the disease. It is
probable that no more than 20 percent of the world population is
protected; for the unprotected, fatality rates after infection
are 30 percent. Another problem is that there are no longer any
manufacturers of smallpox vaccine, which means large-scale
vaccination immediately after an outbreak is currently not
possible. 6) Concerning an inhalation anthrax epidemic, the
scenario is as dangerous as that for smallpox. After 2 to 3 days
anthrax-infected individuals would appear in emergency rooms and
doctors' offices with a variety of nonspecific symptoms such as
fever, cough, and headache. Within a day or two, patients would
become critically ill and then die within 24 to 72 hours. The
fatality rate for anthrax is 80 percent or greater. 7) The author
concludes: "Once the medical community rallied... in educating
peoples and policymakers everywhere about the dread realities of
a nuclear winter. Perhaps the same should now be done with
respect to the realities of biological weapons, which are now
considered to be a more serious threat than the nuclear ones."
-----------
Donald A. Henderson: The looming threat of bioterrorism.
(Science 26 Feb 99 283:1279)
QY: Donald A. Henderson, Johns Hopkins Center for Civilian
Biodefense Studies, Johns Hopkins Univ., Baltimore, MD 21202 US.
-----------
Text Notes:
... ... *Smallpox: This is an acute eruptive contagious disease
caused by a poxvirus (Orthopoxvirus, a member of the family
Poxviridae). The average incubation period is 8 to 14 days.
Following the incubation period, the onset symptoms are
constitutional: chills, high fever, backache, headache. In from 2
to 5 days, these symptoms subside and the skin eruptions appear.
Considering the temporal course of the disease, a smallpox
epidemic would probably not become evident until 2 to 3 weeks
after release of an aerosol.
... ... *plague: In this context, this term refers to the acute
infectious disease caused by the bacterium Yersinia pestis, the
disease marked by high fever, toxemia, and prostration. The
pathogen is usually transmitted to man by fleas that have bitten
infected rodents, and there are various forms of the disease. The
incubation period is 2 to 7 days. The fatality rate is near 50
percent, with usually 100 percent fatality for the pneumonic form
of the disease.
... ... *anthrax: This disease is caused by the bacterium
Bacillus anthracis, and is usually transmitted by infected
animals through traumatized human skin. The disease is marked by
hemorrhage and blood effusions in various organs and body
cavities, and by symptoms of extreme prostration. In the context
of this report, the disease entity of concern is "inhalation
anthrax", which is a more serious human disease than anthrax
contracted from an animal through the skin. Inhalation anthrax
produces hemorrhagic pneumonia with shock and is usually fatal
(fatality above 80 percent).
... ... *botulism: This disease is caused by toxins of the
bacterium Clostridium botulinum, an organism common in soil and
sometimes in animal feces. Symptoms appear 18 to 24 hours after
entry of the toxins, and the most severe symptoms are the result
of effects on the neuromuscular system. Death occurs from
respiratory paralysis or cardiac arrest. The fatality rate is
high. Ordinarily, botulism is not an actual human infection,
since the human disease is almost always caused by ingestion of
food contaminated with toxins produced by C. botulinum, which is
anaerobic and grows only under conditions of low or absent oxygen
(e.g., in canned foods). The botulinum toxins are among the most
highly toxic substances known: the lethal dose for a human is
estimated to be in the range 1 to 2 micrograms.
... ... *tularemia: This disease is caused by the bacterium
Francisella tularensis, a pathogen usually transmitted to humans
by biting arthropods (e.g., insects), direct contact with
infected animal tissue, ingestion of contaminated food or water,
and inhalation of aerosols. Apparently, inhalation of only 50
individual F. tularensis bacteria can result in infection.
Symptoms appear within a week. The disease can usually be
controlled with antibiotics.
... ... *glanders: A common disease of horses, mules, and
donkeys, caused by the bacterium Burkholderia mallei. The
inhalation form of the disease may lead to primary pneumonia.
The disease can usually be controlled with antibiotics.
... ... *typhus: A group of acute infectious and contagious
diseases caused by the bacterial group Rickettsaie. These
diseases are characterized by fever, headache, malaise, and
prostration.
... ... *Q fever: Also caused by a Rickettsaie bacterium, but the
symptoms resemble influenza, nonbacterial pneumonia, hepatitis,
or encephalopathy.
... ... *Venezuelan equine encephalitis: This is a viral disease
usually transmitted by mosquitoes from horses to humans. It is
caused by a togavirus, subgroup alphavirus. In humans, the
symptoms are similar to those of influenza.
... ... *Marburg virus: One of the two notorious African
Hemorrhagic Fevers (the other is Ebola virus), highly virulent,
with infections usually ending in death. These viruses have the
highest mortality rate (as much as 90 percent) of all the viral
hemorrhagic fevers. The disease was first recognized in 1967.
... ... *influenza virus: Any of a group of influenza viruses,
all of the family Orthomyxoviridae. The influenza diseases
usually have a sudden onset, are highly contagious, and easily
produce large-scale epidemics. Apparently, if only a few cells of
the respiratory *epithelium are infected by deposited virus
particles, the infection can proceed. The severity of symptoms
and the outcome depends on which strain of the virus is the
pathogen.
... ... *epithelium: In animals and humans, epithelial cells
compose the cell layers that form the interface between a tissue
and the external environment, for example, the cells of the skin,
the lining of the intestinal tract, and the lung airway passages.
-------------------
Summary & Notes by SCIENCE-WEEK [http://scienceweek.com] 21May99


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IN FOCUS: ON WOMEN IN PHYSICS
"Forty-nine years old; strong-featured face, brooding eyes, a
mass of dark sexy hair she tosses about like a forties movie
vamp, the walk seductive and knowing, the mouth sullen and
grievance-collecting in repose, then surprisingly girlish in
laughter when the eyes fill with a sudden shimmering light. Alma
Norovsky is a theoretical physicist at a university renowned for
its devotion to the life of the mind. Of her colleagues, Alma
says drily: 'They're very theoretical. People are always asking
me how women are treated here. "Women?" I answer. "They're a
theoretical concept."'... Divorced four years from the physicist
husband she married in graduate school, on her own for the first
time in her life, in love with her new independence and happy to
be working here, Alma nevertheless sighs. 'How do you work in
physics, or live among academic liberal men, and not explode all
day long every day? Once in a while I'm able to control myself...
Last year at a conference I was standing with a group of
physicists, all men, and I was introduced to a new member of the
group. He said, "You're the first good-looking physicist I've
ever met." I casually indicated the man standing beside me and
said, "Oh, that's not true. You know Richard here. He's good-
looking, and he's a physicist." They all looked startled, and
then some of them nodded their heads appreciatively. I was proud
of myself then, but usually it's awful. Still. Always. At every
dinner table, in the office, the constant little indications that
you don't really exist. You've got to remind them that you're a
thinking, working being just like themselves all the time. It's
wearing.'"
-----------
Vivian Gornick: _Women in Science: Portraits from a World in
Transition_. (Simon & Schuster, New York 1983)


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