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LIFE SCIENCES
George Zhongji Zou, B.S. in physics, Fudan University, Shanghai, China, and M.S.,
Sam Houston State, studies techniques for measuring and testing superconducting devices.
Here he connects computers to electrical feed through an electromagnetic shielded
enclosure. |
George E. Fox, Ph.D., Department of Biochemical and Biophysical Sciences
In support of long-duration space missions, NASA is exploring means of cultivating
plants in space, including the surface of the moon. This might be done in either
hydroponics systems or directly in the lunar soil. It is of some concern that bacterial
plant pathogens might damage the crops. It therefore would be of interest to monitor the
systems for specific kinds of bacteria. It has been previously shown that ribosomal RNAÕs
(rRNAÕs) and their corresponding genes (rDNAÕs) make excellent monitoring targets. The
purpose of the experimental work conducted during this period was to determine if it would
be feasible to recover rDNA (or rRNA) simulated lunar soils and to identify the organisms
present by probe techniques. In order to do this, a sample of simulated lunar soil was
obtained from Dr. Donald Henninger at NASAÕs Johnson Space Center. Samples of three known
bacteria, Gluconobacter oxydans (ATCC 621), Acetobacter aceti (ATCC 15973), and
Flavobacter aceti (ATCC 108 whose 16S rRNA sequences had been determined previously were
added to samples of the simulated soil individually and in mixtures and incubated in the
presence of added nutrients. DNA was extracted from the samples including controls that
contained no added bacteria. Critical information sought in these first experiments was to
determine: (a) whether normal extraction procedures would be appropriate with this
simulated soil and (b) whether the unused simulated soil had a substantial indigenous
population of microorganisms.
In both the single organism culture and the mixed organism culture, DNA purification
yielded DNA, whereas the control purification yielded no detectable product. The same held
true for PCR amplification: the control yielded no PCR product, whereas the single and
mixed organism genomic DNA purification solutions yielded PCR product. The only organism
detected in the single organism experiment was F. devorans, the organism initially placed
into the culture tube. The mixed culture samples revealed only the sequence for G.
oxydans. It is likely that sequencing of numerous clones would reveal the presence of the
other two organisms as well. Clearly the result points up the fact that one organism can
rapidly out-compete others in a mixed culture system. Identification will have to look for
pathogens in relatively low numbers, hence better done with probes that simultaneously
examine the whole population.
These initial results establish the key point that standard DNA extraction procedures
are not hindered by the presence of the basalt rock. This means that organisms present in
the rock may be isolated, their DNA purified, the genomic DNA subjected to PCR, the PCR
products cloned, the clones individually sequenced or more likely probed as a group, and
the organisms present identified by comparison to known 16S rRNA gene sequences. Under
conditions of these experiments, there were no problems with background interferences from
organisms that may have been present on the basalt rock prior to the experiment.
A reasonable next step would be to examine a simulated lunar soil sample that has been
used for an extended period of time by PCR amplification of rDNA to determine if a
significant microbial ecosystem has developed. If rDNA is readily amplified, a number of
clones will be sequenced in order to determine at the genus level what the major members
of the community are. With this information in hand, probes will be designed to monitor
the relative amounts of various categories of organisms, e.g., nitrogen fixing bacteria.
The results of the initial probe will allow researchers to establish design parameters.
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Periklis Y. Ktonas, Ph.D. Department of Electrical Engineering
Isso has provided two years of funding for this effort to develop a state-of-the-art
proposal to NASA for recording during space flight, as well as on earth, and off-line
analysis of detailed rapid eye movement, heart rate, and respiration patterns during the
sleep of astronauts. These patterns will be analyzed to determine the possible effect of
microgravity on human sleep physiology. The analysis will also attempt to quantify the
degree and severity of space motion sickness and will investigate the development of
screening methodologies for the selection of astronauts who would be affected the least by
microgravity.
During the tenure of this project, ISSO researchers investigated the possibility of
recording similar data at the Sleep Laboratory of The Methodist Hospital in Houston,
Texas, in order to assess the possible effect of head position (and, indirectly, of
gravity) on these patterns in a one-g environment. New statistical procedures were
developed for the automated analysis of the rapid eye movement patterns, and. Researchers
investigated in detail the accuracy of the automated detection method to be used to obtain
these patterns. Finally, researchers obtained up-to-date literature on sleep patterns in
space and located research groups in the greater Houston area working on similar topics.
At present, researchers are finalizing the quantification methodologies to be used for
the analysis of the biosignals. They are also finalizing neurophysiology-based model of
microgravity's influence on sleep rapid eye movement patterns based on animal (monkey)
space flight data.
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Lawrence S. Pinsky, Ph.D., Department of Physics
The radiation dose received by crews on space missions is not just another nuisance
type problem that needs only to be estimated and tabulated. In planning for longer
duration missions, it is one of the major limiting factors and must be a baseline
consideration in the design of any vehicle/mission combination where planners anticipate
either very long durations or exposure outside the geomagnetic environment.
In attempting to model the complex problem of crew radiation exposure during space
flight, various investigators have, in past studies, chosen different techniques.
Arguments have been made for both one-dimensional transport (shielding) calculations and
full three-dimensional geometric reconstructions. Both Monte Carlo techniques and
pseudo-analytic types of calculations have been employed. In all of these efforts, cross
sections for various reactions had to be assembled from sparse data and filled in with
model-dependent calculations. The focus of interest in the past has tended toward the
propagation of nucleons (including nuclear fragments) and their energy loss.
ISSO researchers base their effort on a plan to employ the GEANT Monte Carlo code,
which will add to accounts the cornucopia of other high energy particles produced. In
addition, the GEANT Monte Carlo code is a full three-dimensional calculation that will be
able to use standard CAD formats as an input for spacecraft geometries. Finally, the scope
of the effort is directed toward the development of a versatile code with easily updated
cross-section databases. The intent of the research is not to offer a new version of
reaction cross sections, but, rather, to offer a more precise platform for the comparison
of effects of variations in these values and in spacecraft materials and geometries.
Ultimately, the goal is to produce a reliable platform to aid engineers and scientists in
the prediction of doses for future spacecraft and missions.
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Richard Willson, Ph.D., Department of Chemical Engineering
Interest has developed in applying DNA probes to the act of monitoring microbial
populations in spacecraft living quarters and life support systems. Particularly in
long-duration operations, the reliability and even healthfulness of these systems may be
adversely affected by microbial proliferation during long periods of operation with
minimal maintenance. Traditional microbiological monitoring methods are generally too
non-specific and/or too unwieldy to be taken on long duration missions. Fortunately,
recent breakthroughs in DNA probe monitoring using ribosomal RNA (rRNA) sequence
characterization have made diagnostic tests based on DNA probes commonplace in the
biomedical field, and it is likely that they will be applicable to spacecraft
environmental monitoring.
Most current DNA probe assays are based on the use of methods (e.g., radioactive
isotope labels) impractical for use outside the laboratory. ISSO researchers are exploring
detection methods more suitable for implementation in the spacecraft environment. These
methods include the use of fluorescent and chemiluminescent probe labels, in some cases
amplified by the use of an enzymatic reporter system. A successful collaboration with Dr.
James Chambers of UT San Antonio is continuing, in which investigators have demonstrated
for the first time that two advanced analytical methods, surface-selective fluorometry and
the Light-Addressable Potentiometric Sensor (LAPS) can be used to quantitate DNA probe
hybridization in a competitive assay format. Competition in this system is highly
specific, and is unaffected by the presence of non-homologous genomic DNA. A manuscript on
this work has been accepted for publication.
ISSO researchers believe that this research can lead to the development of DNA probe
assay methods suitable for monitoring the microbiological environment in spacecraft.
Contents
ISSO -- Institute for Space Systems Operations
1992-1993 Annual Report
