EXPOSE is a multi-user facility to be mounted outside of the
International Space Station (ISS). The tray-like structure will
accomodate among others 6 biological PI-experiments or experiment
systems of the ROSE (Responses of Organisms to the Space Environment)
consortium. EXPOSE will support long-term in situ studies of microbes in
artificial meteorites, as well as of microbial communities from special
ecological niches, such as endolithic and evaporitic ecosystems. Each
compartment is either vented, i.e. open to space vacuum, or sealed and
then provided with a defined gas environment. The experiment pockets
will be covered by an optical filter system to control intensity and
spectral range of solar UV irradiation. To achieve maximum insolation,
EXPOSE is mounted on a coarse pointing device. Control of sun exposure
will be achieved by use of shutters. EXPOSE has been selected for the
Early Utilisation Period of the ISS and will stay in space for 1.5
years. The results will contribute to our understanding of
photobiological processes in simulated radiation climates of planets
(e.g. early Earth, early and present Mars, and the role of the ozone
layer in protecting the biosphere from harmful UV-B radiation), as well
as studies of the probabilities and limitations for life to be
distributed beyond its planet of origin.
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[Show abstract][Hide abstract] ABSTRACT: The responses of microorganisms (viruses, bacterial cells, bacterial and fungal spores, and lichens) to selected factors of space (microgravity, galactic cosmic radiation, solar UV radiation, and space vacuum) were determined in space and laboratory simulation experiments. In general, microorganisms tend to thrive in the space flight environment in terms of enhanced growth parameters and a demonstrated ability to proliferate in the presence of normally inhibitory levels of antibiotics. The mechanisms responsible for the observed biological responses, however, are not yet fully understood. A hypothesized interaction of microgravity with radiation-induced DNA repair processes was experimentally refuted. The survival of microorganisms in outer space was investigated to tackle questions on the upper boundary of the biosphere and on the likelihood of interplanetary transport of microorganisms. It was found that extraterrestrial solar UV radiation was the most deleterious factor of space. Among all organisms tested, only lichens (Rhizocarpon geographicum and Xanthoria elegans) maintained full viability after 2 weeks in outer space, whereas all other test systems were inactivated by orders of magnitude. Using optical filters and spores of Bacillus subtilis as a biological UV dosimeter, it was found that the current ozone layer reduces the biological effectiveness of solar UV by 3 orders of magnitude. If shielded against solar UV, spores of B. subtilis were capable of surviving in space for up to 6 years, especially if embedded in clay or meteorite powder (artificial meteorites). The data support the likelihood of interplanetary transfer of microorganisms within meteorites, the so-called lithopanspermia hypothesis.