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about 8 % of MW01 spores survived, and 100 % survived in simulated Martian
conditions, compared to the laboratory controls.
PROTECT Experiment
Spore-forming bacteria are of particular concern in the context of planetary protec-
tion because their tough endospores may withstand certain sterilization procedures
as well as the harsh environments of outer space or planetary surfaces. To test their
hardiness on a hypothetical mission to Mars, spores of
Bacillus subtilis
168 and
Bacillus pumilus
SAFR-032 were exposed for 1.5 years to selected parameters of
space. It was clearly shown that solar extraterrestrial UV radiation (
110 nm)
as well as the Martian UV spectrum (
200 nm) was the most deleterious factor
applied; in some samples, only a few survivors were recovered from spores exposed
in monolayers.
Spores in multilayers survived better by several orders of magnitude. All other
environmental parameters encountered did little harm to the spores, which showed
about 50 % survival or more. The data demonstrate the high chance of survival of
spores on a Mars mission, if protected against solar irradiation. These results will
have implications for planetary protection considerations.
The mutagenic efficiency of space was also studied in spores of
Bacillus subtilis
168. The data show the unique mutagenic power of space and Martian surface
conditions as a consequence of DNA injuries induced by solar UV radiation and
space vacuum or the low pressure of Mars. Spores exposed to space demonstrated
a much broader and more severe stress response than spores exposed to simulated
Martian conditions.
A comparative protein analysis (proteomics) of
Bacillus pumilus
SAFR-032
spores indicated that proteins conferring resistant traits (superoxide dismutase) were
present in higher concentration in space-exposed spores when compared to controls.
Also, the first-generation cells and spores derived from space-exposed samples
exhibited elevated ultraviolet C resistance when compared with their ground control
counterparts. The data generated are important for calculating the probability and
mechanisms of microbial survival in space conditions and assessing microbial
contaminants as risks for forward contamination and in situ life detection.
LiFE Experiment
After 1.5 years in space, samples were retrieved, rehydrated, and spread on different
culture media. The only two organisms able to grow were isolated from a sample
exposed to simulated Mars conditions beneath a 0.1 % T Suprasil neutral density
filter and from a sample exposed to space vacuum without solar radiation exposure,
respectively. The two surviving organisms were identified as
Stichococcus
sp
.
(green
algae) and
Acarospora glaucocarpa
sp
.
(lichened fungal genus). According to the
researchers, the studies provide experimental information on the possibility of
eukaryotic life transfer from one planet to another by means of rocks and of survival
in Mars' environment.
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