Resistance and survival of endolithic microorganisms in outer space and Mars conditions simulated in space
Author(s)
Scalzi, Giuliano
Date Issued
March 20, 2012
Type
Doctoral Thesis
Abstract
Cryptoendolithic microbial communities and epilithic lichens have been considered as appropriate
candidates for the scenario of Lithopanspermia, which proposes a natural interplanetary exchange
of organisms by means of rocks that have been impact ejected from their planet of origin. So far, the
hardiness of these terrestrial organisms in the severe and hostile conditions of space has not been
tested over extended periods of time. A first long-term (1.5 years) exposure experiment in space
was performed with a variety of rock-colonizing eukaryotic organism at the International Space
Station on board of the European EXPOSE-E facility. Organisms were selected that were especially
adapted to cope with the environmental extremes of their natural habitat. It was found that some –
but not all - of those most robust microbial communities from extremely hostile regions on Earth
are also partially resistant against the even more hostile environment of outer space, including high
vacuum, temperature fluctuation, the full spectrum of extraterrestrial solar electromagnetic radiation
and cosmic ionizing radiation. Colonized Antarctic rocks, retrieved from EXPOSE-E after LIFE
experiment, after being plated in MaltAgar medium, showed a development of a green alga and a
pink-coloured fungus; they were isolated from a sample exposed to simulated Mars conditions
beneath a 0.1% Suprasil neutral density filter and from a sample exposed to space vacuum without
solar radiation exposure, respectively. The two organisms able to grow were identified at genus
level by Small SubUnit (SSU) and Internal Transcribed Spacer (ITS) rDNA sequencing as
Stichococcus sp. (green alga) and Acarospora sp. (lichenized fungal genus) respectively. Moreover,
this study has been focused, with a methodological approach, on the new procedures to minimize
the biological cross-contamination resulting from the exploration of the solar system. A model
microbial community (MMC) of known composition, representative of a typical low-biomass
surface sample, was used to examine the effects of variables in sampling matrices, target cell
density/molecule concentration, and cryogenic storage on the overall efficacy of the sampling
regimen. The MMC used in this study comprised 11 distinct species of bacterial, archaeal, and
fungal lineages associated with either spacecraft or clean-room surfaces. The results of this study
empower current knowledge of the limits of life on Earth and beyond and hints future molecularanalysis-
based microbial sampling and processing methodologies.
Additional information
Dottorato di ricerca in Evoluzione biologica e biochimica
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