Abstract
Unravelling how long life can persist under extreme dryness and what kind of environmental extremes can be faced by dried microorganisms, is relevant to understand Mars habitability and to search for life on planets with transient liquid water availability. Since trehalose and sucrose stabilize dried anhydrobiotes, an in silico survey of the genome of the desert cyanobacterium Chroococcidiopsis sp. CCMEE 029 was performed to identify pathways for trehalose and sucrose biosynthesis. The expression of the identified genes was induced in response to desiccation and trehalose and sucrose accumulation was detected in dried cells. This adaptation strategy enabled viability and biomarker permanence under extreme dryness and Mars-like UV flux. Chroococcidiopsis survivors were scored in 7-year dried biofilms mixed with phyllosilicatic Mars regolith simulant and exposed to 5.5 x 103 kJ/m2 of a Mars-like UV flux. No survivors occurred after exposure to 5.5 x 105 kJ/m2, although in dead cells, photosynthetic pigments and nucleic acids, both DNA and RNA, were still detectable. This suggested that dried biofilms mixed with phyllosilicatic Martian regolith simulant are suitable candidates to identify biosignatures embedded in planetary analogue minerals as planned in the future BioSigN (BioSignatures and habitable Niches) space mission to be performed outside the International Space Station.
Highlights
Unraveling how long life can persist under extreme dryness and which environmental extremes can be faced in the dried state is relevant for long-term models of Mars habitability (Davila and Schulze-Makuch, 2016) and for searching for life on planets with transient availability of liquid water (Schulze-Makuch et al, 2017; Wilhelm et al, 2018)
Collection of Microorganisms from Extreme Environments (CCMEE) 029’s genome genes for trehalose biosynthesis according to trehalose synthase (TreY)/TreZ and treS genes encoding a maltose alpha-Dglucosyltransferase (TreS) pathways (Table 2)
In order to investigate the role of trehalose and sucrose in survivability and biomarker preservation under Mars laboratory simulations of the anhydrobiotic cyanobacterium Chroococcidiopsis, an in silico analysis of the genome of the CCMEE 029 strain was performed
Summary
Unraveling how long life can persist under extreme dryness and which environmental extremes can be faced in the dried state is relevant for long-term models of Mars habitability (Davila and Schulze-Makuch, 2016) and for searching for life on planets with transient availability of liquid water (Schulze-Makuch et al, 2017; Wilhelm et al, 2018). According to the so called geogenetic latency hypothesis, subsurface microbes could survive planetary surface extinction and be re-exposed to the surface via geological processes, when conditions allow water to flow (Boston et al, 2019). Dryness is one of the main life-threatening factors; upon desiccation, a small group of taxonomically diverse organisms enter a reversible metabolic dormancy, a phenomenon known as anhydrobiosis (Crowe et al, 1992). Because everything we know about biology we have learned from life on Earth (McKay, 2010), desiccation-tolerant microorganisms might be the best-case biologic scenario for understanding the habitability of Mars (Wilhelm et al, 2018) and identifying protective biomolecules to be used as a biomarker database (Jorge-Villar and Edwards, 2013)
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