Abstract
Dalangtan Playa is the second largest salt playa in the Qaidam Basin, north-western China. The hyper saline deposition, extremely arid climate and high UV radiation make Dalangtan a Mars analogue both for geomorphology and life preservation. To better understand microbial life at Dalangtan, both culture-dependent and culture-independent methods were examined and simultaneously, environment conditions and the evaporitic mineral assemblages were investigated. Ten and thirteen subsurface samples were collected along a 595-cm deep profile (P1) and a 685-cm deep profile (P2) respectively, and seven samples were gathered from surface sediments. These samples are composed of salt minerals, minor silicate mineral fragments and clays. The total bacterial cell numbers are (1.54±0.49) ×105 g−1 for P1 and (3.22±0.95) ×105 g−1 for P2 as indicated by the CAtalyzed Reporter Deposition- Fluorescent in situ Hybridization (CARD-FISH). 76.6% and 75.7% of the bacteria belong to Firmicutes phylum respectively from P1 and P2. In total, 47 bacteria and 6 fungi were isolated from 22 subsurface samples. In contrast, only 3 bacteria and 1 fungus were isolated from 3 surface samples. The isolated bacteria show high homology (≥97%) with members of the Firmicutes phylum (47 strains, 8 genera) and the Actinobacteria phylum (3 strains, 2 genera), which agrees with the result of CARD-FISH. Isolated fungi showed ≥98% ITS1 homology with members of the phylum Ascomycota. Moisture content and TOC values may control the sediments colonization. Given the deliquescence of salts, evaporites may provide refuge for microbial life, which merits further investigation. Halotolerant and spore-forming microorganisms are the dominant microbial groups capable of surviving under extreme conditions. Our results offer brand-new information on microbial biomass in Dalangtan Playa and shed light on understanding the potential microbial life in the dried playa or paleo-lakes on Mars.
Highlights
Mars today presents a cold, hyper-arid environment which is very challenging for life survival
One of the most important food sources for microorganisms, organic carbon is very limited in the surface sediments of Dalangtan Playa with an average total organic carbon (TOC) of 0.03%
A relatively low microbial diversity (105 bacteria g-1) was indicated by both isolation and culture independent methods. Both bacteria and fungi were isolated from Dalangtan Playa where colonization was controlled mainly by moisture content and TOC of samples
Summary
Mars today presents a cold, hyper-arid environment which is very challenging for life survival. The Recurring Slope Linea (RSL) [10] was proposed as evidence for recurring brine on Mars surface during warm seasons [11], other hypotheses are being considered [12]. These observations provided a basis for the possibilities of life existence in saline environments and subsurface aquifer systems on Mars. The conditions referred to above must be considered critical research sites for life detection on Mars [13, 14]
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