Molecular and lipid biomarker analysis of a gypsum‐hosted endoevaporitic microbial community

Abstract

Modern evaporitic microbial ecosystems are important analogs for understanding the record of earliest life on Earth. Although mineral-depositing shallow-marine environments were prevalent during the Precambrian, few such environments are now available today for study. We investigated the molecular and lipid biomarker composition of an endoevaporitic gypsarenite microbial mat community in Guerrero Negro, Mexico. The 16S ribosomal RNA gene-based phylogenetic analyses of this mat corroborate prior observations indicating that characteristic layered microbial communities colonize gypsum deposits world-wide despite considerable textural and morphological variability. Membrane fatty acid analysis of the surface tan/orange and lower green mat crust layers indicated cell densities of 1.6 × 10(9) and 4.2 × 10(9) cells cm(-3) , respectively. Several biomarker fatty acids, ∆7,10-hexadecadienoic, iso-heptadecenoic, 10-methylhexadecanoic, and a ∆12-methyloctadecenoic, correlated well with distributions of Euhalothece, Stenotrophomonas, Desulfohalobium, and Rhodobacterales, respectively, revealed by the phylogenetic analyses. Chlorophyll (Chl) a and cyanobacterial phylotypes were present at all depths in the mat. Bacteriochlorophyl (Bchl) a and Bchl c were first detected in the oxic-anoxic transition zone and increased with depth. A series of monomethylalkanes (MMA), 8-methylhexadecane, 8-methylheptadecane, and 9-methyloctadecane were present in the surface crust but increased in abundance in the lower anoxic layers. The MMA structures are similar to those identified previously in cultures of the marine Chloroflexus-like organism 'Candidatus Chlorothrix halophila' gen. nov., sp. nov., and may represent the Bchl c community. Novel 3-methylhopanoids were identified in cultures of marine purple non-sulfur bacteria and serve as a probable biomarker for this group in the lower anoxic purple and olive-black layers. Together microbial culture and environmental analyses support novel sources for lipid biomarkers in gypsum crust mats.

Biosignature Preservation and Detection in Mars Analog Environments

“…These environments can be stratified due to salinity, density, or temperature with episodic mixing, which can compartmentalize habitability in the water column. While desiccation of ephemeral lakes can make long-term habitability and evolution difficult for some microorganisms in the water column, both microbial and multicellular life have evolved metabolic strategies to survive these events (Jahnke et al, 2014). Additionally, for some specialized microorganisms, the salts and sediments provide needed protection from radiation and are often ecosystems independent of the intermittent water column altogether, such as the endolithic communities found in the halite rocks of the Atacama Desert and the microbial ecosystem present in the sediments of the Pilot Valley basin in Utah (Davila et al, 2015; Lynch et al, 2016).…”

Halophilic microbial communities and their environments

“…Chloroflexi and sulfate reducing bacteria are the main consumers of the cyanobacterial fermentation products [36 ]. A study of lipids in a higher-salinity, gypsum-containing mat at Guerrero Negro provided a wealth of biomarkers witnessing the vertical stratification of different prokaryotes [37]. A metagenomic study of the benthic community of a crystallizer pond on Mallorca, Spain, was carried out with special emphasis on the detection of yet-uncultured methanogenic Archaea adapted to high salt [38 ].…”

Carbon isotopic composition of lipid biomarkers from an endoevaporitic gypsum crust microbial mat reveals cycling of mineralized organic carbon

“…Previously, we reported on the distribution and diversity of the microbes within the distinct colorful laminations of a gypsarenite mat (Jahnke et al, ). Gypsum crusts displaying various degrees of induration are present throughout Pond 9, and they host laminated microbial mats similar to the one studied here (Vogel et al, ).…”

“…The gypsarenite mat studied here is a highly diverse ecosystem composed of multiple trophic levels and reaction networks through which carbon flows (Figure ). The distinct distribution of microbial guilds with depth in these crusts is widespread in evaporitic environments (Caumette, Matheron, Raymond, & Relexans, ; Canfield, Sørensen, & Oren, ; Sørensen, Canfield, Teske, & Oren, ; Oren et al, ; Jahnke et al, ).…”