Hypersaline sapropels act as hotspots for microbial dark matter

Area of Science:

• Astrobiology and Geomicrobiology
• Exploration of extreme environments on Earth as analogues for extraterrestrial life
• Investigation of hypersaline sapropels as potential analogues for early Earth and other celestial bodies

Background:

• Terrestrial analogue sites are vital for understanding life in extreme geochemical conditions similar to early Earth or Mars.
• Hypersaline sapropels represent understudied 'border-of-life' habitats with limited microbiological and physicochemical characterization.
• Low water activity environments are key targets for astrobiological research.

Purpose of the Study:

• To characterize the prokaryotic communities in two distinct hypersaline sapropels.
• To correlate microbial diversity with geochemical milieu and pore water chemistry.
• To infer the role of these communities in carbon cycling.

Main Methods:

• Polyphasic approach combining deep coverage SSU rRNA gene amplicon sequencing and bioinformatics.
• Quantitative real-time polymerase chain reaction (RT-qPCR) for targeted gene detection.
• Comprehensive physicochemical investigations of the sapropel samples.

Main Results:

• Sapropels exhibited analogous elemental and geochemical conditions.
• Prokaryotic communities comprised 59 phyla, with Proteobacteria, Bacteroidetes, and Chloroflexi being most abundant.
• Discovery of 32 candidate divisions and potentially novel prokaryotic lineages, indicating a highly diverse and unique ecosystem.

Conclusions:

• Hypersaline sapropels harbor exceptionally diverse and novel microbial ecosystems.
• These findings contribute to understanding life's limits and phylogenetic diversity.
• The studied sapropels provide valuable insights for astrobiological research and the search for extraterrestrial life.