Microbial diversity and activity in Southern California salterns and bitterns: analogues for remnant ocean worlds

Abstract

Concurrent osmotic and chaotropic stress make MgCl 2 -rich brines extremely inhospitable environments. Understanding the limits of life in these brines is essential to the search for extraterrestrial life on contemporary and relict ocean worlds, like Mars, which could host similar environments. We sequenced environmental 16S rRNA genes and quantified microbial activity across a broad range of salinity and chaotropicity at a Mars-analogue salt harvesting facility in Southern California, where seawater is evaporated in a series of ponds ranging from kosmotropic NaCl brines to highly chaotropic MgCl 2 brines. Within NaCl brines, we observed a proliferation of specialized halophilic Euryarchaeota, which corresponded closely with the dominant taxa found in salterns around the world. These communities were characterized by very slow growth rates and high biomass accumulation. As salinity and chaotropicity increased, we found that the MgCl 2 -rich brines eventually exceeded the limits of microbial activity. We found evidence that exogenous genetic material is preserved in these chaotropic brines, producing an unexpected increase in diversity in the presumably sterile MgCl 2 -saturated brines. Because of their high potential for biomarker preservation, chaotropic brines could therefore serve as repositories of genetic biomarkers from nearby environments (both on Earth and beyond) making them prime targets for future life-detection missions.

Microbial habitability of early Mars lacustrine environments sustained by iron redox cycling

“…Our calculations show that Gale Lake could have maintained a concentration of cells (~10 3 -10 7 cells mL -1 ) similar to modern lakes and oceans. For example, modern terrestrial ocean waters and saltern brines have been shown to support 10 4 -10 6 cells per mL (Bar-On, Phillips and Milo, 2018); 10 4 -10 7 Klempay et al, 2021) depending on depth and other variables. Terrestrial ocean and lake sediments have also been shown to harbor 10 4 -10 9 cells per cm 3 (Kallmeyer et al, 2012;Wurzbacher et al, 2017).…”

Astrobiology of life on Earth

“…Therefore, the apparent limitation of the chaotropicityquantification technique (Cray et al, 2013) at high molar concentrations of MgCl 2 is in reality a biologically pertinent indication that there is no further chaotropic activity. The authors of Fisher et al (2021) were also involved in a study by Klempay et al (2021), which analysed Archaea and Bacteria and water chemistry, in salterns hosting a range of evaporated seawater from San Diego Bay (southern California, USA). The Klempay et al study has implications for interactions of chaotropicity and water activity in relation to biophysical constraints on cellular activity, an issue pertinent to diverse microbial systems (Hallsworth et al, 2007;Alves et al, 2015;Cray et al, 2015).…”

“…The Klempay et al study has implications for interactions of chaotropicity and water activity in relation to biophysical constraints on cellular activity, an issue pertinent to diverse microbial systems (Hallsworth et al, 2007;Alves et al, 2015;Cray et al, 2015). Klempay et al (2021) also used geochemical modelling to speculate that even brines saturated with respect to epsomite (MgSO 4 ) and carnallite (KMgCl 3 Á6H 2 O) can potentially be inhabited by active halophiles; that is, at less than $0.600 water activity which is a value consistent with empirical data for cell division of halophilic/xerophilic Aspergillus penicillioides at high glycerol concentration (Stevenson et al, 2017). The work of Klempay et al makes a strong case that the search for life on Mars should focus on past saline environments.…”

“…(2021) were also involved in a study by Klempay et al . (2021), which analysed Archaea and Bacteria and water chemistry, in salterns hosting a range of evaporated seawater from San Diego Bay (southern California, USA). The Klempay et al .…”

From microbial community structure to metabolic inference using paprica

“…In Bowman and Ducklow (2015) , paprica was used to infer microbial metabolism and results were comparable to other common metabolic inference pipelines such as PICRUSt ( Langille et al, 2013 ). Paprica has been used to understand the temporal dynamics of bacterial and archaeal community structure in coastal ecosystems ( Wilson et al, 2021 ), the microbial diversity of hypersaline lakes ( Klempay et al, 2021 ), and the microbial dynamics in up-flow bioreactors ( Dutta et al, 2020 ). Paprica offers a framework to bridge the gap between taxonomy and marker gene studies, which are economical but indirectly linked to community function, and potential metabolism, which is costly and can be labor intensive to analyze but is directly linked to function ( Bowman and Ducklow, 2015 ).…”