HABITABILITY AND BIOSIGNATURE PRESERVATION IN A SULFATE BRINE: LESSONS FROM THE “SPOTTED” LAKES (Invited Presentation)

Observations of Mars have revealed the widespread presence of paleo-evaporitic deposits, in the form of magnesium sulfate salts. MgSO₄ salts have been known to preserve evidence of life on geological timescales, which makes its discovery beyond Earth of interest to the Astrobiological community. Salts have important implications for biology, as they largely determine the water activity (a_w) of a given system, and can be either kosmotropic (stabilizing) or chaotropic (destabilizing) to biological molecules – thus having important implications for habitability, and preservation of putative biosignatures. The Interior Plateau of British Columbia is host to a unique set of MgSO₄-dominated lakes, which owe their composition to the regional geology. Many of these ephemeral endorheic lakes appear “spotted”, where sub-basins form within the lake margins that are spatially stable over time. Here we present data addressing the role that sulfate and magnesium ions – frequently present in excess of 2 M – have in the composition of present-day microbial communities, and ultimately, how these ions interact with various biomolecules to preserve or degrade them over time. The Basque Lakes, along with Last Chance Lake and Salt Lake, represent chemically complex systems that range in salinity from ~90 ppt to 370 ppt (saturation), with water activities ranging from 0.95 to 0.86 depending on the evaporative state of the lakes. The brines are dominated by halophilic bacteria such as Halomonas and Aliidiomarina, and archaea such as Halorubrum and Natronolimnobius. Work is underway to correlate the microbial community composition of both the brines and sediment, to the abundance of lipid biomarkers, and to understand how both core and intact polar lipids degrade overtime. ATP and DNA degradation experiments, along with studies of amino acid racemization rates are also ongoing, where we are exploring the role that mono- and divalent cations such as Na⁺/Mg²⁺ play in stabilizing molecular compounds vs the stronger anion effects of Cl^-/SO₄^2-. Finally, our team is exploring isotopic trends throughout the brine-sediment system, to inform both nutrient cycling within the community (e.g., δ¹⁵N), as well as salt-based effects on the isotopic fractionation of oxygen and sulfur.