Extremophilic models for astrobiology: haloarchaeal survival strategies and pigments for remote sensing

Abstract

Recent progress in extremophile biology, exploration of planetary bodies in the Solar System, and the detection and characterization of extrasolar planets are leading to new insights in the field of astrobiology and possible distribution of life in the universe. Among the many extremophiles on Earth, the halophilic Archaea (Haloarchaea) are especially attractive models for astrobiology, being evolutionarily ancient and physiologically versatile, potentially surviving in a variety of planetary environments and with relevance for in situ life detection. Haloarchaea are polyextremophilic with tolerance of saturating salinity, anaerobic conditions, high levels of ultraviolet and ionizing radiation, subzero temperatures, desiccation, and toxic ions. Haloarchaea survive launches into Earth's stratosphere encountering conditions similar to those found on the surface of Mars. Studies of their unique proteins are revealing mechanisms permitting activity and function in high ionic strength, perchlorates, and subzero temperatures. Haloarchaea also produce spectacular blooms visible from space due to synthesis of red-orange isoprenoid carotenoids used for photoprotection and photorepair processes and purple retinal chromoproteins for phototrophy and phototaxis. Remote sensing using visible and infrared spectroscopy has shown that haloarchaeal pigments exhibit both a discernible peak of absorption and a reflective "green edge". Since the pigments produce remotely detectable features, they may influence the spectrum from an inhabited exoplanet imaged by a future large space-based telescope. In this review, we focus primarily on studies of two Haloarchaea, Halobacterium sp. NRC-1 and Halorubrum lacusprofundi.

16S rRNA Gene Diversity in Ancient Gray and Pink Salt from San Simón Salt Mines in Tarija, Bolivia

“…A ncient subsurface salt deposits are of interest from the perspective of extremophiles, evolutionary biology, and astrobiology (1,2). Studies on their microbial diversity are needed for expanding our understanding of adaptation to hypersaline environments, including high-salinity/low-water conditions and UV/ionizing radiation tolerance, and potential habitability on Mars (3)(4)(5). To date, relatively few studies have been conducted that address microbial diversity in salt evaporites (6)(7)(8)(9)(10)(11)(12).…”

Molecular insights into the ecology of a psychrotolerant Pseudomonas syringae

“…We also speculate that glycerol is utilized to maintain flexibility of cellular macromolecules and that there is a highly efficient energy Many lines of research in the field of astrobiology focus on polyextremophiles; i.e. those terrestrial microbes widely considered the most likely to be able to function in Martian environments (de la Vega UP and P, 2007;Rummel et al, 2014;DasSarma et al, 2020). While P. syringae Lz4W is not an extremophile or polyextremophile per se, it is native to soils of Antarctica, a region that provides analogue sites for astrobiology studies.…”

Recent advances in understanding extremophiles

“…Although extremophiles are often discussed by the predominate environmental pressure, in reality there are typically multiple extremes (for example, cold and high salinity or heat and acid). When considering these environments on Earth and other extraplanetary bodies, we must look increasingly toward polyextremophiles as the true model organisms for astrobiology 94 .…”