COMPARATIVE BIOMARKER ANALYSIS OF DESERT ALGAE: A METHOD FOR INVESTIGATING TERRESTRIAL ECOSYSTEMS BEFORE THE EVOLUTION OF LAND PLANTS

Because they constitute one of the few land environments dominated by microbial biomass, deserts provide a potentially informative modern analogue for Precambrian terrestrial ecosystems that existed before the rise of embryophytes . Modern microbes adapted to these extreme environments demonstrate biochemical adaptations to terrestrial life, including desiccation tolerance, that likely played an important role in the early colonization of land. Thus, biochemical adaptations to desert environments that have preservation potential may yield biomarkers for early terrestrial organisms. To address this, we analyzed the biopolymer algaenan and sterol lipids from algal cultures isolated from hot and cold desert soils. Algaenan, an although an abundant biomarker in Precambrian bitumens and kerogens, is not an adaptation to terrestrial environments, and at this point its physiological role in algae is unclear. Sterol lipids, however, may play a part in terrestrial adaptations of the cell membranes in desert algae and show promise as potential biomarkers, with a greater diversity of C28 and C29 sterols within a population of desert algae compared to their aquatic relatives. Furthermore, sterol diversity and abundance patterns are consistent with the phylogeny of green algae and land plants, and place sterol biomakers into a meaningful evolutionary framework for this group. A better understanding of the preservable cellular components of desert microorganisms will ultimately provide a means to track their early evolutionary history on land and may provide us with an ecophysiological biomaker.