Abstract

Biotic perchlorate reduction, a metabolic process that potentially occurs on Mars, has long been the subject of speculation in astrobiology. To determine whether it could be a viable metabolic strategy on the Red Planet, we sought to determine whether biotic perchlorate reduction could evolve and persist in Mars-analog environments on Earth. In this study, we introduce Gene Dive, a novel computational methodology that leverages profile hidden Markov models, sequence alignment, phylogenetic tree construction, and Faith's phylogenetic diversity to probe the prevalence and diversity of perchlorate reducing genes in metagenomes. To determine whether biotic perchlorate reduction persists in a wide range of environments, including Mars-analogs, we used Gene Dive to study its prevalence across 124 metagenomes sampled from diverse environments worldwide. Our research presents the first-ever identification of perchlorate reducing genes in certain Mars-analog environments of the McMurdo Dry Valleys, the Atacama Desert, and the Namib Desert. We also show that these sites host some of the highest diversity in perchlorate reducing genes, suggesting that perchlorate reduction has persisted in these environments over long timescales. We found differing diversity patterns between the genes involved in perchlorate and nitrate reduction. For example, perchlorate reduction genes like chlorite dismutase (Cld) and perchlorate reductase (PcrA, a member of the DMSO reductase protein family) experience heightened diversity in environments which have experienced little environmental change over million-year timescales, such as the McMurdo Dry Valleys, the Atacama Desert, the Namib Desert, and the Amazon Rainforest. This contrasts with nitrate reductase (NarG), which experiences heightened diversity only in nutrient rich highly productive environments, such as the Auka Hydrothermal Vents and the Amazon Rainforest. Together these results suggests that nitrate reduction might be more environmentally influenced, while perchlorate reduction appears more universally selected, persisting in stable and undisturbed systems. Our findings underscore the importance of perchlorate reducing genes in our ongoing quest to understand the potential for life on Mars and guide the search for suitable model organisms to deepen our understanding of potential life on the Red Planet.

Degree

College and Department

Life Sciences; Biology

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