Insights from the Metagenome of an Acid Salt Lake: The Role of Biology in an Extreme Depositional Environment

Sarah Stewart Johnson,Bethany L Ehlmann,Marc Gerard Chevrette,Kathleen Counter Benison,Paul Jaak Janssen

doi:10.1371/journal.pone.0122869

Abstract

The extremely acidic brine lakes of the Yilgarn Craton of Western Australia are home to some of the most biologically challenging waters on Earth. In this study, we employed metagenomic shotgun sequencing to generate a microbial profile of the depositional environment associated with the sulfur-rich sediments of one such lake. Of the 1.5 M high-quality reads generated, 0.25 M were mapped to protein features, which in turn provide new insights into the metabolic function of this community. In particular, 45 diverse genes associated with sulfur metabolism were identified, the majority of which were linked to either the conversion of sulfate to adenylylsulfate and the subsequent production of sulfide from sulfite or the oxidation of sulfide, elemental sulfur, and thiosulfate via the sulfur oxidation (Sox) system. This is the first metagenomic study of an acidic, hypersaline depositional environment, and we present evidence for a surprisingly high level of microbial diversity. Our findings also illuminate the possibility that we may be meaningfully underestimating the effects of biology on the chemistry of these sulfur-rich sediments, thereby influencing our understanding of past geobiological conditions that may have been present on Earth as well as early Mars.

Highlights

Acidic brine lakes are not common, and those that occur naturally are relatively new to scientific study [1, 2]
Silicate minerals, which could be detrital or authigenic, comprised half the sediment with the remainder composed of clearly authigenic iron oxides, sulfate salts, and chloride salts (Fig 2)
Though detected with x-ray diffraction (XRD), no discrete grains of quartz were observed in scanning electron microscopy (SEM); these may have been obscured by coatings of precipitated phases

Summary

Introduction

Acidic brine lakes are not common, and those that occur naturally are relatively new to scientific study [1, 2]. The Metagenome of an Acid Salt Lake geochemistry, water stress due to desiccation, dramatic diurnal temperature changes, and high levels of solar radiation. These environments are of particular interest as a source of novel genetic diversity and the understanding of life in conditions of relevance to Earth’s past. Evidence of ancient and widespread acid salt lake and groundwater systems has been recently uncovered over much of the North American mid-continent [14, 15] These discoveries have prompted a reevaluation of how past surface conditions can be reconstructed along with further investigations into the geochemistry and ecology of acid saline systems in general [14, 16]

Methods

Results

Conclusion