Metagenomic Insights into Microbial Metabolisms of a Sulfur-Influenced Glacial Ecosystem

Abstract

Biological sulfur cycling in polar, low-temperature ecosystems is an understudied phenomenon in part due to difficulty of access and the ephemeral nature of such environments. One such environment where sulfur cycling plays an important role in microbial metabolisms is located at Borup Fiord Pass (BFP) in the Canadian High Arctic. Here, transient springs emerge from the toe of a glacier creating a large proglacial aufeis (spring-derived ices) that are often covered in bright yellow/white sulfur, sulfate, and carbonate mineral precipitates that are accompanied by a strong odor of hydrogen sulfide. Metagenomic sequencing from multiple sample types at sites across the BFP glacial system produced 31 highly complete metagenome assembled genomes (MAGs) that were queried for sulfur-, nitrogen- and carbon-cycling/metabolism genes. Sulfur cycling, especially within the Sox complex of enzymes, was widespread across the isolated MAGs and taxonomically associated with the bacterial classes Alpha-, Beta-, Gamma-, and Epsilon- Proteobacteria. While this does agree with previous research from BFP implicating organisms within the Gamma- and Epsilon- Proteobacteria as the primary classes responsible for sulfur oxidation, our new data suggests putative sulfur oxidation by organisms within Alpha- and Beta- Proteobacterial classes which was not predicted. These findings indicate that in a low-temperature, ephemeral sulfur-based environment such as this, functional redundancy may be a key mechanism that microorganisms use to co-exist whenever energy is limited and/or focused by redox chemistry. ImportanceBorup Fiord Pass is a unique environment characterized by a sulfur-enriched glacial ecosystem, in the low-temperature environment of the Canadian High Arctic. This unique combination makes BFP one of the best analog sites for studying icy, sulfur-rich worlds outside of our own, such as Europa and Mars. The site also allows investigation of sulfur-based microbial metabolisms in cold environments here on Earth. Herein, we report whole genome sequencing data that suggests sulfur cycling metabolisms at BFP are more widely used across bacterial taxa than predicted. From our data, the metabolic capability of sulfur oxidation among multiple community members appears likely due to functional redundancy within their genomes. Functional redundancy, with respect to sulfur-oxidation at BFP, may indicate that this dynamic ecosystem hosts microorganisms that are able to use multiple sulfur electron donors alongside other important metabolic pathways, including those for carbon and nitrogen.