Extremophiles in an Antarctic Marine Ecosystem

TLDR

Marine microbial surveys reveal a large unknown diversity, yet sequencing alone is limited by database bias and biogeographic patterns, raising concerns that future environmental shifts may alter Southern Ocean diversity by excluding rare extremophiles. The study targets the extremophile community between the Polar Front and the Southern Antarctic Circumpolar Current to evaluate metagenomics as a bioprospecting tool for novel functional activity. The authors performed metagenomic sequencing to assess microbial composition and diversity north of the winter sea ice limit, between the SACCF and the Polar Front. Sequencing revealed that while common marine microbes dominated, they carried secondary metabolism genes of interest, and although rare, extremophiles spanned diverse genera, making them promising targets for novel functions.

Abstract

Recent attempts to explore marine microbial diversity and the global marine microbiome have indicated a large proportion of previously unknown diversity. However, sequencing alone does not tell the whole story, as it relies heavily upon information that is already contained within sequence databases. In addition, microorganisms have been shown to present small-to-large scale biogeographical patterns worldwide, potentially making regional combinations of selection pressures unique. Here, we focus on the extremophile community in the boundary region located between the Polar Front and the Southern Antarctic Circumpolar Current in the Southern Ocean, to explore the potential of metagenomic approaches as a tool for bioprospecting in the search for novel functional activity based on targeted sampling efforts. We assessed the microbial composition and diversity from a region north of the current limit for winter sea ice, north of the Southern Antarctic Circumpolar Front (SACCF) but south of the Polar Front. Although, most of the more frequently encountered sequences were derived from common marine microorganisms, within these dominant groups, we found a proportion of genes related to secondary metabolism of potential interest in bioprospecting. Extremophiles were rare by comparison but belonged to a range of genera. Hence, they represented interesting targets from which to identify rare or novel functions. Ultimately, future shifts in environmental conditions favoring more cosmopolitan groups could have an unpredictable effect on microbial diversity and function in the Southern Ocean, perhaps excluding the rarer extremophiles.