# Water mass specific genes dominate the Southern Ocean microbiome

## TL;DR

This study reveals unique microbial genes in the Southern Ocean, highlighting their adaptation to specific water masses and polar conditions.

## Contribution

The study introduces a new gene catalog from the Southern Ocean, showing water-mass-specific adaptations and novel genetic diversity.

## Key findings

- 38% of the identified genes lack homologs in existing marine gene catalogs.
- Southern Ocean gene assemblages share a polar signature with the Arctic Ocean but are structured by water masses.
- The study highlights adaptations in Pelagibacter and DMSP cleavage by polar-adapted bacteria.

## Abstract

The Southern Ocean (SO) plays a key role in regulating global biogeochemical cycles and climate, yet microbial genes sustaining its biological activity remain poorly characterized. We introduce a microbial genes collection from 218 metagenomes sampled during the Antarctic Circumnavigation Expedition, the majority of which are missing from functional databases. 38% even lack homologs in current reference marine gene catalogs, defining a singular genetic seascape. We show that SO gene assemblages exhibit a common polar signature with the Arctic Ocean while being structured by water masses at the SO-scale. We analyze genomic markers of diverse SO biomes, focusing on dimethylsulphoniopropionate (DMSP) cleavage by polar-adapted bacteria, organic matter consumption in the blooming Mertz polynya and adaptation to polar conditions in the ubiquitous bacteria Pelagibacter. Our work takes a step towards a comprehensive understanding of SO’s plankton ecology and evolution, capturing the current state of the unique microbial diversity in this rapidly changing Ocean.

Southern Ocean microbial communities are less well studied. Here, the authors generate a circumpolar-scale gene catalog from 218 metagenomics samples revealing broadscale uniqueness and water-mass–specific adaptations of the Southern Ocean microbiome.