Microbial taxonomic and functional diversity across the Drake Passage and the west Antarctic Peninsula

Antarctica and the Southern Ocean are central to the Earth’s climate and oceanic circulation systems. Microbial communities inhabiting the Southern Ocean drive biogeochemical cycles, underpin trophodynamics, and  affect atmospheric chemistry. The ongoing climate crisis is affecting these processes, with possible cascading effects on the structure and functioning of phytoplankton communities in the surface waters of the Southern Ocean. The CLAW hypothesis, which describes a feedback mechanism between phytoplankton, the dimethylsulphide (DMS) production, the cloud condensation nuclei (CCN) formation, and albedo, represents a prominent link between the changing marine microbial dynamics and climate. Additionally, marine DMS production appears to be influenced by the availability of microbially-derived vitamin B12, involved in the methionine biosynthesis, and is already regarded as a limiting factor for the phytoplankton growth, thus playing a role in shaping microbial community structure. Understanding the role of the ocean microbiome in these processes is therefore essential to evaluate how marine microbial communities impact climate regulation, and vice versa.

Previous studies on the surface waters of the west Antarctic Peninsula and in the Southern Ocean have described taxonomic profiles of marine microorganisms and identified metabolic functions related to degradation of phytoplankton-derived organic matter. However, the role of the functional diversity in the interplay between climate change, microbial communities, and DMS-cycling pathway remains poorly understood. Here, we present an integrated analysis of the microbial functional diversity of surface waters along the Drake Passage and the west Antarctic Peninsula, sampled during the 2023/24 Austral Summer. Shotgun metagenomic sequencing and 16S rRNA amplicon analysis were performed, and enabled the description of spatial distribution of genes involved in DMS and cobalamin biosynthesis pathways along the transect. We coupled this data with chlorophyll chemotaxonomy and geochemical analyses. This integrated approach holds the potential to advance our understanding of microbial responses to the impacts of climate change, and the identification of specific microbial pathways that could enhance climate change in the Southern Ocean, ultimately helping to fill gaps in climate change modeling.