Dimethylsulfoniopropionate and marine microbial associations along an Antarctic glacial–open ocean interface

Abstract

Antarctica is a seasonally active region for marine organic sulfur cycling and ocean-atmospheric sulfur fluxes. Organic sulfur compounds, such as dimethylsulfoniopropionate and dimethylsulfide, produced by microbes are key chemical currencies in interspecies interactions, which in turn, underpin marine sulfur dynamics. This study examined Antarctic phytoplankton-bacteria associations and their influence on marine sulfur cycling along a coastal gradient from an inner fjord of the Sørsdal glacier to the open ocean (six sites). Phytoplankton abundance increased with distance from the glacier, corresponding with an increase in dimethylsulfoniopropionate concentrations (dissolved 13–28 nM; total 73–140 nM) and phytoplankton dimethylsulfoniopropionate lyase activity. Microbial community composition varied with glacial-influence, and overall abundance declined with distance from the glacier. We identified strong associations between dominant phytoplankton genera (Cylindrotheca, Corethron, Chaetoceros, Fragilariopsis, Leptocylindrus/Dactyliosolen, and Phaeocystis) and bacteria from the Rhodobacteraceae (i.e., Roseobacter group), highlighting the prevalence of these species' complexes in Antarctic waters. Specifically, pigment markers of Phaeocystis sp. and amplicon sequence variants (ASVs) belonging to Octadecabacter and Sulfitobacter correlated positively with dissolved dimethylsulfoniopropionate concentrations and phytoplankton dimethylsulfoniopropionate lyase activity, supporting their role in marine sulfur metabolism and extending the known geographical range of sulfur-mediated phytoplankton associations with the Roseobacter group. In broadening the reported range of these interorganism interactions to Antarctic waters, these results extend the prevalence and weight of the role of sulfur-based dependencies in structuring marine microbial communities