Metagenome dataset

The trace element iron (Fe) is a major constraint for microbially-mediated processes in the Southern Ocean. The accelerated melting of glaciers could present a novel source of Fe, but whether glacial Fe is bioavailable to marine microbes is not known. We investigated the response of marine heterotrophic prokaryotes to Fe contained in colloids (20 nm – 200 nm) of glacial origin collected on Kerguelen Island (Southern Ocean). We followed prokaryotic growth in incubation experiments amended either with colloids of glacial or non-glacial origin and determined community composition and the abundance of genes involved in Fe-related processes in metagenomes and MAGs at the final time point. Glacial colloids stimulated the growth of prokaryotic taxa belonging to Pseudomonadaceae and Vibrionaceae, while Rhodobacteraceae, Flavobacteriaceae and Alteromonadaceae were the dominant contributors to the communities in the incubations amended with non-glacial colloids. Metagenomic analysis revealed a higher abundance of genes involved in the biosynthesis of the siderophores pyoverdine and vibrioferrin as well as their respective transporters in the presence of glacial colloids as compared to the non-glacial colloids. Genes for the transport of both siderophores were present in diverse MAGs, while biosynthesis genes were detected in fewer ones. MAGs belonging to Nitrincolaceae and Pseudomonadaceae had among the highest gene counts for the synthesis and transport of both siderophores. Our results suggest that the utilization of siderophores facilitates the access to Fe from glacial colloids and point to the key role of specific prokaryotes rendering this source of Fe available to Southern Ocean microbial communities.