New Views on Cobalamin in Marine Microbial Ecosystems

) has long been recognized as a key cofactor required for phytoplankton growth and as a basis for ecological interactions between phytoplankton and bacteria in the sea. New findings, however, have revealed new functional roles of microbes in cobalamin production and use and illuminated a diversity of cobalamin-related compounds in the ocean. Recent studies have also made it clear that cobalamin limitation of primary productivity and phytoplankton growth is widespread, with seasonal and regional patterns, and that cobalamin can structure microbial interactions that form the basis of key processes in the marine environment. Here, we review recent progress regarding the ecology, biochemistry, evolution, and biogeochemistry of cobalamin and its impacts on microbial processes in the marine water column. We then highlight priority research directions to better illuminate the impact of cobalamin on the future of marine ecosystems.