Award: OCE-1342694

We studied the biogeochemistry of an organic sulfur compound with an outsized impact on the ocean and atmosphere: dimethylsulfoniopropionate (DMSP). DMSP accumulates in marine phytoplankton cells where it serves to counteract the high salt concentration in the marine environment and deter zooplankton predators. When DMSP is released by the phytoplankton cells (either by exudation or death), marine bacteria consume it and, depending on which of two pathways they use for degradation, release the sulfur atom in DMSP back into seawater or in gaseous form to the atmosphere. Our team learned that about half the bacterial cells in the surface ocean are able to consume DMSP, which is quite high in light of the wide variety of other compounds available to them in seawater, including other organic sulfur compounds that were discovered in this project. DMSP-degrading bacteria are spread across a variety of species, exhibiting considerable diversity in their phylogeny, which degradation genes they carry, their distribution in the ocean, and the phytoplankton cells they typically associate with. However, only bacteria in one taxonomic group (the Alphaproteobacteria) have genes for both of the degradation pathways, indicating their particular importance at the crucial point in the marine sulfur cycle where the fate of DMSP sulfur is determined. The gaseous DMSP degradation product formed by marine bacteria, dimethylsulfide (DMS), is the largest natural source of atmospheric sulfur. It contributes to aerosols and acts as cloud condensation nuclei, affecting Earth's cloud cover. Last Modified: 01/25/2020 Submitted by: Mary Ann Moran