Microbial controls on DMSP degradation and DMS formation in the Sargasso Sea
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Bacterial degradation of dimethylsulfoniopropionate (DMSP) represents one of the main sources of the climatically–active trace gas dimethylsulfide (DMS) in the upper ocean. Short-term enrichment studies to stimulate specific pathways of DMSP degradation in oligotrophic waters from the Sargasso Sea were used to explore regulatory connections between the different bacterial DMSP degradation steps and determine potential biological controls on DMS formation in the open ocean. Experiments were conducted with surface water at the BATS station in the western North Atlantic Ocean. We added selected organic substrates (25 nmol L−1 final concentration) to induce different steps of DMSP degradation in the microbial community, and then measured DMSP dynamics (assimilation and turnover rates), DMS yields (using 35sulfur-DMSP tracer), and bacterial production rates. In most treatments, the main fate of consumed S-DMSP was excretion as a non-volatile S product. 35S-DMSP tracer turnover rates (accumulation + assimilation + excretion of transformed products as DMS or others) increased upon addition of DMSP and glucose, but not acrylate, methymercaptopropionate (MMPA), methanethiol, DMS or glycine betaine. DMS yields from 35S-DMSP never exceeded 16 % except in a short term DMSP enrichment, for which the yield reached 45 % (±17 %). Results show that availability of non-sulfur containing labile C sources (glucose, acrylate) decreased bacterial DMS production while stimulating bacterial heterotrophic production, and suggest an influence of bacterial sulfur demand in controlling DMS-yielding pathways. However, regulatory effects on 35S-DMSP fate were not consistent across all reduced sulfur compounds (i.e., methanethiol or MMPA), and may reflect alternate roles of DMSP as a bacterial energy source and osmolyte.
KeywordsDimethylsulfoniopropionate DMSP Dimethylsulfide DMS Sargasso sea Bacterioplankton
We thank John Dacey and Dede Toole for the invitation to join two BATS cruises in the Sargasso Sea; Naomi Levine, Aimee Neely, Dacha Atienza and Vanessa Varaljay for helpful advice; and Daniela del Valle for DMSP analyses and fruitful discussions. The captain and crew of the R/V Atlantic explorer, and the BATS team, especially Mike Lomas and Steven Bell, are gratefully acknowledged. This project was funded by 7th Framework Programme (FP7) Marie Curie Fellowship (GenS FP7-MC-IOF-219811) and a fellowship”Beatriu de Pinós” from the Catalan Government (to MVC), the Gordon and Betty Moore Foundation, and the National Science Foundation (OCE0724017 to MAM and RPK, OCE-0928968 to RPK and OCE0425166 to J. Dacey and D. Toole).
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