SRA

Dimethylsulfoniopropionate (DMSP), is one of the Earth's most abundant organosulfur molecules, and the major precursor for gaseous dimethyl sulfide (DMS). DMSP and DMS have important roles in global sulfur cycling and atmospheric chemistry. It was thought that only eukaryotes produce significant amounts of DMSP, but many marine heterotrophic bacteria also produce DMSP and contain the dsyB or mmtN reporter genes for DMSP synthesis. Here we present the first depth profiled case study of bacterial DMSP production in one marine environment — the East China Sea (ECS). The concentrations of total DMSP (DMSPt) decreased with the depth from surface water (10.23–88.42 nM, SW) to near bottom water (3.22–11.45 nM, NBW), while the percentage of particulate DMSP likely apportioned mainly to bacterial origin (DMSPp 0.22–3 µm) increased with the depth, from 7.7% ± 2.9% in the surface to 13.4% ± 3.0% in the near bottom water. Furthermore, high level of DMSPt (16.29 ± 1.07 nmol·g-1) was detected in the oxic seabed sediment (OSS) and was mainly apportioned to be in the bacteria-dominant particulate form (14.19 ± 1.70 nmol·g-1, 86.9% ± 5.3%). Meanwhile, the genetic potential for DMSP synthesis via the bacterial dsyB/mmtN-dependent pathway was prominent in the ECS samples , with the proporition in total bacteria increased from SW to BW water and then to OSS samples. Microbial enrichment for DMSP-producing bacteria identified many different taxonomic groups of DMSP-producing bacteria with their intracellular DMSP concentrations ranging from 0.7 mM to 63.1 mM. These bacteria were likely producing DMSP in the original ECS environment since dsyBs and mmtNs found in some of these bacteria were present in the natural metagenomic data and representatives were able to produce DMSP in the seawater incubation experiment. This study supports the hypotheses that heterotrophic bacteria may have a significant role in marine DMSP production and that bacterial contribution to total DMSP increases with the depth, especially in the oxic sediment.