Novel Insights into Dimethylsulfoniopropionate Catabolism by Cultivable Bacteria in the Arctic Kongsfjorden

Dimethylsulfoniopropionate (DMSP) is one of the most abundant organic sulfur compounds in the oceans, which is mainly degraded by bacteria through two pathways, a cleavage pathway and a demethylation pathway. Its volatile catabolites dimethyl sulfide (DMS) and methanethiol (MT) in these pathways play important roles in the global sulfur cycle and have potential influences on the global climate. Intense DMS/DMSP cycling occurs in the Arctic. However, little is known about the diversity of cultivable DMSP-catabolizing bacteria in the Arctic and how they catabolize DMSP. Here, we screened DMSP-catabolizing bacteria from Arctic samples and found that bacteria of four genera (Psychrobacter, Pseudoalteromonas, Alteromonas, and Vibrio) could grow with DMSP as the sole carbon source, among which Psychrobacter and Pseudoalteromonas are predominant. Four representative strains (Psychrobacter sp. K31L, Pseudoalteromonas sp. K222D, Alteromonas sp. K632G, and Vibrio sp. G41H) from different genera were selected to probe their DMSP catabolic pathways. All these strains produce DMS and MT simultaneously during their growth on DMSP, indicating that all strains likely possess the two DMSP catabolic pathways. On the basis of genomic and biochemical analyses, the DMSP catabolic pathways in these strains were proposed. Bioinformatic analysis indicated that most Psychrobacter and Vibrio bacteria have the potential to catabolize DMSP via the demethylation pathway and that only a small portion of Psychrobacter strains may catabolize DMSP via the cleavage pathway. This study provides novel insights into DMSP catabolism in marine bacteria. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is abundant in the oceans. The catabolism of DMSP is an important step of the global sulfur cycle. Although Gammaproteobacteria are widespread in the oceans, the contribution of Gammaproteobacteria in global DMSP catabolism is not fully understood. Here, we found that bacteria of four genera belonging to Gammaproteobacteria (Psychrobacter, Pseudoalteromonas, Alteromonas and Vibrio), which were isolated from Arctic samples, were able to grow on DMSP. The DMSP catabolic pathways of representative strains were proposed. Bioinformatic analysis indicates that most Psychrobacter and Vibrio bacteria have the potential to catabolize DMSP via the demethylation pathway and that only a small portion of Psychrobacter strains may catabolize DMSP via the cleavage pathway. Our results suggest that novel DMSP dethiomethylases/demethylases may exist in Pseudoalteromonas, Alteromonas, and Vibrio and that Gammaproteobacteria may be important participants in the marine environment, especially in polar DMSP cycling.