Genomic analysis of Cobetia sp. D5 reveals its role in marine sulfur cycling.

Dimethylsulfoniopropionate (DMSP) is one of the most abundant sulfur-containing organic compounds on the earth, which is an important carbon and sulfur source and plays an important role in the global sulfur cycle. Marine microorganisms are an important group involved in DMSP metabolism. The strain Cobetia sp. D5 was isolated from seawater samples in the Yellow Sea area of Qingdao during an algal bloom. There is still limited knowledge on the capacity of DMSP utilization of Cobetia bacteria. The study reports the whole genome sequence of Cobetia sp. D5 to understand its DMSP metabolism pathway. The genome of Cobetia sp. D5 consists of a circular chromosome with a length of 4,233,985 bp and the GC content is 62.56%. Genomic analysis showed that Cobetia sp. D5 contains a set of genes to transport and metabolize DMSP, which can cleave DMSP to produce dimethyl sulphide (DMS) and 3-Hydroxypropionyl-Coenzyme A (3-HP-CoA). DMS diffuses into the environment to enter the global sulfur cycle, whereas 3-HP-CoA is catabolized to acetyl CoA to enter central carbon metabolism. Thus, this study provides genetic insights into the DMSP metabolic processes of Cobetia sp. D5 during a marine algal bloom, and contributes to the understanding of the important role played by marine bacteria in the global sulfur cycle.

Effects of micro- and nano-plastics on growth, antioxidant system, DMS, and DMSP production in Emiliania huxleyi.

Due to the potential impacts of microplastics (MPs) and nanoplastics (NPs) on algal growth and thereby affect the climate-relevant substances, dimethylsulfoniopropionate (DMSP) and dimethyl sulfide (DMS), we studied the polystyrene (PS) MPs and NPs of 1 µm and 80 nm impacts on the growth, chlorophyll content, reactive oxygen species (ROS), antioxidant enzyme activity, and DMS/DMSP production in Emiliania huxleyi. E. huxleyi is a prominent oceanic alga that plays a key role in DMS and DMSP production. The results revealed that high concentrations of MPs and NPs inhibited the growth, carotenoid (Car), and Chl a concentrations of E. huxleyi. However, short-time exposure to low concentrations of PS MPs and NPs stimulated the growth of E. huxleyi. Furthermore, high concentrations of MPs and NPs resulted in an increase in the superoxide anion radical (O2.-) production rate and a decrease in the malondialdehyde (MDA) content compared with the low concentrations. Exposure to MPs and NPs at 5 mg L-1 induced superoxide dismutase (SOD) activity as a response to scavenging ROS. High concentrations of MPs and NPs significantly inhibited the production of DMSP and DMS. The findings of this study support the potential ecotoxicological impacts of MPs and NPs on algal growth, antioxidant system, and dimethylated sulfur compounds production, which maybe potentially impact the global climate.

Novel insights into dimethylsulfoniopropionate cleavage by deep subseafloor fungi.

Dimethylsulfoniopropionate (DMSP), a key organic sulfur compound in marine and subseafloor sediments, is degraded by phytoplankton and bacteria, resulting in the release of the climate-active volatile gas dimethylsulfide (DMS). However, it remains unclear if dominant eukaryotic fungi in subseafloor sediments possess specific abilities and metabolic mechanisms for DMSP degradation and DMS formation. Our study provides the first evidence that fungi from coal-bearing sediments ∼2 km below the seafloor, such as Aspergillus spp., Chaetomium globosum, Cladosporium sphaerospermum, and Penicillium funiculosum, can degrade DMSP and produce DMS. In Aspergillus sydowii 29R-4-F02, which exhibited the highest DMSP-dependent DMS production rate (16.95 pmol/µg protein/min), two DMSP lyase genes, dddP and dddW, were identified. Remarkably, the dddW gene, previously observed only in bacteria, was found to be crucial for fungal DMSP cleavage. These findings not only extend the list of fungi capable of degrading DMSP, but also enhance our understanding of DMSP lyase diversity and the role of fungi in DMSP decomposition in subseafloor sedimentary ecosystems.

Influence of the community assemblage on sulfur distributions in the South China sea.

Marine distribution of dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) is greatly affected by the community structures of bacteria, phytoplankton, and zooplankton. Spatial distributions of dissolved and particulate DMSP (DMSPd,p), and DMS were measured and their relationships with DMSP lyase activity (DLA), abundance of DMSP-consuming bacteria (DCB), and the community structures of phytoplankton, zooplankton, and bacteria were determined during summer in the South China Sea (SCS). The depth distributions of DMSPd,p exhibited a similar trend with Chl a, reaching their maxima in the mixing layer. The DMS concentration was positively correlated with DCB abundance and DLA, indicating that DCB and DMSP lyase had a significant effect on DMS production. High DMS concentrations in the horizontal distribution coincided with high DCB abundance and DLA and may be due to the rapid growth of phytoplankton resulting from the high dissolved inorganic nitrogen concentration brought by the cold vortices. Moreover, the highest copepod abundance at station G3 coincided with the highest DMS concentrations there among stations B4, F2, and G3. These results suggest that copepod may play an important role in DMS production. The bacterial SAR11 clade was positively correlated with DLA, indicating its significant contribution to DMSP degradation in the SCS. These findings contribute to the understanding of the effect of the community assemblage on DMSP/DMS distributions in the SCS dominated by mesoscale vortices.

The Stereochemical Course of DmdC, an Enzyme Involved in the Degradation of Dimethylsulfoniopropionate.

The acyl-CoA dehydrogenase DmdC is involved in the degradation of the marine sulfur metabolite dimethylsulfonio propionate (DMSP) through the demethylation pathway. The stereochemical course of this reaction was investigated through the synthesis of four stereoselectively deuterated substrate surrogates carrying stereoselective deuterations at the α- or the ß-carbon. Analysis of the products revealed a specific abstraction of the 2-pro-R proton and of the 3-pro-S hydride, establishing an anti elimination for the DmdC reaction.

Strong chemotaxis by marine bacteria towards polysaccharides is enhanced by the abundant organosulfur compound DMSP.

The ability of marine bacteria to direct their movement in response to chemical gradients influences inter-species interactions, nutrient turnover, and ecosystem productivity. While many bacteria are chemotactic towards small metabolites, marine organic matter is predominantly composed of large molecules and polymers. Yet, the signalling role of these large molecules is largely unknown. Using in situ and laboratory-based chemotaxis assays, we show that marine bacteria are strongly attracted to the abundant algal polysaccharides laminarin and alginate. Unexpectedly, these polysaccharides elicited stronger chemoattraction than their oligo- and monosaccharide constituents. Furthermore, chemotaxis towards laminarin was strongly enhanced by dimethylsulfoniopropionate (DMSP), another ubiquitous algal-derived metabolite. Our results indicate that DMSP acts as a methyl donor for marine bacteria, increasing their gradient detection capacity and facilitating their access to polysaccharide patches. We demonstrate that marine bacteria are capable of strong chemotaxis towards large soluble polysaccharides and uncover a new ecological role for DMSP in enhancing this attraction. These navigation behaviours may contribute to the rapid turnover of polymers in the ocean, with important consequences for marine carbon cycling.

Similar but different: Characterization of dddD gene-mediated DMSP metabolism among coral-associated Endozoicomonas.

Endozoicomonas are often predominant bacteria and prominently important in coral health. Their role in dimethylsulfoniopropionate (DMSP) degradation has been a subject of discussion for over a decade. A previous study found that Endozoicomonas degraded DMSP through the dddD pathway. This process releases dimethyl sulfide, which is vital for corals coping with thermal stress. However, little is known about the related gene regulation and metabolic abilities of DMSP metabolism in Endozoicomonadaceae. In this study, we isolated a novel Endozoicomonas DMSP degrader and observed a distinct DMSP metabolic trend in two phylogenetically close dddD-harboring Endozoicomonas species, confirmed genetically by comparative transcriptomic profiling and visualization of the change of DMSP stable isotopes in bacterial cells using nanoscale secondary ion spectrometry. Furthermore, we found that DMSP cleavage enzymes are ubiquitous in coral Endozoicomonas with a preference for having DddD lyase. We speculate that harboring DMSP degrading genes enables Endozoicomonas to successfully colonize various coral species across the globe.

Microbial drivers of DMSO reduction and DMS-dependent methanogenesis in saltmarsh sediments.

Saltmarshes are highly productive environments, exhibiting high abundances of organosulfur compounds. Dimethylsulfoniopropionate (DMSP) is produced in large quantities by algae, plants, and bacteria and is a potential precursor for dimethylsulfoxide (DMSO) and dimethylsulfide (DMS). DMSO serves as electron acceptor for anaerobic respiration leading to DMS formation, which is either emitted or can be degraded by methylotrophic prokaryotes. Major products of these reactions are trace gases with positive (CO2, CH4) or negative (DMS) radiative forcing with contrasting effects on the global climate. Here, we investigated organic sulfur cycling in saltmarsh sediments and followed DMSO reduction in anoxic batch experiments. Compared to previous measurements from marine waters, DMSO concentrations in the saltmarsh sediments were up to ~300 fold higher. In batch experiments, DMSO was reduced to DMS and subsequently consumed with concomitant CH4 production. Changes in prokaryotic communities and DMSO reductase gene counts indicated a dominance of organisms containing the Dms-type DMSO reductases (e.g., Desulfobulbales, Enterobacterales). In contrast, when sulfate reduction was inhibited by molybdate, Tor-type DMSO reductases (e.g., Rhodobacterales) increased. Vibrionales increased in relative abundance in both treatments, and metagenome assembled genomes (MAGs) affiliated to Vibrio had all genes encoding the subunits of DMSO reductases. Molar conversion ratios of <1.3 CH4 per added DMSO were accompanied by a predominance of the methylotrophic methanogens Methanosarcinales. Enrichment of mtsDH genes, encoding for DMS methyl transferases in metagenomes of batch incubations indicate their role in DMS-dependent methanogenesis. MAGs affiliated to Methanolobus carried the complete set of genes encoding for the enzymes in methylotrophic methanogenesis.

Molecular discoveries in microbial DMSP synthesis.

Dimethylsulfoniopropionate (DMSP) is one of the Earth's most abundant organosulfur compounds because many marine algae, bacteria, corals and some plants produce it to high mM intracellular concentrations. In these organisms, DMSP acts an anti-stress molecule with purported roles to protect against salinity, temperature, oxidative stress and hydrostatic pressure, amongst many other reported functions. However, DMSP is best known for being a major precursor of the climate-active gases and signalling molecules dimethylsulfide (DMS), methanethiol (MeSH) and, potentially, methane, through microbial DMSP catabolism. DMSP catabolism has been extensively studied and the microbes, pathways and enzymes involved have largely been elucidated through the application of molecular research over the last 17 years. In contrast, the molecular biology of DMSP synthesis is a much newer field, with the first DMSP synthesis enzymes only being identified in the last 5 years. In this review, we discuss how the elucidation of key DMSP synthesis enzymes has greatly expanded our knowledge of the diversity of DMSP-producing organisms, the pathways used, and what environmental factors regulate production, as well as to inform on the physiological roles of DMSP. Importantly, the identification of key DMSP synthesis enzymes in the major groups of DMSP producers has allowed scientists to study the distribution and predict the importance of different DMSP-producing organisms to global DMSP production in diverse marine and sediment environments. Finally, we highlight key challenges for future molecular research into DMSP synthesis that need addressing to better understand the cycling of this important marine organosulfur compound, and its magnitude in the environment.

Microbial Dimethylsulfoniopropionate Cycling in Deep Sediment of the Mariana Trench.

Dimethylsulfoniopropionate (DMSP) and related organic sulfur compounds play key roles in global sulfur cycling. Bacteria have been found to be important DMSP producers in seawater and surface sediments of the aphotic Mariana Trench (MT). However, detailed bacterial DMSP cycling in the Mariana Trench subseafloor remains largely unknown. Here, the bacterial DMSP-cycling potential in a Mariana Trench sediment core (7.5 m in length) obtained at a 10,816-m water depth was investigated using culture-dependent and -independent methods. The DMSP content fluctuated along the sediment depth and reached the highest concentration at 15 to 18 cm below the seafloor (cmbsf). dsyB was the dominant known DMSP synthetic gene, existing in 0.36 to 1.19% of the bacteria, and was identified in the metagenome-assembled genomes (MAGs) of previously unknown bacterial DMSP synthetic groups such as Acidimicrobiia, Phycisphaerae, and Hydrogenedentia. dddP, dmdA, and dddX were the major DMSP catabolic genes. The DMSP catabolic activities of DddP and DddX retrieved from Anaerolineales MAGs were confirmed by heterologous expression, indicating that such anaerobic bacteria might participate in DMSP catabolism. Moreover, genes involved in methanethiol (MeSH) production from methylmercaptopropionate (MMPA) and dimethyl sulfide (DMS), MeSH oxidation, and DMS production were highly abundant, suggesting active conversions between different organic sulfur compounds. Finally, most culturable DMSP synthetic and catabolic isolates possessed no known DMSP synthetic and catabolic genes, and actinomycetes could be important groups involved in both DMSP synthesis and catabolism in Mariana Trench sediment. This study extends the current understanding of DMSP cycling in Mariana Trench sediment and highlights the need to uncover novel DMSP metabolic genes/pathways in extreme environments. IMPORTANCE Dimethylsulfoniopropionate (DMSP) is an abundant organosulfur molecule in the ocean and is the precursor for the climate-active volatile gas dimethyl sulfide. Previous studies focused mainly on bacterial DMSP cycling in seawater, coastal sediment, and surface trench sediment samples, but DMSP metabolism in the Mariana Trench (MT) subseafloor sediments remains unknown. Here, we describe the DMSP content and metabolic bacterial groups in the subseafloor of the MT sediment. We found that the tendency for vertical variation of the DMSP content in the MT was distinct from that of the continent shelf sediment. Although dsyB and dddP were the dominant DMSP synthetic and catabolic genes in the MT sediment, respectively, both metagenomic and culture methods revealed multiple previously unknown DMSP metabolic bacterial groups, especially anaerobic bacteria and actinomycetes. The active conversion of DMSP, DMS, and methanethiol may also occur in the MT sediments. These results provide novel insights for understanding DMSP cycling in the MT.

Discovery of dimethylsulfoxonium propionate lyases - a missing enzyme relevant to the global sulfur cycle.

Six dimethylsulfoniopropionate (DMSP) lyases have been shown to cleave the marine sulfur metabolite dimethylsulfoxonium propionate (DMSOP) into DMSO and acrylate. This discovery characterises a missing enzyme relevant to the global sulfur cycle.

Dimethylsulfoniopropionate decorated cryogels as synthetic spatially structured habitats of marine bacterial communities.

In microbial consortia bacteria often settle on other organisms that provide nutrients and organic material for their growth. This is true for the plankton where microalgae perform photosynthesis and exude metabolites that feed associated bacteria. The investigation of such processes is difficult since algae provide bacteria with a spatially structured environment with a gradient of released organic material that is hard to mimic. Here we introduce the design and synthesis of a cryogel-based microstructured habitat for bacteria that provides dimethylsulfoniopropionate (DMSP) as a carbon and sulfur source for growth. DMSP, a widely distributed metabolite released by algae, is thereby made available for bacteria in a biomimetic manner. Based on a novel DMSP derived building block (DMSP-HEMA), we synthesized cryogels providing structured surfaces for settlement and delivering the organic material fueling bacterial growth. By monitoring bacterial settlement and performance we show that the cryogels represent microbial arenas mimicking the ecological situation in the plankton.

Airborne dimethyl sulfide (DMS) cues dimethylsulfoniopropionate (DMSP) increases in the intertidal green alga Ulva fenestrata.

Although the use of airborne molecules as infochemicals is common in terrestrial plants, it has not been shown to occur in an ecologically relevant context in marine seaweeds. Like terrestrial plants, intertidal plants spend part of their lives emersed at low tide and release volatile organic compounds (VOCs) into the air when they are grazed or physiologically stressed. We hypothesized seaweeds could use airborne VOCs as infochemicals and respond to them by upregulating a keystone defensive metabolite, dimethylsulfoniopropionate (DMSP). We conducted laboratory and field experiments in which Ulva fenestrata was exposed to airborne dimethyl sulfide (DMS), a volatile antiherbivore and antioxidant metabolite released when the seaweed is grazed or physiologically stressed. In the laboratory, U. fenestrata exposed to DMS had 43-48% higher DMSP concentrations, relative to controls, 6-9 days after exposure. In the field, U. fenestrata 1 m downwind of DMS emitters had 19% higher DMSP concentrations than upwind seaweeds after 11 days. To our knowledge, this is the first demonstration of a marine plant using an airborne molecule released when damaged to elicit defensive responses. Our study suggests that the ability to detect airborne compounds has evolved multiple times or before the divergence of terrestrial plants and green algae.

Complete genome sequence of one novel marine Pseudomonas sp. BSw22131 growing with dimethylsulfoniopropionate (DMSP) as the sole carbon source.

Members of the genus Pseudomonas have been frequently isolated from the marine environment, indicating their ecological role in native habitats. One bacterial strain, Pseudomonas sp. BSw22131, was isolated from seawater in Kongsfjorden, Svalbard. The bacterium can grow with algae-derived dimethylsulfoniopropionate (DMSP) as the sole carbon source. Here, we sequenced the complete genome of strain BSw22131, which contained a single circular chromosome of 5,739,290 (G + C content of 58.23 mol%) without any plasmids. A total of 5362 protein-coding genes, 65 tRNA genes, and 16 rRNA genes were obtained. Genome sequence analysis revealed that strain BSw22131 was not only a potential novel species of the genus Pseudomonas but also different from Pseudomonas sp. DMSP-1 that was isolated from the same habitat and also utilized DMSP as the sole carbon source for growth. The results can be helpful for understanding the catabolism of the genus Pseudomonas in sulfur cycling in the Arctic fjord ecosystem.

A new dimethylsulfoniopropionate lyase of the cupin superfamily in marine bacteria.

Dimethylsulfoniopropionate (DMSP) is a marine organosulfur compound with important roles in stress protection, marine biogeochemical cycling, chemical signalling and atmospheric chemistry. Diverse marine microorganisms catabolize DMSP via DMSP lyases to generate the climate-cooling gas and info-chemical dimethyl sulphide. Abundant marine heterotrophs of the Roseobacter group (MRG) are well known for their ability to catabolize DMSP via diverse DMSP lyases. Here, a new DMSP lyase DddU within the MRG strain Amylibacter cionae H-12 and other related bacteria was identified. DddU is a cupin superfamily DMSP lyase like DddL, DddQ, DddW, DddK and DddY, but shares <15% amino acid sequence identity with these enzymes. Moreover, DddU proteins forms a distinct clade from these other cupin-containing DMSP lyases. Structural prediction and mutational analyses suggested that a conserved tyrosine residue is the key catalytic amino acid residue in DddU. Bioinformatic analysis indicated that the dddU gene, mainly from Alphaproteobacteria, is widely distributed in the Atlantic, Pacific, Indian and polar oceans. For reference, dddU is less abundant than dddP, dddQ and dddK, but much more frequent than dddW, dddY and dddL in marine environments. This study broadens our knowledge on the diversity of DMSP lyases, and enhances our understanding of marine DMSP biotransformation.

Sulfoquinovose is a widespread organosulfur substrate for Roseobacter clade bacteria in the ocean.

Sulfoquinovose (SQ) is one of the most abundant organosulfur compounds in the biosphere, and its biosynthesis and degradation can represent an important contribution to the sulfur cycle. To data, in marine environments, the microorganisms capable of metabolising SQ have remained unidentified and the sources of SQ are still uncertain. Herein, the marine Roseobacter clade bacteria (RCB) Dinoroseobacter shibae DFL 12 and Roseobacter denitrificans OCh 114 were found to grow using SQ as the sole source of carbon and energy. In the presence of SQ, we identified a set of highly up-regulated proteins encoded by gene clusters in these two organisms, of which four homologues to proteins in the SQ monooxygenase pathway of Agrobacterium fabrum C58 may confer the ability to metabolise SQ to these marine bacteria. The sulfite released from SQ desulfonation by FMN-dependent SQ monooxygenase (SmoC) may provide bacteria with reduced sulfur for assimilation, while proteins associated with sulfite production via assimilatory sulfate reduction were significantly down-regulated. Such SQ catabolic genes are restricted to a limited number of phylogenetically diverse bacterial taxa with the predominate genera belonging to the Roseobacter clade (Roseobacteraceae). Moreover, transcript analysis of Tara Oceans project and coastal Bohai Sea samples provided additional evidence for SQ metabolism by RCB. SQ was found to be widely distributed in marine phytoplankton and cyanobacteria with variable intracellular concentrations ranging from micromolar to millimolar levels, and the amounts of SQ on particulate organic matter in field samples were, on average, lower than that of dimethylsulfoniopropionate (DMSP) by one order of magnitude. Together, the phototroph-derived SQ actively metabolised by RCB represents a previously unidentified link in the marine sulfur cycle.

Ubiquitous occurrence of a dimethylsulfoniopropionate ABC transporter in abundant marine bacteria.

Dimethylsulfoniopropionate (DMSP) is a ubiquitous organosulfur compound in marine environments with important functions in both microorganisms and global biogeochemical carbon and sulfur cycling. The SAR11 clade and marine Roseobacter group (MRG) represent two major groups of heterotrophic bacteria in Earth's surface oceans, which can accumulate DMSP to high millimolar intracellular concentrations. However, few studies have investigated how SAR11 and MRG bacteria import DMSP. Here, through comparative genomics analyses, genetic manipulations, and biochemical analyses, we identified an ABC (ATP-binding cassette)-type DMSP-specific transporter, DmpXWV, in Ruegeria pomeroyi DSS-3, a model strain of the MRG. Mutagenesis suggested that DmpXWV is a key transporter responsible for DMSP uptake in strain DSS-3. DmpX, the substrate binding protein of DmpXWV, had high specificity and binding affinity towards DMSP. Furthermore, the DmpX DMSP-binding mechanism was elucidated from structural analysis. DmpX proteins are prevalent in the numerous cosmopolitan marine bacteria outside the SAR11 clade and the MRG, and dmpX transcription was consistently high across Earth's entire global ocean. Therefore, DmpXWV likely enables pelagic marine bacteria to efficiently import DMSP from seawater. This study offers a new understanding of DMSP transport into marine bacteria and provides novel insights into the environmental adaption of marine bacteria.

Recent insights into oceanic dimethylsulfoniopropionate biosynthesis and catabolism.

Dimethylsulfoniopropionate (DMSP), a globally important organosulfur compound is produced in prodigious amounts (2.0 Pg sulfur) annually in the marine environment by phytoplankton, macroalgae, heterotrophic bacteria, some corals and certain higher plants. It is an important marine osmolyte and a major precursor molecule for the production of climate-active volatile gas dimethyl sulfide (DMS). DMSP synthesis take place via three pathways: a transamination 'pathway-' in some marine bacteria and algae, a Met-methylation 'pathway-' in angiosperms and bacteria and a decarboxylation 'pathway-' in the dinoflagellate, Crypthecodinium. The enzymes DSYB and TpMMT are involved in the DMSP biosynthesis in eukaryotes while marine heterotrophic bacteria engage key enzymes such as DsyB and MmtN. Several marine bacterial communities import DMSP and degrade it via cleavage or demethylation pathways or oxidation pathway, thereby generating DMS, methanethiol, and dimethylsulfoxonium propionate, respectively. DMSP is cleaved through diverse DMSP lyase enzymes in bacteria and via Alma1 enzyme in phytoplankton. The demethylation pathway involves four different enzymes, namely DmdA, DmdB, DmdC and DmdD/AcuH. However, enzymes involved in the oxidation pathway have not been yet identified. We reviewed the recent advances on the synthesis and catabolism of DMSP and enzymes that are involved in these processes.

Comparative Analysis of Sulfonium-π, Ammonium-π, and Sulfur-π Interactions and Relevance to SAM-Dependent Methyltransferases.

We report the measurement and analysis of sulfonium-π, thioether-π, and ammonium-π interactions in a ß-hairpin peptide model system, coupled with computational investigation and PDB analysis. These studies indicated that the sulfonium-π interaction is the strongest and that polarizability contributes to the stronger interaction with sulfonium relative to ammonium. Computational studies demonstrate that differences in solvation of the trimethylsulfonium versus the trimethylammonium group also contribute to the stronger sulfonium-π interaction. In comparing sulfonium-π versus sulfur-π interactions in proteins, analysis of SAM- and SAH-bound enzymes in the PDB suggests that aromatic residues are enriched in close proximity to the sulfur of both SAM and SAH, but the populations of aromatic interactions of the two cofactors are not significantly different, with the exception of the Me-π interactions in SAM, which are the most prevalent interaction in SAM but are not possible for SAH. This suggests that the weaker interaction energies due to loss of the cation-π interaction in going from SAM to SAH may contribute to turnover of the cofactor.

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.