Utilization of dimethyl sulfide as a sulfur source with the aid of light by Marinobacterium sp. strain DMS-S1

Strain DMS-S1 isolated from seawater was able to utilize dimethyl sulfide (DMS) as a sulfur source only in the presence of light in a sulfur-lacking medium. Phylogenetic analysis based on 16S ribosomal DNA genes indicated that the strain was closely related to Marinobacterium georgiense. The strain produced dimethyl sulfoxide (DMSO), which was a main metabolite, and small amounts of formate and formaldehyde when grown on DMS as the sole sulfur source. The cells of the strain grown with succinate as a carbon source were able to use methyl mercaptan or methanesulfonate besides DMS but not DMSO or dimethyl sulfone as a sole sulfur source. DMS was transformed to DMSO primarily at wavelengths between 380 and 480 nm by heat-stable photosensitizers released by the strain. DMS was also degraded to formaldehyde in the presence of light by unidentified heat-stable factors released by the strain, and it appeared that strain DMS-S1 used the degradation products, which should be sulfite, sulfate, or methanesulfonate, as sulfur sources.     

Utilization of Dimethyl Sulfide as a Sulfur Source with the Aid of Light by Marinobacterium sp. Strain DMS-S1

Strain DMS-S1 isolated from seawater was able to utilize dimethyl sulfide (DMS) as a sulfur source only in the presence of light in a sulfur-lacking medium. Phylogenetic analysis based on 16S ribosomal DNA genes indicated that the strain was closely related to Marinobacterium georgiense. The strain produced dimethyl sulfoxide (DMSO), which was a main metabolite, and small amounts of formate and formaldehyde when grown on DMS as the sole sulfur source. The cells of the strain grown with succinate as a carbon source were able to use methyl mercaptan or methanesulfonate besides DMS but not DMSO or dimethyl sulfone as a sole sulfur source. DMS was transformed to DMSO primarily at wavelengths between 380 and 480 nm by heat-stable photosensitizers released by the strain. DMS was also degraded to formaldehyde in the presence of light by unidentified heat-stable factors released by the strain, and it appeared that strain DMS-S1 used the degradation products, which should be sulfite, sulfate, or methanesulfonate, as sulfur sources.     

Dynamics of Dimethyl Sulfide in a Marine Microbial Mat

Abstract The microbial mat was chosen as a model ecosystem to study dynamics of dimethyl sulfide (DMS) in marine sediments in order to gain insight into key processes and factors which determine emission rates. A practical advantage, compared to open ocean ecosystems, is that microbial mats contain high biomasses of different functional groups of bacteria involved in DMS dynamics, and that DMS concentrations are generally high enough to allow direct measurement of emission rates. Field data showed that, during the seasonal development of microbial mats, concentrations of chlorophyll a corresponded to dimethylsulfoniopropionate (DMSP). DMSP is an important precursor of DMS. It was demonstrated, with laboratory cultures, that various species of benthic diatoms produce substantial amounts of DMSP. The abundances of aerobic and anaerobic DMS- or DMSO-utilizing bacteria were estimated using the most-probable-number technique. Laboratory experiments with relatively undisturbed sediment cores showed that microbial mats act as a sink for DMS under oxic/light (day) conditions, and as a source of DMS under anoxic/dark (night) conditions. Axenic culture studies with Chromatium vinosum M2 and Thiocapsa pfennigii M8 (isolated from a microbial mat) showed that, under anoxic/light conditions, DMS was quantitatively converted to dimethylsulfoxide (DMSO). T. roseopersicina M11 converted DMSP to DMS and acrylate, apparently without use of either substrate. Received: 5 May 1997; Accepted: 21 August 1997     

Phylogenetic identification and metabolism of marine dimethylsulfide-consuming bacteria

Microbial consumption is one of the main processes, along with photolysis and ventilation, that remove the biogenic trace gas dimethylsulfide (DMS) from the surface ocean. Although a few isolates of marine bacteria have been studied for their ability to utilize DMS, little is known about the characteristics or phylogenetic affiliation of DMS consumers in seawater. We enriched coastal and open-ocean waters with different carbon sources to stimulate different bacterial communities (glucose-consuming bacteria, methyl group-consuming bacteria and DMS consumers) in order to test how this affected DMS consumption and to examine which organisms might be involved. Dimethylsulfide consumption was greatly stimulated in the DMS addition treatments whereas there was no stimulation in the other treatments. Analysis of microbial DNA by two different techniques (sequenced bands from DGGE gels and clone libraries) showed that bacteria grown specifically with the presence of DMS were closely related to the genus Methylophaga. We also followed the fate of consumed DMS in some of the enrichments. Dimethylsulfide was converted mostly to DMSO in glucose or methanol enrichments, whereas it was converted mostly to sulfate in DMS enrichments, the latter suggesting use of DMS as a carbon and energy source. Our results indicate that unlike the biochemical precursor of DMS, dimethylsulfoniopropionate (DMSP), which is consumed by a broad spectrum of marine microorganisms, DMS seems to be utilized as a carbon and electron source by specialists. This is consistent with the usual observation that DMSP turns over at much higher rates than DMS.     

Oxidation of Dimethyl Sulfide to Dimethyl Sulfoxide by Phototrophic Purple Bacteria

Enrichment cultures of phototrophic purple bacteria rapidly oxidized up to 10 mM dimethyl sulfide (DMS) to dimethyl sulfoxide (DMSO). DMSO was qualitatively identified by proton nuclear magnetic resonance. By using a biological assay, DMSO was always quantitatively recovered from the culture media. DMS oxidation was not detected in cultures incubated in the dark, and it was slow in cultures exposed to full daylight. Under optimal conditions, the second-order rate constant for DMS oxidation was 6 day⁻¹ mg of protein⁻¹ ml⁻¹. The rate constant was reduced in the presence of high concentration of sulfide (>1 mM), but was not affected by the addition of acetate. DMS was also oxidized to DMSO by a pure strain (tentatively identified as a Thiocystis sp.) isolated from the enrichment cultures. DMS supported growth of the enrichment cultures and of the pure strain by serving as an electron source for photosynthesis. A determination of the amount of protein produced in the cultures and an estimation of the electron balance suggested that the two electrons liberated during the oxidation of DMS to DMSO were quantitatively used to reduce carbon dioxide to biomass. The oxidation of DMS by phototrophic purple bacteria may be an important source of DMSO detected in anaerobic ponds and marshes.     

Dimethyl sulphide and methanethiol formation in microbial mats: potential pathways for biogenic signatures

Mechanisms of dimethyl sulphide (DMS) and methanethiol (MT) production and consumption were determined in moderately hypersaline mats, Guerrero Negro, Mexico. Biological pathways regulated the net flux of DMS and MT as revealed by increases in flux resulting from decreased salinity, increased temperature and the removal of oxygen. Dimethylsulphoniopropionate (DMSP) was not present in these microbial mats and DMS and MT are probably formed by the reaction of photosynthetically produced low-molecular weight organic carbon and biogenic hydrogen sulphide derived from sulphate reduction. These observations provide an alternative to the notion that DMSP or S-containing amino acids are the dominant precursors of DMS in intertidal sediment systems. The major sink for DMS in the microbial mats was biological consumption, whereas photochemical oxidation to dimethylsulphoxide was the major sink for DMS in the overlying water column. Diel flux measurements demonstrated that significantly more DMS is released from the system during the night than during the day. The major consumers of DMS in the presence of oxygen were monooxygenase-utilizing bacteria, whereas under anoxic conditions, DMS was predominantly consumed by sulphate-reducing bacteria and methanethiol was consumed by methanogenic bacteria. Aerobic and anaerobic consumption rates of DMS were nearly identical. Mass balance estimates suggest that the consumption in the water column is likely to be smaller than net the flux from the mats. Volatile organic sulphur compounds are thus indicators of high rates of carbon fixation and sulphate reduction in these laminated sediment ecosystems, and atmospheric sulphur can be generated as a biogenic signature of the microbial mat community.     

Phylogenetic analysis of culturable dimethyl sulfide-producing bacteria from a spartina-dominated salt marsh and estuarine water

Dimethylsulfoniopropionate (DMSP), an abundant osmoprotectant found in marine algae and salt marsh cordgrass, can be metabolized to dimethyl sulfide (DMS) and acrylate by microbes having the enzyme DMSP lyase. A suite of DMS-producing bacteria isolated from a salt marsh and adjacent estuarine water on DMSP agar plates differed markedly from the pelagic strains currently in culture. While many of the salt marsh and estuarine isolates produced DMS and methanethiol from methionine and dimethyl sulfoxide, none appeared to be capable of producing both methanethiol and DMS from DMSP. DMSP, and its degradation products acrylate and beta-hydroxypropionate but not methyl-3-mecaptopropionate or 3-mercaptopropionate, served as a carbon source for the growth of all the alpha- and beta- but only some of the gamma-proteobacterium isolates. Phylogenetic analysis of 16S rRNA gene sequences showed that all of the isolates were in the group Proteobacteria, with most of them belonging to the alpha and gamma subclasses. Only one isolate was identified as a beta-proteobacterium, and it had >98% 16S rRNA sequence homology with a terrestrial species of Alcaligenes faecalis. Although bacterial population analysis based on culturability has its limitations, bacteria from the alpha and gamma subclasses of the Proteobacteria were the dominant DMS producers isolated from salt marsh sediments and estuaries, with the gamma subclass representing 80% of the isolates. The alpha-proteobacterium isolates were all in the Roseobacter subgroup, while many of the gamma-proteobacteria were closely related to the pseudomonads; others were phylogenetically related to Marinomonas, Psychrobacter, or Vibrio species. These data suggest that DMSP cleavage to DMS and acrylate is a characteristic widely distributed among different phylotypes in the salt marsh-estuarine ecosystem.     

Dimethylsulfide is an energy source for the heterotrophic marine bacterium Sagittula stellata

Dimethylsulfide (DMS) is a volatile organosulfur compound, ubiquitous in the oceans, that has been credited with various roles in biogeochemical cycling and in climate control. Various oceanic sinks of DMS are known - both chemical and biological - although they are poorly understood. In addition to the utilization of DMS as a carbon or a sulfur source, some Bacteria are known to oxidize it to dimethylsulfoxide (DMSO). Sagittula stellata is a heterotrophic member of the Alphaproteobacteria found in marine environments. It has been shown to oxidize DMS during heterotrophic growth on sugars, but the reasons for and the mechanisms of this oxidation have not been investigated. Here, we show that the oxidation of DMS to DMSO is coupled to ATP synthesis in S. stellata and that DMS acts as an energy source during chemoorganoheterotrophic growth of the organism on fructose and on succinate. DMS dehydrogenase (which is responsible for the oxidation of DMS to DMSO in other marine Bacteria) and DMSO reductase activities were absent from cells grown in the presence of DMS, indicating an alternative route of DMS oxidation in this organism.     

Growth of Rhodopseudomonas capsulata under anaerobic dark conditions with dimethyl sulfoxide

The photosynthetic bacterium, Rhodopseudomonas capsulata, could be cultured anaerobically in the absence of light on a synthetic medium with glucose as the carbon source only when dimethyl sulfoxide (DMSO) was added. The extent of growth was proportional to both DMSO and glucose concentrations. Optimal growth was achieved with 20 mm DMSO and 0.25% glucose. Under the best conditions, cells divided with a doubling time of 12 h. Pyruvate also supported the anaerobic dark growth of R. capsulata when DMSO was present. R. capsulata, R. sphaeroides, and R. palustris strains were all able to grow under anaerobic dark conditions with DMSO. Experiments using [¹⁴C]DMSO showed that more than 95% of the ¹⁴C was converted by cultures of R. capsulata to a volatile compound, identified as dimethyl sulfide (DMS) by gas chromatography, thus demonstrating that DMSO was being reduced to DMS during growth. These results indicate that R. capsulata requires a terminal electron acceptor for anaerobic dark growth and that DMSO can serve that function.     

SIP metagenomics identifies uncultivated Methylophilaceae as dimethylsulphide degrading bacteria in soil and lake sediment

Dimethylsulphide (DMS) has an important role in the global sulphur cycle and atmospheric chemistry. Microorganisms using DMS as sole carbon, sulphur or energy source, contribute to the cycling of DMS in a wide variety of ecosystems. The diversity of microbial populations degrading DMS in terrestrial environments is poorly understood. Based on cultivation studies, a wide range of bacteria isolated from terrestrial ecosystems were shown to be able to degrade DMS, yet it remains unknown whether any of these have important roles in situ. In this study, we identified bacteria using DMS as a carbon and energy source in terrestrial environments, an agricultural soil and a lake sediment, by DNA stable isotope probing (SIP). Microbial communities involved in DMS degradation were analysed by denaturing gradient gel electrophoresis, high-throughput sequencing of SIP gradient fractions and metagenomic sequencing of phi29-amplified community DNA. Labelling patterns of time course SIP experiments identified members of the Methylophilaceae family, not previously implicated in DMS degradation, as dominant DMS-degrading populations in soil and lake sediment. Thiobacillus spp. were also detected in ¹³C-DNA from SIP incubations. Metagenomic sequencing also suggested involvement of Methylophilaceae in DMS degradation and further indicated shifts in the functional profile of the DMS-assimilating communities in line with methylotrophy and oxidation of inorganic sulphur compounds. Overall, these data suggest that unlike in the marine environment where gammaproteobacterial populations were identified by SIP as DMS degraders, betaproteobacterial Methylophilaceae may have a key role in DMS cycling in terrestrial environments.     

The bacteria of the sulphur cycle

This paper concentrates on the bacteria involved in the reductions and oxidations of inorganic sulphur compounds under anaerobic conditions. The genera of the dissimilatory sulphate-reducing bacteria known today are discussed with respect to their different capacities to decompose and oxidize various products of fermentative degradations of organic matter. The utilization of molecular hydrogen and formate by sulphate reducers shifts fermentations towards the energetically more favourable formation of acetate. Since acetate amounts to about two-thirds of the degradation products of organic matter, the complete anaerobic oxidation of acetate by several genera of the sulphate-reducing bacteria is an important function for terminal oxidation in sulphate-sufficient environments. The results of pure culture studies agree well with ecological investigations of several authors who showed the significance of sulphate reduction for the complete oxidation of organic matter in anaerobic marine habitats. In the dissimilatory sulphur-reducing bacteria of the genus Desulfuromonas the oxidation of acetate is linked to the reduction of elemental sulphur. Major characteristics of the anaerobic, sulphide-oxidizing phototrophic green and purple sulphur bacteria as well as of some facultative anoxygenic cyanobacteria, are given. By the formation of elemental sulphur and sulphate, these bacteria establish sulphur cycles with the sulphide-forming bacteria. In view of the morphological diversity of the sulphate-reducing bacteria and question of possible evolutionary relations to phototrophic sulphur bacteria is raised.     

Oxidation of dimethyl sulfide byPseudomonas acidovorans DMR-11 isolated from peat biofilter

Summary Pseudomonas acidovorans DMR-11, capable of oxidizing dimethyl sulfide (DMS), was isolated from peat biofilter. DMS as a sole carbon or energy source was not degraded, but it was co-degraded in the medium containing organic carbon sources. The removal rate of DMS in heat-treated glucose medium was 1.12×10^–17 mole/h cell at 30 °C. Dimethyl sulfoxide (DMSO) was the only product of DMS oxidation and was formed stoichiometrically. DMS was reversibly evolved in excess of DMSO. The cell free extract of strain DMR-11 oxidized DMS in presence of NADPH.     

Methylated sulfur compounds in microbial mats: in situ concentrations and metabolism by a colorless sulfur bacterium.

The concentrations of the volatile organic sulfur compounds methanethiol, dimethyl disulfide, and dimethyl sulfide (DMS) and the viable population capable of DMS utilization in laminated microbial ecosystems were evaluated. Significant levels of DMS and dimethyl disulfide (maximum concentrations of 220 and 24 nmol cm3 of sediment-1, respectively) could be detected only at the top 20 mm of the microbial mat, whereas methanethiol was found only at depth horizons from 20 to 50 mm (maximum concentration of 42 nmol cm3 of sediment-1). DMS concentrations in the surface layer doubled after cold hydrolysis of its precursor, dimethylsulfoniopropionate. Most-probable-number counts revealed 2.2 x 10(5) cells cm3 of sediment-1, in the 0- to 5-mm depth horizon, capable of growth on DMS as the sole source of energy. An obligately chemolithoautotrophic bacillus designated strain T5 was isolated from the top layer of the marine sediment. Continuous culture studies in which DMS was the growth-limiting substrate revealed a maximum specific growth rate of 0.10 h-1 and a saturation constant of 90 mumol liter-1 for aerobic growth on this substrate.     

Methylated sulfur compounds in microbial mats: in situ concentrations and metabolism by a colorless sulfur bacterium

The concentrations of the volatile organic sulfur compounds methanethiol, dimethyl disulfide, and dimethyl sulfide (DMS) and the viable population capable of DMS utilization in laminated microbial ecosystems were evaluated. Significant levels of DMS and dimethyl disulfide (maximum concentrations of 220 and 24 nmol cm3 of sediment-1, respectively) could be detected only at the top 20 mm of the microbial mat, whereas methanethiol was found only at depth horizons from 20 to 50 mm (maximum concentration of 42 nmol cm3 of sediment-1). DMS concentrations in the surface layer doubled after cold hydrolysis of its precursor, dimethylsulfoniopropionate. Most-probable-number counts revealed 2.2 x 10(5) cells cm3 of sediment-1, in the 0- to 5-mm depth horizon, capable of growth on DMS as the sole source of energy. An obligately chemolithoautotrophic bacillus designated strain T5 was isolated from the top layer of the marine sediment. Continuous culture studies in which DMS was the growth-limiting substrate revealed a maximum specific growth rate of 0.10 h-1 and a saturation constant of 90 mumol liter-1 for aerobic growth on this substrate.     

Scatchard analysis of methane sulfinic acid production from dimethyl sulfoxide: a method to quantify hydroxyl radical formation in physiologic systems

A major impediment to the confirmation of free radical mechanisms in pathogenesis is a lack of direct, chemical evidence that oxygen centered free radicals actually arise in living tissues in quantities sufficient to cause serious damage. This investigation was conducted to validate the use of dimethyl sulfoxide (DMSO) as a quantitative molecular probe for the generation of hydroxyl radicals (HO.) under physiologic conditions. Reaction of HO. with DMSO produces methane sulfinic acid (MSA) as a primary product, which can be detected by a simple colorimetric assay. To develop a method for estimating total HO. production, we studied two model systems: the superoxide driven Fenton reaction in vitro, using xanthine oxidase as the source of superoxide, and a computer model of Fenton chemistry. Measured MSA production both in vitro and in the computer model was a predictable function of the concentrations of DMSO and competing scavengers of HO., according to the principle of competition kinetics. Both experimental results and model calculations showed that Scatchard analysis may be used to infer total HO. generation, despite the presence of scavengers other than DMSO, such as mannitol. Thus, methane sulfinic acid production from DMSO holds promise as an easily measured marker for HO. formation in biologic systems pretreated with DMSO, and Scatchard analysis of repeated experiments with varying DMSO concentrations can yield an estimate of total HO. generation.     

Optimisation of a fast DMS sensor (FDS) for real time quantification of dimethyl sulfide production by algae

Production of dimethyl sulfide (DMS) from marine samples is often quantified using gas chromatography techniques. Typically, these are labour intensive and have a slow sample turnover rate. Here we demonstrate the use of a portable fast DMS sensor (FDS) that utilises the chemiluminescent reaction of DMS and ozone to measure DMS production in aqueous samples, with a maximum frequency of 10?Hz. We have developed a protocol for quantifying DMS production that removes potential signal interference from other biogenic trace gases such as isoprene (2-methyl-1,3-butadiene) and hydrogen sulfide. The detection limit was 0.89?pM (0.02?ppbv) when using a DMS standard gas mixture. The lowest DMS production rates quantified with the FDS and verified using conventional gas chromatography with flame photometric detection (GC-FPD) were around 0.01?nmol?min^?1. There was a strong correlation in DMS production when comparing the FDS and GC-FPD techniques with a range of marine samples (e.g., r ² ?=?0.94 for Emiliania huxleyi). However, the combined dataset showed the FDS measured 22% higher DMS production than the GC-FPD, with the differences in rates likely due to interfering gases, for example hydrogen sulfide and isoprene. This possible overestimation of DMS production is smaller than the two-fold difference in DMS production between day and night samples from a culture of E. huxleyi. The response time of the instrument to changes in DMS production is method dependent (e.g., geometry of incubation vessel, bubble size) and was approximately 4?min under our conditions when using a culture of E. huxleyi (800?ml) with aeration at 100?ml?min^?1. We suggest the FDS can reduce sample handling, is suitable for short- and long-term measurements of DMS production in algal cultures, and will widen the range of DMS research in marine environments.