ISOLATION AND CHARACTERIZATION OF A STRAIN OF RHODOBACTER-SULFIDOPHILUS - A BACTERIUM WHICH GROWS AUTOTROPHICALLY WITH DIMETHYLSULFIDE AS ELECTRON-DONOR

A marine photosynthetic bacterium (strain SH1) was isolated after enrichment under phototrophic conditions in media containing dimethylsulphide (DMS) and bicarbonate (HCO3-) as potential carbon sources. Analysis of culture medium using nuclear magnetic resonance spectrometry showed that during phototrophic and chemotrophic growth of strain SH1 on DMS/HCO3- dimethylsulphoxide (DMSO) was produced from DMS. These results indicate that strain SH1 grew autotrophically with DMS serving as an electron donor in photosynthesis and respiration, but not as a carbon source. Biochemical characterization and 165 rRNA analysis indicated that the isolate was a strain of Rhodobacter sulfidophilus. An assay for the enzyme catalysing the oxidation of DMS (DMS:acceptor oxidoreductase) was developed by measuring electron transfer from DMS to 2,6-dichlorophenolindophenol (DCPIP). This reaction was dependent on phenazine ethosulphate to mediate electron transfer from DMS:acceptor oxidoreductase to DCPIP. DMS:acceptor oxidoreductase was found to have a periplasmic location in strain SH1 as was a reduced methylviologen:DMSO oxidoreductase activity. Zymogram staining patterns of periplasmic fractions indicated that DMS: acceptor oxidoreductase and DMSO reductase were distinct enzymes. This was confirmed by resolution of the two activities by gel filtration.