Physiology and biochemistry of sulfur and selenium volatilization and the production of antimicrobial agents by marine and estuarine bacteria

Dimethylsulfoniopropionate (DMSP) is an abundant sulfonium compound in marine environments and is produced by many species of phytoplankton, macroalgae and cordgrass. When these organisms senesce and decay, DMSP is released into the water column where it is available as a carbon and energy source for the bacterial community. One of the primary routes of DMSP metabolism is through its enzymatic cleavage by the enzyme DMSP lyase, which results in the production of dimethylsulfide, the dominant marine sulfur gas, and acrylate. The work presented in this study focuses on DMSP metabolism in bacterial isolates by identifying the cellular location of DMSP lyase and understanding the induction process involved in its synthesis. The differences in DMSP metabolism identified among the bacterial isolates included; location of the lyase, induction by DMSP/acrylate and their structural analogs, constitutive lyase expression, and lyase stability. Furthermore, β-hydroxypropionate was identified as a product of acrylate metabolism. 16S rDNA sequence analysis showed that the DMS-producing isolates were of the Proteobacteria phylum.; Sulfur and selenium undergo similar chemical and biological reactions. The volatilization of selenium in the form of dimethylselenide among selenium contaminated soils is a potential means of bioremediation and therefore selenium was tested as a substitute for sulfur in DMSP synthesis and metabolism. Organically synthesized dimethylselenonioproionate (DMSeP), the selenium analog of DMSP, served as an inducer and substrate for DMSP lyase in pure cultures of marine bacteria and estuarine sediments. Furthermore, the cordgrass Spartina alterniflora, which synthesizes and stores DMSP was capable of biotransforming selenate to DMSeP when grown in selenium contaminated soils.; Marine organisms display an ability to produce diverse secondary metabolites. Several marine bacteria were isolated from salt marsh sediment that displayed antimicrobial activity. One isolate in particular identified as a Pseudoalteromonas species produced an antimicrobial substance that inhibited the growth of several drug-resistant clinical isolates. Partial purification of this antibiotic identified it as a heat labile, negatively charged and highly polar molecule. This discovery is supportive of the fact that the genus Pseudoalteromonas may represent a group of marine organisms that are able to produce unique biologically active metabolites.