Analysis of microbial metabolism of biosulfur compounds and adaptive evolution for the degradation of xenobiotics

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Microbial dimethyl sulfide (DMS) conversion is thought to be involved in the global sulfur cycle. We isolated Pseudomonas putida strain DS1 from soil as a bacterium utilizing DMS as a sole sulfur source, and tried to elucidate the DMS conversion mechanism of strain DS1 at biochemical and genetic level. Strain DS1 oxidized DMS to dimethyl sulfone ( DMSO_2) via dimethyl sulfoxide, whereas the oxidation was repressed in the presence of sulfate, suggesting that a sulfate starvation response is involved in DMS utilization by starin DS1. Two of the five DMS-utilization-defective mutants isolated by transposon5 (Th5) mutagenesis had a Tn5 insertion in the ssuEAECBF operon, which has been reported to encode a two-component monooxygenase system (SsuED), an ABC-type transporter (SsuABC), and a small protein (SsuF), and also to play a key role in utilization of sulfonates and sulfate esters in another bacterium, P.pulida strain S-313. Disniption of ssuD and SsuD enzymatic activity demonstrated that methanesulfonate is a metabolic intermediate of DMS and desulfonated by SsuD.Disruption of ssuC cr ssuF also led to a DMS-utilization-defective phenotype. Another two mutants bad a defect in a gene homologous to pa2354 from P.aeruginosa PA01, which encodes a putative transcriptional regulator, while the remaining mutant had a defect in cysM encoding O-acetylserine(thio)-lyase B.