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

微生物转化二甲基硫(DMS)被认为参与了全球硫循环。本研究以DMS为唯一硫源，从土壤中分离得到恶臭假单胞菌DS1菌株，并试图从生化和遗传水平上阐明其转化DMS的机理。菌株DS1通过二甲基亚砜将DMS氧化为二甲基亚砜(DMSO2)，而在硫酸盐存在下，DMS的氧化被抑制，这表明DMS的利用与硫酸盐饥饿反应有关。通过转座子5(Th5)诱变获得的5株DMS利用缺陷突变株中，有2株在SsuEECBF操纵子中插入了Tn5，该操纵子编码一个双组分单加氧酶系统(Ssued)、一个ABC型转运蛋白(SsuABC)和一个小蛋白(SsuF)，并在另一株细菌--P.Pulida菌株S-313中对磺酸盐和硫酸酯的利用起到关键作用。SsuD和SsuD酶活性的检测表明，甲烷磺酸盐是DMS的代谢中间产物，并被SsuD脱磺。SsuC cr ssuF的破坏也导致了DMS利用缺陷的表型。另外两个突变株与来自铜绿假单胞菌PA01的pa2354同源的基因存在缺陷，该基因编码一个可能的转录调节因子，而其余的突变株在编码O-乙酰丝氨酸(硫代)裂解酶B的cysM基因上存在缺陷。

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.