CASCADE REGULATION OF DIMETHYL-SULFOXIDE REDUCTASE (DOR) GENE-EXPRESSION IN THE FACULTATIVE PHOTOTROPH RHODOBACTER-SPHAEROIDES 2.4.1(T)

Under anaerobic-dark growth conditions, in the presence of the alterna tive electron acceptor dimethyl sulfoxide (DMSO) or trimethylamine N-o xide (TMAO), Rhodobacter sphaeroides 2.4.1(T) respires anaerobically u sing the molybdoenzyme DMSO reductase (DMSOR), Genes encoding DMSOR an d associated proteins are encoded by genes of the dor locus. Previousl y, pie demonstrated that the expression of DMSOR is regulated by both the oxygen status of the cell via the FnrL protein and by the presence of DMSO or TMAO, presumably through the DorS-DorR two component senso r-regulator system. Here we further investigate expression of the dor genes through the use of transcriptional lacZ fusions to the dorS, dor R, and dorC promoters. The expression of dorC::lacZ was strongly induc ed by the absence of oxygen and presence of DMSO. In accordance with o ur previous findings of DMSOR activity, dorC::lacZ expression was redu ced by up to one-third when cells were grown photosynthetically in the presence of DMSO with medium or high light, compared to the expressio n observed after anaerobic-dark growth. The induction of dorC::lacZ ex pression in the presence of DMSO was dependent on the DorS and DorR pr oteins. Expression of the dorS and dorR genes was also induced in the absence of oxygen. In an FnrL mutant, dorS::lacZ expression was not in duced when oxygen tensions in the media were lowered, in contrast to w hat occurred in the wild-type strain. The expression of dorS::lacZ and dorR::lacZ was dependent on the DorS and DorR proteins themselves, su ggesting the importance of autoregulation, These results demonstrate a cascade regulation of dor gene expression, where the expression of th e regulatory proteins DorS and DorR governs the downstream regulation of the dorCBA operon encoding the structural proteins of DMSOR.