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J Bacteriol, June 1998, p. 2924-2930, Vol. 180, No. 11
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Cascade Regulation of Dimethyl Sulfoxide Reductase (dor) Gene Expression in the Facultative Phototroph Rhodobacter sphaeroides 2.4.1T

Nigel J. Mouncey and Samuel Kaplan*

Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center Medical School, Houston, Texas 77030

Received 30 December 1997/Accepted 25 March 1998

Under anaerobic-dark growth conditions, in the presence of the alternative electron acceptor dimethyl sulfoxide (DMSO) or trimethylamine N-oxide (TMAO), Rhodobacter sphaeroides 2.4.1T respires anaerobically using the molybdoenzyme DMSO reductase (DMSOR). Genes encoding DMSOR and associated proteins are encoded by genes of the dor locus. Previously, we 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 sensor-regulator system. Here we further investigate expression of the dor genes through the use of transcriptional lacZ fusions to the dorS, dorR, and dorC promoters. The expression of dorC::lacZ was strongly induced by the absence of oxygen and presence of DMSO. In accordance with our previous findings of DMSOR activity, dorC::lacZ expression was reduced by up to one-third when cells were grown photosynthetically in the presence of DMSO with medium or high light, compared to the expression observed after anaerobic-dark growth. The induction of dorC::lacZ expression in the presence of DMSO was dependent on the DorS and DorR proteins. Expression of the dorS and dorR genes was also induced in the absence of oxygen. In an FnrL mutant, dorS::lacZ expression was not induced when oxygen tensions in the media were lowered, in contrast to what occurred in the wild-type strain. The expression of dorS::lacZ and dorR::lacZ was dependent on the DorS and DorR proteins themselves, suggesting the importance of autoregulation. These results demonstrate a cascade regulation of dor gene expression, where the expression of the regulatory proteins DorS and DorR governs the downstream regulation of the dorCBA operon encoding the structural proteins of DMSOR.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center Medical School, 6431 Fannin, Houston, TX 77030. Phone: (713) 500-5502. Fax: (713) 500-5499. E-mail: skaplan{at}utmmg.med.uth.tmc.edu.

J Bacteriol, June 1998, p. 2924-2930, Vol. 180, No. 11
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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