Molybdate-dependent expression of dimethylsulfoxide reductase in Rhodobacter capsulatus

Expression of the dimethylsulfoxide respiratory (dor) operon of Rhodobacter is regulated by oxygen, light intensity and availability of substrate. Sin ce dimethylsulfoxide reductase contains a pterin molybdenum cofactor, the r ole of molybdate in the regulation of dor operon expression was investigate d, In this report we show that the molybdate-responsive transcriptional reg ulator, MopB, and molybdate are essential for maximal dimethylsulfoxide red uctase activity and expression of a dorA::lacZ transcriptional fusion in Rh odobacter capsulatus. In contrast, mop genes are not required for the expre ssion of the periplasmic nitrate reductase or xanthine dehydrogenase in R. capsulatus under conditions of molybdenum sufficiency. This is the first re port demonstrating a clear functional difference between the ModE homologue s MopB and MopA in this bacterium. The results suggest that MopA is primari ly involved in the regulation of nitrogen fixation gene expression in respo nse to molybdate while MopB has a role in nitrogen fixation and dimethylsul foxide respiration. (C) 2000 Federation of European Microbiological Societi es. Published by Elsevier Science B.V. All rights reserved.