ANALYSIS OF THE FNRL GENE AND ITS FUNCTION IN RHODOBACTER-CAPSULATUS

The fnr gene encodes a regulatory protein involved in the response to oxygen in a variety of bacterial genera. For example, it was previousl y shown that the anoxygenic, photosynthetic bacterium Rhodobacter spha eroides requires the fnrL gene for growth under anaerobic, photosynthe tic conditions, Additionally, the FnrL protein in R. sphaeroides is re quired for anaerobic growth in the dark with an alternative electron a cceptor, but it is not essential for aerobic growth. In this study, th e fnrL locus from Rhodobacter capsulatus was cloned and sequenced. Sur prisingly, an R. capsulatus strain with the fnrL gene deleted grows li ke the wild type under either photosynthetic or aerobic conditions but does not grow anaerobically with alternative electron accepters such as dimethyl sulfoxide (DMSO) or trimethylamine oxide. It is demonstrat ed that the c-type cytochrome induced upon anaerobic growth on DMSO is not synthesized in the R. capsulatus fnrL mutant. In contrast to wild -type strains, R. sphaeroides and R. capsulatus fnrL mutants do not sy nthesize the anaerobically, DMSO-induced reductase. Mechanisms that ex plain the basis for FnrL function in both organisms are are dicussed.