Aerobic Respiration and Its Regulation in the Metal Reducer .

MR-1 is a facultative anaerobe known for its ability to reduce metal oxides. Anaerobic respiration, especially metal reduction, has been the subject of extensive research. In contrast, aerobic respiration has received less attention. expresses - and -type cytochrome oxidases and a -type quinol oxidase. The -type oxidase, which in other bacteria is the major oxygen reductase under oxygen replete conditions, does not appear to contribute to aerobic respiration and growth in . Our results indicated that although the -type oxidase does not play a role in aerobic growth on lactate, the preferred carbon source for , it is involved in growth on pyruvate or acetate. These results highlight the importance of testing multiple carbon and energy sources when attempting to identify enzyme activities and mutant phenotypes. Several regulatory proteins contribute to the regulation of aerobic growth in including CRP and ArcA. The 3',5'-cAMP phosphodiesterase (CpdA) appears to play a more significant role in aerobic growth than either CRP or ArcA, yet the deficiency does not appear to be the result of reduced oxidase genes expression. Interestingly, the ∆ mutant was more deficient in aerobic respiration with several carbon sources tested compared to ∆, which was moderately deficient only in the presence of lactate. To identify the reason for ∆ aerobic growth deficiency, we isolated a suppressor mutant with transposon insertion in SO_3550. Inactivation of this gene, which encodes an anti-sigma factor, restored aerobic growth in the mutant to wild-type levels. Inactivation of SO_3550 in wild-type cells, however, did not affect aerobic growth. The genome encodes two additional CRP-like proteins that we designated CrpB and CrpC. Mutants that lack and were deficient in aerobic growth, but this deficiency was not due to the loss of oxidase gene expression.