A novel gene, torB, for trimethylamine N-oxide reductase in Escherichia coli.

Abstract

Trimethylamine N-oxide (TMAO) reductase which is involved in anaerobic respiration is one of the molybdenum-containing enzymes in Escherichia coli. A mutant defective in the activity of TMAO reductase was isolated by inserting phage Mudl. The mutation was localized at 0.7 min adjacent to chlG on the E. coli chromosome, and was designated torB. The torB mutant grown anaerobically with TMAO contained 10-30% of the enzyme activity in the parent strain grown under the same condition and about 80% of the enzyme protein immuno-reactive with an antiserum against the TMAO reductase. The content of molybdopterin, an organic moiety of molybdenum cofactor, in the immuno-precipitate from extracts of the torB mutant was rather low, about 60% of that in the immuno-precipitate from the parent strain. The mutant showed a normal level of another molybdenum enzyme nitrate reductase activity when anaerobically grown with nitrate. These findings suggest that the torB gene is involved in the formation of the active enzyme of TMAO reductase through the processing of molybdenum cofactor. There was a marked expression of torB under anaerobic conditions, and TMAO was not required for it.Some bacteria can use trimethylamine N-oxide (TMAO) as a terminal electron acceptor under anaerobic conditions (3). In Escherichia cold, the electron transport system of TMAO reduction is composed of some dehydrogenases, cytochromes, quinones, and TMAO reductase. This bacterium has three to four forms of TMAO reductase which are electrophoretically distinguishable (27). TMAO reductase I and III are inducible by TMAO and are composed of two identical peptides and a single one, respectively (28; Yamamoto and Hinakura, unpublished). TMAO reductase

A regulatory mutant of the trimethylamine N-oxide reductase of Escherichia coli K12

“…On the contrary, the nitrate reductase, the FDHpMs, the FDHBv and the fumarate reductase activities were found to be similar to that of the parental strain ( Table 2). No -cross-reacting material was found with a serum raised against the TMAO reductase confirming • the difference from torB, which has retained 80% of the Tor protein [18].…”

“…The strong linkage with both markers, 83% and 63%, respectively, indicates that the affected gene is located between them ( Fig. 1) and, consequently, is different from the torB gene described by Yamamoto et al [18]. It will be hereafter referred to as torR.…”

Dimethyl sulfoxide reductase of Escherichia coli: an investigation of function and assembly by use of in vivo complementation

“…However, the overlapping substrate specificity of these enzymes has confounded determination of the precise role of each reductase in the anaerobic electron transport chain. In vitro studies have shown that DMSO reductase can catalyze the reduction of both DMSO and TMAO (33), and this property has led to the use of the term constitutive TMAO reductase (37). We recommend that this enzyme be referred to as DMSO reductase and not as constitutive TMAO reductase to avoid further confusion in this area of research.…”

“…These activities in E. coli were shown to be derived from an anaerobically expressed reductase encoded by the dms operon (3) J. BACTERIOL. and by an inducible TMAO reductase encoded by the tor gene (28,37). Several forms of inducible TMAO reductase have been characterized; however, antibodies raised against the major inducible, purified TMAO reductase cross-reacted with all of the inducible expressed forms.…”

Effect of the tor mutation in Escherichia coli on the trimethylamine N-oxide, nitrate and dimethylsulfoxide reductases, the formate dehydrogenases N and H and nitrate repression.

“…Takagi and Ishimoto (30) have isolated a for mutant of E. coli which is defective in TMAO reductase activity but shows nitrate reductase activity in intact cells. This mutant, strain TR111, does not contain an immunologically detectable protein of TMAO reductase (35). However, we recently found that nitrate reductase activity was low in cell-free extracts prepared from the mutant.…”