Trimethylamine N-oxide (TMAO) reductase activity in chlorate-resistant or respiration-deficient mutants ofEscherichia coli

Abstract

The trimethylamine N-oxide (TMAO) reductase of Escherichia coli is induced when the organism is grown anaerobically in the presence of TMAO [1,2]. It is a membrane bound enzyme which can accept electrons from formate, NADH or reduced viologen dyes [2]. Similarly to the nitrate reductase system of E. coli, under anaerobic conditions, TMAO reductase appears to act as a terminal electron acceptor for respiratory electron flow [13]. Kim and Chang [4] report evidence suggesting a close similarity between nitrate and TMAO reductases from a chlorate-resistant mutant of Salmonella typhimurium which lacked both activities. In the present paper we make use of several mutants of E. coli to demonstrate that (i) membrane associated electron transport between NADH and TMAO requires quinones and cytochromes, and (ii) chlorate-resistant mutants of E. coli lacking nitrate reductase activity are not necessarily deficient in TMAO reductase activity, indicating that these enzymes are functionally and genetically distinct.