The anaerobic growth of Escherichia coli is supported by energy production coupled to the reduction of electron acceptors including nitrate, fumarate, trimethylamine 1V oxide (TMAO), and dimethyl sulfoxide (DMSO) (1,9,11,18). Reduction of tetrahydrothiophene oxide (13) also effectively elevates the growth levels of the cell in anaerobiosis. So far, terminal enzymes in electron transport, nitrate reductase (4, 8), fumarate reductase (5), TMAO reductase (23), and DMSO reductase (19) have been purified and characterized as distinct enzymes. Among these enzymes TMAO reductase and DMSO reductase have broad specificity for substrates; TMAO reductase can reduce TMAO, adenosine 1V oxide, y-picoline N -oxide, hydroxylamine and chlorate (23), and these compounds, except adenosine 1V oxide, and S-oxides including DMSO and L-methionine sulfoxide are utilized by DMSO reductase as substrates (19). In this study we examined the effects of some N-oxide or S-oxide compounds on the anaerobic growth of E. coli, and investigated whether enzymes specific for the reduction of the respective oxides would be induced.E. coli strain K10 was used in this study. The cells were transferred from a slant culture to LB medium (14) and incubated at 37°C overnight. The culture obtained was inoculated into a fresh LB in a flask capped with a rubber septum with glass tubings. The size of inoculation was 2.5%. The concentration of each oxide compound was 30 mM in LB medium. The cells were anaerobically grown by bubbling nitrogen and harvested by centrifugation at 10,000 x g for 10 min. The optical density at 660 nm (0D660) of the cultures was measured in a 10 x 10 mm cuvette with a spectrophotometer (Jasco Uvidec 340). When the 0D660 was higher than 0.5, the culture was diluted with saline for the measurement. The amount of cells grown was estimated on the basis that l 0D660 corresponds to 0.40 mg of dry

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