Superoxide dismutase (SOD) is generally regarded as having a defensive role against oxygen toxicity in various organisms. In accordance with that idea, the total level of SOD activity in aerobically grown Escherichia coli cells is distinctly higher than that in anaerobically grown cells (1); in addition, anaerobically grown E. coli contain only iron-containing SOD (Fe SOD), while aerobically grown cells contain in addition manganese-containing SOD (Mn SOD) and a hydrid SOD with a protein moiety which is a hydrid between protein subunits of Fe and Mn SOD (1). In the preceding paper, we reported that the addition of nitrate to anaerobic cultures of E. coli increased SOD activity (2). Under anaerobic conditions, E. coli obtains energy either by fermentation or by anaerobic respiration with alternative electron acceptors such as nitrate, fumarate, dimethyl sulfoxide (DMSO) or trimethylamine N-oxide (TMAO) (3)(4)(5). In this study, we examine the effect of these acceptors on anaerobic synthesis of SOD in E. coli.
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Miyake et al. (1988) studied this question.