期刊
MICROBIOLOGY-SGM
卷 154, 期 -, 页码 989-994出版社
SOC GENERAL MICROBIOLOGY
DOI: 10.1099/mic.0.2007/012682-0
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The respiratory chain of the ethanol-producing bacterium Zymomonas mobilis is able to oxidize both species of nicotinamide cofactors, NADH and NADPH. A mutant strain with a chloramphenicol-resistance determinant inserted in ndh (encoding an NADH: CoQ oxidoreductase of type 11) lacked the membrane NADH and NADPH oxidase activities, while its respiratory D-lactate oxidase activity was increased. Cells of the mutant strain showed a very low respiration rate with glucose and no respiration with ethanol. The aerobic growth rate of the mutant was elevated; exponential growth persisted longer, resulting in higher biomass densities. For the parent strain a similar effect of aerobic growth stimulation was achieved previously in the presence of submillimolar cyanide concentrations. It is concluded (i) that the respiratory chain of Z mobilis contains only one functional NAD(P)H dehydrogenase, product of the ndh gene, and (ii) that inhibition of respiration, whether resulting from a mutation or from inhibitor action, stimulates Z mobilis aerobic growth due to redirection of the NADH flux from respiration to ethanol synthesis, thus minimizing accumulation of toxic intermediates by contributing to the reduction of acetaldehyde to ethanol.
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