Kalnenieks Uldis, Galinina Nina, Strazdina Inese, Kravale Zane, Pickford James L, Rutkis Reinis, Poole Robert K
Institute of Microbiology and Biotechnology, University of Latvia, Kronvalda Boulv. 4, LV-1586, Riga, Latvia.
Department of Molecular Biology and Biotechnology, The University of Sheffield, Firth Court, Western Bank, Sheffield S10 2TN, UK.
Microbiology (Reading). 2008 Mar;154(Pt 3):989-994. doi: 10.1099/mic.0.2007/012682-0.
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 II) 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.
产乙醇细菌运动发酵单胞菌的呼吸链能够氧化两种烟酰胺辅因子，即NADH和NADPH。在ndh（编码II型NADH：辅酶Q氧化还原酶）中插入氯霉素抗性决定子的突变菌株缺乏膜NADH和NADPH氧化酶活性，而其呼吸性D-乳酸氧化酶活性增加。突变菌株的细胞在以葡萄糖为底物时呼吸速率非常低，以乙醇为底物时则不呼吸。突变体的好氧生长速率提高；指数生长期持续更长时间，导致生物量密度更高。对于亲本菌株，先前在亚毫摩尔浓度的氰化物存在下也实现了类似的好氧生长刺激效果。得出以下结论：（i）运动发酵单胞菌的呼吸链仅包含一种功能性NAD(P)H脱氢酶，即ndh基因的产物；（ii）呼吸抑制，无论是由突变还是抑制剂作用引起，都会刺激运动发酵单胞菌的好氧生长，这是由于NADH通量从呼吸转向乙醇合成，从而通过将乙醛还原为乙醇来减少有毒中间体的积累，将其积累降至最低。
