Institute for Microbial Biotechnology and Metagenomics, University of the Western Cape, Modderdam Road, Bellville, Cape Town, South Africa.
Biotechnol Bioeng. 2013 Apr;110(4):1057-65. doi: 10.1002/bit.24774. Epub 2012 Dec 25.
Geobacillus thermoglucosidasius is a Gram-positive, thermophilic bacterium capable of ethanologenic fermentation of both C5 and C6 sugars and may have possible use for commercial bioethanol production [Tang et al., 2009; Taylor et al. (2009) Trends Biotechnol 27(7): 398-405]. Little is known about the physiological changes that accompany a switch from aerobic (high redox) to microaerobic/fermentative (low redox) conditions in thermophilic organisms. The changes in the central metabolic pathways in response to a switch in redox potential were analyzed using quantitative real-time PCR and proteomics. During low redox (fermentative) states, results indicated that glycolysis was uniformly up-regulated, the Krebs (tricarboxylic acid or TCA) cycle non-uniformly down-regulated and that there was little to no change in the pentose phosphate pathway. Acetate accumulation was accounted for by strong down-regulation of the acetate CoA ligase gene (acs) in addition to up-regulation of the pta and ackA genes (involved in acetate production), thus conserving ATP while reducing flux through the TCA cycle. Substitution of an NADH dehydrogenase (down-regulated) by an up-regulated NADH:FAD oxidoreductase and up-regulation of an ATP synthase subunit, alongside the observed shifts in the TCA cycle, suggested that an oxygen-scavenging electron transport chain likely remained active during low redox conditions. Together with the observed up-regulation of a glyoxalase and down-regulation of superoxide dismutase, thought to provide protection against the accumulation of toxic phosphorylated glycolytic intermediates and reactive oxygen species, respectively, the changes observed in G. thermoglucosidasius NCIMB 11955 under conditions of aerobic-to-microaerobic switching were consistent with responses to low pO(2) stress.
解淀粉芽胞杆菌是一种革兰氏阳性、嗜热细菌，能够进行 C5 和 C6 糖的乙醇发酵，并且可能有用于商业生物乙醇生产的潜力 [Tang 等人，2009 年；Taylor 等人（2009 年）趋势生物技术 27（7）：398-405]。在嗜热生物中，从需氧（高氧化还原）到微需氧/发酵（低氧化还原）条件的转变伴随的生理变化知之甚少。使用定量实时 PCR 和蛋白质组学分析了响应氧化还原电势变化的中心代谢途径的变化。在低氧化还原（发酵）状态下，结果表明糖酵解普遍上调，三羧酸（TCA）循环非均匀下调，戊糖磷酸途径几乎没有变化。由于乙酸辅酶 A 连接酶基因（acs）的强烈下调以及 pta 和 ackA 基因（参与乙酸产生）的上调，导致乙酸积累，从而在减少 TCA 循环通量的同时保存 ATP。取代下调的 NADH 脱氢酶（down-regulated）为上调的 NADH:FAD 氧化还原酶和上调的 ATP 合酶亚基，以及观察到的 TCA 循环的转变，表明在低氧化还原条件下，可能仍然存在氧气清除电子传递链。与观察到的糖醛酸酶上调和超氧化物歧化酶下调一起，分别认为提供对有毒磷酸化糖酵解中间产物和活性氧积累的保护，在 G. thermoglucosidasius NCIMB 11955 中观察到的变化与低 pO2 应激的反应一致。
