胞内氧化还原水平对嗜热厌氧乙醇菌 发酵代谢的影响

辅酶NADH/NAD+在细胞内氧化还原反应中起着重要的作用,是细胞生长和能量代谢必不可少的辅因子。调节微生物胞内NADH/NAD+的比率是定向改变微生物代谢,高效获得目标代谢产物的有效手段。嗜热厌氧乙醇菌(Thermoanaerobacter ethanolicus)是高温厌氧菌中乙醇产量较高的代表性菌株,本文利用不同氧化还原态的碳源改变T.ethanolicus的胞内NADH/NAD+含量和比例,进而研究了其对细胞生长、代谢产物分布的影响。以不同比例的葡萄糖/甘露醇作为混合碳源发酵,胞内氧化还原水平、细胞的生长特性、代谢产物都发生了不同程度的差异,以葡萄糖作为唯一碳源进行培养时,T.ethanolicus生长良好,乙醇产量为0.79g/L,但胞内NADH/NAD+比值和乙醇/乙酸的比值都比较低,分别为0.47和4.82;随着葡萄糖在混合碳源中比例的下降,NADH/NAD+比值增高,发酵产物中乙醇/乙酸比值也呈现上升的趋势。而以甘露醇作为唯一碳源时,发酵产物中乙醇浓度为0.389g/L,NADH/NAD+比值和乙醇/乙酸的比值分别为1.04和16.0。

Effects of Intracellular Redox Level on Fermentation Metabolism of Thermoanaerobacter ethanolicus

Coenzyme NADH/NAD+ plays an important role in intracellular oxidation-reduction reactions,and is a necessary cofactor for cell growth and energy metabolism.Regulating the intracellular NADH/NAD+ ratio of microorganisms is an effective means to alter microbial metabolic pathway directionally and obtain the target metabolic products efficiently.Thermoanaerobacter ethanolicus is a representative thermophilic anaerobic and ethanologenic bacteria.This study altered intracellular NADH/NAD+ ratio using carbon sources at different redox status.Then its effect on cell growth and distribution of metabolic products was studied.When glucose and mannitol at different ratios were used as the substrate for fermentation,variations occurred with respect to intracellular redox level,growth characteristics of cells and metabolic products.When glucose was used as the only carbon source,T.ethanolicus grew well,and the ethanol production was 0.79g/L.However,both of the intracellular NADH/NAD+ ratio and ethanol/acetic acid ratio were low,being 0.474 and 4.82 respectively.As the ratio of glucose in the mixed carbon source decreased,the NADH/NAD+ ratio increased,and the ethanol/acetic acid ratio in the fermentation products also showed an increasing trend.When mannitol was used as the only carbon source,the ethanol concentration in the fermentation products was 0.389g/L,and the NADH/NAD+ ratio and ethanol/acetic acid ratio were 1.04 and 16.0 respectively.