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| Effects of Intracellular Redox Level on Fermentation Metabolism of Thermoanaerobacter ethanolicus |
| SUN Huan-min, GUO Min, IRBIS Cha-gan |
| Laboratory of Bio-conversion, Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, China |
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Abstract 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.
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Received: 11 May 2012
Published: 25 July 2012
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