Improving the stability of glutamate fermentation by Corynebacterium glutamicum via supplementing sorbitol or glycerol

Abstract

Background

Corynebacterium glutamicum is widely used in glutamate fermentation. The fermentation feature of the strain varies sometimes. These variations may lead to the reduction in the ability of the strain to resist environmental changes and to synthesize glutamate, resulting in abnormal glutamate fermentations.

Results

In the abnormal glutamate fermentations, glutamate accumulation stopped after glucose feeding and the final glutamate concentration was at a lower level (50 to 60 g/L). The r_NAD ⁺/r_NADH ratio was lower than that in normal batch which was reflected by lower oxidation-reduction potential (ORP) value. The abnormal fermentation performance was improved when glucose was co-fed with sorbitol/glycerol at a weight ratio of 5:1 or adding 10 to 15 g/L of sorbitol/glycerol in the initial medium. Under these conditions, glutamate synthesis continued after substrate(s) feeding and final glutamate concentration was restored to normal levels (≥72 g/L). r_NAD ⁺/r_NADH ratio, ORP, and pyruvate dehydrogenase (PDH), isocitrate dehydrogenase (ICDH), and cytochrome c oxidase (CcO) activities were maintained at higher levels.

Conclusions

Sorbitol and glycerol were not used as carbon sources for the fermentation. They were considered as effective protective agents to increase cells' resistance ability against environmental changes and maintain key enzymes activities.

Keywords

Enzyme activity / Fermentative stability / Glutamate fermentation / Oxidation-reduction potential / Protective substance / r_NAD ⁺/r_NADH

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