On-line Glucose Concentration Prediction and Control for Improving Glutamate Fermentation Performance / 微生物学通报

In industrial glutamate fermentation, intermitted feeding glucose with the help of off-line glucose measurement is generally necessary. This kind of feeding strategy could cause large variations in glucose concentration so that it is not favorable for the achievement of efficient and stable glutamate fermentation. Glutamate fermentation is characterized with typical non-growth association behavior, and during glutamate production phase glucose consumption is closely correlated with ammonia consumption. In this study, glucose concentration was controlled at various pre-determined levels by predicting glucose consumption amount and thus its concentration with the aid of on-line monitoring ammonia consumption. When glucose concentration was controlled around a lower level of 5 g/L~10 g/L, the final glutamate concentration could reach a relatively higher level of 80 g/L. In this way, the huge osmotic stress change due to the large glucose concentration variation with the intermitted feeding method could be avoided and the glutamate fermentation performance enhancement be expected.

Purification and characterization of glutamate dehydrogenase. from Corynebacterium glutamicum S9114 / 生物工程学报

Glutamate dehydrogenase (GDH) is a key enzyme in the biosynthesis of glutamate. The GDHs from Corynebacterium glutamicum S9114 the most commonly used strain in glutamate fermentation, were purified and their molecular structures and properties characterized. The coenzymes were also studied in the hope to increase glutamate production. Cells were harvested at mid-exponential phase by centrifugation and washed with Tris-HCl buffer containing DTT and EDTA (pH 7.5). The cells were then disrupted using a French pressure cell press and the supernatant was collected by centrifugation. The extract was concentrated by 70-fold using the AKTA-100 FPLC system employing a DEAE-cellulose ion exchange column, a hydrophobic interaction chromatography (HIC) and Sephadex G-200 gel filtration. The purified extracts contained NADPH-dependent GDH and NADH-dependent GDH. Both of the enzymes were highly specific for the coenzymes. The molecular masses of the NADPH-dependent GDH and its subunit were 188kD and 32kD respectively, suggesting the enzyme is a homo-hexamer. Our data reported for the first time the presence of NADH- dependent GDH in Corynebacterium glutamicum S9114, similar to other microorganisms containing both GDHs. The NADPH-dependent and NADH-dependent GDH in Corynebacterium glutamicum S9114 may participate in the assimilation and dissimilation of ammonia respectively. The absorptions of NADPH-dependent GDH was very weak at 280nm but very high at 215nm, suggesting a low phenylalanine and tyrosine content in the enzyme.