Abstract
It is a simple and effective method to control the production of fermented products by metal ions. In this study, effect of KCl on γ-PGA production by B. subtilis GXA-28 was investigated. K+ was proved to be the true effector, and concentration of 201.2 mM was optimized for γ-PGA production. Addition of KCl to medium effectively reduced broth viscosity from 4289.5 mPa · s to 748.0 mPa · s by 82.6% and increased γ-PGA yield from 18.36 g/L to 25.62 g/L by 39.5%. Although high concentration KCl (>67.1 mM) suppressed cell growth, the maximum biomass with 201.2 mM had been brought forward to 16 h and had a marked effect in prolonging cell viability. Metabolic flux and key enzyme activities analysis indicated that enhanced GDH, GOGAT and GLR are important for γ-PGA production. Specifically, the expression of pgsB was improved 9.6-fold by KCl added, which might be another reason for enhanced γ-PGA production. In addition, that modulation of the D/L-glutamate ratio in γ-PGA and molecular weight could also be accomplished by variation of KCl concentrations. This work provided a simple control strategy for γ-PGA production, and it will be applied to γ-PGA production on a large scale in the future.
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