Metabolic studies of temperature control strategy on poly(γ-glutamic acid) production in a thermophilic strain Bacillus subtilis GXA-28

• A thermophilic strain B. subtilis GXA-28 and its product were characterized.
• γ-PGA yield reach 19.92 g/L and molecular weight reach 3.03 × 106 Da at 45 °C.
• MFA results indicate that temperature presents a marked impact on γ-PGA production.
• Enzyme activity analysis shows that ICDH and GDH are the positive regulators.
• Provide a potential strain and a temperature control strategy for γ-PGA production.

A thermophilic strain Bacillus subtilis GXA-28 with capability of γ-PGA production was characterized, and its product was identified. The effect of temperatures on cell growth, γ-PGA yield and molecular weight were investigated. Results showed that γ-PGA yield reached 19.92 g/L at 45 °C with a high productivity of 0.91 g/L/h, and the molecular weight reached 3.03 × 106 Da. Then, the flux distribution and the key enzyme activities at 2-oxoglutarate branch under specified temperature were determined to illustrate the possible metabolic mechanism contributing to the improved γ-PGA production. Results indicated that the fluxes from iso-citrate to 2-oxoglutarate and from 2-oxoglutarate to glutamate were increased with high activity of isocitrate dehydrogenase and glutamate dehydrogenase, which led to enhance γ-PGA production. This work firstly employed temperature control strategy to improve γ-PGA production, and provided novel information on the metabolic mechanism of γ-PGA biosynthesis in Bacillus species.