γ-PGA Fermentation by Bacillus subtilis PG-001 with Glucose Feedback Control pH-stat Strategy

Area of Science:

• Biotechnology
• Biopolymer Production
• Microbial Fermentation

Background:

• Poly-γ-glutamic acid (γ-PGA) is a biodegradable and non-toxic biopolymer with diverse applications.
• Industrial production of γ-PGA relies on fermentation by Bacillus species.

Purpose of the Study:

• To determine the optimal pH for γ-PGA production by Bacillus subtilis PG-001.
• To investigate the impact of pH control strategies on γ-PGA yield, quality, and fermentation efficiency.

Main Methods:

• Glucose fed-batch fermentation with non-controlled and controlled pH conditions.
• Comparative analysis of γ-PGA synthesis and cell growth at different pH levels (pH 6, 6.5, and 7).
• Implementation of a glucose feedback control pH-stat strategy.

Main Results:

• Optimal pH for γ-PGA production was found to be 6.5, with repressed synthesis below pH 6.
• Fermentation at pH 6.5 yielded 11.8 g/L γ-PGA and 0.7 g/g yield, outperforming pH 7 (10.5 g/L, 0.56 g/g).
• The glucose feedback control strategy increased γ-PGA concentration to 15.5 g/L and viscosity to 11458 cP, while reducing alkali consumption by 57%.

Conclusions:

• pH 6.5 is optimal for Bacillus subtilis PG-001 γ-PGA fermentation, enhancing yield and reducing degradation.
• A glucose feedback control pH-stat strategy is effective for increasing γ-PGA production and viscosity.
• The developed fed-batch fermentation strategy shows high feasibility for industrial scale-up of γ-PGA production.