Metabolomic insights into glutamate-induced γ-PGA biosynthesis and process optimization in Bacillus subtilis SCP017-03 for scalable production.

This study focuses on the glutamate-dependent strain Bacillus subtilis SCP017-03, systematically investigating its metabolic mechanism for synthesizing γ-polyglutamic acid (γ-PGA) in the presence of exogenous glutamate, as well as optimizing its fermentation conditions. Metabolomic analysis revealed that glutamate addition significantly altered the cellular metabolic profile, with 480 out of 1674 metabolites showing differential expression. Notably, pathways such as the TCA cycle, glycolysis, glutathione metabolism, and amino acid metabolism were significantly upregulated, enhancing precursor supply and energy metabolism, thereby promoting γ-PGA synthesis. Based on these findings, fermentation conditions were optimized in a 5-L bioreactor. Yeast extract was identified as the optimal nitrogen-rich nutrient, and at an addition level of 7.5 g/L, the γ-PGA yield reached 87 g/L. The optimal conversion efficiency and yield were achieved with a 5% addition of monosodium glutamate. Molecular weight analysis showed that the resulting γ-PGA predominantly ranged from 1071 to 4897 kDa, making it suitable for agricultural applications. In a 30-L scale-up fermentation, γ-PGA production reached 71 g/L through optimized aeration, agitation, and feeding strategies, demonstrating the scalability of the process. Finally, optimized spray-drying conditions (inlet temperature of 160 °C) resulted in a 67% recovery rate with a desirable product appearance. This study provides important metabolic regulation strategies and engineering optimization foundations for the efficient industrial production of γ-PGA.