Engineering of Bacillus subtilis KH2 for effective production of poly-γ-glutamic acid from glutamate waste based on...

Glutamate waste liquor (GWL) is acidic wastewater from monosodium glutamate process. Poly-γ-glutamic acid (γ-PGA) production using this abundant industrial waste is an economical and environmentally friendly method. The development of cost-effective production from GWL requires understanding the inhibitory mechanism in γ-PGA producers. In this study, γ-PGA fermentation profile of Bacillus subtilis KH2 using GWL was studied. An inhibitory effect in glutamate consumption was observed during γ-PGA production. To systematically analyze the response pattern of B. subtilis KH2 to GWL addition, comparative transcriptomics was performed. Transcriptomic analysis indicated that GWL led to decreased expression of genes associated with γ-PGA polymerization, while upregulating genes related to glycolysis, TCA cycle and glutamate precursor synthesis. Subsequent gene overexpression experiments elucidated the pivotal regulatory role of swrA in the GWL-mediated suppression of γ-PGA biosynthesis. Finally, by a combination of metabolic engineering targets, the highest γ-PGA titer of 32.24 g/L was achieved by B. subtilis KH2Δres1Δres2ΔgudBΔrocG using GWL in shake-flask fermentation, accompanied by an increased glutamate consumption rate of 59.37 %. This study provides insights into the GWL inhibitory mechanisms in B. subtilis KH2 and demonstrates the potential application of B. subtilis KH2 for cost-effective production from industrial waste.