Exogenous Addition of MBP-Tagged γ-Polyglutamic Acid-Degrading Enzyme: A Novel Strategy for Controlled and Targeted Molecular Weight Regulation and Yield Enhancement in γ-Polyglutamic Acid Fermentation

Abstract Poly(γ-glutamic acid) (γ-PGA) of defined molecular weight (Mw) is critical for applications, but conventional regulation suffers from harsh conditions or poor precision. We developed a novel strategy, exogenous addition of a fusion γ-PGA-degrading enzyme (MBP-PgdS), to overcome the limitations of strain engineering and in vitro hydrolysis. The pgdS gene from Bacillus licheniformis was heterologously expressed in Escherichia coli with an MBP tag, yielding 232.27 mg/L. The purified enzyme reached 85.36% purity, with optimum catalysis at 43 °C and pH 7.4. In vitro, hydrolysis time flexibly regulated molecular weight over 18.09–766.83 kDa. During γ-PGA fermentation, exogenous MBP-PgdS reduced Mw to ∼50 kDa, decreased broth viscosity and increased yield by 28.3% (38.94 to 49.95 g/L). The strategy requires no genetic modification of the production strain and fits existing fermentation processes. It benefits industrial production of γ-PGA with customized molecular weight, but its economics still need pilot-scale validation.