Genome mining of carbohydrate-active enzymes (CAZyme) and poly-γ-glutamic acid (γ-PGA) synthesis by Bacillus velezensis (WA11) directly from lignocellulosic biomass-based substrate

Poly-γ-glutamic acid (γ-PGA/PGA), a non-toxic and biodegradable polymer with additional diverse properties such as higher heat resistance and water retention, is widely implicated in myriad applications, including agricultural and food processing, medical treatments, and cosmetics. The industrial bio-based production of γ-PGA is primarily hindered by the potential of microbial strains and substrate costs, which are attributed primarily to the carbon sources. The present study is a proof-of-concept study, wherein a bacterial isolate, Bacillus velezensis WA11 strain, was employed for the production of γ-PGA from sugarcane bagasse (lignocellulosic biomass) without any pretreatment or pre-processing. The CAZyme annotation identified several enzyme families involved in metabolizing complex polysaccharides, including cellulose, xylan, and lignin. We obtained 104.3 g/L γ-PGA production with a productivity of 1.09 g/L/h in the optimized synthetic medium containing maltose as a carbon source, 2.9-fold higher than the earlier study using maltose as a carbon source. Further, substituting maltose with untreated sugarcane bagasse resulted in 12 g/L of γ-PGA, higher than most of the reported studies utilizing pretreated lignocellulosic biomass (LCB) lysates for producing γ-PGA. The present study demonstrates the production of γ-PGA using lignocellulosic biomass without pretreatment, providing a chemical-free, sustainable avenue for directly utilizing untreated lignocellulosic biomass (LCB) to produce expensive polymers by employing potential bacterial strains.