Tailor-made poly-γ-glutamic acid production

Poly-gamma-glutamic acid (gamma-PGA), which is produced by several Bacillus species, is a chiral biopolymer composed of D- and L-glutamate monomers and has various industrial applications. However, synthesized gamma-PGA exhibits great structural diversity, and the structure must be controlled to broaden its industrial use. The biochemical pathways for gamma-PGA production suggest that the polymer properties molecular weight (MW) and stereochemical composition are influenced by (1) the affinity of gamma-PGA synthetase for the two alternative glutamate enantiomers and (2) glutamate racemase activity; hence, the availability of the monomers. In this study, we report tailormade gamma-PGA synthesis with B. subtilis by combining PGA synthetase and glutamate racemase genes from several Bacillus strains. The production of structurally diverse gamma-PGA was thereby achieved. Depending on the PGA synthetase and glutamate racemase origins, the synthesized gamma-PGA contained 3-60% D-glutamate. The exchange of PGA synthetase changed the MW from 40 to 8500 kDa. The results demonstrate the production of low-, medium-, and high-MW gamma-PGA with the same microbial chassis.