Mutations in genes encoding antibiotic substances increase the synthesis of poly-γ-glutamic acid in Bacillus amyloliquefaciens LL3

Poly-gamma-glutamic acid (-PGA) is an important natural biopolymer that is used widely in fields of foods, medicine, cosmetics, and agriculture. Several B.amyloliquefaciens LL3 mutants were constructed to improve -PGA synthesis via single or multiple marker-less in-frame deletions of four gene clusters (itu, bae, srf, and fen) encoding antibiotic substances. -PGA synthesis by the srf mutant showed a slight increase (4.1g/L) compared with that of the wild-type strain (3.3g/L). The itusrf mutant showed increased -PGA yield from 3.3 to 4.5g/L, with an increase of 36.4%. The -PGA yield of the itusrffen and itusrffenbae mutants did not show a further increase. The four gene clusters' roles in swarming motility and biofilm formation were also studied. The srf and bae mutant strains were both significantly defective in swarming, indicating that bacillaene and surfactin are involved in swarming motility of B.amyloliquefaciens LL3. Furthermore, srf and itu mutant strains were obviously defective in biofilm formation; therefore, iturin and surfactin must play important roles in biofilm formation in B.amyloliquefaciens LL3.