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

ABSTRACT

Poly-γ-glutamic acid (γ-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 γ-PGA synthesis via single or multiple marker-less in-frame deletions of four gene clusters (itu, bae, srf, and fen) encoding antibiotic substances. γ-PGA synthesis by the Δsrf mutant showed a slight increase (4.1 g/L) compared with that of the wild-type strain (3.3 g/L). The ΔituΔsrf mutant showed increased γ-PGA yield from 3.3 to 4.5 g/L, with an increase of 36.4%. The γ-PGA yield of the ΔituΔsrfΔfen and ΔituΔsrfΔfenΔbae mutants did not show a further increase. The four gene clusters' roles in swarming motility and biofilm formation were also studied. The Δsrf and Δbae mutant strains were both significantly defective in swarming, indicating that bacillaene and surfactin are involved in swarming motility of B. amyloliquefaciens LL3. Furthermore, Δsrf and Δitu mutant strains were obviously defective in biofilm formation; therefore, iturin and surfactin must play important roles in biofilm formation in B. amyloliquefaciens LL3.