Poly‐γ‐glutamic acid overproduction of Bacillus licheniformis ATCC 9945a by developing a novel optimum culture medium and glutamate pulse feeding using different experimental design approaches

Abstract

AbstractThe commercial production of multifunctional, biocompatible, and biodegradable biopolymers such as poly‐γ‐glutamic acid via microbial fermentation requires the development of simple and cheap methods for mass production. This study optimized the poly‐γ‐glutamic acid production of Bacillus licheniformis ATCC 9945a in several steps. At first, the most critical components of the culture medium, including l‐glutamic acid, citric acid, and glycerol, were selected by screening nine factors through the Plackett–Burman experimental design and then were optimized using the response surface method and the central composite design algorithm. Under optimal conditions, the production of poly‐γ‐glutamic acid increased by more than 4.2 times from 11.2 to 47.2 g/L. This is one of the highest production rates of this strain in submerged batch fermentation reported so far using the optimized medium compared to the conventional base medium. A novel and efficient sudden pulse feeding strategy (achieved by a novel one‐factorial statistical technique) of l‐glutamic acid to the optimized medium increased biopolymer production from 47.2 to 66.1 g/L, the highest value reported in published literature with this strain. This simple, reproducible, and cheap fermentation process can considerably enhance the commercial applications of the poly‐γ‐glutamic acid synthesized by B. licheniformis ATCC 9945a.