Optimization Of Solid State Fermentation Of Poly-γ-Glutamic Acid By Bacillus Subtilis ME714

Poly (γ-glutamic acid)(γ-PGA) is a water soluble poly amino acids which have excellent characters such as completely biodegradable, non-toxic to human and environment.γ-PGA and its derivates have potential applications in a wide range of industry and agriculture such as food, cosmetics, medicine and manure. Thus this natural and multifunctional biopolymer is worth researching and developing to a commercial material.The solid state fermentation medium ofγ-PGA biosynthesis by Bacillus subtilis ME714, which was a newly isolated strain by our lab, was optimized. Methods such as simple factor experiment, orthogonal design, RBF neural network and Genetic algorithm were involved in this work. The higherγ-PGA yield was achieved in the conditions that described as following (g/kg): soybean cake powder and wheat bran (5∶5 w/w) as the mixed substrates supplemented with sodium glutamate (31.8 g/kg), urea(28.3 g/kg), trisodium citrate (24 g/kg), starch 46 (g/kg) and mineral salts (ZnSO₄ 0.36 g/kg, MnSO₄ 0.1 g/kg, MgSO₄ 0.5 g/kg, CaCl₂ 0.2 g/kg), with initial ratio of substrate weight (g) and solution volume (mL) 1∶1, initial pH 8.0, inoculum level 8%, at 37℃incubated 36h. No substrate disturbance was made during the cultivation. The yield is 75.3 g/kg, which is increased by 43.16 % compared to the original medium.Scale-up ofγ-PGA biosynthesis was devolped. Both perlite and chaff as carriers have well performance during scale-up cultivation ofγ-PGA. The yield is increased by 8.6%, when chaff was applied, 11.1% for perlite, compared to original culture.In this research, effect ofγ-PGA concentration in the animal feed on Kunming mice growth was investigated. The results showed animal feed containing 5 g/kgγ-PGA had markedly increased the weight of 5～6 weeks old mice, while inhibited the growth of 3～4 weeks old mice. Feeding with 2.5 g/kgγ-PGA also has statistical reverse effect on the growth of 3～4 weeks old mice...