| Poly(γ-glutamic acid)(γ-PGA) is an unusual anionic,water-soluble and high viscous polymer in which glutamate is polymerized by amide linkages between a-amino andγ-carboxylic acid groups.For its excellent characters,potential applications ofγ-PGA have been of interest in the past few years in a broad range of industrial fields.It has been used as thickeners,humectant and drug carrier.In this study a novel isolate named Bacillus subtilis ZJUTZY was used to produce Poly-gamma-glumatic acid(γ-PGA).Then the effects of the fermentation conditions were studied by response surface and orthogonal test on the basis of one factor test.The result showed that The optimum medium was sucrose 50 g/L,peptone 60.9 g/L,glutamic acid 81.8 g/L, NaCl 7.5 g/L and K2HPO4 0.75 g/L;the optimum initial pH,the liquid volume and inoculated ratio were 7.0,30 ml and 3.3%respectively.The largest product was increased from 22.24 g/L to 49.90 g/L,which was 2.24 times of the initial yield.For the medium composition contains a high content of peptone,which is a high cost organic nitrogen source after optimization,it must be necessary to reduce cost of production.In this study,the method of transformation was utilized to produceγ-PGA.With no other carbon and nitrogen sources in the medium,Bacillus subtilis ZJUTZY was used to transformγ-PGA from glutamic acid.The optimum transformation condition was as follows:glutamic acid 80 g/L,initial pH 7,liquid volume in flask 27%,transformation liquid:second level seed liquid=4:1(v/v), temperature 30℃,time 16h.Bacillus subtilis ZJUTZY was utilized to produce poly-gamma-glutamic acid.The yield of crude product was 31.76 g in 1L broth.Based on the determination of HPLC,50.5%of the crude product wasγ-PGA.On the basis of method of Coomassie brilliant blue G250,no protein was found in the crude product.The crude product was then purified by strong basic anion exchange resin,most unwanted poly-saccharide was moved,and 80.9%γ-PGA was yield.
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