Screening Of A γ-Polyglutamic Acid Strain And The Application Of Its Fermentation Products

In order to provide a theoretical basis to develop the fermentation products as an agriculture aquasorb,a new γ-PGA producing strain was filtered out systematically. The strain was identified as Bacillus subtilis through morphology and molecular biology.Its Fermentation products were analyzed qualitatively and quantitatively,its optimum fermentation culture conditions were explored and the water holding capacity of its fermentation products was investigatived at series of different ratios orderly.The results are as follows:(1)The strain producing poly(γ-glutamic acid) which was screened from the fermented bean curd was named as strain pga-1,it growed quickly and its surface was sticky.By the gram staining showed that it was gram positive bacteria,it was identified as Bacillus subtilis based on 16 S r RNA.Acid hydrolysis of the fermentation which detected by High Performance Liquid Chromatography(HPLC) showed that glutamate was the single production,which was the same as paper chromatography.(2)It was at 15 h that it reached its largest number of bacteria when it was grown in a medium containing glucose 30.0 g/L,yeast extract 8.0 g/L,K2HPO4·3H2O 2.0 g/L,Mg SO4·7H2O 0.25 g/L,glutamate 30.0 g/L, p H as 7.0-7.5 with sharking. And it was considered as its suitable propagation medium.(3) This strain productedγ-PGA stability,its fermentation products γ-PGA was increased from 9.13 g/L to 18.15 g/L during 10 times subculture,which had reached an increase of 98.80 percent.The γ-PGA production 18.41 g/L was obtained when it was grown in a medium that citric acid and glycerol were acted as the carbon source under the condition at constant temperature 37℃,200 r/min for 60 h with sharking.(4) The initial culture medium contained citric acid 10 g/L,glycerin 60 g/L,NH4 Cl 7.0,glutamate 20.0 g/L,K2HPO4·3H2O 0.5 g/L,Fe Cl3·6H2O 0.05 g/L,Ca Cl2·2H2O 0.15 g/L,Mg SO4·7H2O 0.5 g/L,Mn SO4·H2O 0.1 g/L,p H as 7.0-7.5. Under its optimum fermentation culture conditions which contained citric acid 12 g/L,glycerin 80 g/L,glutamate 30.0 g/L,inoculum 5% and other things being equal,its the highest yield of γ-PGA could be 28.90 g/L.(5)The soil moisture dealed with 2 and 5 times dilution of its fermentation products were 3.09% and 1.37%,they were 3.5 and 1.5 times higher than CK respectively. Therefore,their water retention capacity was significant.(6) After incubating 15 d,the soil moisture dealed with its bean dregs fermentation products γ-PGA were the highest as 9.20%,the second was 6.39% which was dealed with the chemical aquasorb,they were 1.68 and 1.17 times higher than CK respectively.The soil moisture dealed with CK was significantly lower than the other two treatments with its 5.48%.So the water retention capacity of bean dregs fermentation products γ-PGA was better than the chemical aquasorb.(7)In the study of exploring their water retention capacity,the more inputting of γ-PGA they were,the better water retention capacity they had,but the lower seed germination rate and seedling growth they performed,so the appropriate using of γ-PGA needed to be explored.In the 5 experimental treatment 1:20,1:80,1:100,1:150 and 1:300,the germination rate and wheat seedling shoot were the most highest as 95.33% and 11.07 cm at the same time,therefore the appropriate using of its bean dregs fermentation products should be the proportion of 1:150.In other words the appropriate using of γ-PGA should be the proportion of 1:600(g/g),which were friendly for the seed germination rate and seedling growth.In summary,the Bacillus subtilis D-6 productedγ-PGA stability and it was more potential after been optimized.The water retention capacity of its fermentation broth and its bean dregs fermentation products γ-PGA were significant,the appropriate using of its bean dregs fermentation products at the proportion of 1:150 not only could improve the the soil moisture,but also could promote the seed germination rate and seedling growth.