Screening of amylase-producing strains in Guangxi mangrove soil and optimization of enzyme-producing conditions

Objective: An amylase-producing strain was screened and identified from mangrove soil in Shijiao Mangrove Nature Reserve of Guangxi. The amylase-producing process was optimized by Plackett-Burman design and response surface optimization, in order to establish the fermentation process of high amylase production.Methods: The amylase-producing strain was obtained from mangrove soil by plate screening. The strain was identified by physiological, biochemical and 16S rDNA sequencing. The optimized condition for enzyme production was obtained by single factor optimization, Plackett-Burman design and response surface optimization. Results: The amylase-producing strain was obtained from mangrove soil. Bacillus velezensis was identified and named Bacillus velezensis MG5-8. The optimum temperature and pH of the amylase were 70 ℃ and 6.0, respectively. The optimum temperature for amylase production was 30 ℃, the optimum carbon source for amylase production was corn steep liquor powder, and the optimum nitrogen source was soybean powder and beef extract by single factor optimization. The optimum enzyme production conditions were as following: soybean powder 0.51%, beef extract 0.55%, corn steep liquor powder 0.34%. Under these conditions, the theoretical maximum enzyme activity of this strain was 134.03 U/mL. The activity of B. velezensis MG5-8 amylase was 130.28 U/mL,which was 97.2% of the theoretical value and 5.63 folds of the enzyme activity before optimization. Conclusion: A strain producing amylase(B. velezensis MG5-8) is successfully isolated and identified. The maximum enzyme activity is 130.28 U/mL after optimization.