Optimization of Growth Conditions to Identify the Superior Bacillus Strain Which Produce High Yield of Thermostable Alpha Amylase

Abstract

Thermostable α-amylases hold a very important place in commercial industrial applications in Sri Lanka. Therefore, the main aim of this study was to identify superior Bacillus strain and optimize growth conditions that could yield high α-amylase production. Three Bacillus strains, B. amyloliquefaciens ATCC 23350, B. licheniformis ATCC 14580 and B. megaterium ATCC 14581 were used for the study. Shake flask culture experiments were conducted to identify the effect of various fermentation conditions such as growth temperature, incubation period, carbon source, nitrogen source, initial pH and carbon concentration on extracellular α-amylase production. DNSA assay was carried out to determine the enzyme activity. The highest temperature for enzyme activity was reported by B. licheniformis at 85˚C, followed by B. amyloliquefaciens at 75˚C and B. megaterium at 45˚C. Both B. amyloliquefaciens and B. licheniformis were able to give their optimum enzyme production at 37˚C, while B. megaterium at 30˚C in 150 rpm with initial pH of 7. B. licheniformis and B. amyloliquefaciens gave their optimum yield of the enzyme after 48 h of incubation while B. megaterium gave after 24 h of incubation. Among the carbon sources tested cassava starch was able to give the highest enzyme three show high amylase above optimum carbon concentrations according to the Tukey pairwise comparison under ANOVA test than any other carbon concentration. It was observed that gradual increase in extracellular amylase activity up to the optimum and then it was gradually decreased.