Abstract:
Bacillus sp. S11, used as probiotic in Penaeus monodon, produced antimicrobial substance in log phase of growth cycle. In this research, the optimum conditions or production of this antimicrobial substance are medium containing 2% (w/v) yeast extract, 0.25% (w/v) dipotassium phosphate; pH 7.0, 2.0% (v/v) inoculum, and aeration at 200 rpm; 40 C. The purification of the substance was performed by the steps of precipitating with 0-30% ammonium sulfate, running through Sephadex G-50 column chromatography and DEAE-Sephadex column chromatography. The specific activity of this substance increased from 29.10 AU/mg protein of cultured broth to 52.63, 75.36 and 95.23 AU/mg protein, in each step, respectively. The results from SDS-PAGE showed that this molecular weight was approximately 3.5 kDa and consisted of lipid. The antimicrobial activity decreased after incubating at 70 and 80 C for 15 minutes and could not be detected after 60 minutes. Its activity also disappeared after incubating at 100 C for 10 minutes or autoclaving at 121 C for 20 minutes. Antimicrobial substance showed its activity at the conditions of wide range of pH (3-10) and 0-5% (w/v) sodium chloride. Protease could reduce the activity of the substance whereas no effect of alpha-amylase and lipase have been detected.