EFFECTS OF GROWTH CONDITIONS ON ANTIMICROBIAL ACTIVITY OF Bacillus subtilis NN12 AND Bacillus licheniformis KN12 AGAINST Bacillus cereus

Abstract

Overuse/misuse of natural and chemical-synthesized antimicrobials has contributed to the development of resistant microorganisms. In addition, the shortage of new antimicrobials is one of the top concerns around the world. This study, therefore, was conducted with the aim of initial exploiting potential sources of antimicrobial compounds from Bacillus species. The antimicrobial activity against pathogenic bacteria and the effect of culture conditions on the production of antimicrobial compounds from Bacillus subtilis NN12 and Bacillus licheniformis KN12 were investigated. The invitro antagonistic test showed that these two strains were able to strongly inhibit B. cereus. In addition, the effect of culture conditions on the biosynthesis of B. cereus antibacterial compounds of the two studied strains was identified. The results showed that the medium containing 1.0% glucose, 0.5% peptone or yeast extract, at pH 6.0, shaking rate 150rpm for 18 hours, at 33°C is suitable conditions for B. subtilis and the one supplemented with 1.0% glucose or starch, 0.5% urea, pH 5.0, shaking rate 150rpm for 18 hours at 37°C-45°C is the right condition for B. licheniformis KN12. Interestingly the antagonistic activity of B. subtilis culture was sensitive to high temperature and proteinase K, whereas B. licheniformis KN12 culture exhibited thermal stability and proteinase K resistance properties. The results obtained will be the premise for antimicrobial compound research in the near future, contributing to therapeutic methods to fight infectious diseases, the agriculture, and the food industry.