The effect of growth parameters on the antibiotic activity and sporulation in Bacillus spp. isolated from soil.

Fifty-two Bacillus strains, which were isolated from different soil samples, were screened for antibiotic properties. The Bacillus strains were checked for antibacterial properties by the cross-streak method against 5 test pathogens, and 25 Bacillus strains had an effect on the test microorganisms. One strain of Bacillus, which exhibited the largest inhibition zone (25 mm) against Shigella sonnei, was named Bacillus sp. EA62. The antibacterial activity from Bacillus sp. EA62 was tested in six different culture media against Shigella sonnei using the agar well diffusion method. The best activity medium was selected and used for further studies. The influence of the incubation period, pH, and different glucose and nitrogen concentrations on the antibacterial activity was studied. The optimal conditions for the strongest antibiotic activity were found to be 72 hours (18 mm), pH 7.5 (23 mm), 3% glucose (25 mm), and 0.3% nitrogen concentration (23 mm). Additionally, the relationship between the antibiotic activity and sporulation was investigated. Accordingly, it was determined that the increase of the activity paralleled sporulation.