Screening of biosurfactant production by Bacillus spp. potentially inhibiting the growth of Ralstonia solanacearum

Biosurfactants are surfactants produced by living organisms, including microorganisms. Several studies have shown that species from the Bacillus genera are able to synthesize biosurfactants as antimicrobial agents for plant pathogens. This study aims to detect the ability of three isolates of Bacillus indigenous from potato rhizosphere in Bumiaji, Batu, Malang, which are known to potentially inhibit the growth of Ralstonia solanacearum, in producing biosurfactants. This research was started from the rejuvenation of Bacillus spp. isolates, followed by the growth of Bacillus spp. on blood agar and nutrient broth media. The potential of Bacillus in producing biosurfactants was detected from the hemolytic activity in blood agar, the percentage of emulsification activity and the surface tension value of the culture supernatant, also the ability of bacteria to adhere to the hydrocarbon substrate. The results showed that the three Bacillus isolates (Ba-1, Ba-2, and Ba-11) had different abilities in synthesizing biosurfactants. The ability of Ba-1 and Ba-2 in.producing biosurfactant were indicated by hemolytic activity on blood agar, decreased surface tension of 18.44 and 14.90, as well as adherence activity of 13.46% and 38.46%, respectively. The ability of Ba-11 to produce biosurfactants was indicated by a decrease in surface tension up to 32.54, emulsification activity of 90%, and adherence activity of 10%. Biosurfactants from isolates of Bacillus spp. potential to be applied in controlling the development of R. solanacearum.