Optimization and antimicrobial properties of biosurfactant production by four indigenous soil bacterial species

Abstract

Biosurfactants of microbial origin are metabolites; hence their production is dependent on the growth of the producing microbe. The objective of this study was to assess the optimum conditions for biosurfactant by four bacterial species. Biosurfactant detection was carried out using emulsification index, drop collapse and oil displacement assays. Functional composition of the crude biosurfactant was determined using gas chromatography-mass spectroscopy (GC-MS). In the presence of Pseudomonas fuscoginae significantly higher EI₂₄ of 53.98% and 52.60% was observed in media that contained glucose or sodium acetate as carbon source, respectively. When P. fuscoginae or P. aeruginosa was used for inoculation, highest EI₂₄ of 61.18% and 48.40% was observed in media that contained potassium nitrate as nitrogen source. In the medium that was inoculated with either B. subtilis or B. proteolyticus, highest EI₂₄ of 53.65% and 49.63% was observed in the presence of tryptone and peptone, respectively. At the respective pH used for investigation, significantly highest EI₂₄ was observed at pH 6, when inoculated with the respective isolates. In the case of incubation temperature, positive results were obtained throughout the incubation period at 25 and 30 ^oC. This was also irrespective of the isolate used for inoculation. All the extracted biosurfactants showed antimicrobial potentials against the test pathogens used for investigation. Characterization of the crude biosurfactant revealed the presence of compounds with antimicrobial properties. The study was able to provide useful information on optimum conditions for biosurfactant production by test bacterial species and the potential for possible application of the biosurfactants as antimicrobial agents.