Screening and Optimization of Biosurfactant Production by Bacillus subtilis from Restaurant Wastewater Contaminated Soil

Biosurfactant production from Bacillus subtilis RT9(4)B isolated from restaurant wastewater contaminated soil was investigated. The isolated Bacillus subtilis RT9(4)B was screened for biosurfactant production using the emulsification index, oil displacement, zone of haemolysis, surface tension and a positive drop collapse method. Effects of carbon and nitrogen sources, pH, temperature and incubation periods on biosurfactant production were determined by optimization. The biosurfactant characterization was by Fourer Transform Infra-Red and Gas Chromatography Mass Spectrometry analyses. Preliminary assessment showed that the emulsification index was 56.41 ± 1.30 %, oil displacement, 6.02 ± 1.24 mm, zone of haemolysis, 5.12 ± 1.06 mm, surface tension, 29.46 ± 0.62 mN/m and a positive drop collapse test. At optimal conditions of temperature (40 ºC), pH (7), carbon and nitrogen sources (lactose, 20 g/l and urea, 1.5 g/l respectively), the surfactant reduced surface tension up to 11.10 ± 0.78 mN/m and the emulsification index rose to 95.51 ± 2.66%. The highest biosurfactant produced was 3.73 ± 0.19 g/L at 72 h. Bacillus subtilis RT9(4)B produced lipopeptide type biosurfactant containing hexadecanoic, octadecanoic acid, peptides, aliphatic, alkyl and esters