Plant saponins are attractive biosurfactants and have been used to enhance phytoremediation. There are only limited reports on saponins produced by bacteria. Here, we report structural and functional characterization of a novel saponin produced by Bacillus sp. IITD106. Biosurfactant production was determined by emulsion index, drop collapse, oil displacement and hemolytic assays. The biosurfactant was stable over a range of temperature (30 °C to 70 °C), salinity (0-150 g liter-1) and pH (4-10). The surface tension of the medium reduced from 58.89 mN/m to 27.29 mN/m using the isolated biosurfactant. Chromatographic analysis revealed the biosurfactant to be a glycolipid. LCMS, FT-IR and NMR analysis identified the biosurfactant to be a saponin containing two sugar groups and a 5 ringed triterpene sapogenin unit. Genome sequencing of the strain revealed the presence of genes responsible for biosynthesis of saponin. Statistical optimization of culture medium resulted in 9.3-fold increase in biosurfactant production. Kinetics study of biosurfactant production performed in a stirred tank batch bioreactor resulted in 6.04 g liter-1 and 6.9 g liter-1 biomass and biosurfactant concentration, respectively. The biosurfactant was found to solubilize polycyclic aromatic hydrocarbons. The potential of cell free biosurfactant containing broth to enhance oil recovery was tested in a sand pack column and recovery of 63% of residual oil was observed. To our knowledge this is the first report of saponin production by any of the strains of Bacillus.
Keywords: Bioreactor; Emulsion index; Media optimization; Oil recovery; PAH solubilization; Saponins.
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