Microbial enhanced oil recovery potential of surfactin-producing Bacillus subtilis AB2.0

Abstract Bacillus subtilis AB2.0 showed to produce a surface-active compound that was identified by mass spectrometry analysis as a surfactin. Four different isoforms were identified in the protonated form [M+H]+ with m/z of 1030.6350, 1044.6511, 1058.6661 and 1072.6848. They were constituted of fatty acids varying from C13 to C16; however, about 70% of the isoforms showed m/z of 1058.6661 and the fatty acid C15. Based on the AB2.0 genome sequence, only one gene group related to surfactin biosynthesis was found. Strain AB2.0 produced 99.6 mg/l of surfactin in Tryptic Soy Broth after 48 h. The biosurfactant presented an emulsification activity of 45.7% in this growth condition. It considerably decreased the water surface tension from 72.0 mN/m to 24.7 mN/m and the interfacial tension of n-hexadecane from 30.1 mN/m to 7.5 mN/m, as well as of a medium crude oil from 42.3 mN/m to 6.9 mN/m and of a light crude oil from 36.4 to 3.8 mN/m. Calcite flotation test was conducted to access the wettability reversal of the biosurfactant in high salinity condition similar to that observed in an oil production reservoir, and AB2.0 reversed 100% using concentrations as low as 25 ppm of biosurfactant. Oil contaminated sand columns were used to simulate microbial enhanced oil recovery at different temperatures and high salinity. When surfactin from AB2.0 was added to the sand columns, the TPH concentration in liquid phases recovered was enhanced up to 24× indicating that AB2.0 is an excellent candidate for its application in MEOR in subsurface environments.