Characterization of Surfactin Produced by Bacillus subtilis Isolate BS5

Abstract

Physical and chromatographic characterization of the surfactin biosurfactant produced by Bacillus subtilis isolate BS5 has been conducted to study its potentiality for industrial application. The crude extract of test surfactin appeared as off-white to buff flake-like amorphous residue with bad odor similar to sour pomegranate. Test surfactin showed solubility in aqueous solution at pH>5 with optimum solubility at pH 8-8.5. It was also soluble in organic solvents like ethanol, acetone, methanol, butanol, chloroform, and dichloromethane. Surfactin crystals appeared rectangular with blunt corners and were arranged perpendicular to each other making a plus sign. Extracted surfactin showed high surface activity, as it could lower the surface tension of water from about 70 to 36 mN/m at approximately 15.6 mg/l. Moreover, test surfactin exhibited excellent stabilities at high temperatures (100 degrees C for up to 1 h at and autoclaving at 121 degrees C for 10 min), salinities (up to 6% NaCl), and over a wide range of pH (5-13). Test surfactin in the cell-free supernatant or crude culture broth forms showed high emulsification indices against kerosene (62.5% and 59%, respectively), diesel (62.5% and 66%, respectively), and motor oil (62% and 66%, respectively). These characters can effectively make test surfactin, in its crude forms, a potential candidate for the use in bioremediation of hydrocarbon-contaminated sites or in the petroleum industry. Chromatographic characterization of test surfactin, using high-performance liquid chromatography technique, revealed that the extracted surfactin contained numerous isoforms, of which six were found in the standard surfactin preparation (Fluka). Additional peaks appeared in the test surfactin and not in the standard one. These peaks may correspond to new surfactin isoforms that may be present in the test surfactin produced by B. subtilis isolate BS5.