Isolation of biosurfactant‐producing bacteria, product characterization, and evaluation

A gram‐positive, nonfermentative, rod‐shaped bacterium designated ST‐5, identified as Rhodococcus , was isolated from Kuwait soil. Grown on hydrocarbon, such as kerosene and n‐paraffin, the bacterium produced surface‐active compounds (biosurfactants). Measurements of surface tension, critical micelle dilution and emulsifying activity indicated that the biosurfactant is produced as a primary metabolite. The ST‐5 culture surface‐active component is mainly glycolipid in nature. Whole‐culture broth dropped surface tension to values below 27 mN/m and was stable during exposure to high salinity (10% NaCl), elevated temperatures (120°C for 15 min) and a wide range of pH values. The culture broth was effective in recovering up to 86% of the residual oil from oil‐saturated sand packs, indicating potential value in enhanced oil‐recovery processes.