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). Neasurements 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 giycolipid in nature. Whole-culture broth dropped surface tension to values below 27 mN/m and was stable during exposure to high salinity (10% NaCI), 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.
The nutritional requirements and growth characteristics of a biosurfactant-producingRhodococcus bacterium isolated from Kuwaiti soil were determined. Maximum cell yields (6.6 g/l) and biosurfactant production were achieved with a medium containing 2% (v/v)n-paraffin as a carbon and energy source, 0.2% lactose broth, optimal concentrations of nitrogen (nitrate), phosphorus, iron, magnesium and sodium sources, and minimal concentrations of potassium and trace element sources. The optimal pH was 6.8 for surfactant production and optimal temperature was 37°C. The biosurfactant produced after 16 to 33 h growth in a 7 I fermenter decreased both surface tension and interfacial tension of culture broth to below 27 and 1.8 mN/m, respectively, and was effective at critical micelle dilutions of 10(-3). Data on biosurfactant biosynthesis suggest that the product is produced as a primary metabolite and, therefore, could be produced effectively under continuous fermentation conditions.
Isolation of auxotrophic mutants and conjugal transfer of plasmids are successfully demonstrated in four obligate methylotrophic strains isolated a t Kuwait Institute for Scientific Research (KISR). Out of 11 auxotrophic, mutants, three required methionine and two leucine. Complete transfer of plasmid R68.45 from Pseudomoms to KISR methylotrophs and vice versa have been achieved with a low transfer rate.
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