Production of biosurfactant from Iranian oil fields by isolated Bacilli

Crude oil and water samples were collected from selected Iranian oil reservoirs. Experimental works were carried out in laboratory conditions. The samples have been grown on PYG medium and incubated at 30-80 °C. Thirty-six mesophile and thermophile bacterial strains have been isolated. All the isolates were able to grow at aerobic condition. Batch growth kinetic studies were carried out in a 500 ml. shake flask. Out of 36 isolated strains from 24 crude oil and water samples, 35 strains were gram positive rod. Shaped spore forming bacteria and one strain was coccid form. Eight out to 35 bacillus species were capable of producing surfactant. Production of biosurfactant was found to be cell growth associated. The ability of surfactant producing bacteria indicated by reduction of surface tension (ST) and interfacial tension (IFT) of the supernatant. Eight strains obtained the IFT reduction in crude oil, hexadecane, sucrose, glucose, fructose and mannose medium as a sole source of carbon and energy at 40 °C by 15-30 mN/m. Results showed that all the bacteria are producing more surfactant when glucose is the carbon source. Further screening of biosurfactant producer showed that three of the isolated strains resulted the maximum ST and IFT. Effect of temperature on these three isolates investigated at 30-80 °C, above 50 °C surfactant production was dramatically reduced. The isolated strains had the capacity to produce the surfactant at 3-5% NaCl a wide rang of pH (6.5-8.5).