Effects of Nitrogen and Carbon Sources on Biosurfactant Production by Hydrocarbon-utilizing Stenotrophomonas sp.

Aim: This study investigated effects of nitrogen and carbon sources on the production of biosurfactant by a hydrocarbon-utilizing bacterium, Stenotrophomonas sp.

Methodology: The hydrocarbon-utilizing bacterium was isolated with Bushnell Haas (BH) broth using enrichment method. Biosurfactant production was screened by evaluating the following characteristics: Emulsification index (E-24), oil spreading (displacement), tilted glass slide, haemolysis on blood agar, and lipase production. Effects of combination of nitrogen sources (yeast extract and NH4NO3, yeast extract and urea, yeast extract and asparagine, yeast extract and peptone, NaNO3 and peptone, NaNO3 and asparagine, and yeast extract and NaNO3) and carbon sources (glucose, fructose, galactose, cassava peel, soya bran, olive oil, sucrose, crude oil, diesel and glycerol) on biosurfactant production were determined with emulsion stability and surface tension as responses. The bacterium was identified based on phenotypic, microscopic, and biochemical characteristics.

Results: The isolate produced colonies on BH agar containing either naphthalene or hexadecane as sole source of carbon after 48-h incubation. Screening characteristics for the production of biosurfactant by the isolate were as follows: 46% emulsification index, 3.1 cm2 oil displacement, 1.8 cm zone of clearance on tributyrin agar, γ-haemolysis, and positive tilted glass slide. The best carbon source with the highest emulsion stability (51.6%) was fructose whereas the best surface tension reduction (30.85 mN/m) was observed with olive oil as carbon sources after 7 days of incubation. For nitrogen, the combination of yeast extract and NH4NO3 gave the highest emulsion stability (60.7%) and the best surface tension reduction (39.58 mN/m). The data obtained were significant at P<0.05 and the bacterial isolate identified as Stenotrophomonas sp.

Conclusion: This study has demonstrated the ability of the hydrocarbon-utilizing bacterium, Stenotrophomonas sp. to produce biosurfactant, indicated by reduction of surface tension and formation of stable emulsion. This method of biosurfactant production can be further scaled up for industrial purpose.