Isolation and partial characterization of a biosurfactant mixture produced by Sphingobacterium sp. isolated from soil.

Strain 6.2S, isolated from soil and identified as a Sphingobacterium sp., is the first strain in this genus to be reported as a biosurfactant producer, being able to reduce the surface tension of its culture supernatant to 32 mN/m. In this work, biosurfactants from the culture supernatant were purified and partially characterized. The crude extract (10 g/L) was very effective in reducing surface tension (22 mN/m). Thin layer chromatography (TLC) indicated that a mixture of various biosurfactants was present in the 6.2S crude extract. After purification, Fraction A, a phospholipid mixture, reduced surface tension to 33 mN/m. Fraction B was a mixture of lipopetides and at least one glycolipid. The surface tension-concentration curve showed two plateaux, the first of which can be attributed to a critical aggregation concentration of the biosurfactant with a protein (2.7 g/L) and the second to the true cmc in water (6.3g/L).