AIMS

To isolate and characterize the biosurfactant-producing micro-organism from petroleum-contaminated soil as well as to determine the biochemical properties of the biosurfactant.

METHODS AND RESULTS

A novel rhamnolipid-producing Pseudomonas aeruginosa (GenBank accession number GQ241355) strain was isolated from a petroleum-contaminated soil. Surface active compound was separated by solvent extraction of the acidified culture supernatant. The extract was able to reduce the surface tension of water from 72 to 44 mN m(-1) at a critical micelle concentration of 11.27 +/- 1.85 mg l(-1). It showed better activity (based on microdilution method) against Gram-positive (<or= 31 mg ml(-1)) bacteria and filamentous fungi (<or= 50 mg ml(-1)) than Gram-negative bacteria (>or= 125 mg ml(-1)) with mild toxicity (HC(50)- 38 +/- 8.22 microg ml(-1)) to red blood cells. Fourier transform infrared spectroscopy revealed the presence of aliphatic chain, hydroxyl groups, ester and glycosidic bonds. Presence of nineteen rhamnolipid homologues with variation in chain length and saturation was revealed from liquid chromatography coupled to mass spectrometry with electrospray ionization.

CONCLUSION

The results indicate that the isolated biosurfactant has a novel combination of rhamnolipid congeners with unique properties.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study provides a biosurfactant, which can be used as a biocontrol agent against phytopathogens (Fusarium proliferatum NCIM 1105 and Aspergillus niger NCIM 596) and exploited for biomedical applications.