Structural Diversity of the Lipopeptide Biosurfactant Produced by a Newly Isolated Strain, Geobacillus thermodenitrifcans ME63

Thegenus Geobacillus is activein degradation of hydrocarbons in thermophilic and facultative environmentssince it was first reported in 1920. Here, we report a new strain, Geobacillus thermodenitrificans ME63, isolated froman oilfield with the ability of producing the biosurfactant. The composition,chemical structure, and surface activity of the biosurfactant producedby G. thermodenitrificans ME63 wereinvestigated by using a combination of the high-performance liquidchromatography, time-of-flight ion mass spectrometry, and surfacetensiometer. The biosurfactant produced by strain ME63 was identifiedas surfactin with six variants, which is one of the representativefamily of lipopeptide biosurfactants. The amino acid residue sequencein the peptide of this surfactin is N-Glu -> Leu -> Leu -> Val -> Leu -> Asp -> Leu-C. The criticalmicelle concentration (CMC) of the surfactin is 55 mg L-1, and the surface tension at CMC is 35.9 mN m(-1), which is promising in bioremediation and oil recovery industries.The surface activity and emulsification properties of biosurfactantsproduced by G. thermodenitrificans ME63showed excellent resistance to temperature changes, salinity changes,and pH changes.