Pseudomonas aeruginosa UG2 rhamnolipid biosurfactants: structural characterization and their use in removing hydrophobic compounds from soil

Abstract

The structure of two rhamnolipid biosurfactants produced by Pseudomonas aeruginosa UG2 was studied. Analyses by gas chromatography - mass spectrometry and nuclear magnetic resonance spectroscopy showed these two rhamnolipids to be α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate and 2-O-α-L-rhamnopyranosyl-α-L-rhamnopyranosyl-β-hydroxydecanoyl-β-hydroxydecanoate. The ability of UG2 rhamnolipid biosurfactants to enhance removal of naphthalene, anthracene, phenanthrene, fluorene, 2,2′,5,5′-tetrachlorobiphenyl, and 3,3′,4,4′,5,5′-hexachlorobiphenyl into the aqueous phase was affected by soil type, hydrocarbon equilibration time, and biosurfactant adsorption to soil. Partially purified UG2 biosurfactants at a concentration of 5 g/L removed approximately 10% more hydrocarbon from a sandy loam soil than silt loam soil. High levels of UG2 rhamnolipids adsorbed to soil. In 18% (w/v) soil slurries 74, 49, 38, and 20% of 0.5, 1, 2, and 5 g UG2 rhamnolipids/L, respectively, were bound to the soil phase. Sodium dodecyl sulphate recovered lower levels and Witconol SN70 higher levels of phenanthrene and 2,2′,5,5′-tetrachlorobiphenyl than UG2 biosurfactants.Key words: biosurfactant, hydrocarbon, Pseudomonas aeruginosa, remediation.