Enhancement of phenanthrene solubilization and biodegradation by trehalose lipid biosurfactants

Effects of trehalose lipid biosurfactants produced by Rhodococcus erythropolis on the solubilization and biodegradation of phenanthrene (PHE) were investigated. Based on surface tension measurements, the average critical micelle concentration (CMC) of trehalose lipids was determined to be approximately 16 mg total organic carbon (TOC)/L. In solubilization assays, the addition of biosurfactants at 20-fold the CMC increased the apparent solubility of PHE by more than 30-fold. Using a known PHE degrader (isolate P5-2), batch PHE biodegradation experiments were conducted, with and without trehalose lipids, in three systems: Water (devoid of soil solids), soil (Kenansville loamy sand having 0.72% organic matter), and soil-water slurry. Addition of trehalose lipids at 10-fold the CMC enhanced both the rate and the extent of PHE mineralization by isolate P5-2 in the liquid culture. The addition of biosurfactant (32.2 mg TOC/kg soil) to the soil system also increased both the initial rate (by more than twofold) and the extent of PHE mineralization. Biosurfactants increased the rate, but not the extent, of PHE mineralization in the soil-water slurry. The results obtained in the present study indicate that the trehalose lipid biosurfactants produced by R. erythropolis have good solubilization capacity for hydrophobic organic compounds and great potential for applications in bioremediation of sites contamination with polycyclic aromatic hydrocarbons.