Effects of biosurfactants on fate and transport of phenanthrene in subsurface environments

Effects of trehalose lipid biosurfactants produced by Rhodococcus erythropolis ATCC 4277 on solubilization and biodegradation of phenanthrene (PHE) were investigated. Addition of the biosurfactant at 20 times critical micelle concentration (CMC) increased the apparent aqueous solubility of PHE by more than 30 times. No inhibitory effect of trehalose lipids on a PHE-degrading organism (Isolate P5-2) was observed. The biosurfactant greatly enhanced phenanthrene mineralization by Isolate P5-2 in all aqueous, soil, and soil-water slurry systems tested.; Influence of the biosurfactant on PHE mineralization by two soil microorganisms, Isolate P5-2 and Pseudomonas strain R, was also compared under different environmental conditions. The test microorganisms demonstrated significant difference in the PHE mineralization capabilities. While Isolate P5-2 mineralized phenanthrene faster than P. strain R in aqueous phase, P. strain R having more hydrophobic surface greatly exceeded Isolate P5-2 in ability to access soil-sorbed phenanthrene.; Isolate P5-2 had a relatively more polar surface than P. strain R, and the apparent cell hydrophobicity of the strain was minimally affected with the addition of trehalose lipids. Nevertheless, the biosurfactant substantially improved phenanthrene mineralization by Isolate P5-2 in all systems tested. Contrary to Isolate P5-2, the apparent cell hydrophobicity was significantly stimulated with increasing concentration of the biosurfactant for P. strain R. However, effect of the biosurfactant on phenanthrene mineralization appeared to be insignificant for this organism.; Finally, effects of a surfactant-producing microorganism on phenanthrene biodegradation by the two PHE-degrading microorganisms in batch soil and soil column systems were investigated. Co-inoculation with the surfactant-producing bacteria significantly enhanced phenanthrene biodegradation by P. strain R but it did not affect the biodegradation by Isolate P5-2 in both batch and column systems. Production of biosurfactants by the surfactant-producing bacteria was negligible in the systems under the given experimental conditions of this research. This study demonstrated that bioaugmentation with surfactant-producing bacteria could enhance in situ bioremediation of soils contaminated with polycyclic aromatic hydrocarbons (PAHs) and the beneficial effect of the bioaugmentation depended on types of PAHs-degrading microorganisms present.