Biosurfactant- and biodegradation-enhanced partitioning of polycyclic aromatic hydrocarbons from nonaqueous-phase liquids.

A study was conducted on the effect of two different biological factors, microbial surfactants and biodegradation, on the kinetics of partitioning of polycyclic aromatic hydrocarbons (PAHs) from nonaqueous-phase liquids (NAPLs). The effect of rhamnolipid biosurfactants on partitioning into the aqueous phase of naphthalene, fluorene, phenanthrene, and pyrene, initially dissolved in di-2-ethylhexyl phthalate (DEHP) or 2,2,4,4,6,8,8-heptamethylnonane (HMN), was determined in multiple-solute experiments. Biosurfactants at a concentration above the CMC enhanced the partitioning rate of fluorene, phenanthrene, and pyrene but were ineffective with naphthalene. Enhancement of partitioning was also observed in the presence of suspended humic acid-clay complexes, which simulated the solids often present in the subsurface. Biosurfactants sorbed to the complexes modified PAH partitioning between the NAPL and these solids, increasing the fraction of solid-phase PAH. Biodegradation-driven partitioning was estimated in mineralization experiments with phenanthrene initially present in HMN and three representative soil bacterial strains, differing in their potential adherence to the NAPL. In the three cases, the rates of mineralization were very similar and significantly higher than the abiotic rate of partitioning. Our study suggests that in NAPL-polluted sites, partitioning of PAH may be efficiently enhanced by in situ treatments involving the use of biosurfactants and biodegradation.

Flow cytometry discrimination between bacteria and clay-humic acid particles during growth-linked biodegradation of phenanthrene by Pseudomonas aeruginosa 19SJ.

Abstract Methods that quickly assess microbial density and aggregation in soil and sediments are needed in environmental microbiology. We report a flow cytometry method that uses the green and orange emission of the fluorochrome SYTO-13 to discriminate between bacteria and clay-humic acid particles. This approach distinguishes single or clustered bacteria, and clusters of bacteria and abiotic particles during the growth of the biosurfactant-producing strain Pseudomonas aeruginosa 19SJ on solid phenanthrene in the presence of humic acid-clay complexes.