Biodegradation Rate Enhancement of Hydrocarbons by an Oleophilic Fertilizer and a Rhamnolipid Biosurfactant

The oleophilic fertilizer Inipol EAP 22 and a microbial biosurfactant (rhamnolipid) were investigated for their ability to increase the rate of biodegradation of aliphatic and aromatic hydrocarbons by pure bacterial cultures. Both Inipol EAP 22 and rhamnolipid were found to lower the surface tension of a phosphate buffered solution to 32 mN m⁻¹. Each surfactant dramatically increased the apparent aqueous solubility of solid 2-methylnaphthalene, and were capable of emulsifying liquid hydrocarbons. Biodegradation experiments were carried out with the TOL plasmid-containing strain, Pseudomonas putida (ATCC30015); the OCT plasmid-containing strain, P. oleovorans (ATCC29347); and an unknown naphthalene-degrading strain (ATCC15075). Cells were grown under conditions where biodegradative enzymes were induced before their utilization. Model studies were conducted to investigate the ability of Inipol EAP 22 and rhamnolipid to enhance the rate of transport and uptake of hydrocarbons into bacterial cells, and to assess the impact that increasing the apparent aqueous solubility of hydrocarbons has on their rate of biodegradation. The extent of rate enhancement of compound mineralization resulting from surfactant addition was significantly greater for the sparingly soluble alkanes, hexadecane and octadecane, than for the more soluble aromatics, toluene and 2-methylnaphthalene. The results suggest that increasing the bioavailability of hydrocarbons to bacteria may be a useful method to accelerate the rate of biodegradation at contaminated sites. Lastly, the data supports the hypothesis that surface-active components present in the oleophilic fertilizer formulation, Inipol EAP 22, may have significantly contributed to the positive results reported in tests of remedial agent impact on bioremediation, which was used as a supplemental cleanup technology on Exxon Valdez crude oil contaminated Alaskan beaches.