Physical and metabolic interactions of Pseudomonas sp strain JA5-B45 and Rhodococcus sp strain F9-D79 during growth on crude oil and effect of a chemical surfactant on them

Methods to enhance crude oil biodegradation by mixed bacterial cultures, fo r example, (bio)surfactant addition, are complicated by the diversity of mi crobial populations within a given culture. The physical and metabolic inte ractions between Rhodococcus sp. strain F9-D79 and Pseudomonas sp. strain J A5-B45 were examined during growth on Bow River crude oil. The effects of a nonionic chemical surfactant, Igepal CO-630 (nonylphenol ethoxylate), also were evaluated. Strain F9-D79 grew attached to the oil-water interface and produced a mycolic acid-containing capsule. Crude oil emulsification and s urface activity were associated with the cellular fraction. Strain JA5-B45 grew in the aqueous phase and was unable to emulsify oil, but cell-free sup ernatants mediated kerosene-water emulsion formation. In coculture, stable emulsions were formed and strain JA5-B45 had an affinity for the capsule pr oduced by strain F9-D79. Igepal CO-630 inhibited F9-D79 cells from adhering to the interface, and cells grew dispersed in the aqueous phase as 0.5-mum cocci rather than 2.5-mum rods. The surfactant increased total petroleum h ydrocarbon removal by strain JA5-B45 from 4 to 22% and included both satura ted compounds and aromatics. In coculture, TPH removal increased from 13 to 40% following surfactant addition. The culture pH normally increased from 7.0 to between 7.5 and 8.5, although addition of Igepal CO-630 to F9-D79 cu ltures resulted in a drop to pH 5.5. We suggest a dual role for the nonylph enol ethoxylate surfactant in the coculture: (i) to improve hydrocarbon upt ake by strain JA5-B45 through emulsification and (ii) to prevent strain F9- D79 from adhering to the oil-water interface, indirectly increasing hydroca rbon availability. These varied effects on hydrocarbon biodegradation could explain some of the known diversity of surfactant effects.