title: 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.
abstract: Methods to enhance crude oil biodegradation by mixed bacterial cultures, for example, (bio)surfactant addition, are complicated by the diversity of microbial populations within a given culture. The physical and metabolic interactions between Rhodococcus sp. strain F9-D79 and Pseudomonas sp. strain JA5-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 surface activity were associated with the cellular fraction. Strain JA5-B45 grew in the aqueous phase and was unable to emulsify oil, but cell-free supernatants mediated kerosene-water emulsion formation. In coculture, stable emulsions were formed and strain JA5-B45 had an affinity for the capsule produced 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-microm cocci rather than 2.5-microm rods. The surfactant increased total petroleum hydrocarbon removal by strain JA5-B45 from 4 to 22% and included both saturated 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 cultures resulted in a drop to pH 5.5. We suggest a dual role for the nonylphenol ethoxylate surfactant in the coculture: (i) to improve hydrocarbon uptake by strain JA5-B45 through emulsification and (ii) to prevent strain F9-D79 from adhering to the oil-water interface, indirectly increasing hydrocarbon availability. These varied effects on hydrocarbon biodegradation could explain some of the known diversity of surfactant effects.
authors.affiliation: Microbial Biotechnology Laboratory, Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada. jvanhamme@alumni.waterloo.ca
authors.forename: J D
authors.initials: JD
authors.lastname: Van Hamme
authors.forename: O P
authors.initials: OP
authors.lastname: Ward
mesh_terms: D001673:Biodegradation, Environmental; D003470:Culture Media; D017753:Ecosystem; D017830:Octoxynol; D010578:Petroleum / Q000378:metabolism*; D011092:Polyethylene Glycols / Q000494:pharmacology; D011549:Pseudomonas / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D012240:Rhodococcus / Q000187:drug effects* / Q000254:growth & development* / Q000378:metabolism; D013501:Surface-Active Agents / Q000494:pharmacology*
chemical_list: D003470:Culture Media; D010578:Petroleum; D013501:Surface-Active Agents; D011092:Polyethylene Glycols; D017830:Octoxynol; C010615:Nonidet P-40