Impact of surfactants on the biotransformation of methyl ricinoleate into γ-decalactone by Yarrowia lipolytica

Surfactants play a key role in the biotechnological degradation of hydrophobic substrates, however this role is often misunderstood. During the biotransformation of methyl ricinoleate into the aroma compound γ-decalactone by the yeast Yarrowia lipolytica, a direct contact occurs between the surface of the cells and the small droplets of substrate. The impact of a series of surfactants on this process was investigated. Both ionic surfactants tested were toxic towards the yeast. This effect may be linked to a decrease in the cell membrane integrity. The interfacial area of the emulsion varied according to the non-ionic surfactant used, and this factor was correlated with the productivity of the biotransformation. By evaluating the effect of surfactants on the capacity of the cells to adhere to decane (MATH test), it was shown that the adhesion of methyl ricinoleate on yeast surface is not a rate-limiting point for the process. © 2004 Elsevier B.V. All rights reserved

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, 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-μm cocci rather than 2.5-μm 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