Emulsification of crude oil by an alkane-oxidizingRhodococcusspecies isolated from seawater

Abstract

A Rhodococcus species, the best of 99 oil-emulsifying bacteria isolated from globally distributed seawater samples, was characterized. The bacterium produced very stable oil-in-water emulsions from different crude oils with various contents of aliphatic and aromatic compounds by utilizing the C11 to C33 n-alkanes as carbon and energy sources. The presence of alkanes induced the formation of a hydrophobic cell surface that permitted oil-associated exponential growth and where an extensive emulsification of the residual oil and accumulation of acidic oxidation products occurred. The acidic products were consumed in a second step characterized by linear growth and an increasing number of cells growing in the water phase. Adhesion of cells resulted in some stabilization of oil droplets, but the most extensive emulsification occurred at the end of the exponential phase and coincided with an increasing number of cells in the water phase. No surfactant could be detected in the water phase during exponential growth, but a polymeric compound with emulsifying activity, tightly bound to the oil droplets, could be isolated. This suggests that the emulsification was caused by the release of the hydrophobic cell surface discarded by the cells during conditions of growth limitations.Key words: Rhodococcus,emulsification, adhesion, n-alkanes, hydrophobicity.

Stabilization of water/gas oil emulsions by desulfurizing cells of Gordonia alkanivorans RIPI90A

“…The polymers can be expressed on the cell surface and so react with the organic phase and disperse it (Bredholt et al, 1998). It has been reported that some intact and washed bacteria can stabilize oil/water emulsions by adhering to the oil-water interface; these bacteria hinder the coalescence of oil droplets and interact to form emulsion gels.…”

“…In biphasic systems, emulsification is not always just the result of the activity of biosurfactants; certain intact bacterial cells are also able to stabilize oil/water emulsions without changing the interfacial tension, by inhibition of droplet coalescence (Bredholt et al, 1998;Dorobantu et al, 2004).…”

Chemostat Approach for the Directed Evolution of Biodesulfurization Gain-of-Function Mutants

“…For screening of bacterial growth on organosulfur compounds, emulsion agar containing 1% (vol/vol) dodecane was prepared as described previously (2). The sulfur concentration in the oil was 25 mM.…”

Study Onmicrobial Diversity of Biosurfactant Producing Bacteria From Contaminated Enviromental Samples.

“…It enhances the bioavailability of the oil and thus increases the biodegradation rate (Bredholt et al, 1998;Minf et al, 2011;Hassanshahian et al, 2012). Very often the growth of microorganisms on hydrocarbons is accompanied by the emulsification of the hydrocarbon in the medium, and in most cases this has been attributed to the production of surface-active compounds (Desai and Banat,1997).…”