Effect of protein on the emulsifying activity of emulsan

Many bioemulsifiers are polymers produced by hydrocarbon-degrading bacteria. The best studied example is emulsan, an extracellular product of the Acinetobacter calcoaceticus strain RAG-1. Emulsan is an amphipathic lipopolysaccharide containing varying quantities of non-covalently bound protein. The latter was shown to enhance significantly the emulsifying activity of deproteinized emulsan towards aliphatic and aromatic hydrocarbons. The protein component was separated from emulsan by treatment with emulsan depolymerase followed by column chromatography. The protein fraction responsible for emulsifying activity enhancement appeared as a high molecular weight aggregate containing a major subunit of 29 kD. The latter was also detected by SDS-PAG electrophoresis of the initial and fractionated emulsan. The data are discussed in terms of the concept that protein/polysaccharide structures form mixed interfacial layers with higher stability than either polymer by itself.