Biological modification of hydrophobic group of a lipopolysaccharide biosurfactant,emulsan,produced by acinetobacter calcoaceticus RAG-1

Abstract

Emulsan is an extracellular polyanionic lipopolysaccharide produced by Gram-negative hydrocarbon-degrading bacterium,Acinetobacter calcoaceticus RAG-1. Emulsan contains about 15\% long fatty acid esters which are thought to modulate hydrophilic-lipophilic balance. It was found that the composition of fatty acid esters of emulsan could be significantly altered by supplying the different types of chemicals as a carbon and energy source in the culture medium. Emulsan having the modified fatty acid group also showed the different emulsifying activity in hydrocarbon-in-water system. Emulsan contained at least 10 different fatty acids and major components were found to be 3-hydroxydodecanoic acid,hexadecanoic acid,and octa decenoic acid. Among themm,3-hydroxydodecanoic acid seems to be the most important fatty acid in the active emulsan preparations. Molecular weight of emulsan samples produced from different carbon sources was in the range of $9.0 \times 10^6-1.4 \times 10^7$ and there was no corelation between emulsifying activity and molecular weight of emulsan with different fatty acid composition. Emulsan did not appreciably reduce surface and interfacial tension,but it was a very effective emulsifying agent for hydrocarbons in water even at a content as low as 0.0013\%-0.013\%. It implies that emulsan is a good emulsifier rather than a good surfactant. Emulsan effectively protected oil-in-water emulsions from coalescence and give the enhanced stability.