BIOENGINEERING OF EMULSIFIER STRUCTURE - EMULSAN ANALOGS

Strategies were investigated to modulate the side chain structure of e mulsans formed by Acinetobacter calcoaceticus RAG-1. Analysis of emuls an fatty acid side chain groups by gas chromatography - mass spectrome try (GC-MS) revealed that by providing the exogenous n-alkanoic fatty acids 15:0, 16:0, and 17:0, emulsan analogs were formed with 53, 46, a nd 44 mol%, respectively, of fatty acid substituents with chain length s equal to that of the carbon source. In contrast, the increase in emu lsan fatty acids of chain lengths less than 15 or greater than 17 by p roviding corresponding shorter and longer chain length fatty acids as carbon sources was not substantial. When [1-C-13]-labeled (99% enriche d) palmitic acid was used as a carbon source along with acetate, analy sis of m/z 75/74 and 87/88 isotopomer ratios by GC-MS indicated that 8 4 and 86% of the 16:0 and 16:1 (9-cis) side groups, respectively, were incorporated intact from the 16:0 carbon source. The percentage of 14 -, 15-, 16-, 17-, and 18-carbon chain length fatty acid esters that we re monounsaturated were 11, 26, 50, 70, and 85%, respectively. Based o n the observed percentage of unsaturated chain length dependence and a lmost identical enrichment at C-1 of 16:0 and 16:1 (9-cis) side groups from [1-C-13]-labeled experiments, it was concluded that desaturation of preformed n-alkanoic acids was the predominant mechanism of their formation. Further work established correlations between side chain st ructure and product emulsification specificity/activity, so that bioen gineered emulsans with improved selectivity can now be formed.