Control of unsaturated fatty acid substituents in emulsans

The ability to regulate the content of unsaturated fatty acids (FAs) of emulsans (EMs) formed by Acinetobacter calcoaceticus RAG-I was studied. Studies of EM biosynthesis with C-13(1)-labeled FAs demonstrated that 95 +/- 7% of 16:1(9-cis) incorporated into EMs (EM-FAs) were formed by desaturation of the carbon source 16:0. An aerobic desaturation mechanism involving Delta-9 desaturase activity was proposed to explain these results. The direct incorporation of Delta-9-cis unsaturated acids occured concurrently with a decrease in the content of other 9-cis unsaturated EM-FAs. Important factors which ultimately determined the composition of unsaturated EM-FAs were the following: (i) feedback inhibition of Delta-9 desaturase activity, (ii) direct incorporation of FAs from a carbon source and (iii) two-carbon unit elongation or removal. The incorporation of polyunsaturated FAs into EMs was also accomplished by the selective feeding method. For example, by feeding RAG-1 with 18:2(9,12-trans), an EM was formed that contained almost 55 nmol/mg-EM (GC-MS). The surface activities of the new EMs from unsaturated FAs were evaluated. (C) 1999 Elsevier Science Ltd. All rights reserved.