The fatty acid (FA) profiles of the myxobacteria Stigmatella aurantiaca and Myxococcus xanthus were investigated by acidic methanolysis of total cell extracts and GC or GC-MS analysis. The main components were 13-methyltetradecanoic acid (iso-15: 0) and (Z)- hexadec-11-enoic acid (16: 1, ω-5 cis). The biosynthesis of iso-FAs was investigated in several feeding experiments. Feeding of isovaleric acid (IVA) to a mutant impaired in the ...