Abstract
1. Some members of the genus Butyrivibrio, including a general fatty acid auxotroph (strain S2), contain as a major part of their complex lipids a high-molecular-weight component that is probably formed by the union of two fatty acid chains [Hazlewood & Dawson (1979) J. Gen. Microbiol. 112, 15--27]. 2. Proton and 13C n.m.r. and i.r. and mass spectroscopy were used to examine a homologous series of these moieties and, in addition, the hydrocarbon derivative of one homologue and several synthetic compounds. 3. The results indicate that the high-molecular-weight components are a series of long-chain dicarboxylic acids containing vicinal dimethyl branching, located near the centre of the chain.