The growth of Mycobacterium convolutum on solid n-alkane substrates: effect on cellular lipid composition

Growth rates and cell yields of Mycobacterium convolutum strain R22 grown on a wide range of both odd- and even-numbered carbon solid n-alkanes decreased as the substrate carbon number increased. Cellular lipid was 2.5 times higher following growth on the hydrocarbon substrates. The amount of polar lipid was found to be about half of the cellular lipid in docosane through octacosane-grown cells. Phosphatidylethanolamine represented about 50% of the polar phospholipid in hydrocarbon- and nonhydrocarbon-grown cells. Phosphatidylserine, diphosphatidylglycerol, and phosphatidic acid were also found. The amount of phosphatidylserine was higher (10-14%) in docosane through octacosane-grown cells. There was a correspondingly smaller amount of diphosphatidylglycerol. These lipid changes may be associated with the assimilation of the hydrophobic substrates. The failure to detect label in lipids of solid n-alkane-grown cells incubated in the presence of [14C]acetate suggested that de novo synthesis of fatty acids did not occur to an appreciable extent. Transport of [14C]acetate and incorporation into cellular protein was not inhibited. Polar lipid fatty acid analyses indicated there was no direct incorporation of the oxidized substrate. The results suggest that beta-oxidation and a subterminal oxidative cleavage appear to be the major catabolic routes providing fatty acids, which are then incorporated into lipid.