Direct incorporation of octanoate into long-chain fatty acids by soluble enzymes of Mycobacterium tuberculosis

Effect of growth temperature on the fatty acid composition of Mycobacterium phlei

In Mycobacterium phlei, fatty acid unsaturation increased with decreasing temperature. The 10-hexadecenoic acid content increased as the temperature was reduced from 35 degrees C to 26-20 degrees C. At lower temperatures tuberculostearic acid decreased while oleic and linoleic acids increased, the latter being found in M. phlei for the first time. Concomitantly palmitic acid content decreased, and the 6- and 9-hexadecenoic acids increased slightly on reducing the temperature from 35 to 10 degrees C. Thus, down to 26-20 degrees C palmitic acid was mainly replaced by 10-hexadecenoic acid. From this range down to 10 degrees C, palmitic and tuberculostearic acids were replaced by oleic and linoleic acids. Consequently, fatty acid branching decreased and mean chain length increased, as the temperature was reduced. These observations support the view that regulation of membrane fatty acid composition is part of microbial temperature adaptation, and that the mechanism behind the responses might be more complex than generally believed.

Elongation of fatty acids in Mycobacterium tuberculosis

Cell-free extracts of the H37Ra strain of Mycobacterium tuberculosis contain a soluble enzyme system which catalyzes an elongation reaction of long-chain fatty acids. The predominant reaction involves the addition of a single C(2) unit to the acceptor fatty acid; the elongation takes place exclusively at the carboxyl end of the acceptor molecule. The endogenous acceptor lipid can be removed by solvent extraction of the enzyme system. The lipid-depleted enzyme can be fully reactivated with external acyl coenzyme A, after which elongation with acetyl coenzyme A takes place. The elongation reaction is avidin-insensitive and does not require adenosine triphosphate. Reduced nicotinamide adenine dinucleotide is the source of reducing equivalent, whereas reduced nicotinamide adenine dinucleotide phosphate is without effect.