Mycolic acid metabolic filiation and location in Mycobacterium aurum and Mycobacterium phlei

Abstract

Synchronous cultures of Mycobacterium aurum were used to prove a close relationship between cellular division and active synthesis of mycolic acids (characteristic long‐chain 3‐hydroxyacids, branched at position 2), confirming previous proposals. Mycolic acid biosynthesis was studied in two species (Mycobacterium phlei and M. aurum) each producing three types of mycolic acids: di‐unsatured mycolates, oxomycolates and wax‐ester mycolates (ester of dicarboxymycolic acid and 2‐icosanol or 2‐octadecanol). It was shown that unsaturated mycolates and oxomycolic acids were not directly related, whereas a metabolic filiation was confirmed between oxomycolate and wax ester mycolate: the latter derived, whereas a metabolic filiation was confirmed between oxomycolate and wax ester mycolate: the latter derived from the former by a Baeyer‐Villiger oxidation step, as has been proposed on the basis of structural considerations. By observing the labelling of the different mycolate pools in the cell, i.e. the organic‐solvent‐extractable fraction (essentially containing esters of trehalose and of glycerol) and the cell residue (assumed to be the cell‐wall polymers), it was clear that oxomycolates and unsaturated mycolates appeared first in the extractable lipids, then in the wall‐linked mycolates while wax‐ester mycolates appeared first as wall‐linked derivatives. Thus, it is proposed that mycolates could follow separate routes involving differently located enzymes to reach their complex forms either in extractable lipids or in the wall‐linked arabino‐galactan. Copyright © 1989, Wiley Blackwell. All rights reserved