Identification of the Polyketide Synthase Involved in the Biosynthesis of the Surface-Exposed Lipooligosaccharides in Mycobacteria

Lipooligosaccharides (LOS) are highly antigenic glycolipids produced by a number ofMycobacterium species, which include “M. canettii ,” a member of theM. tuberculosis complex, and the opportunistic pathogensM. marinum andM. kansasii . The various LOS share a core composed of trehalose esterified by at least 1 mole of polymethyl-branched fatty acid (PMB-FA) and differ from one another by their oligosaccharide extensions. In this study, we identified a cluster of genes, MSMEG_4727 through MSMEG_4741, likely involved in the synthesis of LOS inM. smegmatis . Disruption of MSMEG_4727 (the ortholog ofpks5 ofM. tuberculosis ), which encodes a putative polyketide synthase, resulted in the concomitant abrogation of the production of both PMB-FA and LOS in the mutant strain. Complementation of the mutant with the wild-type gene fully restored the phenotype. We also showed that, in contrast to the case for “M. canettii ” andM. marinum , LOS are located in deeper compartments of the cell envelope ofM. smegmatis . The availability of two mycobacterial strains differing only in LOS production should help in defining the biological role(s) of this important glycolipid.