Identification of the Polyketide Synthase Involved in the Biosynthesis of the Surface-Exposed Lipooligosaccharides in Mycobacteria
Abstract
ABSTRACT Lipooligosaccharides (LOS) are highly antigenic glycolipids produced by a number of Mycobacterium species, which include “ M. canettii ,” a member of the M. tuberculosis complex, and the opportunistic pathogens M. marinum and M. 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 in M. smegmatis . Disruption of MSMEG_4727 (the ortholog of pks5 of M. 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 ” and M. marinum , LOS are located in deeper compartments of the cell envelope of M. smegmatis . The availability of two mycobacterial strains differing only in LOS production should help in defining the biological role(s) of this important glycolipid.