Role of the pks15/1Gene in the Biosynthesis of Phenolglycolipids in the Mycobacterium tuberculosisComplex

Diesters of phthiocerol and phenolphthiocerol are important virulence factors ofMycobacterium tuberculosisand Mycobacterium leprae, the two main mycobacterial pathogens in humans. They are both long-chain β-diols, and their biosynthetic pathway is beginning to be elucidated. Although the two classes of molecules share a common lipid core, phthiocerol diesters have been found in all the strains of the M. tuberculosiscomplex examined although phenolphthiocerol diesters are produced by only a few groups of strains. To address the question of the origin of this diversity 8 reference strains and 10 clinical isolates of M. tuberculosiswere analyzed. We report the presence of glycosylated p-hydroxybenzoic acid methyl esters, structurally related to the type-specific phenolphthiocerol glycolipids, in the culture media of all reference strains of M. tuberculosis, suggesting that the strains devoid of phenolphthiocerol derivatives are unable to elongate the putativep-hydroxybenzoic acid precursor. We also show that all the strains of M. tuberculosisexamined and deficient in the production of phenolphthiocerol derivatives are natural mutants with a frameshift mutation in pks15/1whereas a single open reading frame for pks15/1is found in Mycobacterium bovisBCG, M. leprae,and strains of M. tuberculosisthat produce phenolphthiocerol derivatives. Complementation of the H37Rv strain of M. tuberculosis,which is devoid of phenolphthiocerol derivatives, with the fusedpks15/1gene from M. bovisBCG restored phenolphthiocerol glycolipids production. Conversely, disruption of thepks15/1gene in M. bovisBCG led to the abolition of the synthesis of type-specific phenolphthiocerol glycolipid. These data indicate that Pks15/1 is involved in the elongation of p-hydroxybenzoic acid to givep-hydroxyphenylalkanoates, which in turn are converted, presumably by the PpsA-E synthase, to phenolphthiocerol derivatives.