CONICET | Buscador de Institutos y Recursos Humanos

The genera mycobacterium, which includes the causative agent of tuberculosis, unlike other microorganisms has two fatty acid synthase (FAS) systems, FAS I and FAS II, working in concert with the polyketide synthases (PKS) to produce the vast diversity and complexity of their lipids. Briefly, FAS I performs de novo biosynthesis of acyl-CoAs and FAS-II elongates them to synthetize very long-chain meromycolyl-ACPs (up to C56), which become the precursors of mycolic acids. These mycolic acids are the main component of the cell envelope which is a key factor related with the persistence of M. tuberculosis within the cell and the intrinsic resistance of this microorganism to a broad array of antibiotics. Elucidation of mechanisms modulating fatty acid biosynthesis would shed light on the capacity of M. tuberculosis to adapt and survive within the infected host.To study the interaction between these two systems we constructed a conditional mutant of fasI gene to be able to reduce the levels of this enzyme. Although we found that the levels of fasI gene expression was reduced, the production of mycolic acids continued. The mycolic acid de novo production using radioactive acetate incorporation as well as mycolic acid accumulation by LC-MS experiments were analyzed and in both case a diminish wasn´t seen.Then we performed a shotgun proteomic analysis in order to study general proteins expression responsible for the phenotype observed. We found that many proteins involved in the synthesis and the assembly of mycolic acids in the envelope were upregulated in FasI reduced condition.We also shown that the fatty acids necessary to synthesize mycolic acids were taken from TAG, a storage lipid produced by mycobacteria. We demonstrate in this work that when FasI expression is reduced and a fatty acid limiting condition is generated, mycobacteria prefers to produce mycolic acids instead of phospholipids, leading to the arrest of the growth and lysis of the bacterium.