Evolution of Mycolic Acid Biosynthesis Genes and Their Regulation during Starvation in Mycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis, the etiological agent of tuberculosis, is a Gram-positive bacterium with a unique cell envelope composed of an essential outer membrane. Mycolic acids, which are very-long-chain (up to C 100 ) fatty acids, are the major components of this mycomembrane. The enzymatic pathways involved in the biosynthesis and transport of mycolates are fairly well documented and are the targets of the major antituberculous drugs. In contrast, only fragmented information is available on the expression and regulation of the biosynthesis genes. In this study, we report that the hadA, hadB, and hadC genes, which code for the mycolate biosynthesis dehydratase enzymes, are coexpressed with three genes that encode proteins of the translational apparatus. Consistent with the well-established control of the translation potential by nutrient availability, starvation leads to downregulation of the hadABC genes along with most of the genes required for the synthesis, modification, and transport of mycolates. The downregulation of a subset of the biosynthesis genes is partially dependent on Rel Mtb , the key enzyme of the stringent response. We also report the phylogenetic evolution scenario that has shaped the current genetic organization, characterized by the coregulation of the hadABC operon with genes of the translational apparatus and with genes required for the modification of the mycolates. IMPORTANCEMycobacterium tuberculosis infects one-third of the human population worldwide, and despite the available therapeutic arsenal, it continues to kill millions of people each year. There is therefore an urgent need to identify new targets and develop a better understanding of how the bacterium is adapting itself to host defenses during infection. A prerequisite of this understanding is knowledge of how this adaptive skill has been implanted by evolution. Nutrient scarcity is an environmental condition the bacterium has to cope with during infection. In many bacteria, adaptation to starvation relies partly on the stringent response. M. tuberculosis's unique outer membrane layer, the mycomembrane, is crucial for its viability and virulence. Despite its being the target of the major antituberculosis drugs, only scattered information exists on how the genes required for biosynthesis of the mycomembrane are expressed and regulated during starvation. This work has addressed this issue as a step toward the identification of new targets in the fight against M. tuberculosis. Mycobacterium tuberculosis, the etiological agent of tuberculosis, infects one-third of humans worldwide, with 9 million new cases and 1.5 million people dying each year from this disease (77). A long-standing challenge to the fight against tuberculosis is the ability of the pathogen to develop a nonreplicating, persistent, drug-tolerant form (1-3). In addition, the emergence of multidrug-resistant (MDR), extremely drug-resistant (XDR) (4, 5), and total-drug-resistant (TDR) strains (6) underscores the urgent need to identify new therapeutic targe...

Mycoloyltransferases: A large and major family of enzymes shaping the cell envelope of Corynebacteriales

“…A recent study found that genes involved in mycolic acid biosynthesis, modification and transport are regulated upon starvation in M. tuberculosis. Among these, M. tuberculosis fbpA and fpbB were down-regulated upon starvation (29). Consistent with these studies, fbpA and fbpB were also found to be downregulated upon extended intracellular persistence of M. tuberculosis into macrophages, an environment where nutrients availability become rapidly limiting (30).…”

Trehalose recycling promotes energy-efficient mycomembrane reorganization in nutrient-limited mycobacteria

“…The three isoforms of the TMM-consuming Antigen 85 complex, encoded in M. tuberculosis by fbpA, fbpB and fbpC , have partially redundant acceptor specificities (Jackson et al, 1999; Puech et al, 2002). However only fbpC is upregulated in nutrient-starved M. tuberculosis (Betts et al, 2002; Jamet et al, 2015) making Ag85C an obvious candidate for performing synthetic reactions under that condition. Perhaps the more interesting question, however, is the source of the energetically-expensive TMM building blocks.…”

Role of long-chain acyl-CoAs in the regulation of mycolic acid biosynthesis in mycobacteria

“…Thus, this cross-regulation might occur at a higher hierarchical level where a more global regulator might act in response to a generalized stress signal generated by the inhibition of MA biosynthesis, turning down other enzymes related to this metabolism. In relation to these results, it has been recently demonstrated that starvation of M. tuberculosis also leads to a generalized downregulation of genes required for the synthesis (this include fasII , mabA-inhA and hadABC operon genes), modification and transport of mycolates [ 49 ]. As this is a highly energy-consuming process, it is physiologically relevant for the cell to slow down its synthesis during nutrient scarcity.…”