Induction of a Novel Class of Diacylglycerol Acyltransferases and Triacylglycerol Accumulation in Mycobacterium tuberculosis as It Goes into a Dormancy-Like State in Culture

Abstract

Mycobacterium tuberculosis enters the host by inhalation of an infectious aerosol and replicates in the alveolar macrophages until the host's immune defense causes bacteriostasis, which leads the pathogen to go into nonreplicative drug-resistant dormancy. The dormant pathogen can survive for decades till the host's immune system is weakened and active tuberculosis develops. Even though fatty acids are thought to be the major energy source required for the persistence phase, the source of fatty acids used is not known. We postulate that the pathogen uses triacylglycerol (TG) as a storage form of fatty acids. Little is known about the biosynthesis of TG in M. tuberculosis. We show that 15 mycobacterial genes that we identified as putative triacylglycerol synthase (tgs) when expressed in Escherichia coli showed TGS activity, and we report some basic catalytic characteristics of the most active enzymes. We show that several tgs genes are induced when the pathogen goes into the nonreplicative drug-resistant state caused by slow withdrawal of O 2 and also by NO treatment, which is known to induce dormancy-associated genes. The gene (Rv3130c) that shows the highest TGS activity when expressed in E. coli shows the highest induction by hypoxia and NO treatment. Biochemical evidence shows that TG synthesis and accumulation occur under both conditions. We conclude that TG may be a form of energy storage for use during long-term dormancy. Therefore, TG synthesis may be an appropriate target for novel antilatency drugs that can prevent the organism from surviving dormancy and thus assist in the control of tuberculosis.

Substantial molecular evolution and mutation rates in prolonged latent Mycobacterium tuberculosis infection in humans

“…We note, however, that genes Rv3805c (aftB) and Rv3130c (tgs1), which both contained putative deleterious mutations in isolate R98-3208 (Link 2), have been previously implicated in processes that may influence the development of antibiotic resistance and tolerance (Daniel et al, 2004;Safi et al, 2013). However, the putatively deleterious tgs1 mutation in R98-3208 is particularly intriguing in a purely metabolic context as it is essential for accumulation of triacylglycerol (TAG) in response to hypoxia and other stresses (Daniel et al, 2004). Furthermore, TAG-synthesis plays a direct role in promoting entry into a dormancy-like state (Daniel et al, 2004).…”

“…However, the putatively deleterious tgs1 mutation in R98-3208 is particularly intriguing in a purely metabolic context as it is essential for accumulation of triacylglycerol (TAG) in response to hypoxia and other stresses (Daniel et al, 2004). Furthermore, TAG-synthesis plays a direct role in promoting entry into a dormancy-like state (Daniel et al, 2004). Increased expression of tgs1, observed in certain Beijing lineages of Mtb, is speculated to offer increased survival within host tissues as a consequence of high TAG-levels (Reed et al, 2007).…”

Conserved Pro-Glu (PE) and Pro-Pro-Glu (PPE) Protein Domains Target LipY Lipases of Pathogenic Mycobacteria to the Cell Surface via the ESX-5 Pathway

“…Besides the removal of the secretion domain, processing could also have a functional implication. M. tuberculosis utilizes fatty acids as the principal energy source during the latent stage of infection (50 -52), and it has been shown that it stores fatty acids in the form of TAGs (51). Dormancy leads to high up-regulation of LipY tub , whereas a ⌬lipY tub mutant has a severely compromised ability to degrade stored TAGs upon starvation (32).…”

Interplay of human macrophages and Mycobacterium tuberculosis phenotypes

“…This constitutes a way for mycobacteria to exploit host lipids and is substantiated by the accumulation of lipid droplets inside Mtb with similar composition as the host cell lipid bodies. This was hypothesized to occur by hydrolysis of host TAG by a mycobacterial lipase [289], followed by import of the fatty acids into the bacterial cytoplasm and local de novo synthesis of TAG [290]. Although TAG constitutes a carbon source for mycobacteria, intracellular counts of M. avium did not change.…”

“…One of the upregulated genes in the dosR regulon, tgs1, encodes a triacylglycerol synthase involved in the accumulation of TAG-containing lipid droplets inside the Mtb cytosol [321]. Staining of sputum samples for lipids revealed lipid droplet accumulation in sputum bacteria [319,322] reminiscent of stressed or dormant Mtb phenotypes [290,321] and of bacilli in foamy macrophages [288]. Furthermore, time to positivity of sputum samples correlated with the proportion of lipid droplet-positive bacteria [319], indicating that this subpopulation requires more time to resume growth upon inoculation into broth.…”