Carbon flux rerouting during Mycobacterium tuberculosis growth arrest

Abstract

SummaryA hallmark of the Mycobacterium tuberculosis life cycle is the pathogen's ability to switch between replicative and non-replicative states in response to host immunity. Transcriptional profiling by qPCR of~50 M. tuberculosis genes involved in central and lipid metabolism revealed a re-routing of carbon flow associated with bacterial growth arrest during mouse lung infection. Carbon rerouting was marked by a switch from metabolic pathways generating energy and biosynthetic precursors in growing bacilli to pathways for storage compound synthesis during growth arrest. Results of flux balance analysis using an in silico metabolic network were consistent with the transcript abundance data obtained in vivo. Similar transcriptional changes were seen in vitro when M. tuberculosis cultures were treated with bacteriostatic stressors under different nutritional conditions. Thus, altered expression of key metabolic genes reflects growth rate changes rather than changes in substrate availability. A model describing carbon flux rerouting was formulated that (i) provides a coherent interpretation of the adaptation of M. tuberculosis metabolism to immunity-induced stress and (ii) identifies features common to mycobacterial dormancy and stress responses of other organisms.

Glycolytic and Non-glycolytic Functions of Mycobacterium tuberculosis Fructose-1,6-bisphosphate Aldolase, an Essential Enzyme Produced by Replicating and Non-replicating Bacilli

“…Interestingly, no significant up-or down-regulation of the overall class II aldolase activity of the cultures was found whatever the growth conditions tested (Table 1). Although surprising in light of what had been reported earlier for other glyoxylate cycle and gluconeogenetic genes (6,12,13,57), our results are consistent with those of some 30 transcriptomics studies performed on M. tuberculosis bacilli grown under various stress conditions (e.g. inside macrophages and in the presence of SDS, drugs, NO, low oxygen tension, low iron, low nutrient, and various mutant backgrounds).…”

Latent Tuberculosis Infection: Myths, Models, and Molecular Mechanisms

“…Global transcriptional analysis revealed that 38 genes were downregulated in the ⌬sigE mutant, including genes involved in protein translation, mycolic acid biosynthesis, transcriptional regulation, and electron transport. Conversely, the genes aceA (icl), Rv1130, and gltA1 (encoding citrate synthase 3) showed significantly increased expression in the ⌬sigE mutant relative to the wild-type strain (206,257,273).…”

“…The M. tuberculosis genome contains a large number of duplicated genes annotated as encoding ␤-oxidation enzymes, allowing the organism to catabolize a wide range of fatty acids through successive rounds of ␤-oxidation. Even-number-chain fatty acids are degraded to acetyl coenzyme A (AcCoA), and oddnumber-chain fatty acids are degraded to both AcCoA and propionyl coenzyme A (PropCoA) (206).…”

Clonal Diversification and Changes in Lipid Traits and Colony Morphology in Mycobacterium abscessus Clinical Isolates

“…fad23 is orthologous to fadD26 in M. tuberculosis, with 52% amino acid identity and sharing of conserved domains specific to FAAL family proteins. fadD26 is well described as playing a crucial role in the biosynthesis of complex lipids that populate the outer cell envelope in M. tuberculosis (28,32).…”

“…The accumulation of triacylglycerol (TAG) and the downregulation of synthesis of complex lipids occur in M. tuberculosis in response to various stressors in the human lung, such as hypoxia and low pH, presumably enabling the use of host fatty acids and cholesterol for an energy source (26)(27)(28)(29). To test if TAG accumulation occurs in M. abscessus during chronic human lung infection, we performed TLC to separate TAG, using the samples normalized by copy numbers of the 16S rRNA gene.…”