Mycobacterial fatty acid catabolism is repressed by FdmR to sustain lipogenesis and virulence.

Host-derived fatty acids are an important carbon source for pathogenic mycobacteria during infection. How mycobacterial cells regulate the catabolism of fatty acids to serve the pathogenicity, however, remains unknown. Here, we identified a TetR-family transcriptional factor, FdmR, as the key regulator of fatty acid catabolism in the pathogen Mycobacterium marinum by combining use of transcriptomics, chromatin immunoprecipitation followed by sequencing, dynamic 13C-based flux analysis, metabolomics, and lipidomics. An M. marinum mutant deficient in FdmR was severely attenuated in zebrafish larvae and adult zebrafish. The mutant showed defective growth but high substrate consumption on fatty acids. FdmR was identified as a long-chain acyl-coenzyme A (acyl-CoA)-responsive repressor of genes involved in fatty acid degradation and modification. We demonstrated that FdmR functions as a valve to direct the flux of exogenously derived fatty acids away from ß-oxidation toward lipid biosynthesis, thereby avoiding the overactive catabolism and accumulation of biologically toxic intermediates. Moreover, we found that FdmR suppresses degradation of long-chain acyl-CoAs endogenously synthesized through the type I fatty acid synthase. By modulating the supply of long-chain acyl-CoAs for lipogenesis, FdmR controls the abundance and chain length of virulence-associated lipids and mycolates and plays an important role in the impermeability of the cell envelope. These results reveal that despite the fact that host-derived fatty acids are used as an important carbon source, overactive catabolism of fatty acids is detrimental to mycobacterial cell growth and pathogenicity. This study thus presents FdmR as a potentially attractive target for chemotherapy.

Housecleaning of pyrimidine nucleotide pool coordinates metabolic adaptation of nongrowing Mycobacterium tuberculosis.

The ability of Mycobacterium tuberculosis (Mtb) to adopt a slowly growing or nongrowing state within the host plays a critical role for the bacilli to persist in the face of a prolonged multidrug therapy, establish latency and sustain chronic infection. In our previous study, we revealed that genome maintenance via MazG-mediated elimination of oxidized dCTP contributes to the antibiotic tolerance of nongrowing Mtb. Here, we provide evidence that housecleaning of pyrimidine nucleotide pool via MazG coordinates metabolic adaptation of Mtb to nongrowing state. We found that the ΔmazG mutant fails to maintain a nongrowing and metabolic quiescence state under dormancy models in vitro. To investigate bacterial metabolic changes during infection, we employed RNA-seq to compare the global transcriptional response of wild-type Mtb and the ΔmazG mutant after infection of macrophages. Pathway enrichment analyses of the differentially regulated genes indicate that the deletion of mazG in Mtb not only results in DNA instability, but also perturbs pyrimidine metabolism, iron and carbon source uptake, catabolism of propionate and TCA cycle. Moreover, these transcriptional signatures reflect anticipatory metabolism and regulatory activities observed during cell cycle re-entry in the ΔmazG mutant. Taken together, these results provide evidence that pyrimidine metabolism is a metabolic checkpoint during mycobacterial adaptation to nongrowing state.

Oxidation of dCTP contributes to antibiotic lethality in stationary-phase mycobacteria.

Growing evidence shows that generation of reactive oxygen species (ROS) derived from antibiotic-induced metabolic perturbation contribute to antibiotic lethality. However, our knowledge of the mechanisms by which antibiotic-induced oxidative stress actually kills cells remains elusive. Here, we show that oxidation of dCTP underlies ROS-mediated antibiotic lethality via induction of DNA double-strand breaks (DSBs). Deletion of mazG-encoded 5-OH-dCTP-specific pyrophosphohydrolase potentiates antibiotic killing of stationary-phase mycobacteria, but did not affect antibiotic efficacy in exponentially growing cultures. Critically, the effect of mazG deletion on potentiating antibiotic killing is associated with antibiotic-induced ROS and accumulation of 5-OH-dCTP. Independent lines of evidence presented here indicate that the increased level of DSBs observed in the ΔmazG mutant is a dead-end event accounting for enhanced antibiotic killing. Moreover, we provided genetic evidence that 5-OH-dCTP is incorporated into genomic DNA via error-prone DNA polymerase DnaE2 and repair of 5-OH-dC lesions via the endonuclease Nth leads to the generation of lethal DSBs. This work provides a mechanistic view of ROS-mediated antibiotic lethality in stationary phase and may have broad implications not only with respect to antibiotic lethality but also to the mechanism of stress-induced mutagenesis in bacteria.