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

Diversity and function of viral AMGs associated with DNA biosynthesis in the Napahai plateau wetland

Viruses play an important role in microbial community structure and biodiversity by lysing host cells, and can also affect host metabolic pathways by expressing auxiliary metabolic genes (AMGs). As a unique low-latitude, high-altitude seasonal plateau wetland in China, Napahai has high research value. However, studies on the genetic diversity of AMGs and viruses associated with DNA biosynthesis have not been reported. Based on metagenomics, with the phylogenetic tree, PCoA, and α diversity analysis, we found that three DNA biosynthesis-related viral AMGs (cobS, mazG, and purM) in the Napahai plateau wetland were rich in genetic diversity, uniqueness, and differences compared with other habitats and host sources. Through the KEGG metabolic pathway and metabolic flow analysis of Pseudomonas mandelii (SW-3) and phage (VSW-3), the AMGs (cobS, mazG, and purM) genes of the three related viruses involved in DNA biosynthesis were upregulated and their expression increased significantly. In general, we systematically described the genetic diversity of AMGs associated with DNA biosynthesis in plateau wetland ecosystems and clarified the contribution of viral AMGs in the Napahai plateau wetland to DNA biosynthesis, as well as the changes of metabolites and genes. It further expands the understanding of phage-host interactions, which is of great significance for further revealing the role of viral AMGs in the biological evolution and biogeochemical cycle of wetland ecosystems.

Rifampicin drug resistance and host immunity in tuberculosis: more than meets the eye

Tuberculosis (TB) is the leading cause of death due to an infectious agent, with more than 1.5 million deaths attributed to TB annually worldwide. The global dissemination of drug resistance across Mycobacterium tuberculosis (Mtb) strains, causative of TB, resulted in an estimated 450 000 cases of drug-resistant (DR) TB in 2021. Dysregulated immune responses have been observed in patients with multidrug resistant (MDR) TB, but the effects of drug resistance acquisition and impact on host immunity remain obscure. In this review, we compile studies that span aspects of altered host-pathogen interactions and highlight research that explores how drug resistance and immunity might intersect. Understanding the immune processes differentially induced during DR TB would aid the development of rational therapeutics and vaccines for patients with MDR TB.

Structural analysis of the housecleaning nucleoside triphosphate pyrophosphohydrolase MazG from Mycobacterium tuberculosis

The housecleaning enzyme of Mycobacterium tuberculosis (Mtb), MazG, is a nucleoside triphosphate pyrophosphohydrolase (NTP-PPase) and can hydrolyze all canonical or non-canonical NTPs into NMPs and pyrophosphate. The Mycobacterium tuberculosis MazG (Mtb-MazG) contributes to antibiotic resistance in response to oxidative or nitrosative stress under dormancy, making it a promising target for treating TB in latent infection patients. However, the structural basis of Mtb-MazG is not clear. Here we describe the crystal structure of Mtb-MazG (1-185) at 2.7 Å resolution, composed of two similar folded spherical domains in tandem. Unlike other all-α NTP pyrophosphatases, Mtb-MazG has an N-terminal extra region composed of three α-helices and five β-strands. The second domain is global, with five α-helices located in the N-terminal domain. Gel-filtration assay and SAXS analysis show that Mtb-MazG forms an enzyme-active dimer in solution. In addition, the metal ion Mg²⁺ is bound with four negative-charged residues Glu119, Glu122, Glu138, and Asp141. Different truncations and site-directed mutagenesis revealed that the full-length dimeric form and the metal ion Mg²⁺ are indispensable for the catalytic activity of Mtb-MazG. Thus, our work provides new insights into understanding the molecular basis of Mtb-MazG.

Metabolic Profiles of Clinical Isolates of Drug-Susceptible and Multidrug-Resistant Mycobacterium tuberculosis: A Metabolomics-Based Study

Background

Mycobacterium tuberculosis (MTB) is a global and highly deleterious pathogen that creates an enormous pressure on global public health. Although several effective drugs have been used to treat tuberculosis, the emergence of multidrug-resistant Mycobacterium tuberculosis (MDR-MTB) has further increased the public health burden. The aim of this study was to describe in depth the metabolic changes in clinical isolates of drug-susceptible Mycobacterium tuberculosis (DS-MTB) and MDR-MTB and to provide clues to the mechanisms of drug resistance based on metabolic pathways.

Methods

Based on the minimum inhibition concentration (MIC) of multiple anti-tuberculosis drugs, two clinical isolates were selected, one DS-MTB isolate (isoniazid MIC=0.06 mg/L, rifampin MIC=0.25 mg/L) and one MDR-MTB isolate (isoniazid MIC=4 mg/L, rifampin MIC=8 mg/L). Through high-throughput metabolomics, the metabolic profiles of the DS-MTB isolate and the MDR-MTB isolate and their cultured supernatants were revealed.

Results

Compared with the DS-MTB isolate, 128 metabolites were significantly altered in the MDR-MTB isolate and 66 metabolites were significantly altered in the cultured supernatant. The differential metabolites were significantly enriched in pyrimidine metabolism, purine metabolism, nicotinate and nicotinamide metabolism, arginine acid metabolism, and phenylalanine metabolism. Furthermore, metabolomics analysis of the bacterial cultured supernatants showed a significant increase in 10 amino acids (L-citrulline, L-glutamic acid, L-aspartic acid, L-norleucine, L-phenylalanine, L-methionine, L-tyrosine, D-tryptophan, valylproline, and D-methionine) and a significant decrease in 2 amino acids (L-lysine and L-arginine) in MDR-MTB isolate.

Conclusion

The present study provided a metabolite alteration profile as well as a cultured supernatant metabolite alteration profile of MDR-MTB clinical isolate, providing clues to the potential metabolic pathways and mechanisms of multidrug resistance.

Phenotypic adaptation of Mycobacterium tuberculosis to host-associated stressors that induce persister formation

Mycobacterium tuberculosis exhibits a remarkable ability to interfere with the host antimicrobial response. The pathogen exploits elaborate strategies to cope with diverse host-induced stressors by modulating its metabolism and physiological state to prolong survival and promote persistence in host tissues. Elucidating the adaptive strategies that M. tuberculosis employs during infection to enhance persistence is crucial to understanding how varying physiological states may differentially drive disease progression for effective management of these populations. To improve our understanding of the phenotypic adaptation of M. tuberculosis, we review the adaptive strategies employed by M. tuberculosis to sense and coordinate a physiological response following exposure to various host-associated stressors. We further highlight the use of animal models that can be exploited to replicate and investigate different aspects of the human response to infection, to elucidate the impact of the host environment and bacterial adaptive strategies contributing to the recalcitrance of infection.

The H2O2 Concentration-Dependent Kinetics of Gene Expression: Linking the Intensity of Oxidative Stress and Mycobacterial Physiological Adaptation

Defence against oxidative stress is crucial for Mycobacterium tuberculosis to survive and replicate within macrophages. Mycobacteria have evolved multilayer antioxidant systems, including scavenging enzymes, iron homeostasis, repair pathways, and metabolic adaptation, for coping with oxidative stress. How these systems are coordinated to enable the physiological adaptation to different intensities of oxidative stress, however, remains unclear. To address this, we investigated the expression kinetics of the well-characterized antioxidant genes at bacteriostatic H₂O₂ concentrations ranging from 1 mM to 10 mM employing Mycolicibacterium smegmatis as a model. Our results showed that most of the selected genes were expressed in a H₂O₂ concentration-dependent manner, whereas a subset exhibited sustained induction or repression without dose–effect, reflecting H₂O₂ concentration-dependent physiological adaptations. Through analyzing the dynamics of the coordinated gene expression, we demonstrated that the expressions of the H₂O₂ scavenging enzymes, DNA damage response, and Fe–S cluster repair function were strikingly correlated to the intensity of oxidative stress. The sustained induction of mbtB, irtA, and dnaE2 indicated that mycobacteria might deploy increased iron acquisition and error-prone lesion bypass function as fundamental strategies to counteract oxidative damages, which are distinct from the defence tactics of Escherichia coli characterized by shrinking the iron pool and delaying the DNA repair. Moreover, the distinct gene expression kinetics among the tricarboxylic acid cycle, glyoxylate shunt, and methylcitrate cycle suggested that mycobacteria could dynamically redirect its metabolic fluxes according to the intensity of oxidative stress. This work defines the H₂O₂ concentration-dependent gene expression kinetics and provides unique insights into mycobacterial antioxidant defence strategies.