Multiple acyl-CoA dehydrogenase deficiency kills Mycobacterium tuberculosis in vitro and during infection

Host and bacterial lipid metabolism during tuberculosis infections: possibilities to synergise host- and bacteria-directed therapies

Mycobacterium tuberculosis (Mtb) is the causative pathogen of tuberculosis, the most lethal infectious disease resulting in 1.3 million deaths annually. Treatments against Mtb are increasingly impaired by the growing prevalence of antimicrobial drug resistance, which necessitates the development of new antibiotics or alternative therapeutic approaches. Upon infecting host cells, predominantly macrophages, Mtb becomes critically dependent on lipids as a source of nutrients. Additionally, Mtb produces numerous lipid-based virulence factors that contribute to the pathogen's ability to interfere with the host's immune responses and to create a lipid rich environment for itself. As lipids, lipid metabolism and manipulating host lipid metabolism play an important role for the virulence of Mtb, this review provides a state-of-the-art overview of mycobacterial lipid metabolism and concomitant role of host metabolism and host-pathogen interaction therein. While doing so, we will emphasize unexploited bacteria-directed and host-directed drug targets, and highlight potential synergistic drug combinations that hold promise for the development of new therapeutic interventions.

Inhibitors of the Thioesterase Activity of Mycobacterium tuberculosis Pks13 Discovered Using DNA-Encoded Chemical Library Screening

DNA-encoded chemical library (DEL) technology provides a time- and cost-efficient method to simultaneously screen billions of compounds for their affinity to a protein target of interest. Here we report its use to identify a novel chemical series of inhibitors of the thioesterase activity of polyketide synthase 13 (Pks13) from Mycobacterium tuberculosis (Mtb). We present three chemically distinct series of inhibitors along with their enzymatic and Mtb whole cell potency, the measure of on-target activity in cells, and the crystal structures of inhibitor-enzyme complexes illuminating their interactions with the active site of the enzyme. One of these inhibitors showed a favorable pharmacokinetic profile and demonstrated efficacy in an acute mouse model of tuberculosis (TB) infection. These findings and assay developments will aid in the advancement of TB drug discovery.

Itaconic acid inhibits nontuberculous mycobacterial growth in pH dependent manner while 4-octyl-itaconic acid enhances THP-1 clearance of nontuberculous mycobacteria in vitro

Increasingly prevalent, nontuberculous mycobacteria (NTM) infections affect approximately 20% of people with cystic fibrosis (CF). Previous studies of CF sputum identified lower levels of the host metabolite itaconate in those infected with NTM. Itaconate can inhibit the growth of M. tuberculosis (MTB) in vitro via the inhibition of the glyoxylate cycle enzyme (ICL), but its impact on NTM is unclear. To test itaconic acid's (IA) effect on NTM growth, laboratory and CF clinical strains of Mycobacterium abscessus and Mycobacterium avium were cultured in 7H9 minimal media supplemented with 1-10 mM of IA and short-chain fatty acids (SCFA). M. avium and M. abscessus grew when supplemented with SCFAs, whereas the addition of IA (≥ 10 mM) completely inhibited NTM growth. NTM supplemented with acetate or propionate and 5 mM IA displayed slower growth than NTM cultured with SCFA and ≤ 1 mM of IA. However, IA's inhibition of NTM was pH dependent; as similar and higher quantities (100 mM) of pH adjusted IA (pH 7) did not inhibit growth in vitro, while in an acidic minimal media (pH 6.1), 1 to 5 mM of non-pH adjusted IA inhibited growth. None of the examined isolates displayed the ability to utilize IA as a carbon source, and IA added to M. abscessus isocitrate lyase (ICL) decreased enzymatic activity. Lastly, the addition of cell-permeable 4-octyl itaconate (4-OI) to THP-1 cells enhanced NTM clearance, demonstrating a potential role for IA/itaconate in host defense against NTM infections.

Iron-related gene mutations driving global Mycobacterium tuberculosis transmission revealed by whole-genome sequencing

BACKGROUND

Iron plays a crucial role in the growth of Mycobacterium tuberculosis (M. tuberculosis). However, the precise regulatory mechanism governing this system requires further elucidation. Additionally, limited studies have examined the impact of gene mutations related to iron on the transmission of M. tuberculosis globally. This research aims to investigate the correlation between mutations in iron-related genes and the worldwide transmission of M. tuberculosis.

RESULTS

A total of 13,532 isolates of M. tuberculosis were included in this study. Among them, 6,104 (45.11%) were identified as genomic clustered isolates, while 8,395 (62.04%) were classified as genomic clade isolates. Our results showed that a total of 12 single nucleotide polymorphisms (SNPs) showed a positive correlation with clustering, such as Rv1469 (ctpD, C758T), Rv3703c (etgB, G1122T), and Rv3743c (ctpJ, G676C). Additionally, seven SNPs, including Rv0104 (T167G, T478G), Rv0211 (pckA, A302C), Rv0283 (eccB3, C423T), Rv1436 (gap, G654T), ctpD C758T, and etgB C578A, demonstrated a positive correlation with transmission clades across different countries. Notably, our findings highlighted the positive association of Rv0104 T167G, pckA A302C, eccB3 C423T, ctpD C758T, and etgB C578A with transmission clades across diverse regions. Furthermore, our analysis identified 78 SNPs that exhibited significant associations with clade size.

CONCLUSIONS

Our study reveals the link between iron-related gene SNPs and M. tuberculosis transmission, offering insights into crucial factors influencing the pathogenicity of the disease. This research holds promise for targeted strategies in prevention and treatment, advancing research and interventions in this field.

Tar patties are hotspots of hydrocarbon turnover and nitrogen fixation during a nearshore pollution event in the oligotrophic southeastern Mediterranean Sea

Weathered oil, that is, tar, forms hotspots of hydrocarbon degradation by complex biota in marine environment. Here, we used marker gene sequencing and metagenomics to characterize the communities of bacteria, archaea and eukaryotes that colonized tar patties and control samples (wood, plastic), collected in the littoral following an offshore spill in the warm, oligotrophic southeastern Mediterranean Sea (SEMS). We show potential aerobic and anaerobic hydrocarbon catabolism niches on tar interior and exterior, linking carbon, sulfur and nitrogen cycles. Alongside aromatics and larger alkanes, short-chain alkanes appear to fuel dominant populations, both the aerobic clade UBA5335 (Macondimonas), anaerobic Syntropharchaeales, and facultative Mycobacteriales. Most key organisms, including the hydrocarbon degraders and cyanobacteria, have the potential to fix dinitrogen, potentially alleviating the nitrogen limitation of hydrocarbon degradation in the SEMS. We highlight the complexity of these tar-associated communities, where bacteria, archaea and eukaryotes co-exist, likely exchanging metabolites and competing for resources and space.

MceG stabilizes the Mce1 and Mce4 transporters in Mycobacterium tuberculosis

Lipids are important nutrients for Mycobacterium tuberculosis (Mtb) to support bacterial survival in mammalian tissues and host cells. Fatty acids and cholesterol are imported across the Mtb cell wall via the dedicated Mce1 and Mce4 transporters, respectively. It is thought that the Mce1 and Mce4 transporters are comprised of subunits that confer substrate specificity and proteins that couple lipid transport to ATP hydrolysis, similar to other bacterial ABC transporters. However, unlike canonical bacterial ABC transporters, Mce1 and Mce4 appear to share a single ATPase, MceG. Previously, it was established that Mce1 and Mce4 are destabilized when key transporter subunits are rendered nonfunctional; therefore, we investigated here the role of MceG in Mce1 and Mce4 protein stability. We determined that key residues in the Walker B domain of MceG are required for the Mce1- and Mce4-mediated transport of fatty acids and cholesterol. Previously, it has been established that Mce1 and Mce4 are destabilized and/or degraded when key transporter subunits are rendered nonfunctional, thus we investigated a role for MceG in stabilizing Mce1 and Mce4. Using an unbiased quantitative proteomic approach, we demonstrate that Mce1 and Mce4 proteins are specifically degraded in mutants lacking MceG. Furthermore, bacteria expressing Walker B mutant variants of MceG failed to stabilize Mce1 and Mce4, and we show that deleting MceG impacts the fitness of Mtb in the lungs of mice. Thus, we conclude that MceG represents an enzymatic weakness that can be potentially leveraged to disable and destabilize both the Mce1 and Mce4 transporters in Mtb.

Systematic analysis of lysine crotonylation in human macrophages responding to MRSA infection

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most commonly encountered bacteria found in healthcare clinics and has been ranked a priority 2 pathogen. Research is urgently needed to develop new therapeutic approaches to combat the pathogen. Variations in the pattern of protein posttranslational modifications (PTMs) of host cells affect physiological and pathological events, as well as therapeutic effectiveness. However, the role of crotonylation in MRSA-infected THP1 cells remains unknown. In this study, we found that crotonylation profiles of THP1 cells were altered after MRSA infection. It was then confirmed that lysine crotonylation profiles of THP1 cells and bacteria were different; MRSA infection inhibited global lysine crotonylation (Kcro) modification but partially elevated Kcro of host proteins. We obtained a proteome-wide crotonylation profile of THP1 cells infected by MRSA further treated by vancomycin, leading to the identification of 899 proteins, 1384 sites of which were down-regulated, and 160 proteins with 193 sites up-regulated. The crotonylated down-regulated proteins were mainly located in cytoplasm and were enriched in spliceosome, RNA degradation, protein posttranslational modification, and metabolism. However, the crotonylated up-regulated proteins were mainly located in nucleus and significantly involved in nuclear body, chromosome, ribonucleoprotein complex, and RNA processing. The domains of these proteins were significantly enriched on RNA recognition motif, and linker histone H1 and H5 families. Some proteins related to protecting against bacterial infection were also found to be targets of crotonylation. The present findings point to a comprehensive understanding of the biological functions of lysine crotonylation in human macrophages, thereby providing a certain research basis for the mechanism and targeted therapy on the immune response of host cells against MRSA infection.

Identification and metabolomic characterization of potent anti-MRSA phloroglucinol derivatives from Dryopteris crassirhizoma Nakai (Polypodiaceae)

Traditional Chinese medicine (TCM) has been used to treat infectious diseases and could offer potential drug leads. This study evaluates the in vitro antimicrobial activities from commercially sourced Dryopteris crassirhizoma Nakai (Polypodiaceae) whose authenticity was confirmed by DNA barcoding based on the ribulose bisphosphate carboxylase (rbcL) gene. Powdered rhizomes were sequentially extracted using n-hexane, dichloromethane, ethyl acetate, and methanol at ambient temperature. The dried extracts at different concentrations were tested for antimicrobial activities against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), and Mycobacterium smegmatis. D. crassirhizoma extracts exhibited significant antimicrobial activities only against MRSA (minimum inhibitory concentration: 3.125 μg/ml n-hexane extract). Activity-led fractionations of D. crassirhizoma and characterization by ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) targeted a fraction (A3), with two anti-MRSA phloroglucinol derivatives, flavaspidic acid AB and norflavaspidic acid AB—being greatly enriched in the latter. The impact of A3 on MRSA cells was examined using untargeted metabolomic analysis and compared to that of other established antibiotics (all treatments normalized to MIC₅₀ at 6 h). This suggested that norflavaspidic acid AB had distinctive effects, one of which involved targeting bioenergetic transformation, metabolism, and particularly acetyl-CoA, on MRSA cells. No cytotoxicity was observed for the norflavaspidic acid AB-enriched fraction against murine HepG2 cells. This study requires further experimental validation but can have indicated a naturally available compound that could help counter the threat of clinically relevant strains with antibiotic resistance.

Characterizing the Mechanisms of Metalaxyl, Bronopol and Copper Sulfate against Saprolegnia parasitica Using Modern Transcriptomics

Saprolegniasis, which is caused by Saprolegnia parasitica, leads to considerable economic losses. Recently, we showed that metalaxyl, bronopol and copper sulfate are good antimicrobial agents for aquaculture. In the current study, the efficacies of metalaxyl, bronopol and copper sulfate are evaluated by in vitro antimicrobial experiments, and the mechanism of action of these three antimicrobials on S. parasitica is explored using transcriptome technology. Finally, the potential target genes of antimicrobials on S. parasitica are identified by protein–protein interaction network analysis. Copper sulfate had the best inhibitory effect on S. parasitica, followed by bronopol. A total of 1771, 723 and 2118 DEGs upregulated and 1416, 319 and 2161 DEGs downregulated S. parasitica after three drug treatments (metalaxyl, bronopol and copper sulfate), separately. Additionally, KEGG pathway analysis also determined that there were 17, 19 and 13 significantly enriched metabolic pathways. PPI network analysis screened out three important proteins, and their corresponding genes were SPRG_08456, SPRG_03679 and SPRG_10775. Our results indicate that three antimicrobials inhibit S. parasitica growth by affecting multiple biological functions, including protein synthesis, oxidative stress, lipid metabolism and energy metabolism. Additionally, the screened key genes can be used as potential target genes of chemical antimicrobial drugs for S. parasitica.

Significance of mitochondrial fatty acid β-oxidation for the survivability of Aurantiochytrium limacinum ATCC MYA-1381 during sugar starvation

Thraustochytrids are marine protists that accumulate large amounts of palmitic acid and docosahexaenoic acid in lipid droplets. Random insertional mutagenesis was adopted for Aurantiochytrium limacinum ATCC MYA-1381 to search for genes that regulate lipid metabolism in thraustochytrids. A mutant strain, M17, was selected because of its significant decrease in myristic acid, palmitic acid, and triacylglycerol contents and cell growth defect. Genome analysis revealed that the gene encoding for mitochondrial electron-transfer flavoprotein ubiquinone oxidoreductase (ETFQO) was lacking in the M17 strain. This mutant strain exhibited a growth defect at the stationary phase, possibly due to stagnation of mitochondrial fatty acid β-oxidation and branched-chain amino acid degradation, both of which were caused by lack of ETFQO. This study shows the usability of random insertional mutagenesis to obtain mutants of lipid metabolism in A. limacinum and clarifies that ETFQO is integral for survival under sugar starvation in A. limacinum.

Bottlenecks and opportunities in antibiotic discovery against Mycobacterium tuberculosis

Tuberculosis (TB) persists as a major global health issue and a leading cause of death by a single infectious agent. The global burden of TB is further exacerbated by the continuing emergence and dissemination of strains of Mycobacterium tuberculosis resistant to multiple antibiotics. The need for novel drugs that can be used to shorten the course for current TB drug regimens as well as combat the persistent threat of antibiotic resistance has never been greater. There have been significant advances in the discovery of de novo TB treatments, with the first TB-specific drugs in 45 years approved for use. However, there are still issues that restrict the pipeline of new antitubercular chemotherapies. The rate of failure of TB drug candidates in clinical trials remains high, while the validation of new TB drug targets and subsequent identification of novel inhibitors remains modest.

Characterization of Acyl-CoA Oxidases from the Lipolytic Yeast Candida aaseri SH14

The lipolytic yeast Candida aaseri SH14 contains three Acyl-CoA oxidases (ACOXs) which are encoded by the CaAOX2, CaAOX4, and CaAOX5 genes and catalyze the first reaction in the β-oxidation of fatty acids. Here, the respective functions of the three CaAOX isozymes were studied by growth analysis of mutant strains constructed by a combination of three CaAOX mutations in minimal medium containing fatty acid as the sole carbon source. Substrate specificity of the CaAOX isozymes was analyzed using recombinant C. aaseri SH14 strains overexpressing the respective genes. CaAOX2 isozyme showed substrate specificity toward short- and medium-chain fatty acids (C6-C12), while CaAOX5 isozyme preferred long-chain fatty acid longer than C12. CaAOX4 isozyme revealed a preference for a broad substrate spectrum from C6-C16. Although the substrate specificity of CaAOX2 and CaAOX5 covers medium- and long-chain fatty acids, these two isozymes were insufficient for complete β-oxidation of long-chain fatty acids, and therefore CaAOX4 was indispensable.

Degradation of Exogenous Fatty Acids in Escherichia coli

Many bacteria possess all the machineries required to grow on fatty acids (FA) as a unique source of carbon and energy. FA degradation proceeds through the β-oxidation cycle that produces acetyl-CoA and reduced NADH and FADH cofactors. In addition to all the enzymes required for β-oxidation, FA degradation also depends on sophisticated systems for its genetic regulation and for FA transport. The fact that these machineries are conserved in bacteria suggests a crucial role in environmental conditions, especially for enterobacteria. Bacteria also possess specific enzymes required for the degradation of FAs from their environment, again showing the importance of this metabolism for bacterial adaptation. In this review, we mainly describe FA degradation in the Escherichia coli model, and along the way, we highlight and discuss important aspects of this metabolism that are still unclear. We do not detail exhaustively the diversity of the machineries found in other bacteria, but we mention them if they bring additional information or enlightenment on specific aspects.