The opportunistic pathogen Pseudomonas aeruginosa exploits bacterial biotin synthesis pathway to benefit its infectivity

Structure and catalytic mechanism of exogenous fatty acid recycling by AasS, a versatile acyl-ACP synthetase

Fatty acids (FAs) are essential building blocks for all the domains of life, of which bacterial de novo synthesis, called type II FA synthesis (FAS II), is energetically expensive. The recycling of exogenous FAs (eFAs) partially relieves the FAS II demand and, therefore, compromises the efficacy of FAS II-directed antimicrobials. The versatile acyl-acyl carrier protein (ACP) synthetase, AasS, enables bacterial channeling of diverse eFA nutrients through holo-ACP, an activated form of ACP. However, the molecular mechanism for AasS catalysis is not fully understood. Here we report a series of cryo-electron microscopy structures of AasS from the bioluminescent bacterium Vibrio harveyi to provide insights into the catalytic cycle. AasS forms a ring-shaped hexamer, with each protomer folding into two distinct domains. Biochemical and structural analysis suggests that AasS accommodates distinct eFA substrates and the conserved W230 residue has a gating role. Adenosine triphosphate and Mg2+ binding converts the AasS hexamer to a tetramer, which is likely needed for the acyl adenylate intermediate formation. Afterward, AasS reverts to the hexamer conformation in adaption to acyl-ACP production. The complete landscape for eFA scavenging lays a foundation for exploiting the versatility of AasS in biopharmaceuticals.

Globotriaosylceramide as a potential biomarker for auxiliary detection of lower respiratory tract infections of Pseudomonas aeruginosa

Lower respiratory tract infections (LRTIs) caused by Pseudomonas aeruginosa (PA) are a significant health concern, notably among vulnerable populations. The glycosphingolipid receptor globotriaosylceramide (Gb3) has been implicated in PA pathogenicity, however, its clinical implications remain underexplored. The present study aimed to investigate the clinical value of Gb3 concentrations in serum and bronchoalveolar lavage fluid (BALF) as a biomarker for PA-induced LRTIs. In the current prospective study, 54 PA-infected patients and 54 healthy individuals were enrolled as controls. Gb3 levels were measured using a Gb3 ELISA kit and the levels of inflammatory markers were assessed. The diagnostic accuracy of Gb3 was evaluated using receiver operating characteristic (ROC) curve analysis. The patients with PA-induced LRTIs exhibited significantly higher Gb3 concentration levels in both serum and BALF compared with those noted in healthy controls, with more pronounced elevations noted in BALF. The area under the ROC curve was 0.899 for serum Gb3 and 0.812 for BALF Gb3, indicating high sensitivity and specificity for diagnosis of PA infection. Gb3 levels were also found to be correlated with C-reactive protein and procalcitonin levels, suggesting its potential in reflecting infection severity. Overall, the present findings revealed a significant association between Gb3 levels and PA-induced LRTIs, proposing Gb3 as a promising biomarker for early detection and diagnosis. Further research is warranted to validate the role of Gb3 in various patient populations and to explore its dynamics over the course of infection.

Performance and intestinal health of piglets in the nursery phase subjected to diets with condensed black wattle (Acacia mearnsii) tannin

OBJECTIVE

The objective of this study was to evaluate the use of condensed tannin from black acacia (Acacia mearnsii) as a substitute additive for zinc oxide and growth-promoting antibiotics on the performance, digestibility, and intestinal health of piglets in the nursery phase.

METHODS

A total of 200 PIC piglets that were 22 days old and weighed 6.0±0.9 kg were subjected to four treatments in the nursery phase (22 to 64 days of age): CONTR (control diet); ENR+ZnO (control diet + 10 mg/kg of enramycin + 2,500 mg/kg of zinc oxide during the first 21 days); BUT (control diet + 900 mg/kg of sodium butyrate) and TAN (control diet + 2,000 mg/kg of condensed tannin). The experimental design was a randomized block with 4 treatments and 10 replicates, with a pen of five animals each as the experimental unit. The zootechnical performance, diarrhea index score, dietary digestibility and metagenomics of the deep rectum microbiota were evaluated.

RESULTS

The TAN had greater weight gain in the nursery phase and final weight (p<0.05) than the CONTR (394 vs 360 g/d, and 22.6 vs 21.1 kg, respectively), with these values being intermediate for the ENR+ZnO and BUT (365 and 382 g/d, and 21.3 and 22.1 kg, respectively). There was no difference between treatments for semi-liquid diarrhea (score 2), but CONTR had more cases of severe diarrhea (score 3; p<0.05) than ENR+ZnO, BUT and TAN, with 42, 18, 29, and 21 cases, respectively. The treatments had no impact on rare taxa or the relative abundances of taxonomic groups (uniformity), but the use of TAN promoted an increase in the abundances of Brevibacillus spp. and Enterococcus spp. compared to the other treatments (p<0.05).

CONCLUSION

The use of condensed tannin from black wattle as a performance-enhancing additive was effective, with effects on performance and intestinal health, demonstrating its potential as a substitute for zinc oxide and enramycin in the diets of piglets in nursery phase.

A bacterial methyltransferase that initiates biotin synthesis, an attractive anti-ESKAPE druggable pathway

The covalently attached cofactor biotin plays pivotal roles in central metabolism. The top-priority ESKAPE-type pathogens, Acinetobacter baumannii and Klebsiella pneumoniae, constitute a public health challenge of global concern. Despite the fact that the late step of biotin synthesis is a validated anti-ESKAPE drug target, the primary stage remains fragmentarily understood. We report the functional definition of two BioC isoenzymes (AbBioC for A. baumannii and KpBioC for K. pneumoniae) that act as malonyl-ACP methyltransferase and initiate biotin synthesis. The physiological requirement of biotin is diverse within ESKAPE pathogens. CRISPR-Cas9-based inactivation of bioC rendered A. baumannii and K. pneumoniae biotin auxotrophic. The availability of soluble AbBioC enabled the in vitro reconstitution of DTB/biotin synthesis. We solved two crystal structures of AbBioC bound to SAM cofactor (2.54 angstroms) and sinefungin (SIN) inhibitor (1.72 angstroms). Structural and functional study provided molecular basis for SIN inhibition of BioC. We demonstrated that BioC methyltransferase plays dual roles in K. pneumoniae infection and A. baumannii colistin resistance.

Antibacterial mechanism of metabolites of Lactobacillus plantarum against Pseudomonas lundensis and their application in dry-aged beef preservation

In this study, the antibacterial mechanism of metabolites of Lactobacillus plantarum SCB2505 (MLp SCB2505) against Pseudomonas lundensis (P. lundensis) SCB2605 was investigated, along with evaluation of their preservative effects on dry-aged beef. The results demonstrated the effective inhibition of MLp SCB2505 on the growth and biofilm synthesis of P. lundensis. The treatment with MLp SCB2505 led to the compromised membrane integrity, as evidenced by reduced intracellular ATP content, increased extracellular AKPase, K+ and protein content, as well as disrupted cell morphology. Further metabolomics analysis revealed that MLp SCB2505 interfered amino acid metabolism, nucleotide metabolism, cofactor and vitamin metabolism, lipid metabolism and respiratory chain in P. lundensis, ultimately leading to the interrupted life activities and even death of the bacteria. Besides, MLp SCB2505 could effectively inhibit the growth of Pseudomonas in dry-aged beef and delay spoilage. These findings propose the potential application of MLp SCB2505 as an antibacterial agent in meat products.

Transfer from ciliate to zebrafish: Unveiling mechanisms and combined effects of microplastics and heavy metals

The impacts and toxicological mechanisms of microplastics (MPs) or heavy metals on aquatic ecosystems have been the subject of extensive research and initial understanding. However, the combined toxicity of co-pollutants on organisms and cumulative toxic effects along the food chain are still underexplored. In this study, the ciliate protozoan Paramecium caudatum and zebrafish Danio rerio were used to represent the microbial loop and the higher trophic level, respectively, to illustrate the progressive exposure of MPs and cadmium (Cd2+). The findings indicate that MPs (ca. 1 ×105 items/L) containing with Cd2+ (below 0.1 µg/L) could permeate the bodies of zebrafish through trophic levels after primary ingestion by ciliates. This could cause adverse effects on zebrafish, including alterations in bioindicators (total sugar, triglycerides, lactate, and glycogen) associated with metabolism, delayed hepatic development, disruption of intestinal microbiota, DNA damage, inflammatory responses, and abnormal cellular apoptosis. In addition, the potential risks associated with the transfer of composite pollutants through the microbial loop into traditional food chain were examined, offering novel insights on the evaluation of the ecological risks associated with MPs. As observed, understanding the bioaccumulation and toxic effects of combined pollutants in zebrafish holds crucial implications for food safety and human health.

Antibacterial activity and mechanism of rose essential oil against Aeromonas veronii isolated from Northern snakehead (Channa argus)

AIMS

To investigate and identify the antibacterial action and mechanism of rose essential oil (REO) against Aeromonas veronii isolated from Northern snakehead for the first time by the phenotypic and metabolic analysis.

METHODS AND RESULTS

The 2-fold broth microdilution and spread-plate method identified that the minimum inhibitory concentration and minimum bactericidal concentration of REO against A. veronii were 1.25 μl ml-1 and REO impaired the growth in a concentration-dependent manner, indicating that REO possessed a significant bacteriostatic activity. Electron microscopy and live-dead cell staining found that REO caused a severe disruption of cellular morphology and increased the membrane permeability. Additionally, REO treatment induced the leakage of intracellular biomolecules such as proteins and nucleic acids from the bacteria. Metabolomics analysis showed that compared with the control, the REO treatment group exhibited a total of 190 differential metabolites (118 down-regulated and 72 up-regulated), which involved in the main metabolic pathways such as biotin metabolism, arginine biosynthesis, glutathione metabolism, lysine degradation, and histidine metabolism and the TCA cycle. These results verified that REO disturbed the metabolic processes of A. veronii to achieve the bacteriostatic effect.

CONCLUSION

The rose essential oil exhibited the effective antibacterial activity against A. veronii via breaking the cellular structure, increasing the membrane permeation and disrupting the metabolic processes.

Dual proteomics of infected macrophages reveal bacterial and host players involved in the Francisella intracellular life cycle and cell to cell dissemination by merocytophagy

Bacterial pathogens adapt and replicate within host cells, while host cells develop mechanisms to eliminate them. Using a dual proteomic approach, we characterized the intra-macrophage proteome of the facultative intracellular pathogen, Francisella novicida. More than 900 Francisella proteins were identified in infected macrophages after a 10-h infection. Biotin biosynthesis-related proteins were upregulated, emphasizing the role of biotin-associated genes in Francisella replication. Conversely, proteins encoded by the Francisella pathogenicity island (FPI) were downregulated, supporting the importance of the F. tularensis Type VI Secretion System for vacuole escape, not cytosolic replication. In the host cell, over 300 proteins showed differential expression among the 6200 identified during infection. The most upregulated host protein was cis-aconitate decarboxylase IRG1, known for itaconate production with antimicrobial properties in Francisella. Surprisingly, disrupting IRG1 expression did not impact Francisella's intracellular life cycle, suggesting redundancy with other immune proteins or inclusion in larger complexes. Over-representation analysis highlighted cell-cell contact and actin polymerization in macrophage deregulated proteins. Using flow cytometry and live cell imaging, we demonstrated that merocytophagy involves diverse cell-to-cell contacts and actin polymerization-dependent processes. These findings lay the groundwork for further exploration of merocytophagy and its molecular mechanisms in future research.Data are available via ProteomeXchange with identifier PXD035145.

Rapid detection of mexX in Pseudomonas aeruginosa based on CRISPR-Cas13a coupled with recombinase polymerase amplification

The principal pathogen responsible for chronic urinary tract infections, immunocompromised hosts, and cystic fibrosis patients is Pseudomonas aeruginosa, which is difficult to eradicate. Due to the extensive use of antibiotics, multidrug-resistant P. aeruginosa has evolved, complicating clinical therapy. Therefore, a rapid and efficient approach for detecting P. aeruginosa strains and their resistance genes is necessary for early clinical diagnosis and appropriate treatment. This study combines recombinase polymerase amplification (RPA) and clustered regularly interspaced short palindromic repeats-association protein 13a (CRISPR-Cas13a) to establish a one-tube and two-step reaction systems for detecting the mexX gene in P. aeruginosa. The test times for one-tube and two-step RPA-Cas13a methods were 5 and 40 min (including a 30 min RPA amplification reaction), respectively. Both methods outperform Quantitative Real-time Polymerase Chain Reactions (qRT-PCR) and traditional PCR. The limit of detection (LoD) of P. aeruginosa genome in one-tube and two-step RPA-Cas13a is 10 aM and 1 aM, respectively. Meanwhile, the designed primers have a high specificity for P. aeruginosa mexX gene. These two methods were also verified with actual samples isolated from industrial settings and demonstrated great accuracy. Furthermore, the results of the two-step RPA-Cas13a assay could also be visualized using a commercial lateral flow dipstick with a LoD of 10 fM, which is a useful adjunt to the gold-standard qRT-PCR assay in field detection. Taken together, the procedure developed in this study using RPA and CRISPR-Cas13a provides a simple and fast way for detecting resistance genes.

Gut microbiota perturbations during larval stages in Bufo gargarizans tadpoles after Cu exposure with or without the presence of Pb

Cu and Pb are ubiquitous environmental contaminants, but there is limited information on their potential impacts on gut microbiota profile in anuran amphibians at different developmental stages during metamorphosis. In this study, Bufo gargarizans tadpoles were chronically exposed to Cu alone or Cu combined with Pb from Gs26 throughout metamorphosis. Morphology of tadpoles, histological characteristic and bacterial community of intestines were evaluated at three developmental stages: Gs33, Gs36, and Gs42. Results showed that Cu and Cu + Pb exposure caused various degrees of morphological and histological changes in guts at tested three stages. In addition, bacterial richness and diversity in tadpoles especially at Gs33 and Gs42 were disturbed by Cu and Cu + Pb. Beta diversity demonstrated that the bacterial community structures were influenced by both heavy metals exposure and developmental stages. Alterations in taxonomic composition were characterized by increased abundance of Proteobacteria and Firmicutes, reduction of Fusobacteriota, as well as decreased Cetobacterium and increased C39 at all three stages. Overall, response of gut bacterial diversity and composition to Cu stress depends on the developmental stage, while the altered patterns of bacterial community at Cu stress could be modified further by the presence of Pb. Moreover, predicted metabolic disorders were associated with shifts in bacterial community, but needs integrated information from metagenomic and metatranscriptomic analyses. These results contribute to the growing body of research about potential ecotoxicological effects of heavy metals on amphibian gut microbiota during metamorphosis.

Chasing the landscape for intrahospital transmission and evolution of hypervirulent carbapenem-resistant Klebsiella pneumoniae

The spread of hypervirulent carbapenem-resistant Klebsiella pneumoniae (Hv-CRKP) is a global health concern. Here, we report the intrahospital colonization and spread of Hv-CRKP isolates in a tertiary hospital from 2017 to 2022. Analyses of 90 nonredundant CRKP isolates from 72 patients indicated that Hv-CRKP transferability relies on the dominant ST11-K64 clone. Whole-genome sequencing of 11 representative isolates gave 31 complete plasmid sequences, including 12 KPC-2 resistance carriers and 10 RmpA virulence vehicles. Apart from the binary vehicles, we detected two types of fusion plasmids, favoring the cotransfer of RmpA virulence and KPC-2 resistance. The detection of ancestry/relic plasmids enabled us to establish genetic mechanisms by which rare fusion plasmids form. Unexpectedly, we found a total of five rmpA promoter variants (P9T-P13T) exhibiting distinct activities and varying markedly in their geographic distributions. CRISPR/Cas9 manipulation confirmed that an active PT11-rmpA regulator is a biomarker for the "high-risk" ST11-K64/CRKP clone. These findings suggest clonal spread and clinical evolution of the prevalent ST11-K64/Hv-CRKP clones. Apart from improved public awareness of Hv-CRKP convergence, our findings might benefit the development of surveillance (and/or intervention) strategies for the dominant ST11-K64 lineage of the Hv-CRKP population in healthcare sectors.