Two Distinct Modes of Lysis Regulation in Campylobacter Fletchervirus and Firehammervirus Phages

Application of a novel phage vB_CjeM_WX1 to control Campylobacter jejuni in foods

Campylobacter jejuni is one of the leading causes of human gastroenteritis. Phage biocontrol is recognized as a natural, environmentally friendly technique that effectively targets pathogens in various foods. In this study, a novel C. jejuni phage named vB_CjeM_WX1 (WX1) was isolated from chicken feces. According to the morphology and genomic analysis, the phage belongs to the Eucampyvirinae genus within the subfamily of Caudoviricetes WX1 exhibited favorable physiological characteristics, as it could maintain its activity even under extreme conditions such as high temperatures (70 °C), acidity (pH = 4), alkalinity (pH = 12), NaCl concentration (1000 mM) and was UV-resistant for 50 min. WX1 could lyse 35 strains of C. jejuni, all of which are highly virulent and multi-drug resistant. Among them, 10 strains of C. jejuni exhibit strong biofilm formation, a critical factor in bacterial persistence and resistance to environmental stressors. The lysis rate of WX1 reached up to 47.3 % in 76 strains of C. jejuni. Phage WX1 inhibited the growth of multi-drug resistant, high virulence and strong biofilm C. jejuni 178-2B in NZCYM broth, as well as greatly reduced biofilm formation on stainless-steel, polyethylene surfaces, and glass. Moreover, phage WX1 decreased the number of C. jejuni in chicken skin to below the detection limit within 48 h. Therefore, phage WX1 can be used in food processing environments and poultry farming, both primary production and during slaughter with a great prospect.

Viral metagenomics combined with non-targeted serum metabolomics reveals the role of enteroviruses in a mouse model of coronary heart disease

BACKGROUND

Coronary heart disease (CHD) is a common cardiovascular disease that is associated with altered gut microbiota. Enteroviruses, an essential component of the gut microbiome, may play an important role in disease progression. However, the relationship between enteroviruses and CHD remains unclear. The development of high-throughput sequencing technologies has facilitated research on the interconnections between viruses and disease-related metabolites.

METHODS AND RESULTS

Mice were fed a high-fat diet (CHD group) or chow diet (Sham group) for 12 weeks, and ligation of the left anterior descending coronary artery was performed at the end of week 8. After 4 weeks, all animals were euthanised. Subsequently, the animals were evaluated for basic haemato-biochemical parameters and cardiac function, and aorta staining was performed. Based on enteroviral metagenomics and serum UPLC-MS/MS metabolomics analyses, we evaluated the association between enteroviral groups and serum metabolites of CHD mouse model. A high-fat diet and coronary ligation enabled the establishment of the CHD mouse model. Notably, the enterovirus spectrum of the sham group was significantly different from that of the CHD group, with 24 viral communities of different family and species classification, such as Tsarbombavirus, Mingyongvirus, Claudivirus, and Firehammervirus, exhibiting significant differences. In addition, 731 Differential metabolites were detected in the serum of both groups of mice. Correlation network analysis revealed a close relationship between various metabolites related to lipid metabolism and different viruses, including Tsarbombavirus, Mingyongvirus, Claudivirus, and Firehammervirus.

CONCLUSIONS

An animal model of CHD, characterised by lipid disturbance and myocardial ischaemia, was established using a high-fat diet and ligation of the left anterior descending branch of the coronary artery. Tsarbombavirus, Firehammervirus, Mingyongvirus, and Claudivirus were associated with metabolites in the lipid metabolism pathway. The results indicate that Tsarbombavirus may be the main genus interacting with CHD-related metabolites in mice. Conclusively, the findings of our study provide novel insights into the potential relationship enterovirus groups and metabolites associated with CHD.

Diverse infective and lytic machineries identified in genome analysis of tailed coliphages against broad spectrum multidrug-resistant Escherichia coli

The emergence of multidrug-resistant (MDR) E. coli with deleterious consequences to the health of humans and animals has been attributed to the inappropriate use of antibiotics. Without effective antimicrobials, the success of modern medicine in treating infections would be at an increased risk. Bacteriophages could be used as an alternative to antibiotics for controlling the dissemination of MDR bacteria. However, before their use, the bacteriophages have to be assessed for the safety aspect. In this study, three broad host range highly virulent coliphage genomes were sequenced, characterized for infective and lytic potential, and checked for the presence of virulence and resistance genes. The genome sequencing indicated that coliphages ϕEC-S-21 and ϕEC-OE-11 belonged to Myoviridae, whereas coliphage ϕEC-S-24 belonged to the Autographiviridae family derived from the Podoviridae family. The genome size of the three coliphages ranged between 24 and 145 kb, with G + C content ranging between 37 and 51%. Coding sequences (CDS) ranged between 30 and 251 amino acids. The CDS were annotated and the proteins were categorized into different modules, viz., phage structural proteins, proteins associated with DNA replication, DNA modification, bacterial cell lysis, phage packaging, and uncharacterized proteins. The presence of tRNAs was detected only in coliphage ϕEC-OE-11. All three coliphages possessed diverse infective and lytic mechanisms, viz., lytic murein transglycosylase, peptidoglycan transglycosylase, n-acetylmuramoyl-l-alanine amidase, and putative lysozyme. Furthermore, the three coliphage genomes showed neither the presence of antibiotic resistance genes nor virulence genes, which makes them desirable candidates for use in phage therapy-based applications.

Functional Analysis of the Endopeptidase and Holin From Planktothrix agardhii Cyanophage PaV-LD

A cyanophage PaV-LD, previously isolated from harmful filamentous cyanobacterium Planktothrix agardhii, was sequenced, and co-expression of its two ORFs in tandem, ORF123 and ORF124, inhibited growth on the model cyanobacterium Synechocystis sp. PCC6803 cells. However, the mechanism of action of ORF123 and ORF124 alone remains to be elucidated. In this study, we aimed to study the individual function of ORF123 or ORF124 from PaV-LD. Our data showed that the ORF123 encoded an endopeptidase, which harbored an M23 family peptidase domain and a transmembrane region. The expression of the endopeptidase in Escherichia coli alone revealed that the protein exhibited remarkable bacteriostatic activity, as evidenced by observation of growth inhibition, membrane damage, and leakage of the intracellular enzyme. Similarly, the holin, a membrane-associated protein encoded by the ORF124, showed weak bacteriostatic activity on E. coli. Moreover, deletion mutations indicated that the transmembrane domains of endopeptidase and holin were indispensable for their bacteriostatic activity. Meanwhile, the bacteriostatic functions of endopeptidase and holin on cyanobacteria cells were confirmed by expressing them in the cyanobacterium Synechocystis sp. PCC6803. Collectively, our study revealed the individual role of endopeptidase or holin and their synergistic bacteriolytic effect, which would contribute to a better understanding of the lytic mechanism of cyanophage PaV-LD.

Functional Dissection of P1 Bacteriophage Holin-like Proteins Reveals the Biological Sense of P1 Lytic System Complexity

P1 is a model temperate myovirus. It infects different Enterobacteriaceae and can develop lytically or form lysogens. Only some P1 adaptation strategies to propagate in different hosts are known. An atypical feature of P1 is the number and organization of cell lysis-associated genes. In addition to SAR-endolysin Lyz, holin LydA, and antiholin LydB, P1 encodes other predicted holins, LydC and LydD. LydD is encoded by the same operon as Lyz, LydA and LydB are encoded by an unlinked operon, and LydC is encoded by an operon preceding the lydA gene. By analyzing the phenotypes of P1 mutants in known or predicted holin genes, we show that all the products of these genes cooperate with the P1 SAR-endolysin in cell lysis and that LydD is a pinholin. The contributions of holins/pinholins to cell lysis by P1 appear to vary depending on the host of P1 and the bacterial growth conditions. The pattern of morphological transitions characteristic of SAR-endolysin–pinholin action dominates during lysis by wild-type P1, but in the case of lydC lydD mutant it changes to that characteristic of classical endolysin-pinholin action. We postulate that the complex lytic system facilitates P1 adaptation to various hosts and their growth conditions.

Campylobacter phages use hypermutable polyG tracts to create phenotypic diversity and evade bacterial resistance

Phase variation is a common mechanism for creating phenotypic heterogeneity of surface structures in bacteria important for niche adaptation. In Campylobacter, phase variation occurs by random variation in hypermutable homonucleotide 7-11 G (polyG) tracts. To elucidate how phages adapt to phase-variable hosts, we study Fletchervirus phages infecting Campylobacter dependent on a phase-variable receptor. Our data demonstrate that Fletcherviruses mimic their host and encode hypermutable polyG tracts, leading to phase-variable expression of two of four receptor-binding proteins. This creates phenotypically diverse phage populations, including a sub-population that infects the bacterial host when the phase-variable receptor is not expressed. Such population dynamics of both phage and host promote co-existence in a shared niche. Strikingly, we identify polyG tracts in more than 100 phage genera, infecting more than 70 bacterial species. Future experimental work may confirm phase variation as a widespread strategy for creating phenotypically diverse phage populations.

Distribution of CRISPR Types in Fluoroquinolone-Resistant Campylobacter jejuni Isolates

To aid development of phage therapy against Campylobacter, we investigated the distribution of the clustered regularly interspaced short palindromic repeats (CRISPR) systems in fluoroquinolone (FQ)-resistant Campylobacter jejuni. A total of 100 FQ-resistant C. jejuni strains from different sources were analyzed by PCR and DNA sequencing to determine resistance-conferring mutation in the gyrA gene and the presence of various CRISPR systems. All but one isolate harbored 1-5 point mutations in gyrA, and the most common mutation was the Thr86Ile change. Ninety-five isolates were positive with the CRISPR PCR, and spacer sequences were found in 86 of them. Among the 292 spacer sequences identified in this study, 204 shared 93-100% nucleotide homology to Campylobacter phage D10, 44 showed 100% homology to Campylobacter phage CP39, and 3 had 100% homology with Campylobacter phage CJIE4-5. The remaining 41 spacer sequences did not match with any phages in the database. Based on the results, it was inferred that the FQ-resistant C. jejuni isolates analyzed in this study were potentially resistant to Campylobacter phages D10, CP39, and CJIE4-5 as well as some unidentified phages. These phages should be excluded from cocktails of phages that may be utilized to treat FQ-resistant Campylobacter.

Bacteriophage-encoded enzymes destroying bacterial cell membranes and walls, and their potential use as antimicrobial agents

Appearance of pathogenic bacteria resistant to most, if not all, known antibiotics is currently one of the most significant medical problems. Therefore, development of novel antibacterial therapies is crucial for efficient treatment of bacterial infections in the near future. One possible option is to employ enzymes, encoded by bacteriophages, which cause destruction of bacterial cell membranes and walls. Bacteriophages use such enzymes to destroy bacterial host cells at the final stage of their lytic development, in order to ensure effective liberation of progeny virions. Nevertheless, to use such bacteriophage-encoded proteins in medicine and/or biotechnology, it is crucial to understand details of their biological functions and biochemical properties. Therefore, in this review article, we will present and discuss our current knowledge on the processes of bacteriophage-mediated bacterial cell lysis, with special emphasis on enzymes involved in them. Regulation of timing of the lysis is also discussed. Finally, possibilities of the practical use of these enzymes as antibacterial agents will be underlined and perspectives of this aspect will be presented.