Tentaclins-A Novel Family of Phage Receptor-Binding Proteins That Can Be Hypermutated by DGR Systems.

Diversity-generating retroelements (DGRs) are prokaryotic systems providing rapid modification and adaptation of target proteins. In phages, the main targets of DGRs are receptor-binding proteins that are usually parts of tail structures and the variability of such host-recognizing structures enables phage adaptation to changes on the bacterial host surface. Sometimes, more than one target gene containing a hypermutated variable repeat (VR) can be found in phage DGRs. The role of mutagenesis of two functionally different genes is unclear. In this study, several phage genomes that contain DGRs with two target genes were found in the gut virome of healthy volunteers. Bioinformatics analysis of these genes indicated that they encode proteins with different topology; however, both proteins contain the C-type lectin (C-lec) domain with a hypermutated beta-hairpin on its surface. One of the target proteins belongs to a new family of proteins with a specific topology: N-terminal C-lec domain followed by one or more immunoglobulin domains. Proteins from the new family were named tentaclins after TENTACLe + proteIN. The genes encoding such proteins were found in the genomes of prophages and phages from the gut metagenomes. We hypothesized that tentaclins are involved in binding either to bacterial receptors or intestinal/immune cells.

Quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe for sensitive and specific detection of Salmonella in food matrices.

As a commonly pathogenic bacterium, the rapid detection of Salmonella outbreaks and assurance of food safety require a highly efficient detection method. Herein, a novel approach to Salmonella detection using quantum dot-labeled phage-encoded RBP 55 as a fluorescent nanoprobe is reported. RBP 55, a novel phage receptor binding protein (RBP), was identified and characterized from phage STP55. RBP 55 was functionalized onto quantum dots (QDs) to form fluorescent nanoprobes. The assay was based on the combination of immunomagnetic separation and RBP 55-QDs, which formed a sandwich composite structure. The results showed a good linear correlation between the fluorescence values and the concentration of Salmonella (101-107 CFU/mL) with a low detection limit of 2 CFU/mL within 2 h. The method was used to successfully detect Salmonella in spiked food samples. This approach can be used for the simultaneous detection of multiple pathogens by labeling different phage-encoded RBPs using polychromatic QDs in the future.

Characterization of Mu-Like Yersinia Phages Exhibiting Temperature Dependent Infection.

Yersinia pestis is the etiological agent of plague. Marmota himalayana of the Qinghai-Tibetan plateau is the primary host of flea-borne Y. pestis. This study is the report of isolation of Mu-like bacteriophages of Y. pestis from M. himalayana. The isolation and characterization of four Mu-like phages of Y. pestis were reported, which were named as vB_YpM_3, vB_YpM_5, vB_YpM_6, and vB_YpM_23 according to their morphology. Comparative genome analysis revealed that vB_YpM_3, vB_YpM_5, vB_YpM_6, and vB_YpM_23 are phylogenetically closest to Escherichia coli phages Mu, D108 and Shigella flexneri phage SfMu. The role of LPS core structure of Y. pestis in the phages' receptor was pinpointed. All the phages exhibit "temperature dependent infection," which is independent of the growth temperature of the host bacteria and dependent of the temperature of phage infection. The phages lyse the host bacteria at 37°C, but enter the lysogenic cycle and become prophages in the chromosome of the host bacteria at 26°C. IMPORTANCE Mu-like bacteriophages of Y. pestis were isolated from M. himalayana of the Qinghai-Tibetan plateau in China. These bacteriophages have a unique temperature dependent life cycle, follow a lytic cycle at the temperature of warm-blooded mammals (37°Ð¡), and enter the lysogenic cycle at the temperature of its flea-vector (26°Ð¡). A switch from the lysogenic to the lytic cycle occurred when lysogenic bacteria were incubated from lower temperature to higher temperature (initially incubating at 26°C and shifting to 37°C). It is speculated that the temperature dependent lifestyle of bacteriophages may affect the population dynamics and pathogenicity of Y. pestis.

Comparative Genomics of a Polyvalent Escherichia-Salmonella Phage fp01 and In Silico Analysis of Its Receptor Binding Protein and Conserved Enterobacteriaceae Phage Receptor.

The polyvalent bacteriophage fp01, isolated from wastewater in Valparaiso, Chile, was described to have lytic activity across bacterial species, including Escherichia coli and Salmonella enterica serovars. Due to its polyvalent nature, the bacteriophage fp01 has potential applications in the biomedical, food and agricultural industries. Also, fundamental aspects of polyvalent bacteriophage biology are unknown. In this study, we sequenced and described the complete genome of the polyvalent phage fp01 (MH745368.2) using long- (MinION, Nanopore) and short-reads (MiSeq, Illumina) sequencing. The bacteriophage fp01 genome has 109,515 bp, double-stranded DNA with an average G+C content of 39%, and 158 coding sequences (CDSs). Phage fp01 has genes with high similarity to Escherichia coli, Salmonella enterica, and Shigella sp. phages. Phylogenetic analyses indicated that the phage fp01 is a new Tequintavirus fp01 specie. Receptor binding protein gp108 was identified as potentially responsible for fp01 polyvalent characteristics, which binds to conserved amino acid regions of the FhuA receptor of Enterobacteriaceae.

A perfect fit: Bacteriophage receptor-binding proteins for diagnostic and therapeutic applications.

Bacteriophages are the most abundant biological entity on earth, acting as the predators and evolutionary drivers of bacteria. Owing to their inherent ability to specifically infect and kill bacteria, phages and their encoded endolysins and receptor-binding proteins (RBPs) have enormous potential for development into precision antimicrobials for treatment of bacterial infections and microbial disbalances; or as biocontrol agents to tackle bacterial contaminations during various biotechnological processes. The extraordinary binding specificity of phages and RBPs can be exploited in various areas of bacterial diagnostics and monitoring, from food production to health care. We review and describe the distinctive features of phage RBPs, explain why they are attractive candidates for use as therapeutics and in diagnostics, discuss recent applications using RBPs, and finally provide our perspective on how synthetic technology and artificial intelligence-driven approaches will revolutionize how we use these tools in the future.

Natural and synthetic inhibitors of a phage-encoded quorum-sensing receptor affect phage-host dynamics in mixed bacterial communities.

Viruses that infect bacteria, called phages, shape the composition of bacterial communities and are important drivers of bacterial evolution. We recently showed that temperate phages, when residing in bacteria (i.e., prophages), are capable of manipulating the bacterial cell-to-cell communication process called quorum sensing (QS). QS relies on the production, release, and population-wide detection of signaling molecules called autoinducers (AI). Gram-negative bacteria commonly employ N-acyl homoserine lactones (HSL) as AIs that are detected by LuxR-type QS receptors. Phage ARM81ld is a prophage of the aquatic bacterium Aeromonas sp. ARM81, and it encodes a homolog of a bacterial LuxR, called LuxRARM81ld. LuxRARM81ld detects host Aeromonas-produced C4-HSL, and in response, activates the phage lytic program, triggering death of its host and release of viral particles. Here, we show that phage LuxRARM81ld activity is modulated by noncognate HSL ligands and by a synthetic small molecule inhibitor. We determine that HSLs with acyl chain lengths equal to or longer than C8 antagonize LuxRARM81ld. For example, the C8-HSL AI produced by Vibrio fischeri that coexists with Aeromonads in aquatic environments, binds to and inhibits LuxRARM81ld, and consequently, protects the host from lysis. Coculture of V. fischeri with the Aeromonas sp. ARM81 lysogen suppresses phage ARM81ld virion production. We propose that the cell density and species composition of the bacterial community could determine outcomes in bacterial-phage partnerships.

Structural basis for host recognition and superinfection exclusion by bacteriophage T5.

A key but poorly understood stage of the bacteriophage life cycle is the binding of phage receptor-binding proteins (RBPs) to receptors on the host cell surface, leading to injection of the phage genome and, for lytic phages, host cell lysis. To prevent secondary infection by the same or a closely related phage and nonproductive phage adsorption to lysed cell fragments, superinfection exclusion (SE) proteins can prevent the binding of RBPs via modulation of the host receptor structure in ways that are also unclear. Here, we present the cryogenic electron microscopy (cryo-EM) structure of the phage T5 outer membrane (OM) receptor FhuA in complex with the T5 RBP pb5, and the crystal structure of FhuA complexed to the OM SE lipoprotein Llp. Pb5 inserts four loops deeply into the extracellular lumen of FhuA and contacts the plug but does not cause any conformational changes in the receptor, supporting the view that DNA translocation does not occur through the lumen of OM channels. The FhuA-Llp structure reveals that Llp is periplasmic and binds to a nonnative conformation of the plug of FhuA, causing the inward folding of two extracellular loops via "reverse" allostery. The inward-folded loops of FhuA overlap with the pb5 binding site, explaining how Llp binding to FhuA abolishes further infection of Escherichia coli by phage T5 and suggesting a mechanism for SE via the jamming of TonB-dependent transporters by small phage lipoproteins.

RB49-like Bacteriophages Recognize O Antigens as One of the Alternative Primary Receptors.

The power of most of the enterobacterial O antigen types to provide robust protection against direct recognition of the cell surface by bacteriophage receptor-recognition proteins (RBP) has been recently recognized. The bacteriophages infecting O antigen producing strains of E. coli employ various strategies to tackle this nonspecific protection. T-even related phages, including RB49-like viruses, often have wide host ranges, being considered good candidates for use in phage therapy. However, the mechanisms by which these phages overcome the O antigen barrier remain unknown. We demonstrate here that RB49 and related phages Cognac49 and Whisky49 directly use certain types of O antigen as their primary receptors recognized by the virus long tail fibers (LTF) RBP gp38, so the O antigen becomes an attractant instead of an obstacle. Simultaneously to recognize multiple O antigen types, LTFs of each of these phages can bind to additional receptors, such as OmpA protein, enabling them to infect some rough strains of E. coli. We speculate that the mechanical force of the deployment of the short tail fibers (STF) triggered by the LTF binding to the O antigen or underneath of it, allows the receptor binding domains of STF to break through the O polysaccharide layer.

Development of a Bacteriophage Cocktail against Pectobacterium carotovorum Subsp. carotovorum and Its Effects on Pectobacterium Virulence.

Pectobacterium carotovorum subsp. carotovorum is a necrotrophic plant pathogen that secretes plant cell wall-degrading enzymes (PCWDEs) that cause soft rot disease in various crops. Bacteriophages have been under consideration as harmless antibacterial agents to replace antibiotics and copper-based pesticides. However, the emergence of bacteriophage resistance is one of the main concerns that should be resolved for practical phage applications. In this study, we developed a phage cocktail with three lytic phages that recognize colanic acid (phage POP12) or flagella (phages POP15 and POP17) as phage receptors to minimize phage resistance. The phage cocktail effectively suppressed the emergence of phage-resistant P. carotovorum subsp. carotovorum compared with single phages in in vitro challenge assays. The application of the phage cocktail to napa cabbage (Brassica rapa subsp. pekinensis) resulted in significant growth retardation of P. carotovorum subsp. carotovorum (P < 0.05) and prevented the symptoms of soft rot disease. Furthermore, phage cocktail treatments of young napa cabbage leaves in a greenhouse environment indicated effective prevention of soft rot disease compared to that in the nonphage negative control. We isolated 15 phage-resistant mutants after a phage cocktail treatment to assess the virulence-associated phenotypes compared to those of wild-type (WT) strain Pcc27. All mutants showed reduced production of four different PCWDEs, leading to lower levels of tissue softening. Ten of the 15 phage-resistant mutants additionally exhibited decreased swimming motility. Taken together, these results show that the phage cocktail developed here, which targets two different types of phage receptors, provides an effective strategy for controlling P. carotovorum subsp. carotovorum in agricultural products, with a potential ability to attenuate P. carotovorum subsp. carotovorum virulence. IMPORTANCE Pectobacterium carotovorum subsp. carotovorum is a phytopathogen that causes soft rot disease in various crops by producing plant cell wall-degrading enzymes (PCWDEs). Although antibiotics and copper-based pesticides have been extensively applied to inhibit P. carotovorum subsp. carotovorum, the emergence of antibiotic-resistant bacteria and demand for harmless antimicrobial products have emphasized the necessity of finding alternative therapeutic strategies. To address this problem, we developed a phage cocktail consisting of three P. carotovorum subsp. carotovorum-specific phages that recognize colanic acids and flagella of P. carotovorum subsp. carotovorum. The phage cocktail treatments significantly decreased P. carotovorum subsp. carotovorum populations, as well as soft rot symptoms in napa cabbage. Simultaneously, they resulted in virulence attenuation in phage-resistant P. carotovorum subsp. carotovorum, which was represented by decreased PCWDE production and decreased flagellum-mediated swimming motility. These results suggested that preparations of phage cocktails targeting multiple receptors would be an effective approach to biocontrol of P. carotovorum subsp. carotovorum in crops.

Exploitation of a Bacterium-Encoded Lytic Transglycosylase by a Human Oral Lytic Phage To Facilitate Infection.

Bacteriophages (phages) are an integral part of the human oral microbiome. Their roles in modulating bacterial physiology and shaping microbial communities have been discussed but remain understudied due to limited isolation and characterization of oral phage. Here, we report the isolation of LC001, a lytic phage targeting human oral Schaalia odontolytica (formerly known as Actinomyces odontolyticus) strain XH001. We showed that LC001 attached to and infected surface-grown, but not planktonic, XH001 cells, and it displayed remarkable host specificity at the strain level. Whole-genome sequencing of spontaneous LC001-resistant, surface-grown XH001 mutants revealed that the majority of the mutants carry nonsense or frameshift mutations in XH001 gene APY09_05145 (renamed ltg-1), which encodes a putative lytic transglycosylase (LT). The mutants are defective in LC001 binding, as revealed by direct visualization of the significantly reduced attachment of phage particles to the XH001 spontaneous mutants compared that to the wild type. Meanwhile, targeted deletion of ltg-1 produced a mutant that is defective in LC001 binding and resistant to LC001 infection even as surface-grown cells, while complementation of ltg-1 in the mutant background restored the LC001-sensitive phenotype. Intriguingly, similar expression levels of ltg-1 were observed in surface-grown and planktonic XH001, which displayed LC001-binding and nonbinding phenotypes, respectively. Furthermore, the overexpression of ltg-1 failed to confer an LC001-binding and -sensitive phenotype to planktonic XH001. Thus, our data suggested that rather than directly serving as a phage receptor, ltg-1-encoded LT may increase the accessibility of phage receptor, possibly via its enzymatic activity, by cleaving the peptidoglycan structure for better receptor exposure during peptidoglycan remodeling, a function that can be exploited by LC001 to facilitate infection. IMPORTANCE The evidence for the presence of a diverse and abundant phage population in the host-associated oral microbiome came largely from metagenomic analysis or the observation of virus-like particles within saliva/plaque samples, while the isolation of oral phage and investigation of their interaction with bacterial hosts are limited. Here, we report the isolation of LC001, the first lytic phage targeting oral Schaalia odontolytica. Our study suggested that LC001 may exploit the host bacterium-encoded lytic transglycosylase function to gain access to the receptor, thus facilitating its infection.

Identification of Phage Receptor-Binding Protein Sequences with Hidden Markov Models and an Extreme Gradient Boosting Classifier.

Receptor-binding proteins (RBPs) of bacteriophages initiate the infection of their corresponding bacterial host and act as the primary determinant for host specificity. The ever-increasing amount of sequence data enables the development of predictive models for the automated identification of RBP sequences. However, the development of such models is challenged by the inconsistent or missing annotation of many phage proteins. Recently developed tools have started to bridge this gap but are not specifically focused on RBP sequences, for which many different annotations are available. We have developed two parallel approaches to alleviate the complex identification of RBP sequences in phage genomic data. The first combines known RBP-related hidden Markov models (HMMs) from the Pfam database with custom-built HMMs to identify phage RBPs based on protein domains. The second approach consists of training an extreme gradient boosting classifier that can accurately discriminate between RBPs and other phage proteins. We explained how these complementary approaches can reinforce each other in identifying RBP sequences. In addition, we benchmarked our methods against the recently developed PhANNs tool. Our best performing model reached a precision-recall area-under-the-curve of 93.8% and outperformed PhANNs on an independent test set, reaching an F1-score of 84.0% compared to 69.8%.

A Novel Bacteriophage with Broad Host Range against Clostridioides difficile Ribotype 078 Supports SlpA as the Likely Phage Receptor.

Bacteriophages represent a promising option for the treatment of Clostridioides difficile (formerly Clostridium difficile) infection (CDI), which at present relies on conventional antibiotic therapy. The specificity of bacteriophages should prevent dysbiosis of the colonic microbiota associated with antibiotic treatment of CDI. While numerous phages have been isolated, none have been characterized with broad host range activity toward PCR ribotype (RT) 078 strains, despite their relevance to medicine and agriculture. In this study, we isolated four novel C. difficile myoviruses: ΦCD08011, ΦCD418, ΦCD1801, and ΦCD2301. Their characterization revealed that each was comparable with other C. difficile phages described in the literature, with the exception of ΦCD1801, which exhibited broad host range activity toward RT 078, infecting 15/16 (93.8%) of the isolates tested. In order for wild-type phages to be exploited in the effective treatment of CDI, an optimal phage cocktail must be assembled that provides broad coverage against all C. difficile RTs. We conducted experiments to support previous findings suggesting that SlpA, a constituent of the C. difficile surface layer (S-layer) is the likely phage receptor. Through interpretation of phage-binding assays, our data suggested that ΦCD1801 could bind to an RT 012 strain only in the presence of a plasmid-borne S-layer cassette corresponding to the slpA allele found in RT 078. Armed with this information, efforts should be directed toward the isolation of phages with broad host range activity toward defined S-layer cassette types, which could form the basis of an effective phage cocktail for the treatment of CDI. IMPORTANCE Research into phage therapy has seen a resurgence in recent years owing to growing concerns regarding antimicrobial resistance. Phage research for potential therapy against Clostridioides difficile infection (CDI) is in its infancy, where an optimal "one size fits all" phage cocktail is yet to be derived. The pursuit thus far has aimed to find phages with the broadest possible host range. However, for C. difficile strains belonging to certain PCR ribotypes (RTs), in particular RT 078, phages with broad host range activity are yet to be discovered. In this study, we isolate four novel myoviruses, including ΦCD1801, which exerts the broadest host range activity toward RT 078 reported in the literature. Through the application of ΦCD1801 to phage-binding assays, we provide data to support the prior notion that SlpA represents the likely phage receptor on the bacterial cell surface. Our finding directs research attention toward the isolation of phages with activity toward strains possessing defined S-layer cassette types.

Needle in a Whey-Stack: PhRACS as a Discovery Tool for Unknown Phage-Host Combinations.

The field of metagenomics has rapidly expanded to become the go-to method for complex microbial community analyses. However, there is currently no straightforward route from metagenomics to traditional culture-based methods of strain isolation, particularly in (bacterio)phage biology, leading to an investigative bottleneck. Here, we describe a method that exploits specific phage receptor binding protein (RBP)-host cell surface receptor interaction enabling isolation of phage-host combinations from an environmental sample. The method was successfully applied to two complex sample types-a dairy-derived whey sample and an infant fecal sample, enabling retrieval of specific and culturable phage hosts. IMPORTANCE PhRACS aims to bridge the current divide between in silico genetic analyses (i.e., phageomic studies) and traditional culture-based methodology. Through the labeling of specific bacterial hosts with fluorescently tagged recombinant phage receptor binding proteins and the isolation of tagged cells using flow cytometry, PhRACS allows the full potential of phageomic data to be realized in the wet laboratory.

Exploitation of a Klebsiella Bacteriophage Receptor-Binding Protein as a Superior Biorecognition Molecule.

Klebsiella pneumoniae is a Gram-negative bacterium that has become one of the leading causes of life-threatening healthcare-associated infections (HAIs), including pneumonia and sepsis. Moreover, due to its increasingly antibiotic resistance, K. pneumoniae has been declared a global top priority concern. The problem of K. pneumoniae infections is due, in part, to the inability to detect this pathogen rapidly and accurately and thus to treat patients within the early stages of infections. The success in bacterial detection is greatly dictated by the biorecognition molecule used, with the current diagnostic tools relying on expensive probes often lacking specificity and/or sensitivity. (Bacterio)phage receptor-binding proteins (RBPs) are responsible for the recognition and adsorption of phages to specific bacterial host receptors and thus present high potential as biorecognition molecules. In this study, we report the identification and characterization of a novel RBP from the K. pneumoniae phage KpnM6E1 that presents high specificity against the target bacteria and high sensitivity (80%) to recognize K. pneumoniae strains. Moreover, adsorption studies validated the role of gp86 in the attachment to bacterial receptors, as it highly inhibits (86%) phage adsorption to its Klebsiella host. Overall, in this study, we unravel the role and potential of a novel Klebsiella phage RBP as a powerful tool to be used coupled with analytical techniques or biosensing platforms for the diagnosis of K. pneumoniae infections.

[Advances of phage receptor binding proteins].

Bacteriophages bind to the bacteria receptor through the receptor binding proteins (RBPs), a process that requires the involvement of complex atomic structures and conformational changes. In response to bacteriophage infection, bacteria have developed a variety of resistance mechanisms, while bacteriophages have also evolved multiple antagonistic mechanisms to escape host resistance. The exploration of the "adsorption-anti adsorption-escape process" between bacteriophages and bacteria helps us better understand the co-evolution process of bacteriophages and bacteria, which is important for the development of phage therapeutic technologies and phage-based biotechnologies. This review summarizes the bacteriophage adsorption related proteins, how bacteriophages escape host resistance based on the RBP alternations, and the recent progress of RBP-related biotechnologies.

A combination therapy of Phages and Antibiotics: Two is better than one.

Emergence of antibiotic resistance presents a major setback to global health, and shortage of antibiotic pipelines has created an urgent need for development of alternative therapeutic strategies. Bacteriophage (phage) therapy is considered as a potential approach for treatment of the increasing number of antibiotic-resistant pathogens. Phage-antibiotic synergy (PAS) refers to sublethal concentrations of certain antibiotics that enhance release of progeny phages from bacterial cells. A combination of phages and antibiotics is a promising strategy to reduce the dose of antibiotics and the development of antibiotic resistance during treatment. In this review, we highlight the state-of-the-art advancements of PAS studies, including the analysis of bacterial-killing enhancement, bacterial resistance reduction, and anti-biofilm effect, at both in vitro and in vivo levels. A comprehensive review of the genetic and molecular mechanisms of phage antibiotic synergy is provided, and synthetic biology approaches used to engineer phages, and design novel therapies and diagnostic tools are discussed. In addition, the role of engineered phages in reducing pathogenicity of bacteria is explored.

Enzyme-Linked Phage Receptor Binding Protein Assays (ELPRA) Enable Identification of Bacillus anthracis Colonies.

Bacteriophage receptor binding proteins (RBPs) are employed by viruses to recognize specific surface structures on bacterial host cells. Recombinant RBPs have been utilized for detection of several pathogens, typically as fusions with reporter enzymes or fluorescent proteins. Identification of Bacillus anthracis, the etiological agent of anthrax, can be difficult because of the bacterium's close relationship with other species of the Bacillus cereussensu lato group. Here, we facilitated the identification of B. anthracis using two implementations of enzyme-linked phage receptor binding protein assays (ELPRA). We developed a single-tube centrifugation assay simplifying the rapid analysis of suspect colonies. A second assay enables identification of suspect colonies from mixed overgrown solid (agar) media derived from the complex matrix soil. Thus, these tests identified vegetative cells of B. anthracis with little processing time and may support or confirm pathogen detection by molecular methods such as polymerase chain reaction.

Characterization and Food Application of the Novel Lytic Phage BECP10: Specifically Recognizes the O-polysaccharide of Escherichia coli O157:H7.

Escherichia coli O157:H7 is a global concern that causes serious diseases, such as hemolytic uremic syndrome and bloody diarrhea. To control E. coli O157:H7 in food, a novel siphophage, BECP10, that targets the O157 serotype was isolated and characterized. Unlike other E. coli phages, BECP10 can only infect E. coli O157 strains, and thus, did not infect other strains. The 48 kbp genome of BECP10 contained 76 open reading frames (ORFs), including 33 putative functional ORFs. The phage did not contain lysogeny-related modules or toxin-associated genes, suggesting that the phage might be strictly lytic. The tail spike protein (TSP) sequence had very low homology with the reported T1-like phages, indicating that TSP might be related to this unique host spectrum. The specific O-antigen residue of E. coli O157:H7 may be a key factor for phage infection by adsorption and receptor identification. The phage exhibited strong antibacterial activity against E. coli O157:H7 over a broad pH range and showed little development of phage-insensitive mutants. The phage sustained viability on the burger patties and reduced E. coli O157:H7 to a non-detectable level without the emergence of resistant cells at low temperatures for five days. Therefore, phage BECP10 might be a good biocontrol agent for E. coli O157:H7-contaminated food matrices.

How does feedback from phage infections influence the evolution of phase variation in Campylobacter?

Campylobacter jejuni (C. jejuni) causes gastroenteritis following the consumption of contaminated poultry meat, resulting in a large health and economic burden worldwide. Phage therapy is a promising technique for eradicating C. jejuni from poultry flocks and chicken carcasses. However, C. jejuni can resist infections by some phages through stochastic, phase-variable ON/OFF switching of the phage receptors mediated by simple sequence repeats (SSR). While selection strength and exposure time influence the evolution of SSR-mediated phase variation (PV), phages offer a more complex evolutionary environment as phage replication depends on having a permissive host organism. Here, we build and explore several continuous culture bacteria-phage computational models, each analysing different phase-variable scenarios calibrated to the experimental SSR rates of C. jejuni loci and replication parameters for the F336 phage. We simulate the evolution of PV rates via the adaptive dynamics framework for varying levels of selective pressures that act on the phage-resistant state. Our results indicate that growth reducing counter-selection on a single PV locus results in the stable maintenance of the phage, while compensatory selection between bacterial states affects the evolutionary stable mutation rates (i.e. very high and very low mutation rates are evolutionarily disadvantageous), whereas, in the absence of either selective pressure the evolution of PV rates results in mutation rates below the basal values. Contrastingly, a biologically-relevant model with two phase-variable loci resulted in phage extinction and locking of the bacteria into a phage-resistant state suggesting that another counter-selective pressure is required, instance, the use of a distinct phage whose receptor is an F336-phage-resistant state. We conclude that a delicate balance between counter-selection and phage-attack can result in both the evolution of phase-variable phage receptors and persistence of PV-receptor-specific phage.

A PolyQ Membrane Protein of Vibrio cholerae Acts as the Receptor for Phage Infection.

Bacteriophage VP1 is a typing phage used for the phage subtyping of Vibrio cholerae O1 biotype El Tor, but the molecular mechanisms of its receptor recognition and the resistance of its host to infection are mostly unknown. In this study, we aimed to identify the host receptor and its role in resistance in natural VP1-resistant strains. Generating spontaneous resistance mutations and genome sequencing mutant strains found the polyQ protein VcpQ, which carries 46 glutamine residues in its Q-rich region, to be responsible for infection by VP1. VcpQ is a membrane protein and possibly forms homotrimers. VP1 adsorbed to V. cholerae through VcpQ. Sequence comparisons showed that 72% of natural VP1-resistant strains have fewer glutamines in the VcpQ Q-rich stretch than VP1-sensitive strains. This difference did not affect the membrane location and oligomer of VcpQ but abrogated VP1 adsorption. These mutant VcpQs did not recover VP1 infection sensitivity in a V. cholerae strain with vcpQ deleted. Our study revealed that the polyQ protein VcpQ is responsible for the binding of VP1 during its infection of V. cholerae and that glutamine residue reduction in VcpQ affects VP1 adsorption to likely be the main cause of VP1 resistance in natural resistant strains. The physiological functions of this polyQ protein in bacteria need further clarification; however, mutations in the polyQ stretch may endow V. cholerae with phage resistance and enhance survival against VP1 or related phages.IMPORTANCE Receptor recognition and binding by bacteriophage are the first step for its infection of bacterial cells. In this study, we found the Vibrio cholerae subtyping phage VP1 uses a polyQ protein named VcpQ (V. cholerae polyQ protein) as the receptor for VP1 infection. Our study reveals the receptor's recognition of phage VP1 during its adsorption and the VP1 resistance mechanism of the wild resistant V. cholerae strains bearing the mutagenesis in the receptor VcpQ. These mutations may confer the survival advantage on these resistant strains in the environment containing VP1 or its similar phages.