Biology subjects

Seed, K.

Publications and source records attributed to Seed, K..

At least 19 recordsLinked to original sources

bioRxiv2026

Repurposing anti-phage defenses to differentially arrest the viral lifecycle reveals the regulatory logic of a parasitic satellite

Mobile genetic elements frequently encode defense mechanisms to protect their bacterial hosts from viral attack. In Vibrio cholerae, these defensive elements include phage-inducible chromosomal island-like elements (PLEs), which are phage satellites that act as highly specialized parasites of the lytic phage ICP1. While PLE transcriptional activation upon ICP1 infection is known to be temporally regulated, the underlying regulatory logic and dependencies on the progression of the phages developmental program required for activation remain unclear. In this study, we took a novel approach to define these dependencies by introducing independent anti-phage defense systems, BREX and DarTG, as molecular roadblocks to impede the ICP1 lifecycle. We discovered that, for both ICP1 and PLE, late-stage gene expression is fundamentally uncoupled from genome replication, representing a striking departure from the standard paradigm for double-stranded DNA phages. While BREX restricts ICP1 to an immediate-early transcriptional state that stalls PLE activation, DarTG allows the phage to execute its full transcriptional cascade despite the total block in DNA replication. This permissive environment provides the necessary cues for complete PLE induction, revealing that the extent of ICP1 transcriptional progression is a key determinant of PLE transcriptional activation. Unlike other phage satellites that rely on a single cue for activation, our results demonstrate that PLE uses a progressive licensing strategy that relies on multiple cues tied to milestones in the phages developmental program. This regulatory architecture ensures robust PLE activation resilient to phage escape.

microbiology↗

bioRxiv2025

Surviving phage attack dynamically regulates bacterial immunity to defeat counterdefenses

Transcriptional repressors with ligand-responsive WYL domains control diverse bacterial defense systems, yet the natural cues driving derepression and the physiological rationale for dynamic regulation in native host-phage contexts remain unknown. Here, we show that restricted phage infection, where defense clears a primary attack, serves as a natural cue for WYL-mediated derepression in Vibrio cholerae. Although not required to block the initial infection, this response increases defense protein abundance, shifting host-phage stoichiometry and priming surviving bacteria to overwhelm phage-encoded counterdefenses in subsequent attacks. We also find that restricted infection co-induces an unlinked anti-plasmid defense via its own WYL repressor, showing that parallel WYL sensors coordinate a broader immune response without regulatory crosstalk. In contrast, productive phage infection triggers horizontal transfer of the defense-encoding mobile element, ensuring its persistence in the population. Together, our work reveals that infection fate dictates divergent outcomes for the expression and dissemination of bacterial immunity.

microbiology↗

bioRxiv2025

Capturing dynamic phage-pathogen coevolution by clinical surveillance

Bacteria harness diverse defense systems that protect against phage predation1, many of which are encoded on horizontally transmitted mobile genetic elements (MGEs)2. In turn, phages evolve counter-defenses3, driving a dynamic arms race that remains underexplored in human disease contexts. For the diarrheal pathogen Vibrio cholerae, a higher burden of its lytic phage, ICP1, in patient stool correlates with reduced disease severity4. However, direct molecular evidence of phage-driven selection of epidemic V. cholerae has not been demonstrated. Here, through clinical surveillance in cholera-endemic Bangladesh, we capture the acquisition of a parasitic anti-phage MGE, PLE11, that initiated a selective sweep coinciding with the largest cholera outbreak in recent records. PLE11 exhibited potent anti-phage activity against co-circulating ICP1, explaining its rapid and dominating emergence. We identify PLE11-encoded Rta as the novel defense responsible and provide evidence that Rta restricts phage tail assembly. Using experimental evolution, we predict phage counteradaptations against PLE11 and document the eventual emergence and selection of ICP1 that achieves a convergent evolutionary outcome. By probing how PLEs hijack phage structural proteins to drive their horizontal transmission while simultaneously restricting phage tail assembly, we discover that PLEs manipulate tail assembly to construct chimeric tails comprised of MGE and phage-encoded proteins. Collectively, our findings reveal the molecular basis of the natural selection of a globally significant pathogen and its virus in a clinically relevant context.

microbiology↗

bioRxiv2025

A Class 1 OLD family nuclease encoded by Vibrio cholerae is countered by a vibriophage-encoded direct inhibitor

Bacteria are constantly threatened by their viral predators (phages), which has resulted in the development of defense systems for bacterial survival. One family of defense systems found widely across bacteria are OLD (for overcoming lysogeny defect) family nucleases. Despite recent discoveries regarding Class 2 and 4 OLD family nucleases and how phages overcome them, Class 1 OLD family nucleases warrant further study as there has only been one anti-phage Class 1 OLD family nuclease described to date. Here, we identify the Vibrio cholerae-encoded Class 1 OLD family nuclease Vc OLD and describe its disruption of genome replication of the lytic vibriophage ICP1. Furthermore, we examine its in vitro activity, identifying Vc OLD as a DNA nickase. Finally, we identify the first direct inhibitor of a Class 1 OLD family nuclease, the ICP1-encoded Oad1. Our research further illuminates Class 1 OLD family nucleases role in phage defense and explores the dynamic arms race between V. cholerae and its predatory phage ICP1.

microbiology↗

bioRxiv2024

The vibriophage-encoded inhibitor OrbA abrogates BREX-mediated defense through the ATPase BrxC

Bacteria and phages are locked in a co-evolutionary arms race where each entity evolves mechanisms to restrict the proliferation of the other. Phage-encoded defense inhibitors have proven powerful tools to interrogate how defense systems function. A relatively common defense system is BREX (Bacteriophage exclusion); however, how BREX functions to restrict phage infection remains poorly understood. A BREX system encoded by the SXT integrative and conjugative element, VchInd5, was recently identified in Vibrio cholerae, the causative agent of the diarrheal disease cholera. The lytic phage ICP1 that co-circulates with V. cholerae encodes the BREX inhibitor OrbA, but how OrbA inhibits BREX is unclear. Here, we determine that OrbA inhibits BREX using a unique mechanism from known BREX inhibitors by directly binding to the BREX component BrxC. BrxC has a functional ATPase domain that, when mutated, not only disrupts BrxC function but also alters how BrxC multimerizes. Furthermore, we find that OrbA binding disrupts BrxC-BrxC interactions. We determine that OrbA cannot bind BrxC encoded by the distantly related BREX system encoded by the SXT VchBan9, and thus fails to inhibit this BREX system that also circulates in epidemic V. cholerae. Lastly, we find that homologs of the VchInd5 BrxC are more diverse than the homologs of the VchBan9 BrxC. These data provide new insight into the function of the BrxC ATPase and highlight how phage-encoded inhibitors can disrupt phage defense systems using different mechanisms. ImportanceWith renewed interest in phage therapy to combat antibiotic-resistant pathogens, understanding the mechanisms bacteria use to defend themselves against phages and the counter-strategies phages evolve to inhibit defenses is paramount. Bacteriophage exclusion (BREX) is a common defense system with few known inhibitors. Here, we probe how the vibriophage-encoded inhibitor OrbA inhibits the BREX system of Vibrio cholerae, the causative agent of the diarrheal disease cholera. By interrogating OrbA function, we have begun to understand the importance and function of a BREX component. Our results demonstrate the importance of identifying inhibitors against defense systems, as they are powerful tools for dissecting defense activity and can inform strategies to increase the efficacy of some phage therapies.

microbiology↗

bioRxiv2024

A phage satellite manipulates the viral DNA packaging motor to inhibit phage and promote satellite spread

ICP1, a lytic bacteriophage of Vibrio cholerae, is parasitized by phage satellites, PLEs, which hijack ICP1 proteins for their own horizontal spread. PLEs dependence on ICP1s DNA replication machinery, and virion components results in inhibition of ICP1s lifecycle. PLEs are expected to depend on ICP1 factors for genome packaging, but the mechanism(s) PLEs use to inhibit ICP1 genome packaging is currently unknown. Here, we identify and characterize Gpi, PLEs indiscriminate genome packaging inhibitor. Gpi binds to ICP1s large terminase (TerL), the packaging motor, and blocks genome packaging. To overcome Gpis negative effect on TerL, a component PLE also requires, PLE uses two genome packaging specifiers, GpsA and GpsB, that specifically allow packaging of PLE genomes. Surprisingly, PLE also uses mimicry of ICP1s pac site as a backup strategy to ensure genome packaging. PLEs pac site mimicry, however, is only sufficient if PLE can inhibit ICP1 at other stages of its lifecycle, suggesting an advantage to maintaining Gpi, GpsA, and GpsB. Collectively, these results provide mechanistic insights into another stage of ICP1s lifecycle that is inhibited by PLE, which is currently the most inhibitory of the documented phage satellites. More broadly, Gpi represents the first satellite-encoded inhibitor of a phage TerL.

microbiology↗

bioRxiv2023

Sporadic phage defense in epidemic Vibrio cholerae mediated by the toxin-antitoxin system DarTG is countered by a phage-encoded antitoxin mimic

Bacteria and their viral predators (phages) are constantly evolving to subvert one another. Many bacterial immune systems that inhibit phages are encoded on mobile genetic elements that can be horizontally transmitted to diverse bacteria. Despite the pervasive appearance of immune systems in bacteria, it is not often known if these immune systems function against phages that the host encounters in nature. Additionally, there are limited examples demonstrating how these phages counter-adapt to such immune systems. Here, we identify clinical isolates of the global pathogen Vibrio cholerae harboring a novel genetic element encoding the bacterial immune system DarTG and reveal the immune systems impact on the co-circulating lytic phage ICP1. We show that DarTG inhibits ICP1 genome replication, thus preventing ICP1 plaquing. We further characterize the conflict between DarTG-mediated defense and ICP1 by identifying an ICP1-encoded protein that counters DarTG and allows ICP1 progeny production. Finally, we identify this protein as a functional antitoxin that abrogates the toxin DarT likely through direct interactions. Following the detection of the DarTG system in clinical V. cholerae isolates, we observed a rise in ICP1 isolates with the functional antitoxin. These data highlight the use of surveillance of V. cholerae and its lytic phages to understand the co-evolutionary arms race between bacteria and their phages in nature. ImportanceThe global bacterial pathogen Vibrio cholerae causes an estimated 1 to 4 million cases of cholera each year. Thus, studying the factors that influence its persistence as a pathogen is of great importance. One such influence is the lytic phage ICP1, as once infected by ICP1, V. cholerae is destroyed. To date, we have observed that the phage ICP1 shapes V. cholerae evolution through the flux of anti-phage bacterial immune systems. Here, we probe clinical V. cholerae isolates for novel anti-phage immune systems that can inhibit ICP1 and discover the toxin-antitoxin system DarTG as a potent inhibitor. Our results underscore the importance of V. cholerae and ICP1 surveillance to elaborate novel means by which V. cholerae can persist in both the human host and aquatic reservoir in the face of ICP1.

microbiology↗

bioRxiv2023

Adaptation to bile and anaerobicity limits Vibrio cholerae phage adsorption

Bacteriophages (viruses of bacteria) play a pivotal role in shaping both the evolution and dynamics of bacterial populations. Bacteria employ arsenals of genetically encoded phage defense systems, but can alternatively achieve protection by changing the availability of cellular resources that phages rely on for propagation. These physiological changes are often adaptive responses to unique environmental signals. The facultative pathogen Vibrio cholerae adapts to both aquatic and intestinal environments with niche-specific physiological changes that ensure its evolutionary success in such disparate settings. In both niches, V. cholerae is susceptible to predation by lytic phages like ICP1. However, both phages and susceptible bacterial hosts coexist in nature, indicating that environmental cues may modulate V. cholerae cell state to protect against phage infection. This work explores one such modification in response to the intestine-specific signals of bile and anaerobicity. We found that V. cholerae grown in these conditions reduces O1-antigen decoration on its outer membrane lipopolysaccharide. Because the O1-antigen is an essential moiety for ICP1 phage infection, we investigated the effect of partial O1-antigen depletion as a mechanism of phage defense and observed that O1-depletion limits phage adsorption. We identified mechanistic contributions to O1-depletion, including the essentiality of a weak acid tolerance system for O1 production at low pH, and alterations in transcriptional profiles indicating limitations in resources for O1-biosynthesis. This analysis illustrates a complex interplay between signals relevant to the intestinal environment and bacterial physiology that provide V. cholerae with protection from phage predation.

microbiology↗

bioRxiv2023

Nuclease genes occupy boundaries of genetic exchange between bacteriophages

Homing endonuclease genes (HEGs) are ubiquitous selfish elements that generate targeted double-stranded DNA breaks, facilitating the recombination of the HEG DNA sequence into the break site and contributing to the evolutionary dynamics of HEG-encoding genomes. Bacteriophages (phages) are well-documented to carry HEGs, with the paramount characterization of HEGs being focused on those encoded by coliphage T4. Recently, it has been observed that the highly sampled vibriophage, ICP1, is similarly enriched with HEGs distinct from T4s. Here, we examined the HEGs encoded by ICP1 and diverse phages, proposing HEG-driven mechanisms that contribute to phage evolution. Relative to ICP1 and T4, we found a variable distribution of HEGs across phages, with HEGs frequently encoded proximal to or within essential genes. We identified large regions (> 10kb) of high nucleotide identity flanked by HEGs, deemed HEG islands, which we hypothesize to be mobilized by the activity of flanking HEGs. Finally, we found examples of domain swapping between phage-encoded HEGs and genes encoded by other phages and phage satellites. We anticipate that HEGs have a larger impact on the evolutionary trajectory of phages than previously appreciated and that future work investigating the role of HEGs in phage evolution will continue to highlight these observations.

genomics↗

bioRxiv2022

A phage weaponizes a satellite recombinase to subvert viral restriction

Bacteria can acquire mobile genetic elements (MGEs) to combat infection by viruses (phages). Satellite viruses, including the PLEs (phage-inducible chromosomal island-like elements) in epidemic Vibrio cholerae, are MGEs that restrict phage replication to the benefit of their host bacterium. PLEs parasitize the lytic phage ICP1, unleashing multiple mechanisms to restrict phage replication and promote their own spread. In the arms race against PLE, ICP1 uses nucleases, including CRISPR-Cas, to destroy PLEs genome during infection. However, through an unknown CRISPR-independent mechanism, specific ICP1 isolates subvert restriction by PLE. Here, we discover ICP1-encoded Adi that counteracts PLE by exploiting the PLEs large serine recombinase (LSR), which normally mobilizes PLE in response to ICP1 infection. Unlike previously characterized ICP1-encoded anti-PLE mechanisms, Adi is not a nuclease itself but instead appears to modulate the activity of the LSR to promote destructive nuclease activity of the LSRs specific attachment site, attP. The PLE LSR, its catalytic activity, and attP are additionally sufficient to sensitize a PLE encoding a resistant variant of the recombination module to Adi activity. This work highlights a unique type of adaptation arising from inter-genome conflicts, in which the intended activity of a protein can be weaponized to overcome the antagonizing genome.

microbiology↗

bioRxiv2022

The RNA-RNA interactome between a phage and its satellite virus reveals a small RNA differentially regulates gene expression across both genomes

Phage satellites exhibit various regulatory mechanisms to manipulate phage gene expression to the benefit of the satellite. While small RNAs (sRNAs) are well documented as regulators of prokaryotic gene expression, they have not been shown to play a regulatory role in satellite-phage conflicts. Vibrio cholerae encodes the phage inducible chromosomal island-like element (PLE), a phage satellite, to defend itself against the lytic phage ICP1. Here we use Hi-GRIL-seq to identify a complex RNA-RNA interactome between PLE and ICP1. Both inter- and intragenome RNA interactions were detected, headlined by the PLE-encoded trans-acting sRNA, SviR. SviR regulates both PLE and ICP1 gene expression uniquely, decreasing translation of ICP1 targets and affecting PLE mRNAs processing. The striking conservation of SviR across all known PLEs suggests the sRNA is deeply rooted in the PLE-ICP1 conflict and implicates sRNAs as unidentified regulators of phage-satellite interactions.

microbiology↗

bioRxiv2021

Evolutionary sweeps of subviral parasites and their phage host bring unique parasite variants and disappearance of a phage CRISPR-Cas system

Vibrio cholerae is a significant threat to global public health in part due to its propensity for large-scale evolutionary sweeps where lineages emerge and are replaced. These sweeps may originate from the Bay of Bengal where bacteriophage predation and the evolution of anti-phage counter defenses is a recurring theme. The bacteriophage ICP1 is a key predator of epidemic V. cholerae and is notable for acquiring a CRISPR-Cas system to combat PLE, a defensive subviral parasite encoded by its V. cholerae host. Here we describe the discovery of five previously unknown PLE variants, including one found during recent surveillance of patient samples in Bangladesh. We also observed a lineage sweep of PLE negative V. cholerae occurring within a patient population in under a year which coincided with a loss of ICP1s CRISPR-Cas system. These findings reinforce the importance of surveillance to better understand the selective pressures that drive pandemic cholera.

microbiology↗

bioRxiv2021

A phage parasite deploys a nicking nuclease effector to inhibit replication of its viral host

PLEs are phage parasites integrated into the chromosome of epidemic Vibrio cholerae. In response to infection by its viral host ICP1, PLE excises, replicates and hijacks ICP1 structural components for transduction. Through an unknown mechanism PLE prevents ICP1 from transitioning to rolling circle replication (RCR), a prerequisite for efficient packaging of the viral genome. Here, we characterize a PLE-encoded nuclease, NixI, that blocks phage development likely by nicking ICP1s genome as it transitions to RCR. NixI-dependent cleavage sites appear in ICP1s genome during infection of PLE(+) V. cholerae. Purified NixI demonstrates in vitro specificity for sites in ICP1s genome and NixI activity is enhanced by a putative specificity determinant co-expressed with NixI during phage infection. Importantly, NixI is sufficient to limit ICP1 genome replication and eliminate progeny production. We identify distant NixI homologs in an expanded family of putative phage satellites in Vibrios that lack nucleotide homology to PLEs but nonetheless share genomic synteny with PLEs. More generally, our results reveal a previously unknown mechanism deployed by phage parasites to limit packaging of their viral hosts genome and highlight the prominent role of nuclease effectors as weapons in the arms race between antagonizing genomes.

microbiology↗

bioRxiv2021

A Tail Fiber Protein and a Receptor-Binding Protein Mediate ICP2 Bacteriophage Interactions with Vibrio cholerae OmpU

ICP2 is a virulent bacteriophage (phage) that preys on Vibrio cholerae. ICP2 was first isolated from cholera patient stool samples. Some of these stools also contained ICP2-resistant isogenic V. cholerae strains harboring missense mutations in the trimeric outer membrane porin protein OmpU, identifying it as the ICP2 receptor. In this study, we identify the ICP2 proteins that mediate interactions with OmpU by selecting for ICP2 host-range mutants within infant rabbits infected with a mixture of wild type and OmpU mutant strains. ICP2 host-range mutants had missense mutations in putative tail fiber gene gp25 and putative adhesin gp23. Using site-specific mutagenesis we show that single or double mutations in gp25 are sufficient to generate the host-range mutant phenotype. However, at least one additional mutation in gp23 is required for robust plaque formation on specific OmpU mutants. Mutations in gp23 alone were insufficient to give a host-range mutant phenotype. All ICP2 host-range mutants retained the ability to plaque on wild type V. cholerae cells. The strength of binding of host-range mutants to V. cholerae correlated with plaque morphology, indicating that the selected mutations in gp25 and gp23 restore molecular interactions with the receptor. We propose that ICP2 host-range mutants evolve by a two-step process where, first, gp25 mutations are selected for their broad host-range, albeit accompanied by low level phage adsorption. Subsequent selection occurs for gp23 mutations that further increase productive binding to specific OmpU alleles, allowing for near wild type efficiencies of adsorption and subsequent phage multiplication. ImportanceConcern over multidrug-resistant bacterial pathogens, including Vibrio cholerae, has led to a renewed interest in phage biology and their potential for phage therapy. ICP2 is a genetically unique virulent phage isolated from cholera patient stool samples. It is also one of three phages in a prophylactic cocktail shown to be effective in animal models of infection and the only one of the three that requires a protein receptor (OmpU). This study identifies a ICP2 tail fiber and a receptor binding protein and examines how ICP2 responds to the selective pressures of phage-resistant OmpU mutants. We found that this particular co-evolutionary arms race presents fitness costs to both ICP2 and V. cholerae.

microbiology↗

bioRxiv2021

A chimeric nuclease substitutes CRISPR-Cas: A phage weaponizes laterally acquired specificity to destroy subviral parasites

Mobile genetic elements, elements that can move horizontally between genomes, have profound effects on their hosts fitness. The PLE is a mobile element that integrates into the chromosome of Vibrio cholerae and parasitizes the bacteriophage ICP1 to move between cells. This parasitism by PLE is such that it abolishes the production of ICP1 progeny and provides a defensive boon to the host cell population. In response to the severe parasitism imposed by PLE, ICP1 has acquired an adaptive CRISPR-Cas system that targets the PLE genome during infection. However, ICP1 isolates that naturally lack CRISPR-Cas are still able to overcome certain PLE variants, and the mechanism of this immunity against PLE has thus far remained unknown. Here we show that ICP1 isolates that lack CRISPR-Cas encode an endonuclease in the same locus, and that the endonuclease provides ICP1 with immunity to a subset of PLEs. Further analysis shows that this endonuclease is of chimeric origin, incorporating a DNA binding domain that is highly similar to some PLE replication origin binding proteins. This similarity allows the endonuclease to bind and cleave PLE origins of replication. The endonuclease appears to exert considerable selective pressure on PLEs and may drive PLE replication module swapping and origin restructuring as mechanisms of escape. This work demonstrates that new genome defense systems can arise through domain shuffling and provides a greater understanding of the evolutionary forces driving genome modularity and temporal succession in mobile elements.

microbiology↗

bioRxiv2020

A phage satellite tunes inducing phage gene expression using a domesticated endonuclease to balance inhibition and virion hijacking

Bacteria persist under constant threat of predation by bacterial viruses (phages). Bacteria-phage conflicts result in evolutionary arms races often driven by mobile genetic elements (MGEs). One such MGE, a phage satellite in Vibrio cholerae called PLE, provides specific and robust defense against a pervasive lytic phage, ICP1. The interplay between PLE and ICP1 has revealed strategies for molecular parasitism allowing PLE to hijack ICP1 processes in order to mobilize. Here, we describe the mechanism of PLE-mediated transcriptional manipulation of ICP1 structural gene transcription. PLE encodes a novel DNA binding protein, CapR, that represses ICP1s capsid morphogenesis operon. Although CapR is sufficient for the degree of capsid repression achieved by PLE, its activity does not hinder the ICP1 lifecycle. We explore the consequences of repression of this operon, demonstrating that more stringent repression achieved through CRISPRi restricts both ICP1 and PLE. We also discover that PLE transduces in modified ICP1-like particles. Examination of CapR homologs led to the identification of a suite of ICP1-encoded homing endonucleases, providing a putative origin for the satellite-encoded repressor. This work unveils a facet of the delicate balance of satellite-mediated inhibition aimed at blocking phage production while successfully mobilizing in a phage-derived particle.

microbiology↗

bioRxiv2020

A family of viral satellites manipulates invading virus gene expression and affects cholera toxin mobilization

Many viruses possess temporally unfolding gene expression patterns aimed at subverting host defenses, commandeering host metabolism, and ultimately producing a large number of progeny virions. High throughput -omics tools, such as RNA-seq, have dramatically enhanced resolution of expression patterns during infection. Less studied have been viral satellites, mobile genomes that parasitize viruses and have far reaching effects on host-cell fitness. By performing RNA-seq on infection time courses, we have obtained the first time-resolved transcriptomes for bacteriophage satellites during lytic infection. Specifically, we have acquired transcriptomes for the lytic Vibrio cholerae phage ICP1 and all five known variants of ICP1s parasite, the Phage Inducible Chromosomal Island-Like Elements (PLEs). PLEs rely on ICP1 for both DNA replication and mobilization, and abolish production of ICP1 progeny in infected cells. We investigated PLEs impact on ICP1 gene expression and found that PLEs did not broadly restrict or reduce ICP1 gene expression. A major exception occurred in ICP1s capsid morphogenesis operon, which was downregulated by each of the PLE variants. This transcriptional manipulation, conserved among PLEs, has also evolved independently in at least one other phage satellite, suggesting that viral satellites may be under strong selective pressure to reduce the capsid expression of their larger host viruses. Surprisingly, PLEs were also found to alter the gene expression of CTX{phi}, the integrative phage that encodes cholera toxin and is necessary for virulence of toxigenic V. cholerae. One PLE, PLE1, upregulated CTX{phi} genes involved in replication and integration, and boosted CTX{phi} mobility following induction of the SOS response. Our data show that PLEs exhibit conserved manipulation of their host-phages gene expression, but divergent effects on CTX{phi}, revealing that PLEs can influence both their hosts resistance to phage and the mobility of virulence encoding elements.

microbiology↗

bioRxiv2019

Dominant Vibrio cholerae phage exhibits lysis inhibition sensitive to disruption by a defensive phage satellite

Bacteriophages and their bacterial hosts are locked in a dynamic evolutionary arms race. Phage satellites, selfish genomic islands which exploit both host bacterium and target phage, further complicate the evolutionary fray. One such tripartite system involves the etiological agent of the diarrheal disease cholera - Vibrio cholerae, the predominant phage isolated from cholera patients - ICP1, and a phage satellite - PLE. When ICP1 infects V. cholerae harboring the integrated PLE genome, PLE accelerates host lysis, spreading the PLE while completely blocking phage production protecting V. cholerae at the population level. Here we identify a single PLE gene, lidI, sufficient to mediate accelerated lysis during ICP1 infection and demonstrate that LidI functions through disrupting lysis inhibition - an understudied outcome of phage infection when phages vastly outnumber their hosts. This work identifies ICP1-encoded holin and antiholin genes teaA and arrA respectively, that mediate this first example of lysis inhibition outside the T-even coliphages. Through lysis inhibition disruption, LidI is sufficient to limit the number of progeny phage produced from an infection. Consequently, this disruption bottlenecks ICP1 evolution as probed by recombination and CRISPR-Cas targeting assays. These studies link novel characterization of the classic phenomenon of lysis inhibition with a conserved protein in a dominant phage satellite, highlighting the importance of lysis timing during infection and parasitization, as well as providing insight into the populations, relationships, and evolution of bacteria, phages, and phage satellites in nature.\n\nImportanceWith increasing awareness of microbiota impacting human health comes intensified examination of, not only bacteria and the bacteriophages that prey upon them, but also the mobile genetic elements (MGEs) that mediate interactions between them. Research is unveiling evolutionary strategies dependent on sensing the milieu: quorum sensing impacts phage infection, phage teamwork overcomes bacterial defenses, and abortive infections sacrifice single cells protecting populations. Yet, the first discovered environmental sensing by phages, known as lysis inhibition (LIN), has only been studied in the limited context of T-even coliphages. Here we characterize LIN in the etiological agent of the diarrheal disease cholera, Vibrio cholerae, infected by a phage ubiquitous in clinical samples. Further, we show that a specific MGE, the phage satellite PLE, collapses LIN with a conserved protein during its anti-phage program. The insights gleaned from this work add to our expanding understanding of microbial fitness in natural contexts beyond the canonical bacterial genome and into the realm of antagonistic evolution driven by phages and satellites.

microbiology↗