Phages make a group decision

A Novel XRE-Type Regulator Mediates Phage Lytic Development and Multiple Host Metabolic Processes in Pseudomonas aeruginosa

Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen, the leading cause of acute and chronic infections in immunocompromised patients, frequently with high morbidity and mortality rates. The xenobiotic response element (XRE) family proteins are the second most common transcriptional regulators (TRs) in P. aeruginosa. However, only a few XRE-like TRs have been reported to regulate multiple bacterial cellular processes, encompassing virulence, metabolism, antibiotic synthesis or resistance, stress responses, and phage infection, etc. Our understanding of what roles these XRE-like small regulatory proteins play in P. aeruginosa remains limited. Here, we aimed to decipher the role of a putative XRE-type transcriptional regulator (designated LfsT) from a prophage region on the chromosome of a clinical P. aeruginosa isolate, P8W. Southern blot and reverse transcription quantitative PCR (RT-qPCR) assays demonstrated that LfsT controlled host sensitivity to the phage PP9W2 and was essential for efficient phage replication. In addition, electrophoretic mobility shift assays (EMSAs) and transcriptional lacZ fusion analyses indicated that LfsT repressed the lysogenic development and promoted the lytic cycle of phage PP9W2 by binding to the promoter regions of the gp71 gene (encoding a CI-like repressor) and several vital phage genes. Combined with RNA-seq and a series of phenotypic validation tests, our results showed that LfsT bound to the flexible palindromic sites within the promoters upstream of several genes in the bacterial genome, regulating fatty acid (FA) metabolism, spermidine (SPD) transport, as well as the type III secretion system (T3SS). Overall, this study reveals novel regulatory roles of LfsT in P. aeruginosa, improving our understanding of the molecular mechanisms behind bacterium-phage interactions. IMPORTANCE This work elucidates the novel roles of a putative XRE family TR, LfsT, in the intricate regulatory systems of P. aeruginosa. We found that LfsT bound directly to the core promoter regions upstream of the start codons of numerous genes involved in various processes, including phage infection, FA metabolism, SPD transport, and the T3SS, regulating as the repressor or activator. The identified partial palindromic motif NAACN(5,8)GTTN recognized by LfsT suggests extensive effects of LfsT on gene expression by maintaining preferential binding to nucleotide sites under evolutionary pressure. In summary, these findings indicate that LfsT enhances metabolic activity in P. aeruginosa, while it reduces host resistance to the phage. This study helps us better understand the coevolution of bacteria and phages (e.g., survival comes at a cost) and provides clues for designing novel antimicrobials against P. aeruginosa infections.

Bacterial MazF/MazE toxin-antitoxin suppresses lytic propagation of arbitrium-containing phages

Temperate phages dynamically switch between lysis and lysogeny in their full life cycle. Some Bacillus-infecting phages utilize a quorum-sensing-like intercellular communication system, the "arbitrium," to mediate lysis-lysogeny decisions. However, whether additional factors participate in the arbitrium signaling pathway remains largely elusive. Here, we find that the arbitrium signal induces the expression of a functionally conserved operon downstream of the arbitrium module in SPbeta-like phages. SPbeta yopM and yopR (as well as phi3T phi3T_93 and phi3T_97) in the operon play roles in suppressing phage lytic propagation and promoting lysogeny, respectively. We further focus on phi3T_93 and demonstrate that it directly binds antitoxin MazE in the host MazF/MazE toxin-antitoxin (TA) module and facilitates the activation of MazF's toxicity, which is required for phage suppression. These findings show events regulated by the arbitrium system and shed light on how the interplay between phages and the host TA module affects phage-host co-survival.

AimR Adopts Preexisting Dimer Conformations for Specific Target Recognition in Lysis-Lysogeny Decisions of Bacillus Phage phi3T

A bacteriophage switches between lytic and lysogenic life cycles. The AimR-AimP-AimX communication system is responsible for phage lysis-lysogeny decisions during the infection of Bacillus subtilis. AimX is a regulator biasing phage lysis, AimR is a transcription factor activating AimX expression, and AimP is an arbitrium peptide that determines phage lysogeny by deactivating AimR. A strain-specific mechanism for the lysis-lysogeny decisions is proposed in SPbeta and phi3T phages. That is, the arbitrium peptide of the SPbeta phage stabilizes the SPbeta AimR (spAimR) dimer, whereas the phi3T-derived peptide disassembles the phi3T AimR (phAimR) dimer into a monomer. Here, we find that phAimR does not undergo dimer-to-monomer conversion upon arbitrium peptide binding. Gel-filtration, static light scattering (SLS) and analytical ultracentrifugation (AUC) results show that phAimR is dimeric regardless of the presence of arbitrium peptide. Small-angle X-ray scattering (SAXS) reveals that the arbitrium peptide binding makes an extended dimeric conformation. Single-molecule fluorescence resonance energy transfer (smFRET) analysis reveals that the phAimR dimer fluctuates among two distinct conformational states, and each preexisting state is selectively recognized by the arbitrium peptide or the target DNA, respectively. Collectively, our biophysical characterization of the phAimR dynamics underlying specific target recognition provides new mechanistic insights into understanding lysis-lysogeny decisions in Bacillus phage phi3T.

Phages and their potential to modulate the microbiome and immunity

Bacteriophages (hence termed phages) are viruses that target bacteria and have long been considered as potential future treatments against antibiotic-resistant bacterial infection. However, the molecular nature of phage interactions with bacteria and the human host has remained elusive for decades, limiting their therapeutic application. While many phages and their functional repertoires remain unknown, the advent of next-generation sequencing has increasingly enabled researchers to decode new lytic and lysogenic mechanisms by which they attack and destroy bacteria. Furthermore, the last decade has witnessed a renewed interest in the utilization of phages as therapeutic vectors and as a means of targeting pathogenic or commensal bacteria or inducing immunomodulation. Importantly, the narrow host range, immense antibacterial repertoire, and ease of manipulating phages may potentially allow for their use as targeted modulators of pathogenic, commensal and pathobiont members of the microbiome, thereby impacting mammalian physiology and immunity along mucosal surfaces in health and in microbiome-associated diseases. In this review, we aim to highlight recent advances in phage biology and how a mechanistic understanding of phage-bacteria-host interactions may facilitate the development of novel phage-based therapeutics. We provide an overview of the challenges of the therapeutic use of phages and how these could be addressed for future use of phages as specific modulators of the human microbiome in a variety of infectious and noncommunicable human diseases.

Structural insights into DNA recognition by AimR of the arbitrium communication system in the SPbeta phage

A newly identified arbitrium communication system regulates the lysis-to-lysogeny decision in a Bacillus bacteriophage. This system contains an arbitrium hexapeptide as a signal, the cellular receptor AimR, and the lysogenic negative regulator AimX. AimR specifically targets the downstream DNA to activate aimX gene expression. The arbitrium peptide binds to AimR, inhibiting its DNA-binding to promote phage lysogeny. Recently, we and other groups have elucidated how arbitrium peptide sensed by AimR. However, the molecular mechanisms of DNA recognition by AimR and the regulation of its DNA-binding activity by the peptide remain largely unknown. Here, we report the crystal structure of the AimR–DNA complex at 2.1 Å resolution. The N-terminal HTH motif recognizes the palindromic DNA sequence, buttressed by interactions between positively charged residues and the DNA phosphate groups. The DNA-bound AimR assembles a more closed dimer than the peptide-bound form. Single-molecule FRET and crosslinking assays revealed that the AimR protein samples both open and closed conformations in solution. Arbitrium peptide binding induces a closed-to-open conformational change of AimR, eliminating DNA targeting. Our structural and functional analysis provides new insights into the DNA recognition mechanism of AimR and its regulation by the arbitrium peptide in the context of phage lysis-lysogeny decisions.

The Diverse Impacts of Phage Morons on Bacterial Fitness and Virulence

The viruses that infect bacteria, known as phages, are the most abundant biological entity on earth. They play critical roles in controlling bacterial populations through phage-mediated killing, as well as through formation of bacterial lysogens. In this form, the survival of the phage depends on the survival of the bacterial host in which it resides. Thus, it is advantageous for phages to encode genes that contribute to bacterial fitness and expand the environmental niche. In many cases, these fitness factors also make the bacteria better able to survive in human infections and are thereby considered pathogenesis or virulence factors. The genes that encode these fitness factors, known as "morons," have been shown to increase bacterial fitness through a wide range of mechanisms and play important roles in bacterial diseases. This review outlines the benefits provided by phage morons in various aspects of bacterial life, including phage and antibiotic resistance, motility, adhesion and quorum sensing.

Structural and functional insights into the regulation of the lysis-lysogeny decision in viral communities

Communication is vital for all organisms including microorganisms, which is clearly demonstrated by the bacterial quorum-sensing system. However, the molecular mechanisms underlying communication among viruses (phages) via the quorum-sensing-like 'arbitrium' system remain unclear. Viral or host densities are known to be related to an increased prevalence of lysogeny; however, how the switch from the lytic to the lysogenic pathway occurs is unknown. Thus, we sought to reveal mechanisms of communication among viruses and determine the lysogenic dynamics involved. Structural and functional analyses of the phage-derived SAIRGA and GMPRGA peptides and their corresponding receptors, phAimR and spAimR, indicated that SAIRGA directs the lysis-lysogeny decision of phi3T by modulating conformational changes in phAimR, whereas GMPRGA regulates the lysis-lysogeny pathway by stabilizing spAimR in the dimeric state. Although temperate viruses are thought to share a similar lytic-lysogenic cycle switch model, our study suggests the existence of alternative strain-specific mechanisms that regulate the lysis-lysogeny decision. Collectively, these findings provide insights into the molecular mechanisms underlying communication among viruses, offering theoretical applications for the treatment of infectious viral diseases.

Phagebook: The Social Network

Much like social networks are used to connect with friends or relatives, bacteria communicate with relatives through quorum sensing. Viruses, though, were thought to be asocial-until now. Erez et al. (2017) reveal that viruses are also sharing information with relatives.

Virus-Derived Peptides for Clinical Applications

Novel affinity agents with high specificity are needed to make progress in disease diagnosis and therapy. Over the last several years, peptides have been considered to have fundamental benefits over other affinity agents, such as antibodies, due to their fast blood clearance, low immunogenicity, rapid tissue penetration, and reproducible chemical synthesis. These features make peptides ideal affinity agents for applications in disease diagnostics and therapeutics for a wide variety of afflictions. Virus-derived peptide techniques provide a rapid, robust, and high-throughput way to identify organism-targeting peptides with high affinity and selectivity. Here, we will review viral peptide display techniques, how these techniques have been utilized to select new organism-targeting peptides, and their numerous biomedical applications with an emphasis on targeted imaging, diagnosis, and therapeutic techniques. In the future, these virus-derived peptides may be used as common diagnosis and therapeutics tools in local clinics.

Papers of note in Nature (7638)

This week’s articles are about peptides that mediate communication between viruses, how microglia induce reactive astrocytes that contribute to neuronal cell death, and how kinases of the Hippo pathway influence breast cell fate.