Transcriptomic Analysis Reveals the Dependency of Pseudomonas aeruginosa Genes for Double-Stranded RNA Bacteriophage phiYY Infection Cycle

Bacteriophage protein Dap1 regulates evasion of antiphage immunity and Pseudomonas aeruginosa virulence impacting phage therapy in mice

Bacteriophages have evolved diverse strategies to overcome host defence mechanisms and to redirect host metabolism to ensure successful propagation. Here we identify a phage protein named Dap1 from Pseudomonas aeruginosa phage PaoP5 that both modulates bacterial host behaviour and contributes to phage fitness. We show that expression of Dap1 in P. aeruginosa reduces bacterial motility and promotes biofilm formation through interference with DipA, a c-di-GMP phosphodiesterase, which causes an increase in c-di-GMP levels that trigger phenotypic changes. Results also show that deletion of dap1 in PaoP5 significantly reduces genome packaging. In this case, Dap1 directly binds to phage HNH endonuclease, prohibiting host Lon-mediated HNH degradation and promoting phage genome packaging. Moreover, PaoP5Δdap1 fails to rescue P. aeruginosa-infected mice, implying the significance of dap1 in phage therapy. Overall, these results highlight remarkable dual functionality in a phage protein, enabling the modulation of host behaviours and ensuring phage fitness.

Molecular characterization and transcriptomic analysis of a novel polymycovirus in the fungus Talaromyces amestolkiae

Talaromyces amestolkiae is an important fungal species owing to its ubiquity in soils, plants, air, and food. In this study, we identified a novel six-segmented polymycovirus, Talaromyces amestolkiae polymycovirus 1 (TaPmV-1). Each of the double-stranded (ds) RNA segments of TaPmV-1 contained a single open reading frame, and the proteins encoded by dsRNA1, dsRNA2, dsRNA3, and dsRNA 5 shared significant amino acid identities of 56, 40, 47, and 43%, respectively, with the corresponding proteins of Aspergillus fumigatus polymycovirus-1(AfuPmV-1). DsRNA1, dsRNA3, and dsRNA5 of TaPmV-1 encoded an RNA-dependent RNA polymerase (RdRp), a viral methyltransferase, and a PAS-rich protein, respectively. The functions of the proteins encoded by dsRNA2, dsRNA4, and dsRNA6 have not been elucidated. Comparison of the virus-infected strain LSH3 with virus-cured strain LSHVF revealed that infection with TaPmV-l may reduce the production of red pigments and induce the clustering of fungal sclerotia. Furthermore, transcriptomic analyses demonstrated that infection with TaPmV-l downregulated the expression of transcripts related to metabolism, and may correlate with the reduced production of red pigments and clustering of sclerotia in T. amestolkiae. These results of this study provide novel insights into the mechanism of fungal gene regulation by polymycovirus infections at the transcriptome level, and this study is the first to report a novel polymycovirus of T. amestolkiae.

Pf4 Phage Variant Infection Reduces Virulence-Associated Traits in Pseudomonas aeruginosa

Pf4 is a filamentous bacteriophage integrated as a prophage into the genome of Pseudomonas aeruginosa PAO1. Pf4 virions can be produced without killing P. aeruginosa. However, cell lysis can occur during superinfection when Pf virions successfully infect a host lysogenized by a Pf superinfective variant. We have previously shown that infection of P. aeruginosa PAO1 with a superinfective Pf4 variant abolished twitching motility and altered biofilm architecture. More precisely, most of the cells embedded into the biofilm were showing a filamentous morphology, suggesting the activation of the cell envelope stress response involving both AlgU and SigX extracytoplasmic function sigma factors. Here, we show that Pf4 variant infection results in a drastic dysregulation of 3,360 genes representing about 58% of P. aeruginosa genome; of these, 70% of the virulence factors encoding genes show a dysregulation. Accordingly, Pf4 variant infection (termed Pf4*) causes in vivo reduction of P. aeruginosa virulence and decreased production of N-acyl-homoserine lactones and 2-alkyl-4-quinolones quorum-sensing molecules and related virulence factors, such as pyocyanin, elastase, and pyoverdine. In addition, the expression of genes involved in metabolism, including energy generation and iron homeostasis, was affected, suggesting further relationships between virulence and central metabolism. Altogether, these data show that Pf4 phage variant infection results in complex network dysregulation, leading to reducing acute virulence in P. aeruginosa. This study contributes to the comprehension of the bacterial response to filamentous phage infection. IMPORTANCE Filamentous bacteriophages can become superinfective and infect P. aeruginosa, even though they are inserted in the genome as lysogens. Despite this productive infection, growth of the host is only mildly affected, allowing the study of the interaction between the phage and the host, which is not possible in the case of lytic phages killing rapidly their host. Here, we demonstrate by transcriptome and phenotypic analysis that the infection by a superinfective filamentous phage variant causes a massive disruption in gene expression, including those coding for virulence factors and metabolic pathways.

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.

Interactions between Jumbo Phage SA1 and Staphylococcus: A Global Transcriptomic Analysis

Staphylococcus aureus (S. aureus) is an important zoonotic pathogen that poses a serious health concern to humans and cattle worldwide. Although it has been proven that lytic phages may successfully kill S. aureus, the interaction between the host and the phage has yet to be thoroughly investigated, which will likely limit the clinical application of phage. Here, RNA sequencing (RNA-seq) was used to examine the transcriptomics of jumbo phage SA1 and Staphylococcus JTB1-3 during a high multiplicity of infection (MOI) and RT-qPCR was used to confirm the results. The RNA-seq analysis revealed that phage SA1 took over the transcriptional resources of the host cells and that the genes were categorized as early, middle, and late, based on the expression levels during infection. A minor portion of the resources of the host was employed to enable phage replication after infection because only 35.73% (997/2790) of the host genes were identified as differentially expressed genes (DEGs). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses showed that the phage infection mainly affected the nucleotide metabolism, protein metabolism, and energy-related metabolism of the host. Moreover, the expression of the host genes involved in anti-phage systems, virulence, and drug resistance significantly changed during infection. This research gives a fresh understanding of the relationship between jumbo phages and their Gram-positive bacteria hosts and provides a reference for studying phage treatment and antibiotics.

Bacteriophage therapy for empyema caused by carbapenem-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa is a frequent causative agent of post-pneumonectomy empyema-associated broncho-pleural fistula (BPF) and it has a high mortality rate. In recent years, the therapeutic potential of bacteriophage therapy has recognized anew as antimicrobial resistance increases globally. Studies are increasingly reporting the efficacy and safety of bacteriophage therapy for the treatment of multidrug-resistant bacterial infections. However, the clinical efficacy of bacteriophage therapy in empyema has seldom been studied. The current study reports the authors' experience with bacteriophage therapy for a 68-year-old Chinese man who suffered BPF-associated empyema and pneumonia caused by carbapenem-resistant P. aeruginosa. A personalized lytic pathogen-specific two-phage preparation was administered to the patient continuously for 24 days in combination with conventional antibiotics. The treatment was well-tolerated, resulting in clearance of the pathogen and improvement of the clinical outcome. This experience shows that a combined conventional antibiotic treatment with bacteriophage therapy may be effective at alleviating a multidrug-resistant bacterial infection in BPF-associated empyema.

Enterococcus faecalis Bacteriophage vB_EfaS_efap05-1 Targets the Surface Polysaccharide and ComEA Protein as the Receptors

Enterococcus faecalis is a Gram-positive opportunistic pathogen that causes nosocomial infections in humans. Due to the growing threat of antibiotic resistance of E. faecalis, bacteriophage therapy is a promising option for treating of E. faecalis infection. Here, we characterized a lytic E. faecalis bacteriophage vB_EfaS_efap05-1 with a dsDNA genome of 56,563 bp. Phage vB_EfaS_efap05-1 had a prolate head and a tail, and belongs to Saphexavirus which is a member of Siphoviridae. Efap05-1 uses either surface polysaccharide or membrane protein ComEA as the receptor because the mutation of both genes (ComEA and UDP-glucose 4-epimerase galE) prevents phage adsorption and leads to phage resistance, and complementation of ComEA or galE could recover its phage sensitivity. Our results provided a comprehensive analysis of a new E. faecalis phage and suggest efap05-1 as a potential antimicrobial agent.

Cell wall deficiency as an escape mechanism from phage infection

The cell wall plays a central role in protecting bacteria from some environmental stresses, but not against all. In fact, in some cases, an elaborate cell envelope may even render the cell more vulnerable. For example, it contains molecules or complexes that bacteriophages recognize as the first step of host invasion, such as proteins and sugars, or cell appendages such as pili or flagella. In order to counteract phages, bacteria have evolved multiple escape mechanisms, such as restriction-modification, abortive infection, CRISPR/Cas systems or phage inhibitors. In this perspective review, we present the hypothesis that bacteria may have additional means to escape phage attack. Some bacteria are known to be able to shed their cell wall in response to environmental stresses, yielding cells that transiently lack a cell wall. In this wall-less state, the bacteria may be temporarily protected against phages, since they lack the essential entities that are necessary for phage binding and infection. Given that cell wall deficiency can be triggered by clinically administered antibiotics, phage escape could be an unwanted consequence that limits the use of phage therapy for treating stubborn infections.

Characterization of an Enterococcus faecalis Bacteriophage vB_EfaM_LG1 and Its Synergistic Effect With Antibiotic

Enterococcus faecalis is a Gram-positive opportunistic pathogen that could cause pneumonia and bacteremia in stroke patients. The development of antibiotic resistance in hospital-associated E. faecalis is a formidable public health threat. Bacteriophage therapy is a renewed solution to treat antibiotic-resistant bacterial infections. However, bacteria can acquire phage resistance quite quickly, which is a significant barrier to phage therapy. Here, we characterized a lytic E. faecalis bacteriophage Vb_EfaM_LG1 with lytic activity. Its genome did not contain antibiotic resistance or virulence genes. Vb_EfaM_LG1 effectively inhibits E. faecalis growth for a short period, and phage resistance developed within hours. However, the combination of antibiotics and phage has a tremendous synergistic effect against E. faecalis, prevents the development of phage resistance, and disrupts the biofilm efficiently. Our results show that the phage-antibiotic combination has better killing efficiency against E. faecalis.