Phage-host co-evolution has led to distinct generalized transduction strategies

Generalized transduction is pivotal in bacterial evolution but lacks comprehensive understanding regarding the facilitating features and variations among phages. We addressed this gap by sequencing and comparing the transducing particle content of three different Salmonella Typhimurium phages (i.e. Det7, ES18 and P22) that share a headful packaging mechanism that is typically initiated from a cognate pac site within the phage chromosome. This revealed substantial disparities in both the extent and content of transducing particles among these phages. While Det7 outperformed ES18 in terms of relative number of transducing particles, both phages contrasted with P22 in terms of content. In fact, we found evidence for the presence of conserved P22 pac-like sequences in the host chromosome that direct tremendously increased packaging and transduction frequencies of downstream regions by P22. More specifically, a ca. 561 kb host region between oppositely oriented pac-like sequences in the purF and minE loci was identified as highly packaged and transduced during both P22 prophage induction and lytic infection. Our findings underscore the evolution of phage transducing capacity towards attenuation, promiscuity or directionality, and suggest that pac-like sequences in the host chromosome could become selected as sites directing high frequency of transduction

A widespread family of phage-inducible chromosomal islands only steals bacteriophage tails to spread in nature

Phage satellites are genetic elements that couple their life cycle to that of helper phages they parasitize, interfering with phage packaging through the production of small capsids, where only satellites are packaged. So far, in all analyzed systems, the satellite-sized capsids are composed of phage proteins. Here, we report that a family of phage-inducible chromosomal islands (PICIs), a type of satellites, encodes all the proteins required for both the production of small-sized capsids and the exclusive packaging of the PICIs into these capsids. Therefore, this new family, named capsid-forming PICIs (cf-PICIs), only requires phage tails to generate PICI particles. Remarkably, the representative cf-PICIs are produced with no cost from their helper phages, suggesting that the relationship between these elements is not parasitic. Finally, our phylogenomic studies indicate that cf-PICIs are present both in gram-positive and gram-negative bacteria and have evolved at least three times independently to spread in nature

Hijacking the hijackers: Escherichia coli pathogenicity islands redirect helper phage packaging for their own benefit

Phage-inducible chromosomal islands (PICIs) represent a novel and universal class of mobile genetic elements, which have broad impact on bacterial virulence. In spite of their relevance, how the Gram-negative PICIs hijack the phage machinery for their own specific packaging and how they block phage reproduction remains to be determined. Using genetic and structural analyses, we solve the mystery here by showing that the Gram-negative PICIs encode a protein that simultaneously performs these processes. This protein, which we have named Rpp (for redirecting phage packaging), interacts with the phage terminase small subunit, forming a heterocomplex. This complex is unable to recognize the phage DNA, blocking phage packaging, but specifically binds to the PICI genome, promoting PICI packaging. Our studies reveal the mechanism of action that allows PICI dissemination in nature, introducing a new paradigm in the understanding of the biology of pathogenicity islands and therefore of bacterial pathogen evolution

Evolutionary and functional history of the Escherichia coli K1 capsule

Escherichia coli is a leading cause of invasive bacterial infections in humans. Capsule polysaccharide has an important role in bacterial pathogenesis, and the K1 capsule has been firmly established as one of the most potent capsule types in E. coli through its association with severe infections. However, little is known about its distribution, evolution and functions across the E. coli phylogeny, which is fundamental to elucidating its role in the expansion of successful lineages. Using systematic surveys of invasive E. coli isolates, we show that the K1-cps locus is present in a quarter of bloodstream infection isolates and has emerged in at least four different extraintestinal pathogenic E. coli (ExPEC) phylogroups independently in the last 500 years. Phenotypic assessment demonstrates that K1 capsule synthesis enhances E. coli survival in human serum independent of genetic background, and that therapeutic targeting of the K1 capsule re-sensitizes E. coli from distinct genetic backgrounds to human serum. Our study highlights that assessing the evolutionary and functional properties of bacterial virulence factors at population levels is important to better monitor and predict the emergence of virulent clones, and to also inform therapies and preventive medicine to effectively control bacterial infections whilst significantly lowering antibiotic usage

Phage-inducible chromosomal islands are ubiquitous within the bacterial universe

Phage-inducible chromosomal islands (PICIs) are a recently discovered family of pathogenicity islands that contribute substantively to horizontal gene transfer, host adaptation and virulence in Gram-positive cocci. Here we report that similar elements also occur widely in Gram-negative bacteria. As with the PICIs from Gram-positive cocci, their uniqueness is defined by a constellation of features: unique and specific attachment sites, exclusive PICI genes, a phage-dependent mechanism of induction, conserved replication origin organization, convergent mechanisms of phage interference, and specific packaging of PICI DNA into phage-like infectious particles, resulting in very high transfer frequencies. We suggest that the PICIs represent two or more distinct lineages, have spread widely throughout the bacterial world, and have diverged much more slowly than their host organisms or their prophage cousins. Overall, these findings represent the discovery of a universal class of mobile genetic elements

The discovery of phage-inducible chromosomal islands (PICIs) in Gram-negative bacteria

Abstract not currently available

Identification and characterization of thousands of bacteriophage satellites across bacteria

Posted September 14, 2022 on bioRxivBacteriophage-bacteria interactions are affected by phage satellites, elements that exploit phages for transfer between bacterial cells. Satellites can encode defense systems, antibiotic resistance genes, and virulence factors, but their number and diversity are unknown for lack of a tool to identify them. We developed a flexible and updateable program to identify satellites in bacterial genomes – SatelliteFinder – and use it to identify the best described families: P4-like, phage inducible chromosomal islands (PICI), capsid-forming PICI, and phage-inducible chromosomal island-like elements (PLE). We vastly expanded the number of described elements to ∼5000, finding hundreds of bacterial genomes with two different families of satellites, and dozens of Escherichia coli genomes with three. Most satellites were found in Proteobacteria and Firmicutes, but some are in novel taxa such as Actinobacteria. We characterized the gene repertoires of satellites, which are variable in size and composition, and their genomic organization, which is very conserved. With the partial exception of PICI and cfPICI, there are few homologous core genes between families of satellites, and even fewer homologous to phages. Hence, phage satellites are ancient, diverse, and probably evolved multiple times independently. Occasionally, core genes of a given family of satellites are found in another, suggesting gene flow between different satellites. Given the many elements found in spite of our conservative approach, the many bacteria infected by phages that still lack known satellites, and the recent proposals for novel families, we speculate that we are at the beginning of the discovery of massive numbers and types of satellites. SatelliteFinder is accessible for the community as a Galaxy service at https://galaxy.pasteur.fr/root?tool_id=toolshed.pasteur.fr/repos/fmareuil/satellitefinder/SatelliteFinder/0.

Identification and characterization of thousands of bacteriophage satellites across bacteria

Posted September 14, 2022 on bioRxivInternational audienceBacteriophage-bacteria interactions are affected by phage satellites, elements that exploit phages for transfer between bacterial cells. Satellites can encode defense systems, antibiotic resistance genes, and virulence factors, but their number and diversity are unknown for lack of a tool to identify them. We developed a flexible and updateable program to identify satellites in bacterial genomes – SatelliteFinder – and use it to identify the best described families: P4-like, phage inducible chromosomal islands (PICI), capsid-forming PICI, and phage-inducible chromosomal island-like elements (PLE). We vastly expanded the number of described elements to ∼5000, finding hundreds of bacterial genomes with two different families of satellites, and dozens of Escherichia coli genomes with three. Most satellites were found in Proteobacteria and Firmicutes, but some are in novel taxa such as Actinobacteria. We characterized the gene repertoires of satellites, which are variable in size and composition, and their genomic organization, which is very conserved. With the partial exception of PICI and cfPICI, there are few homologous core genes between families of satellites, and even fewer homologous to phages. Hence, phage satellites are ancient, diverse, and probably evolved multiple times independently. Occasionally, core genes of a given family of satellites are found in another, suggesting gene flow between different satellites. Given the many elements found in spite of our conservative approach, the many bacteria infected by phages that still lack known satellites, and the recent proposals for novel families, we speculate that we are at the beginning of the discovery of massive numbers and types of satellites. SatelliteFinder is accessible for the community as a Galaxy service at https://galaxy.pasteur.fr/root?tool_id=toolshed.pasteur.fr/repos/fmareuil/satellitefinder/SatelliteFinder/0.

Beyond the CRISPR-Cas safeguard: PICI-encoded innate immune systems protect bacteria from bacteriophage predation

7 páginas, 2 figurasPhage satellites are genetic elements that depend on helper phages for induction, packaging and transfer. To promote their lifestyles, they have evolved elegant and sophisticated strategies to inhibit phage reproduction, which will be reviewed here. We will principally focus on the convergent interference mechanisms used by phage-inducible chromosomal islands (PICIs), which are a family of satellite phages present in both Gram-positive and Gram-negative bacteria. While some PICI elements have been extensively studied for their roles in virulence and antibiotic resistance, recent studies have highlighted their relevance in controlling phage ecology and diversity. In many cases, these interference mechanisms are complemented by additional strategies that promote the preferential PICI packaging and dissemination of these elements in nature. Since the PICI-encoded mechanisms target conserved phage mechanisms, we propose here that the PICIs form part of the initial innate immune system that phages must overcome to infect their bacterial host.This work was supported by grants MR/M003876/1 and MR/S00940X/1 from the Medical Research Council (UK), BB/N002873/1 and BB/S003835/1 from the Biotechnology and Biological Sciences Research Council (BBSRC, UK), Wellcome Trust201531/Z/16/Z, and ERC-ADG-2014 Proposal n 670932 Dut-signal from EU to J.R.P. L.M-R is the recipient of a Spanish postdoctoral fellowship from Fundacio´n Ramo´n Areces. J.R.P. is thankful to the Royal Society and the Wolfson Foundation for providing him support through a Royal Society Wolfson Fellowship.Peer reviewe

Hijacking the hijackers: Escherichia coli phage-inducible chromosomal islands redirect lambda phage packaging for their own benefit

Abstract de la comunicación oral presentada al 8th Congress of European Microbiologist. FEMS 2019. Glasgow, Scotland. 7-11 July 2019(Oral 098) Background: Phage-inducible chromosomal islands (PICIs) are clinically relevant mobile genetic elements widespread among Gram-positive and Gram-negative bacteria. Understanding the different PICI packaging mechanisms is essential to comprehend their intra- and inter-generic transfer, which contribute to bacterial evolution, host adaptation and pathogenesis. Objectives: Hijacking and blocking phage functions is vital for the PICI molecular pirates. They usually encode a battery of genetic resources to interfere with the phage. The objective of this study was to characterise the mechanism employed by EcCICFT073 to hijack the phage TerS, redirecting its affinity to package the PICI dsDNA. Methods: We identified by in vivo (phage evolution, genetic scarless mutations, competition assays) and in vitro (Two-hybrid assays, X-ray crystallography) experiments the molecular mechanism by which EcCICFT073 recruits the phage packaging machinery. Results: This study identified a novel and elegant one-shot strategy used by some cos lambda E. coli PICIs like EcCICFT073. Unlike other cos PICIs that carry the same phage cos sequence, EcCICFT073 carries the lambda phage cosQ and cosN, but a different cosB region (region involved in packaging initiation). Hence, these PICIs have developed a sophisticated strategy by encoding a protein, renamed as Rpp (Redirecting phage packaging) which forms a heterodimer with the phage TerS to perform dual roles: i) forming a new functional hetero DNA-binding (DBD) region that will be used to recognise the PICI cosB site; and ii) this new DBD would be unable to recognise the phage cos site, blocking phage packaging. This novel strategy highlights PICIs as sophisticated parasites in nature