Mosaic structure of Shiga-toxin-2-encoding phages isolated from Escherichia coli O157:H7 indicates frequent gene exchange between lambdoid phage genomes

Johansen, B. Klungseth; Wasteson, Yngvild; Granum, Per Einar; Brynestad, Sigrid

doi:10.1099/00221287-147-7-1929

Cited by 88 publications

(82 citation statements)

References 29 publications

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“…Alternatively, APSE-encoded toxins may target and destroy the cells of attacking parasitoids or other eukaryotic enemies, thereby protecting their aphid hosts. The mosaic structure of APSE genomes, also observed in other lambdoid phage (20), reflects recombination among haplotypes and could promote hypervariability in toxin-encoding capacity of H. defensa isolates. Thus, the phages may enable H. defensa to mount a varied arsenal of toxins to defend aphid hosts against natural enemies, which vary among populations and over time (e.g., refs.…”

Section: The Apse-h Defensa-aphid Consortium As a Complex Mutualisticmentioning

confidence: 99%

“…A TTSS also appears to underlie infection of host cells by the symbionts of Sitophilus weevils (17) and by Photorhabdus species infecting nematodes (18). Such pathogenicity determinants are often transferred horizontally among enteric bacteria via bacteriophage vectors; these transfers have a role in transforming a nonpathogenic to a pathogenic strain (19)(20)(21). Because both pathogenesis and symbiosis share the requirement of bacterial establishment within host cells or tissues, additional mechanisms, already characterized in pathogens, may be incorporated into the symbiotic lifestyle or may underlie variation among symbionts in their effects on hosts.…”

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confidence: 99%

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The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

Moran

Degnan

Santos

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

289

271

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Aphids maintain mutualistic symbioses involving consortia of coinherited organisms. All possess a primary endosymbiont, Buchnera, which compensates for dietary deficiencies; many also contain secondary symbionts, such as Hamiltonella defensa, which confers defense against natural enemies. Genome sequences of uncultivable secondary symbionts have been refractory to analysis due to the difficulties of isolating adequate DNA samples. By amplifying DNA from hemolymph of infected pea aphids, we obtained a set of genomic sequences of H. defensa and an associated bacteriophage. H. defensa harbors two type III secretion systems, related to those that mediate host cell entry by enteric pathogens. The phage, called APSE-2, is a close relative of the previously sequenced APSE-1 but contains intact homologs of the gene encoding cytolethal distending toxin (cdtB), which interrupts the eukaryotic cell cycle and which is known from a variety of mammalian pathogens. The cdtB homolog is highly expressed, and its genomic position corresponds to that of a homolog of stx (encoding Shiga-toxin) within APSE-1. APSE-2 genomes were consistently abundant in infected pea aphids, and related phages were found in all tested isolates of H. defensa, from numerous insect species. Based on their ubiquity and abundance, these phages appear to be an obligate component of the H. defensa life cycle. We propose that, in these mutualistic symbionts, phage-borne toxin genes provide defense to the aphid host and are a basis for the observed protection against eukaryotic parasites.Acrythosiphon pisum ͉ Hamiltonella defensa ͉ lamboid phage ͉ aphid ͉ Enterobacteriaceae

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Section: The Apse-h Defensa-aphid Consortium As a Complex Mutualisticmentioning

confidence: 99%

mentioning

confidence: 99%

The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

Moran

Degnan

Santos

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

289

271

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“…Several authors have shown that Stx2-encoding prophages are highly variable (Johansen et al, 2001) and present a high degree of heterogeneity in terms of induction levels (Muniesa et al, 2004a;Wagner et al, 1999). In agreement with these reports, we found that expression of stx 2 and stx 2 -related genes is heterogeneous in basal and in induced conditions, depending on the strain and on the stx 2 variant.…”

Section: Heterogeneous Expression Of Stx 2 Variantsmentioning

confidence: 99%

Differential expression of stx2 variants in Shiga toxin-producing Escherichia coli belonging to seropathotypes A and C

Sablet¹,

Bertin²,

Vareille³

et al. 2008

Microbiology

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Only a subset of Shiga toxin (Stx)-producing Escherichia coli (STEC) are human pathogens, but the characteristics that account for differences in pathogenicity are not well understood. In this study, we investigated the distribution of the stx variants coding for Stx2 and its variants in highly virulent STEC of seropathotype A and low-pathogenic STEC of seropathotype C. We analysed and compared transcription of the corresponding genes, production of Shiga toxins, and stx-phage release in basal as well as in induced conditions. We found that the stx 2 variant was mainly associated with strains of seropathotype A, whereas most of the strains of seropathotype C possessed the stx 2-vhb variant, which was frequently associated with stx 2 , stx 2-vha or stx 2c . Levels of stx 2 and stx 2 -related mRNA were higher in strains belonging to seropathotype A and in those strains of seropathotype C that express the stx 2 variant than in the remaining strains of seropathotype C. The stx 2-vhb genes were the least expressed, in basal as well as in induced conditions, and in many cases did not seem to be carried by an inducible prophage. A clear correlation was observed between stx mRNA levels and stx-phage DNA in the culture supernatants, suggesting that most stx 2 -related genes are expressed only when they are carried by a phage. In conclusion, some relationship between stx 2 -related gene expression in vitro and the seropathotype of the STEC strains was observed. A higher expression of the stx 2 gene and a higher release of its product, in basal as well as in induced conditions, was observed in pathogenic strains of seropathotype A. A subset of strains of seropathotype C shows the same characteristics and could be a high risk to human health.

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“…Various patterns of stx-phages have been described and since they present a wide range of DNA structures, restriction patterns, host spectra and morphology, they are considered to form a heterogeneous family (Unkmeir & Schmidt, 2000;Schmidt et al, 2000;Johansen et al, 2001). …”

Section: Introductionmentioning

confidence: 99%

Diversity of stx 2 converting bacteriophages induced from Shiga-toxin-producing Escherichia coli strains isolated from cattle

et al. 2004

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The presence of bacteriophages encoding Shiga toxin 2 (stx 2 phages) was analysed in 168 strains of Shiga-toxin-producing Escherichia coli (STEC) isolated from cattle. Following mitomycin C induction, strains carrying stx 2 phages were screened by plaque blot and hybridization with an stx 2 A-probe. In the stx 2 -phage-carrying strains, the amounts of phage production, phage DNA extracted and Stx 2 produced after induction were assessed. The induced stx 2 phages were characterized morphologically and genetically. Assays to obtain lysogens from different strains were also carried out and phages induced from the lysogens were compared with those induced from the STEC isolates. Results indicated that 18 % of the strains carried an inducible stx 2 phage. Most of them showed a direct relationship between phage induction and toxin production. Each strain carried only one inducible stx 2 phage, although a few strains had two copies of the stx 2 in the chromosome. The stx 2 phages showed diverse morphology and a wide variability in their genome. Assays to obtain lysogens showed that not all the phages were transduced with the same frequency and only six lysogens were obtained. Phages in the lysogens were the same as those induced from their respective initial STEC host strains, although the induction and relative toxin production of the lysogens varied. Most phages carried the stx 2 gene, while a few carried stx 2 variants. Infectivity of the phages depended on the different hosts, although O157 : H7 was preferentially infected by phages induced from O157 strains. The results show that inducible stx 2 phages are common among STEC of animal origin and that they may enhance the spread of stx 2 .

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Mosaic structure of Shiga-toxin-2-encoding phages isolated from Escherichia coli O157:H7 indicates frequent gene exchange between lambdoid phage genomes

Cited by 88 publications

References 29 publications

The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

The players in a mutualistic symbiosis: Insects, bacteria, viruses, and virulence genes

Differential expression of stx2 variants in Shiga toxin-producing Escherichia coli belonging to seropathotypes A and C

Diversity of stx 2 converting bacteriophages induced from Shiga-toxin-producing Escherichia coli strains isolated from cattle

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