Bacteriophages ofErwinia amylovora

Abstract

Fifty bacteriophage isolates of Erwinia amylovora, the causal agent of fire blight, were collected from sites in and around the Niagara region of southern Ontario and the Royal Botanical Gardens, Hamilton, Ontario. Forty-two phages survived the isolation, purification, and storage processes. The majority of the phages in the collection were isolated from the soil surrounding trees exhibiting fire blight symptoms. Only five phages were isolated from infected aerial tissue in pear and apple orchards. To avoid any single-host selection bias, six bacterial host strains were used in the initial isolation and enrichment processes. Molecular characterization of the phages with a combination of PCR and restriction endonuclease digestions showed that six distinct phage types, described as groups 1 to 6, were recovered. Ten phage isolates were related to the previously characterized E. amylovora PEa1, with some divergence of molecular markers between phages isolated from different sites. A study of the host ranges of the phages revealed that certain types were unable to efficiently lyse some E. amylovora strains and that some isolates were able to lyse the epiphytic bacterium Pantoea agglomerans. Representatives from the six molecular groups were studied by electron microscopy to determine their morphology. The phages exhibited distinct morphologies when examined by an electron microscope. Group 1 and 2 phages were tailed and contractile, and phages belonging to groups 3 to 6 had short tails or openings with thin appendages. Based on morphotypes, the bacteriophages of E. amylovora were placed in the order Caudovirales, in the families Myoviridae and Podoviridae.Erwinia amylovora, a member of the Enterobacteriaceae, is the causal organism of fire blight, a serious disease of the pome fruit (19-21). The disease-causing organism is currently controlled by the antibiotic streptomycin and pruning. Another control measure became apparent when bacteriophages that were able to infect E. amylovora and an avirulent yellow bacterium commonly found in the orchard ecosystem were discovered (8, 12). The yellow bacterium was subsequently identified as Pantoea agglomerans (ϭErwinia herbicola). Erskine (11) recognized that E. amylovora phages may play an important role in the epidemiology of fire blight and proposed the use of phages released from the yellow saprophytic bacterium (lysogenic antagonists) as biological control agents (11).Richie (16, 17) isolated E. amylovora phages from aerial portions of fire blight-infected trees by using as a host strain E. amylovora 110 Rif (16). The phages, named PEa1 and PEa7, belonged to two distinct groups based on chemical and physical data. Recently, E. amylovora phages were collected from orchards with fire blight symptoms and were characterized by plaque morphology, PCR, restriction fragment polymorphisms, pulse-field gel electrophoresis, and host range studies (18).The objective of this work was to estimate the diversity of bacteriophages collected from orchards in southern Ontario that had ac...

Characterization of a broad-host-range flagellum-dependent phage that mediates high-efficiency generalized transduction in, and between, Serratia and Pantoea

“…Despite a 1998 study specifically assessing the prevalence of broad-host-range phages (Jensen et al, 1998), and recent examples of such phages in Gram-positive genera (Ammann et al, 2008;Chen & Novick, 2009), the consensus remains that phage infection tends to be species and strain specific. However, other examples of broad-host-range phages have been reported (for example, see Gill et al, 2003), and such a stringent model of phage-bacterium interactions fails to explain the abundance of phages in the environment. Neither of the bacterial strains used in this study has been genomically sequenced, and the P. agglomerans strain has not been characterized in detail.…”

Phenotypic and genetic diversity of Erwinia amylovora: the causal agent of fire blight

“…Several phages affecting E. amylovora strains were found (Schnabel and Jones 2001;Gill et al 2003). They differed in genome size and restriction patterns as well as in host range.…”

Phage therapy for plant disease control with a focus on fire blight

“…Ritchie and Klos [55,56] used a single host strain for isolation of phages and reported that the tested E. amylovora phages isolated from aerial parts of apple trees had a narrow host range, as they were able to lyse only isolates of E. amylovora and the closely related saprophyte, P. agglomerans. On the other hand, Gill et al [57] found that phages isolated using a mixture of multiple host strains had a broader host range. During our own investigations, we used several Hungarian E. amylovora strains for the isolation of phages (Schwarczinger and Kolozsvári Nagy, unpublished data).…”

“…The authors found that these phages were highly specific to E. amylovora. In 2003, Gill et al [57] estimated the diversity of bacteriophages collected from orchards in southern Ontario and reported the detailed characteristics of various sets of phages with broad host ranges. Forty-two phage isolates were identified within six distinct phage types based on molecular characterization of the phages using a combination of PCR and restriction endonuclease digestions.…”

“…Since the 1970s, more and more phages have been isolated and subsequently characterized in detail [54][55][56][57][58][59][60][61]. However, until recently, numerous efforts to control fire blight in orchards failed because phage populations declined in the absence of E. amylovora [23,56,58].…”