Phytopathogenic Dickeya species inflict large economic losses on a variety of crops. A
lack of effective chemical control methods has generated interest in the use of bacteriophages
(phages) as a novel tool for biocontrol. In the last decade, six phages have been isolated in
Belgium and Poland using Dickeya solani as the host. Previous work in this laboratory has
isolated ninety phages capable of infecting D. solani. The majority have been morphologically
classified as members of the Ackermannviridae family.
In agreement with findings in Salmonella and Klebsiella species, the capsule of D. solani
is a likely receptor of Ackermannviridae family phages. Analysis of D. solani strains carrying
reporter fusions suggested that the capsule genes are expressed in response to nutritional
stress, however disruption of the capsular polysaccharide cluster did not significantly impact
virulence.
Experiments assessing capsular polysaccharide as a putative receptor for Ackermannviridae family phages in nosocomial pathogen Serratia produced inconclusive results. Phageresistance due to random transposon mutagenesis identified genes encoding transcription
factors and regulators, but none directly linked to capsular polysaccharide production.
Thirteen phages were capable of infecting a wider host range of Dickeya species. Morphological and genomic analysis showed that six were Podoviridae family members, whilst
the other seven were Myoviridae family members. These are part of the recently defined
‘hairy Myoviridae’, characterised by a distinct morphology. Another member of this grouping
was isolated during this study, but is more closely related to phages of Erwinia amylovora.
A subset of the Ackermannviridae family phages were shown to be capable of facilitating
transduction. This makes them unsuitable for use in the environment due to the risk of
deleterious horizontal gene transfer. This is also true for the Myoviridae family members, but
not for one of the Podoviridae family members. This phage could therefore be a promising
candidate for therapeutic use.BBSRC Doctoral Training Partnershi
