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Isolation and characterization of novel soilborne lytic bacteriophages infecting Dickeya spp. biovar 3 (‘D. solani’)

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Abstract

Nine bacteriophages infecting Dickeya spp. biovar 3 (‘Dickeya solani’) were isolated from soil samples collected in different regions in Poland. The phages have a typical morphology of the members of the order Caudovirales, family Myoviridae, with a head diameter of c. 90–100 nm and tail length of c. 120–140 nm. In host range experiments, phage ϕD5 expressed the broadest host range, infecting members of all Dickeya spp., and phage ϕD7 showed the narrowest host range, infecting isolates of Dickeya dadantii and ‘D. solani’ only. None of the phages was able to infect Pectobacterium spp. isolates. All phages were prone to inactivation by pH 2, temperature of 85°C and by UV illumination for 10 min (50 mJ cm−2). Additionally, phages ϕD1, ϕD10 and ϕD11 were inactivated by 5 m NaCl and phage ϕD2 was inactivated by chloroform. Phages ϕD1, ϕD5, ϕD7 and ϕD10 were characterized for optimal multiplicity of infection and the rate of adsorption to the bacterial cells. The latent period was 30 min for ϕD1, 40 min for ϕD5, 20–30 min for ϕD7 and 40 min for ϕD10. The estimated burst size was c. 100 plaque-forming units per infected cell. The bacteriophages were able to completely stop the growth of ‘D. solaniin vitro and to protect potato tuber tissue from maceration caused by the bacteria. The potential use of bacteriophages for the biocontrol of biovar 3 Dickeya spp. in potato is discussed.

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