Spontaneous mutations in hlyD and tuf genes result in resistance of Dickeya solani IPO 2222 to phage φD5 but cause decreased bacterial fitness and virulence in planta

Lytic bacteriophages able to infect and kill Dickeya spp. can be readily isolated from virtually all Dickeya spp. containing environments, yet little is known about the selective pressure those viruses exert on their hosts. Two spontaneous D. solani IPO 2222 mutants (0.8% of all obtained mutants), DsR34 and DsR207, resistant to infection caused by lytic phage vB_Dsol_D5 (phi D5) were identified in this study that expressed a reduced ability to macerate potato tuber tissues compared to the wildtype, phage-susceptible D. solani IPO 2222 strain. Genome sequencing revealed that genes encoding: secretion protein HlyD (in mutant DsR34) and elongation factor Tu (EF-Tu) (in mutant DsR207) were altered in these strains. These mutations impacted the DsR34 and DsR207 proteomes. Features essential for the ecological success of these mutants in a plant environment, including their ability to use various carbon and nitrogen sources, production of plant cell wall degrading enzymes, ability to form biofilms, siderophore production, swimming and swarming motility and virulence in planta were assessed. Compared to the wild-type strain, D. solani IPO 2222, mutants DsR34 and DsR207 had a reduced ability to macerate chicory leaves and to colonize and cause symptoms in growing potato plants.