P-024 - Isolation of a novel Pectobacterium versatile bacteriophage that relies on lipopolysaccharide to recognize host cells

Bacterial soft rot affects various crop plants and is caused by taxonomically diverse bacteria, with Pectobacterium and Dickeya among the most prominent.  Control options are limited, as is common with bacterial phytopathogens, and it has been proposed that use of antagonistic microbes could contribute to future soft rot management.  To better understand the potential of antagonistic microbes, we used P. versatile strain B422 as host to isolate a lytic bacteriophage, which we determined to be part of the family Autographiviridae through whole genome sequencing.  Host range testing of this phage revealed that its host range is limited to a subset of P. versatile strains.  To understand the mechanism underlying the host specificity of this phage, we exposed a P. versatile B422 mutant library to the phage and resistant mutants were isolated.  Twenty-five mutants were confirmed to be resistant and the insertion site of the Tn in these mutants was determined via arbitrary PCR and Sanger sequencing.  We found that over 60% of the mutants were affected in genes relating to biosynthesis of lipopolysaccharide (LPS), suggesting that LPS is critical for infection.  Variability across P. versatile strains in these genes suggests that LPS sugar moiety variations could be the source of host strain specificity for the phage.  We anticipate that further understanding of interaction mechanisms between bacteriophages, host strains, and non-host strains will help guide rational strategies for disease control.