Mutation in a gene required for lipopolysaccharide and enterobacterial common antigen biosynthesis affects virulence in the plant pathogen Erwinia carotovora subsp atroseptica

Spontaneous bacteriophage-resistant mutants of the phytopathogen Erwinia caratovora subsp, atroseptica (Eca) SCRI1043 were isolated and, out of 40, two were found to exhibit reduced virulence in planta, One of these mutants, A5/22, showed multiple fell surface defects including alterations in synthesis of outer membrane proteins, lipopolysaccharide (LPS), enterobacterial common antigen (ECA), and flagella, Mutant A5/22 also showed reduced synthesis of the exoenzymes pectate lyase (Pel) and cellulase (Cel), major virulence factors for this pathogen, Genetic analysis revealed the pronounced pleiotropic mutant phenotype to be due to a defect in a single gene (rffG) that, in Escherichia coli, is involved in the production of EGA. We also show that while other enteric bacteria possess duplicate homologues of this gene dedicated separately to synthesis of LPS and EGA, Eca has a single gene.