Bacteriophage T4 resistant mutants of the plant pathogen Erwinia carotovora.

Bacterial lipopolysaccharide (LPS) has been implied in a variety of pathogenic and symbiotic plant-bacterium interactions. In order to study the role of LPS in pathogenicity of Erwinia carotovora, a broad host range phytopathogen, we isolated LPS defective mutants of two subspecies of Erwinia carotovora, subsp. carotovora (Ecc) and subsp. astroseptica (Eca). This was accomplished by using the Escherichia coli phage T4 as a selective agent. Screening of Erwinia isolates revealed that some of them were sensitive to T4 and thus T4 could be employed in mutant isolation. Fully T4 resistant mutants were all shown to be defective in their LPS structure. Preliminary pathogenicity tests on tobacco did not, however, reveal any decrease in the virulence of the LPS defective strains.