Antiserum againstXanthomonasphytopathogen inhibits host—Pathogen interaction in seedlings ofBrassica campestris

Xanthomonas campestris pv campestris (X.c.c.), the causal agent of crucifer black rot, causes turnip seedlings to collapse and rot. X.c. pv vitians (X.c.v.) is a non-pathogen of turnips and triggers a resistance response. Transconjugants of X.c.c., containing defined fragments of DNA from X.c.v., which have reduced pathogenicity to turnips were constructed. A polyclonal antiserum raised against X.c.v. restored the pathogenicity of one of these transconjugants. Antiserum ‘purged’ by reaction with sonicates of X.c.c. was equally effective in restoring pathogenicity. The purged antiserum recognised considerably fewer components than the original antiserum following Western blotting of bi-dimensional gels. This subset of antigens appeared to be localised primarily on the bacterial cell surface. The results indicate the potential use of purged polyclonal antisera in identifying bacterial determinants that trigger host resistance responses.