Cloning and manipulation of the Corynebacterium pseudotuberculosis recA gene for live vaccine vector development

Corynebacterium pseudotuberculosis is an intracellular bacterial pathogen causing a chronic abscessing disease in sheep and goats called caseous lymphadenitis. We are developing this bacterial species as a live vector system to deliver vaccine antigens to the animal immune system. Foreign genes expressed in bacterial hosts can be unstable so we undertook to delete the C. pseudotuberculosis chromosomal recA gene to determine whether a recA- background would reduce the frequency of recombination in cloned DNA. Homologous DNA recombination within an isogenic recA- C. pseudotuberculosis was 10-12-fold lower than that in the recA+ parental strain. Importantly, the recA mutation had no detectable affect upon the virulence of C. pseudotuberculosis in a mouse model. Taken together these results suggest that a recA- background may be useful in the further development of C. pseudotuberculosis as a vaccine vector.