Foreign gene expression in Corynebacterium pseudotuberculosis: development of a live vaccine vector

A defined phospholipase D mutant of Corynebacterium pseudotuberculosis, designated Toxminus, was used as a live vector to express and deliver a range of candidate vaccine antigens to sheep. Expression levels of the foreign genes in Toxminus were evaluated when directed from a number of different promoters, both constitutively expressed and inducible, as fusions with expressed genes including a signal sequence, and from chromosomal and episomal loci. In general expression levels were low and it appeared that some of the recombinant proteins were tolerated by C. pseudotuberculosis Toxminus better than others. Gene expression was however sufficiently high for three of the genes to elicit antibody responses specific to the recombinant protein following a single dose of the live Toxminus vector vaccine. This work suggests that C. pseudotuberculosis Toxminus has potential for development as a live veterinary vaccine vector.