Potential of conjugal transfer as a strategy for the introduction of recombinant genetic material into strains of Lactobacillus helveticus

Cointegrates generated between a plasmid pIP501 deletion derivative (pVA797 ) and nonconjugative shuttle vector pSA3 were confirmed as capable of excon jugation from lactococci into a range of strains of Lactobacillus helveticu s with the concomitant expression of a recombinant gene. The plasmid cointe grate that was formed appeared to be segregationally stable at 37 degrees C in some host strains. In all strains, however, the plasmid became increasi ngly unstable as the incubation temperature was raised. The technique offer s not only a generalized method for the introduction of novel genetic mater ial into this important industrial microbe but also the possibility of expl oiting the thermal sensitivity of the plasmid to enable it to act as a deli very system for the integration of cloned genes into the bacterial chromoso me, at restrictive temperatures, by recombination at regions of homology.