Insertional inactivation of determinants for Mg2+ and Co2+ transport as a tool for screening recombinant Lactococcus species clones.

Insertional inactivation of the plasmid-encoded determinants for Mg(2+) and Co(2+) transport, orf18/corA, provides a tool for screening recombinant clones in Lactococcus, based on the observation that overexpression of orf18/corA results in cell growth inhibition on certain concentrations of CoCl(2). The lacticin 3147 immunity gene, ltnI, was used to insertionally inactivate orf18/corA. The resulting clones were capable of growth on concentrations of CoCl(2) that were inhibitory to the parent strain. Since only 3 of 17 lactococcal starters naturally harbor corA, the system has potential as a screen for selecting recombinant lactococcal clones.