Insertional inactivation of determinants for Mg²⁺ and Co ²⁺ transport as a tool for screening recombinant Lactococcus species clones

Insertional inactivation of the plasmid-encoded determinants for Mg ²⁺ and Co²⁺ transport, orf18/corA, provides a tool for screening recombinant clones in Lactococcus, based on the observation that overexpression of orfl8/corA results in cell growth inhibition on certain concentrations of CoCl₂. The lacticin 3147 immunity gene, ltnI, was used to insertionally inactivate orfl8/corA. The resulting clones were capable of growth on concentrations of CoCl₂ that were inhibitory to the parent strain. Since only 3 of 17 lactococcal starters naturally harbor cor A, the system has potential as a screen for selecting recombinant lactococcal clones.