ABIG, A GENOTYPICALLY NOVEL ABORTIVE INFECTION MECHANISM ENCODED BY PLASMID PCI750 OF LACTOCOCCUS-LACTIS SUBSP CREMORIS UC653

AbiG is an abortive infection (Abi) mechanism encoded by the conjugati ve plasmid pCI750 originally isolated from Lactococcus lactis subsp. c remoris UC653. Insensitivity conferred by this Abi manifested itself a s complete resistance to phi 712 (936 phage species) with only partial resistance to phi c2 (c2 species), The mechanism did not inhibit phag e DNA replication. The smallest subclone of pCI750 which expressed the Abi phenotype contained a 3.5-kb insert which encoded two potential o pen reading frames. abiGi (750 bp) and abiGii (1,194 bp) were separate d by 2 bp and appeared to share a single promoter upstream of abiGi, T hese open reading frames showed no significant homology to sequences o f either the DNA or protein databases; however, they did exhibit the t ypical low G+C content (29 and 27%, respectively) characteristic of la ctococcal abi genes, In fact, the G+C content of a 7.0-kb fragment inc orporating the abiG locus was 30%, which may suggest horizontal gene t ransfer from a species of low G+C content. In this context, it is nota ble that remnants of IS elements were observed throughout this 7.0-kb region.