The conjugative plasmid pTR2030 encodes two bacteriophage defense mechanisms in lactococci, restriction modification (R+/M+) and abortive infection (Hsp+)

Abstract

pTR2030 is a conjugative plasmid which encodes resistance to bacteriophage in lactococci by a mechanism that aborts the phage infection (Hsp+). Subcloning and in vivo deletion events showed that two independent mechanisms of resistance are located on a 13.6-kilobase Bg/II fragment cloned in pSA3; one mechanism is responsible for the abortive infection, and the other incodes a restriction modification system. The introduction of pTR2030 or the recombinant plasmid pTK6 resulted in the loss of a resident restriction modification plasmid in Lactococcus lactis NCK202 which was not previously identified.