SEGREGATIONAL STABILITY AND COPY NUMBER OF THE THETA-TYPE LACTOCOCCALREPLICON REP22 IN LACTOCOCCUS

Rep22 is the replication region of the lactococcal theta replicating p UCL22 plasmid. The copy number of Rep22-based plasmids in Lactococcus was determined by using a chromosomal DNA fragment from Lactococcus la ctis subsp. lactis MMS368 as reference. Segregational behavior appeare d to be linked to copy number and therefore indicated random distribut ion of copies to daughter cells. Nevertheless, an active partitioning system was detected in the parental plasmid pUCL22. A pUCL22 138-bp DN A restriction fragment bearing a perfect 18-bp inverted repeat was inv olved in the improvement of Rep22-based plasmid segregational stabilit y during discontinuous exponential growth.