Nucleotide sequence and analysis of pBL1, a bacteriocin-producing plasmid from Lactococcus lactis IPLA 972

The complete sequence of the 10.9-kbp bacteriocinogenic plasmid pBL1 from L actococcus lactis subsp. lactis IPLA 972 has been determined. Thirteen ORFs were encountered, of which 5 were incomplete. pBL1 proved to be a narrow-h ost-range plasmid which replicates neither in Bacilus subtilis nor in Lacto bacillus spp. The structural organization of the pBL1 replication region wa s highly similar to other well-known theta-replicating plasmids of lactococ ci. at both the untranslated (the replication origin) and the translated (r epB and orfX) sequences. As in other plasmids the product of orfX was not n ecessary for plasmid replication. However, it was shown to be involved in p lasmid stability. Three genes organized in an operon-like structure encompa ssed, most likely, the bacteriocin-encoding region. Upstream of the origin of replication a nicking site (oriT) was found. This oriT sequence proved t o be functional by mobilization of plasmids wearing it. One complete and se veral partial IS elements were identified on pBL1. (C) 2000 Academic Press.