Characterization of a small erythromycin resistance plasmid pLFE1 from the food-isolate Lactobacillus plantarum M345

This paper reports the complete 4031 bp nucleotide sequence of the small erythromycin resistance plasmid pLFE1 isolated from the raw-milk cheese isolate Lactobacillus plantarum M345. Analysis of the sequence revealed the coding regions for the erythromycin resistance determinant Erm(B). A replication initiation protein RepB was identified belonging to the RepB proteins of the pMV158 family of rolling-circle replicating plasmids.

The transcriptional repressor protein CopG and a small counter transcribed RNA, two elements typically involved in replication control within this family were also found. A putative replication initiation site including a single-strand origin (sso) -like region succeeded by a characteristic pMV158 family double-strand origin (dso) was located upstream of the replication region.

An open reading frame following a typical origin of transfer (oriT) site and coding for a putative truncated mobilization (Mob) protein with a size of 83 aa was detected. The product of the putative mob gene showed large similarity to the N-terminal region of the pMV158 family of Pre/Mob proteins, but was much smaller than other proteins of this family.

We therefore suggest that the Mob function in pLFE1 is supplied in trans from another plasmid present in L plantarum M345. Filter-mating experiments showed that pLFE1 has a broad host-range with transconjugants obtained from Lactobacillus rhamnosus, Lactococcus lactis, Listeria innocua, the opportunistic pathogen Enterococcus faecalis and the pathogen Listeria monocytogenes.