Complete sequence and gene analysis of a cryptic plasmid pLU4 in Lactobacillus reuteri strain LU4 (KCTC 12397BP)

A cryptic plasmid, pLU4, was isolated and sequenced from Lactobacillus reuteri strain LU4, a probiotic strain isolated from human feces in Korea. pLU4 was 33,411 bp in size with a G + C content of 40.1% and contained 41 putative open reading frames (ORFs) of more than 120 bp. Functions were assigned to 24 of these ORFS by a homologous sequence search and domain characterization, and the rest were annotated as conserved hypothetical proteins or hypothetical proteins, based on highly similar proteins found in other Lactobacillus species. A region encoding a cluster of conjugative transfer genes (trs or tra) in pLU4 showed high similarity and co-linearity with the trs region of plca36 and tra region of pLgLA39 from L. casei str. Zhang and L. gasseri, respectively. This is the first report of a trs cluster sequence from plasmids found in L. reuteri species. Comparative gene analysis revealed that pLU4 also encodes highly conserved genes for plasmid replication and stability found in several other Lactobacillus plasmids, indicating that plasmids from the genus Lactobacillus may contribute to horizontal gene transfer and adaptation to the environment. The findings of this study provide important information about these industrially relevant phenotypes and give insight into the structure, function, and evolution of large Lactobacillus conjugative plasmids.