Characterization of Four Novel Plasmids from Lactobacillus plantarum BM4

Lactobacillus plantarum is a widespread probiotic bacterium. Many plasmids from L. plantarum have been identified to encode some important phenotypic traits including carbohydrate metabolism, bacteriocin synthesis, and exopolysaccharide production.
The aim of this study was to identify and characterize the native plasmids from L. plantarum BM4.
Lactobacillus plantarum BM4 was isolated from fermented meat in Guangxi Province, China, and characterized by 16S rRNA sequence. Four plasmids were isolated from L. plantarum BM4, sequenced, and characterized by the bioinformatics method. Moreover, the relative copy numbers of these plasmids were estimated using the droplet digital PCR method.
Four plasmids, designated as pBM1, pBM2, pBM3, and pBM4, were isolated from L. plantarum BM4. By nucleotide sequencing, pBM1, pBM2, pBM3, and pBM4 were characterized as having sizes of 6069 bp, 7042 bp, 8131 bp, and 8892 bp, and G contents of 37.5%, 36.7%, 36.4%, and 34.5%, respectively. Nucleotide sequence analysis revealed 8, 10, 10, and 10 putative open reading frames (ORFs) for pBM1, pBM2, pBM3, and pBM4 plasmids, respectively. Based on sequence alignment, only pBM2 contained replication protein RepB and rep3, which contained a putative repeat origin of replication segment, indicating that the pBM2 belongs to the pUCL287 subfamily of theta-type replicons. Finally, the relative copy numbers of pBM1-4 were estimated to be 82, 24, 34, and 16, copies, respectively.
Four novel plasmids were isolated from L. plantarum BM4 and characterized. These backbones can potentially be developed for use as a cloning or expressing vectors in biotechnology applications.