Characterization of pC7 from Lactobacillus paraplantarum C7 derived from Kimchi and development of lactic acid bacteria–Escherichia coli shuttle vector

Construction of a Recombinant Leuconostoc mesenteroides CJNU 0147 Producing 1,4-Dihydroxy-2-Naphthoic Acid, a Bifidogenic Growth Factor

1,4-Dihydroxy-2-naphthoic acid (DHNA), a precursor of menaquinone (vitamin K2), has an effect on growth stimulation of bifidobacteria and prevention of osteoporosis, making it a promising functional food material. Therefore, we tried to clone the menB gene encoding DHNA synthase from Leuconostoc mesenteroides CJNU 0147. Based on the genome sequence of Leu. mesenteroides ATCC 8293 (GenBank accession no., CP000414), a primer set (Leu_menBfull_F and Leu_menBfull_R) was designed for the PCR amplification of menB gene of CJNU 0147. A DNA fragment (1,190 bp), including the menB gene, was amplified, cloned into pGEM-T Easy vector, and sequenced. The deduced amino acid sequence of MenB (DHNA synthase) protein of CJNU 0147 had a 98% similarity to the corresponding protein of ATCC 8293. The menB gene was subcloned into pCW4, a lactic acid bacteria - E. coli shuttle vector, and transferred to CJNU 0147. The transcription of menB gene of CJNU 0147 (pCW4::menB) was increased, when compared with those of CJNU 0147 (pCW4) and CJNU 0147 (−). The DHNA was produced from it at a detectable level, indicating that the cloned menB gene of CJNU 0147 encoded a DHNA synthase which is responsible for the production of DHNA, resulting in an increase of bifidogenic growth stimulation activity.

Characterization of pR18, a novel rolling-circle replication plasmid from Lactobacillus plantarum

Lactobacillus plantarum PA18, a strain originally isolated from the leaves of Pandanus amaryllifolius, contains a pR18 plasmid. The pR18 plasmid is a 3211bp circular molecule with a G+C content of 35.8%. Nucleotide sequence analysis revealed two putative open reading frames, ORF1 and ORF2, in which ORF2 was predicted (317 amino acids) to be a replication protein and shared 99% similarity with the Rep proteins of pLR1, pLD1, pC30il, and pLP2000, which belong to the RCR pC194/pUB110 family. Sequence analysis also indicated that ORF1 was predicted to encode linA, an enzyme that enzymatically inactivates lincomycin. The result of Southern hybridization and mung bean nuclease treatment confirmed that pR18 replicated via the RCR mechanism. Phylogenetic tree analysis of pR18 plasmid proteins suggested that horizontal transfer of antibiotic resistance determinants without genes encoding mobilization has not only occurred between Bacillus and Lactobacillus but also between unrelated bacteria. Understanding this type of transfer could possibly play a key role in facilitating the study of the origin and evolution of lactobacillus plasmids. Quantitative PCR showed that the relative copy number of pR18 was approximately 39 copies per chromosome equivalent.

Characterization of endogenous plasmids from Lactobacillus salivarius UCC118

The genome of Lactobacillus salivarius UCC118 comprises a 1.83-Mb chromosome, a 242-kb megaplasmid (pMP118), and two smaller plasmids of 20 kb (pSF118-20) and 44 kb (pSF118-44). Annotation and bioinformatic analyses suggest that both of the smaller plasmids replicate by a theta replication mechanism. Furthermore, it appears that they are transmissible, although neither possesses a complete set of conjugation genes. Plasmid pSF118-20 encodes a toxin-antitoxin system composed of pemI and pemK homologs, and this plasmid could be cured when PemI was produced in trans. The minimal replicon of pSF118-20 was determined by deletion analysis. Shuttle vector derivatives of pSF118-20 were generated that included the replication region (pLS203) and the replication region plus mobilization genes (pLS208). The plasmid pLS203 was stably maintained without selection in Lactobacillus plantarum, Lactobacillus fermentum, and the pSF118-20-cured derivative strain of L. salivarius UCC118 (strain LS201). Cloning in pLS203 of genes encoding luciferase and green fluorescent protein, and expression from a constitutive L. salivarius promoter, demonstrated the utility of this vector for the expression of heterologous genes in Lactobacillus. This study thus expands the knowledge base and vector repertoire of probiotic lactobacilli.

Characterisation of pSMA23, a 3.5 kbp plasmid of Lactobacillus casei, and application for heterologous expression in Lactobacillus

The complete nucleotide sequence of plasmid pSMA23 isolated from Lactobacillus casei A23 was determined. Plasmid pSMA23 is a 3497bp circular molecule with a G+C content of 38.18%. Four putative open reading frames were identified. Based on homology, two orfs were identified as genes encoding replication initiation (Rep) and mobilisation (Mob) protein, respectively. Various regulatory regions like promoters, ribosome binding site (RBS), transcriptional terminators were deduced from the sequences of rep and mob. The origin of replication (dso) was predicted. Shuttle vectors pL142 and pL157 were constructed for Escherichia coli and Lactobacillus using rep gene and ori of pSMA23 for replication in Lactobacillus, the ori of the commercial vector pBluescript SkII+ for replication in E. coli, and the erythromycin and chloramphenicol resistance genes of pE194 and pC194, respectively, as selection markers. Transformants of E. coli and Lactobacillus were obtained on media containing erythromycin and chloramphenicol, respectively, suggesting expression of the ermC and cat194 genes in both organisms. The shsp gene of plasmid pSt04 of Streptococcus thermophilus encoding a small heat shock protein and the Lactobacillus plantarum cbh gene encoding conjugated bile salts hydrolase were cloned and successfully expressed in the heterologous host Lb. casei LK1 with the aid of pSMA23-derived vectors.

Characterization of pFMBL1, a small cryptic plasmid isolated from Leuconostoc mesenteroides SY2

A 4661bp cryptic plasmid, pFMBL1, was isolated from Leuconostoc mesenteroides SY2, an isolate from Kimchi, and characterized. Nucleotide sequence analysis revealed two open reading frames, orf1 and orf2. orf2 was 453bp in size and its translation product had 58% identity with a putative protein possibly involved in the replication of pTXL1, a cryptic plasmid from L. mesenteroides ssp. mesenteroides Y110. RNA transcript from orf2 was detected but not from orf1 or intergenic region. Minimum 3.5kb fragment encompassing orf1 and orf2 was required for the replication of pFMBL1 and employed for the construction of Escherichia coli-Leuconostoc shuttle vector, pSJ33E. L. mesenteroides SY1 (another Kimchi isolate), Leuconostoc ssp., and Lactobacillus brevis were successfully transformed with pSJ33E, and the transformation efficiencies were ranged between 1.1x10(1) and 4x10(5)transformants/microg DNA. No single-stranded DNA intermediate was detected from L. mesenteroides SY1 cells harboring pSJ33E, indicating that pFMBL1 probably replicated via theta-type mechanism. pSJ33E was stably maintained in L. mesenteroides SY1 in the absence of erythromycin (Em, 5 microg/ml) and after 1 month of daily subculturing in MRS broth without selective pressure, three percent of cells still retained pSJ33E.