Optimized transformation by electroporation ofLactobacillus plantarum strains with plasmid vectors

Overexpression of Capsular Polysaccharide Biosynthesis Protein in Lactobacillus plantarum P1 to Enhance Capsular Polysaccharide Production for Di-n-butyl Phthalate Adsorption

Exopolysaccharides (EPSs) such as capsular polysaccharide (CPS) are important bioactive carbohydrate compounds and are often used as bioenrichment agents and bioabsorbers to remove environmental pollutants like di-n-butyl phthalate (DBP). Among the EPS-producing bacteria, lactic acid bacteria (LAB) have gained the most attention. As generally recognized as safe (GRAS) microorganisms, LAB can produce EPSs having many different structures and no health risks. However, EPS production by LAB does not meet the needs of large-scale application on an industrial scale. Here, the capA gene (encoding CPS biosynthesis protein) was overexpressed in Lactobacillus plantarum P1 to improve the production of EPSs and further enhance the DBP adsorption capability. Compared with P1, the CPS production in capA overexpressed strain was increased by 11.3 mg/l, and the EPS thickness was increased from 0.0786 ± 0.0224 μm in P1 to 0.1160 ± 0.0480 μm in P1-capA. These increases caused the DBP adsorption ratio of P1-capA to be doubled. Overall, the findings in this study provide a safe method for the adsorption and removal of DBP.

A food-grade fimbrial adhesin FaeG expression system inLactococcus lactisandLactobacillus casei

Enterotoxigenic Escherichia coli (ETEC) infection is the major cause of diarrhea in neonatal piglets. The fimbriae as colonizing factor in the pathogenesis of ETEC constitute a primary target for vaccination against ETEC. Lactic acid bacteria (LAB) are attractive tools to deliver antigens at the mucosal level. With the safety of genetically modified LAB in mind, a food-grade secretion vector (pALRc or pALRb) was constructed with DNA entirely from LAB, including the replicon, promoter, signal peptide, and selection marker alanine racemase gene (alr). To evaluate the feasibility of the system, the nuclease gene (nuc) from Staphylococcus aureus was used as a reporter to be expressed in both Lactococcus lactis and Lactobacillus casei. Subsequently, the extracellular secretion of the fimbrial adhesin FaeG of ETEC was confirmed by Western blot analysis. These results showed that this food-grade expression system has potential as the delivery vehicle for the safe use of genetically modified LAB for the development of vaccines against ETEC infection.

Electroporation enhances the ability of lactobacilli to remove cholesterol

The objective of the present study was to evaluate the effect of electroporation on the membrane properties of lactobacilli and their ability to remove cholesterol in vitro. The growth of lactobacilli cells treated at 7.5 kV/cm for 4 ms was increased by 0.89 to 1.96 log(10) cfu/mL upon fermentation at 37 °C for 20 h, the increase being attributed to the reversible and transient formation of pores and defragmentation of clumped cells. In addition, an increase of cholesterol assimilation as high as 127.2% was observed for most cells electroporated at a field strength of 7.5 kV/cm for 3.5 ms compared with a lower field strength of 2.5 kV/cm. Electroporation also increased the incorporation of cholesterol into the cellular membrane, as shown by an increased cholesterol:phospholipids ratio (50.0-59.6%) upon treatment at 7.5 kV/cm compared with treatment at 2.5 kV/cm. Saturation of cholesterol was observed in different regions of the membrane bilayer such as upper phospholipids, apolar tail, and polar heads, as indicated by fluorescence anisotropy using 3 fluorescent probes. Electroporation could be a useful technique to increase the ability of lactobacilli to remove cholesterol for possible use as cholesterol-lowering adjuncts in the future.

Prophylactic effect of Lactobacillus oral vaccine expressing a Japanese cedar pollen allergen

Lactic acid bacteria (LAB) represent an attractive delivery vehicle for oral allergy vaccine because of their safety as a food microorganism as well as their potent adjuvant activity triggering anti-allergic immune response. Here, we report the generation of recombinant LAB expressing a major Japanese cedar pollen allergen Cry j 1 (Cry j 1-LAB), and their prophylactic effect in vivo. To facilitate heterologous expression, the codon usage in the Cry j 1 gene was optimized for the host LAB strain Lactobacillus plantarum by the recursive PCR-based exhaustive site-directed mutagenesis. Use of the codon-optimized Cry j 1 cDNA and a lactate dehydrogenase gene fusion system led to a successful production of recombinant Cry j 1 in L. plantarum NCL21. We also found that oral vaccination with the Cry j 1-LAB suppressed allergen-specific IgE response and nasal symptoms in a murine model of cedar pollinosis.

Characterization of a cryptic plasmid pD403 from Lactobacillus plantarum and construction of shuttle vectors based on its replicon

A cryptic plasmid pD403 was isolated from Lactobacillus plantarum D403 derived from fermented dairy products. It was 2,791 bp in size with a G+C content of 37%. Nucleotide sequence analysis revealed two open reading frames, orf1 and orf2. ORF1 (318 amino acids) was identified as a replication protein (RepA). ORF2 (137 amino acids) shared 31% similarity with the transcriptional regulator of Ralstonia pickettii 12D. Functional investigation indicated that ORF2 (Tra) had the ability of improving the transformation efficiency. The origin of replication was predicted, suggesting that pD403 was a rolling-circle-replication (RCR) plasmid. An Escherichia coli/Lactobacillus shuttle vector pCD4032 was constructed based on the pD403 replicon, and proved to be successfully transformed into various lactobacilli including Lactobacillus casei, Lactobacillus plantarum, Lactobacillus fermentum, and Lactobacillus brevis. The transformation efficiencies were ranged from 1.3 x 10(2) to 7 x 10(4) transformants per microgram DNA. Furthermore, an expression vector pCD4033 was developed with the promoter of the lactate dehydrogenase from Lactobacillus delbrueckii 11842. The green fluorescent protein (gfp) as a reporter was expressed successfully in various lactobacilli tested, suggesting that the expression vector pCD4033 had the potential to be used as a molecular tool for heterologous gene cloning and expression in lactobacilli.

ATP-dependent leader peptide cleavage by NukT, a bifunctional ABC transporter, during lantibiotic biosynthesis

NukT, a possible ABC transporter maturation and secretion (AMS) protein, may contribute to the cleavage of the leader peptide of NukA, which is the prepeptide of the lantibiotic nukacin ISK-1, and to nukacin ISK-1 transport. In this study, we reconstituted in vitro peptidase activity of the full-length NukT overexpressed in inside-out membrane vesicles of Staphylococcus carnosus TM300. We found that the presence of unusual amino acids in NukA is required for leader peptide cleavage. Furthermore, NukT peptidase activity was inhibited by phenylmethylsulfonyl fluoride, a serine/cysteine protease inhibitor; this finding strongly suggests that NukT, like other AMS proteins, is a cysteine protease. Interestingly, NukT peptidase activity depended on ATP hydrolysis. These results suggest that the N-terminal peptidase domain of NukT may cooperatively function with the C-terminal ATP-binding domain. This is the first in vitro study on lantibiotics that reports the processing mechanism of a full-length bifunctional ABC transporter.

Transformation of Lactobacillus plantarum by electroporation with in vitro modified plasmid DNA

An improved method for the electrotransformation of Lactobacillus plantarum CECT 220 (ATCC 8014) with plasmid DNA isolated from Escherichia coli is described. The two main modifications with respect to existing methods are: (i) isolation of plasmid DNA from E. coli JM110 grown in minimal medium and (ii) in vitro modification of the DNA by cell-free extracts of the host L. plantarum. Optimal electrotransformation was obtained with exponentially growing cells of L. plantarum concentrated to 6x10(9) cfu ml-1, with electric pulses of 13 kV cm-1 in cuvettes with 1 mm inter-electrode distance. We consider that this method constitutes a useful tool for routine manipulation of L. plantarum, and can probably be extended to other lactic acid bacteria.

Heterologous expression and functional analysis of the gene cluster for the biosynthesis of and immunity to the lantibiotic, nukacin ISK-1

Nukacin ISK-1 is a lantibiotic produced by Staphylococcus warneri ISK-1. The gene cluster of nukacin ISK-1 consists of at least nukAMTFEG, ORF1 and ORF7. In this study, we demonstrated the heterologous production of nukacin ISK-1 in Lactococcus lactis by the artificial polycistronic expression of nukAMTFEG-ORF7 under the control of the nisin-controlled expression (NICE) system. Consequently, the recombinant L. lactis showed antimicrobial activity. Mass analysis clarified the presence of nukacin ISK-1 produced in the culture supernatant. These results suggested that the recombinant L. lactis produced nukacin ISK-1 heterologously. Inactivation of nukA, -M or -T resulted in the complete loss of the nukacin ISK-1 production phenotype. This finding suggested that nukAMT are indispensably associated with the biosynthesis of nukacin ISK-1. To our knowledge, this is the first report of the heterologous production of lantibiotic using the NICE system.

Extent of genetic lesions of the arginine and pyrimidine biosynthetic pathways in Lactobacillus plantarum, L. paraplantarum, L. pentosus, and L. casei: prevalence of CO(2)-dependent auxotrophs and characterization of deficient arg genes in L. plantarum

Lactic acid bacteria require rich media since, due to mutations in their biosynthetic genes, they are unable to synthesize numerous amino acids and nucleobases. Arginine biosynthesis and pyrimidine biosynthesis have a common intermediate, carbamoyl phosphate (CP), whose synthesis requires CO(2). We investigated the extent of genetic lesions in both the arginine biosynthesis and pyrimidine biosynthesis pathways in a collection of lactobacilli, including 150 strains of Lactobacillus plantarum, 32 strains of L. pentosus, 15 strains of L. paraplantarum, and 10 strains of L. casei. The distribution of prototroph and auxotroph phenotypes varied between species. All L. casei strains, no L. paraplantarum strains, two L. pentosus strains, and seven L. plantarum strains required arginine for growth. Arginine auxotrophs were more frequently found in L. plantarum isolated from milk products than in L. plantarum isolated from fermented plant products or humans; association with dairy products might favor arginine auxotrophy. In L. plantarum the argCJBDF genes were functional in most strains, and when they were inactive, only one gene was mutated in more than one-half of the arginine auxotrophs. Random mutation may have generated these auxotrophs since different arg genes were inactivated (there were single point mutations in three auxotrophs and nonrevertible genetic lesions in four auxotrophs). These data support the hypothesis that lactic acid bacteria evolve by progressively loosing unnecessary genes upon adaptation to specific habitats, with genome evolution towards cumulative DNA degeneration. Although auxotrophy for only uracil was found in one L. pentosus strain, a high CO(2) requirement (HCR) for arginine and pyrimidine was common; it was found in 74 of 207 Lactobacillus strains tested. These HCR auxotrophs may have had their CP cellular pool-related genes altered or deregulated.

Development of a host-vector system for Lactobacillus plantarum L137 isolated from a traditional fermented food produced in the Philippines

Lactobacillus plantarum NC13, a strain derived from the L. plantarum strain L137 isolated from a traditional fermented food produced in the Philippines, contains 9 of the 15 plasmids in the parental strain. To construct a shuttle vector between L. plantarum and Escherichia coli for genetic manipulation of L137 and its derivatives, recombinant plasmids were prepared by using the 9-plasmid DNA mixture and an E. coli vector, pBluescript II SK+. The resultant recombinant plasmids were re-transferred to L. plantarum NCL21, an NC13-derived strain cured of 3 of the 9 plasmids, and 3 recombinant plasmids were obtained. The smallest plasmid, pRN14, contained a small cryptic plasmid, pLTK2, which is one of the plasmids in L. plantarum L137. Thus, the complete nucleotide sequence of pLTK2 was determined. The pLTK2 is 2295 bp in length, and has a major open reading frame of 951 bp. An encoded sequence of 317-amino acids showed extensive similarity with genes encoding replication protein (repA). A putative replication origin in pLTK2 also showed high homology to those of other gram-positive bacterial plasmids that replicate by the rolling circle mechanism. The shuttle vector pRN14 contained the erythromycin resistance gene and the ColE1 and pLTK2 replication origins. Transformation of L. plantarum strains with pRN14 by electroporation was optimized to give a transformation efficiency of 2 x 10(4) transformants/ mug plasmid. Plasmid pRN14 was stably maintained in strain NCL21, as well as in L. casei K95-5.

Characterization of cadmium uptake in Lactobacillus plantarum and isolation of cadmium and manganese uptake mutants

Two different Cd(2+) uptake systems were identified in Lactobacillus plantarum. One is a high-affinity, high-velocity Mn(2+) uptake system which also takes up Cd(2+) and is induced by Mn(2+) starvation. The calculated K(m) and V(max) are 0.26 microM and 3.6 micromol g of dry cell(-1) min(-1), respectively. Unlike Mn(2+) uptake, which is facilitated by citrate and related tricarboxylic acids, Cd(2+) uptake is weakly inhibited by citrate. Cd(2+) and Mn(2+) are competitive inhibitors of each other, and the affinity of the system for Cd(2+) is higher than that for Mn(2+). The other Cd(2+) uptake system is expressed in Mn(2+)-sufficient cells, and no K(m) can be calculated for it because uptake is nonsaturable. Mn(2+) does not compete for transport through this system, nor does any other tested cation, i.e., Zn(2+), Cu(2+), Co(2+), Mg(2+), Ca(2+), Fe(2+), or Ni(2+). Both systems require energy, since uncouplers completely inhibit their activities. Two Mn(2+)-dependent L. plantarum mutants were isolated by chemical mutagenesis and ampicillin enrichment. They required more than 5,000 times as much Mn(2+) for growth as the parental strain. Mn(2+) starvation-induced Cd(2+) uptake in both mutants was less than 5% the wild-type rate. The low level of long-term Mn(2+) or Cd(2+) accumulation by the mutant strains also shows that the mutations eliminate the high-affinity Mn(2+) and Cd(2+) uptake system.

Genetics of lactobacilli in food fermentations

Lactobacilli play a substantial role in food biotechnology and influence our quality of life by their fermentative and probiotic properties. Despite their obvious importance in fermentation ecology and biotechnology only recent years have brought some insight into the genetics of lactobacilli. These genetic investigations allow the elucidation of traits determinative for competitiveness and ecology and thus product safety and quality. They have concentrated only on a small selection of lactobacilli whereas others are hardly touched or remained recalcitrant to genetic analysis and manipulation. The knowledge gained on the biochemistry, physiology, ecology and especially genetics is a prerequisite for the deliberate application and improved handling of lactobacilli in traditional and novel applications. In this review, the achievements in the genetics of lactobacilli are described including detection systems, genetic elements, host vector systems, gene cloning and expression and risk assessment of genetically engineered lactobacilli.

Oxygen-dependent regulation of the expression of the catalase gene katA of Lactobacillus sakei LTH677

The catalase gene katA of Lactobacillus sakei LTH677 was cloned and expressed in Escherichia coli UM2, Lactobacillus casei LK1, and Lactobacillus curvatus LTH1432. The last host is a catalase-deficient plasmid-cured derivative of a starter organism used in meat fermentation. The regulation of katA expression was found to be the same in L. sakei LTH677 and the recombinant strains. The addition of H2O2 to anaerobic cultures, as well as a switch to aerobic conditions, resulted in a strong increase in KatA activity. The expression was investigated in more detail with L. sakei LTH677 and L. curvatus LTH4002. The recombinant strain LTH4002 did not accumulate H2O2 under glucose-limited aerobic conditions and remained viable in the stationary phase. Under inductive conditions, the katA-specific mRNA and the apoenzyme were synthesized de novo. Deletion derivatives of the katA promoter were produced, and the regulatory response was investigated by fusion to the beta-glucuronidase reporter gene gusA and expression in L. sakei LTH677. The fact that gene expression was subject to induction was confirmed at the level of transcription and protein synthesis. A small putative regulatory sequence of at least 25 bp was identified located upstream of the -35 site. Competition experiments performed with L. sakei LTH677 harboring the fusion constructs consisting of the katA promoter and gusA revealed that an activator protein is involved in the transcriptional induction of katA.

Plasmids in Lactobacillus

This review describes Lactobacillus plasmids on distribution, structure, function, vector construction, vector stability, application, and prospective. About 38% of species of the genus Lactobacillus were found to contain plasmids with different sizes (from 1.2 to 150 kb) and varied numbers (1 or more). Some Lactobacillus plasmids with small sizes were highly similar to those of single strand plasmids from other Gram-positive bacteria. The extensive sequence homologies of plus origins, replication initiation proteins, minus origins, cointegration sites, and the presence of single strand intermediates supported the fact that these small Lactobacillus plasmids replicate with a rolling-circle replication mechanism. Some Lactobacillus plasmid replicons were of broad host range that could function in other Gram-positive bacteria, and even in Escherichia coli, while replicons of other Gram-positive bacteria also function in Lactobacillus. Although most Lactobacillus plasmids are cryptic, some plasmid-encoded functions have been discovered and applied to vector construction and Lactobacillus identification, detection, and modification.

Arginine biosynthesis and regulation in Lactobacillus plantarum: the carA gene and the argCJBDF cluster are divergently transcribed

A cluster of citrulline biosynthetic genes has been cloned and sequenced from a fragment of Lactobacillus plantarum CCM 1904 (ATCC 8014) DNA isolated as complementing a Bacillus subtilis argF mutation. The gene order was carA-argCJBDF, with carA transcribed divergently from the arg cluster. Although other gram-positive bacteria show similar arg clusters, this arrangement for carA is thus far unprecedented. Downstream from the arg cluster, two open reading frames (ORF7 and ORF8) having unknown functions were found. Sequence analysis of the end of a 10.5-kb cloned DNA fragment showed that argF was 3.5 kb from the ldhL gene coding for L-(+)-lactate dehydrogenase. A tree representation of amino acid sequence clustering relationships of 31 ornithine carbamoyltransferases (OTCases) from various organisms revealed two prokaryotic groups: one with ArgF of L. plantarum and one with ArgF of B. subtilis, which are paralogous. This divergence was not observed in vivo because an L. plantarum argF mutant (AM 1215) harboring no OTCase activity was complemented by the argF genes of L. plantarum and B. subtilis. No OTCase activity was detectable when L. plantarum was grown in the presence of saturating amounts of arginine or citrulline. Arginine may repress the citrulline biosynthetic genes in L. plantarum by using 11 identified DNA motifs which resemble the Escherichia coli ARG box consensus and which are in most cases separated by multiples of 11 bp, corresponding to a DNA helical turn. The carA and argCJBDF genes are divergently transcribed. Their putative promoters are 6 bp apart and are partially overlapped by putative ARG boxes, suggesting concerted transcription regulation.

Structure and organisation of the pyrimidine biosynthesis pathway genes in Lactobacillus plantarum: a PCR strategy for sequencing without cloning

This report describes the sequence and structural organisation of the pyrimidine biosynthesis pathway genes of Lactobacillus plantarum CCM 1904. It also describes an in vitro technique based on PCR for sequencing without cloning. This new technique was developed because it was impossible to clone certain parts of the L. plantarum genomic DNA in the Escherichia coli host. L. plantarum pyr genes are organised as a 9.8-kb operon with the following order: pyrR, pyrB, pyrC, pyrAA, pyrAB, pyrD, pyrF and pyrE. There are two major differences from the pyrimidine operons of Bacillus subtilis (Quinn et al., J. Bacteriol. 266 (1991) 9113-9127; Turner et al., J. Bacteriol, 176 (1994) 3708-3722) and Bacillus caldolyticus (Ghim et al., Microbiology 140 (1994) 479-491): the absence of pyrP encoding for uracil permease, and the absence of an open reading frame named orf2, whose function is unknown. Two mutually exclusive stem-loop structures were predicted at the 5'-end of L. plantarum pyr mRNA; this operon could be regulated by transcriptional attenuation under the control of PyrR. Complementation of E. coli pyrD, pyrF and pyrE mutants was obtained with a L. plantarum genomic DNA library. Alignment of the L. plantarum Pyr proteins with other known procaryotic Pyr proteins indicates that they display highly conserved regions in Gram-positive and Gram-negative bacteria.

Cloning and expression of the Zymomonas mobilis "production of ethanol" genes in Lactobacillus casei

This study describes the expression of the Zymomonas mobilis genes coding for pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) in Lactobacillus casei 686. To promote transcription, the promoter and ribosome binding site (RBS) from the Lactococcus lactis subsp. lactis-derived vector, pMGE36e, were inserted upstream of the pdc gene. The former sequences were positioned such that translation of pdc was coupled to translation of an 81-base pair open reading frame terminating within the pdc initiation site. The recombinant plasmid (pRSG02) was electroporated into L. casei, and transformants were obtained. Northern analysis confirmed the production of a 3. 1-kb transcript corresponding to the predicted size of the PET operon. Western blot analyses revealed that the recombinant strain expressed both enzymes. The recombinant produced more than twice the ethanol produced by the parental L. casei strain.

Efficient transformation of Lactobacillus sake by electroporation

A procedure to transform intact Lactobacillus sake cells by electroporation was developed through a systematic examination of the effect of changes in various parameters on the transformation efficiency of Lact. sake strain 64F. The most critical factors were found to be the electrical parameters, the composition of washing and electroporation/storage solutions, and the presence of MgCI₂ in the expression medium. Under optimal conditions transformation efficiencies up to 10⁷ transformants (μg supercoiled DNA)^-1 were obtained. The optimized procedure was successfully applied to other Lact. sake strains and consistently yielded from 10⁴ to 10⁷ transformants (μg supercoiled DNA)^-1.

Use of homologous expression-secretion signals and vector-free stable chromosomal integration in engineering of Lactobacillus plantarum for alpha-amylase and levanase expression

The genuine alpha-amylase gene from Bacillus licheniformis (amyL) is not expressed in Lactobacillus plantarum, but replacement of the amyL promoter by a strong L. plantarum promoter leads to efficient expression of the gene and secretion of more than 90% of the alpha-amylase into the culture supernatant. A series of L. plantarum genetic cassettes (transcription and translation with or without secretion) were cloned by translation fusion of random DNA fragments to the silent amyL coding frame in the pGIP212 probe vector (P. Hols, A. Baulard, D. Garmyn, B. Delplace, S. Hogan, and J. Delcour, Gene 118:21-30, 1992). Five different cassettes were sequenced and found to harbor genetic signals similar to those of other gram-positive bacteria. The functions of the cloned cassettes and the cassettes isolated previously from Enterococcus faecalis were compared in E. faecalis and L. plantarum, respectively. All signals were well recognized in L. plantarum, but cassettes isolated from L. plantarum led to a low level of amylase production in E. faecalis, suggesting that the L. plantarum signals are more species specific. Six transcriptional or translational fusions were constructed to express the Bacillus subtilis levanase gene (sacC) in L. plantarum. All of these constructions were capable of inducing levanase production and secretion in the culture supernatant, and, furthermore, L. plantarum strains harboring the most efficient fusions could grow in MRS medium containing inulin as the major carbon source. Finally, a two-step chromosomal integration procedure was used to achieve efficient stabilization of an amylase construction without any residual resistance marker or vector sequence.