Integration and expression of alpha-amylase and endoglucanase genes in the Lactobacillus plantarum chromosome

Current Progress in Production of Building-Block Organic Acids by Consolidated Bioprocessing of Lignocellulose

Several organic acids have been indicated among the top value chemicals from biomass. Lignocellulose is among the most attractive feedstocks for biorefining processes owing to its high abundance and low cost. However, its highly complex nature and recalcitrance to biodegradation hinder development of cost-competitive fermentation processes. Here, current progress in development of single-pot fermentation (i.e., consolidated bioprocessing, CBP) of lignocellulosic biomass to high value organic acids will be examined, based on the potential of this approach to dramatically reduce process costs. Different strategies for CBP development will be considered such as: (i) design of microbial consortia consisting of (hemi)cellulolytic and valuable-compound producing strains; (ii) engineering of microorganisms that combine biomass-degrading and high-value compound-producing properties in a single strain. The present review will mainly focus on production of organic acids with application as building block chemicals (e.g., adipic, cis,cis-muconic, fumaric, itaconic, lactic, malic, and succinic acid) since polymer synthesis constitutes the largest sector in the chemical industry. Current research advances will be illustrated together with challenges and perspectives for future investigations. In addition, attention will be dedicated to development of acid tolerant microorganisms, an essential feature for improving titer and productivity of fermentative production of acids.

Criteria for lactic acid bacteria screening to enhance silage quality

The main challenge of ensiling is conserving the feed through a fermentative process that results in high nutritional and microbiological quality while minimizing fermentative losses. This challenge is of growing interest to farmers, industry and research and involves the use of additives to improve the fermentation process and preserve the ensiled material. Most studies involved microbial additives; lactic acid bacteria (LAB) have been the focus of much research and have been widely used. Currently, LABs are used in modern and sustainable agriculture because of their considerable potential for enhancing human and animal health. Although the number of studies evaluating LABs in silages has increased, the potential use of these micro-organisms in association with silage has not been adequately studied. Fermentation processes using the same strain produce very different results depending on the unique characteristics of the substrate, so the choice of silage inoculant for different starting substrates is of extreme importance to maximize the nutritional quality of the final product. This review describes the current scenario of the bioprospecting and selection process for choosing the best LAB strain as an inoculant for ensiling. In addition, we analyse developments in the fermentation process and strategies and methods that will assist future studies on the selection of new strains of LAB as a starter culture or inoculant.

Alternative strategies for lignocellulose fermentation through lactic acid bacteria: the state of the art and perspectives

Lactic acid bacteria (LAB) have a long history in industrial processes as food starters and biocontrol agents, and also as producers of high-value compounds. Lactic acid, their main product, is among the most requested chemicals because of its multiple applications, including the synthesis of biodegradable plastic polymers. Moreover, LAB are attractive candidates for the production of ethanol, polyhydroalkanoates, sweeteners and exopolysaccharides. LAB generally have complex nutritional requirements. Furthermore, they cannot directly ferment inexpensive feedstocks such as lignocellulose. This significantly increases the cost of LAB fermentation and hinders its application in the production of high volumes of low-cost chemicals. Different strategies have been explored to extend LAB fermentation to lignocellulosic biomass. Fermentation of lignocellulose hydrolysates by LAB has been frequently reported and is the most mature technology. However, current economic constraints of this strategy have driven research for alternative approaches. Co-cultivation of LAB with native cellulolytic microorganisms may reduce the high cost of exogenous cellulase supplementation. Special attention is given in this review to the construction of recombinant cellulolytic LAB by metabolic engineering, which may generate strains able to directly ferment plant biomass. The state of the art of these strategies is illustrated along with perspectives of their applications to industrial second generation biorefinery processes.

Comparative genome analysis of Lactobacillus mudanjiangensis, an understudied member of the Lactobacillus plantarum group

The genus Lactobacillus is known to be extremely diverse and consists of different phylogenetic groups that show a diversity that is roughly equal to the expected diversity of a typical bacterial genus. One of the most prominent phylogenetic groups within this genus is the Lactobacillus plantarum group, which contains the understudied Lactobacillus mudanjiangensis species. Before this study, only one L. mudanjiangensis strain, DSM 28402^T, had been described, but without whole-genome analysis. In this study, three strains classified as L. mudanjiangensis were isolated from three different carrot juice fermentations and their whole-genome sequence was determined, together with the genome sequence of the type strain. The genomes of all four strains were compared with publicly available L. plantarum group genome sequences. This analysis showed that L. mudanjiangensis harboured the second largest genome size and gene count of the whole L. plantarum group. In addition, all members of this species showed the presence of a gene coding for a cellulose-degrading enzyme. Finally, three of the four L. mudanjiangensis strains studied showed the presence of pili on scanning electron microscopy (SEM) images, which were linked to conjugative gene regions, coded on a plasmid in at least two of the strains studied.

Development of a novel selection/counter-selection system for chromosomal gene integrations and deletions in lactic acid bacteria

Background

The underlying mechanisms by which probiotic lactic acid bacteria (LAB) enhance the health of the consumer have not been fully elucidated. Verification of probiotic modes of action can be achieved by using single- or multiple-gene knockout analyses of bacterial mutants in in vitro or in vivo models. We developed a novel system based on an inducible toxin counter-selection system, allowing for rapid and efficient isolation of LAB integration or deletion mutants. The Lactococcus lactis nisin A inducible promoter was used for expression of the Escherichia coli mazF toxin gene as counter-selectable marker.

Results

The flippase (FLP)/flippase recognition target (FRT) recombination system and an antisense RNA transcript were used to create markerless chromosomal gene integrations/deletions in LAB. Expression of NisR and NisK signalling proteins generated stable DNA integrations and deletions. Large sequences could be inserted or deleted in a series of steps, as demonstrated by insertion of the firefly bioluminescence gene and erythromycin resistance marker into the bacteriocin operons or adhesion genes of Lactobacillus plantarum 423 and Enterococcus mundtii ST4SA.

Conclusions

The system was useful in the construction of L. plantarum 423 and E. mundtii ST4SA bacteriocin and adhesion gene mutants. This provides the unique opportunity to study the role of specific probiotic LAB genes in complex environments using reverse genetics analysis. Although this work focuses on two probiotic LAB strains, L. plantarum 423 and E. mundtii ST4SA, the system developed could be adapted to most, if not all, LAB species.

Electronic supplementary material

The online version of this article (10.1186/s12867-019-0127-x) contains supplementary material, which is available to authorized users.

Targeted gene inactivation in Lactobacillus gallinarum ATCC 33199 using chromosomal integration

Although Lactobacillus species have been administered widely as probiotics in poultry production, the mechanisms responsible for their functionality are not well understood. The genetic tools available for use in lactobacilli are advanced but have not been applied widely to investigate their probiotic functionality in poultry. The genome sequence of Lactobacillus gallinarum ATCC 33199, originally isolated from the chicken crop, has recently been made available suggesting this organism as a potentially important model organism for probiotic research in poultry. In this study, we demonstrated the functionality of the pORI28 system for construction of isogenic knockout mutants in L. gallinarum ATCC 33199 using insertional inactivation of lacL as proof-of-principle. The establishment of an effective chromosomal integration system for use in L. gallinarum ATCC 33199 will provide a platform for functional genomic analyses to investigate the functionality of this model organism in the gastrointestinal tract of poultry.

Genetic Tools for the Enhancement of Probiotic Properties

The Lactobacillus genus is a diverse group of microorganisms, many of which are of industrial and medical relevance. Several Lactobacillus species have been used as probiotics, organisms that when present in sufficient quantities confer a health benefit to the host. A significant limitation to the mechanistic understanding of how these microbes provide health benefits to their hosts and how they can be used as therapeutic delivery systems has been the lack of genetic strategies to efficiently manipulate their genomes. This article will review the development and employment of traditional genetic tools in lactobacilli and highlight the latest methodologies that are allowing for precision genome engineering of these probiotic organisms. The application of these tools will be key in providing mechanistic insights into probiotics as well as maximizing the value of lactobacilli as either a traditional probiotic or as a platform for the delivery of therapeutic proteins. Finally, we will discuss concepts that we consider relevant for the delivery of engineered therapeutics to the human gut.

Towards lactic acid bacteria-based biorefineries

Lactic acid bacteria (LAB) have long been used in industrial applications mainly as starters for food fermentation or as biocontrol agents or as probiotics. However, LAB possess several characteristics that render them among the most promising candidates for use in future biorefineries in converting plant-derived biomass-either from dedicated crops or from municipal/industrial solid wastes-into biofuels and high value-added products. Lactic acid, their main fermentation product, is an attractive building block extensively used by the chemical industry, owing to the potential for production of polylactides as biodegradable and biocompatible plastic alternative to polymers derived from petrochemicals. LA is but one of many high-value compounds which can be produced by LAB fermentation, which also include biofuels such as ethanol and butanol, biodegradable plastic polymers, exopolysaccharides, antimicrobial agents, health-promoting substances and nutraceuticals. Furthermore, several LAB strains have ascertained probiotic properties, and their biomass can be considered a high-value product. The present contribution aims to provide an extensive overview of the main industrial applications of LAB and future perspectives concerning their utilization in biorefineries. Strategies will be described in detail for developing LAB strains with broader substrate metabolic capacity for fermentation of cheaper biomass.

Generation of food-grade recombinant Lactobacillus casei delivering Myxococcus xanthus prolyl endopeptidase

Prolyl endopeptidases (PEP) (EC 3.4.21.26), a family of serine proteases with the ability to hydrolyze the peptide bond on the carboxyl side of an internal proline residue, are able to degrade immunotoxic peptides responsible for celiac disease (CD), such as a 33-residue gluten peptide (33-mer). Oral administration of PEP has been suggested as a potential therapeutic approach for CD, although delivery of the enzyme to the small intestine requires intrinsic gastric stability or advanced formulation technologies. We have engineered two food-grade Lactobacillus casei strains to deliver PEP in an in vitro model of small intestine environment. One strain secretes PEP into the extracellular medium, whereas the other retains PEP in the intracellular environment. The strain that secretes PEP into the extracellular medium is the most effective to degrade the 33-mer and is resistant to simulated gastrointestinal stress. Our results suggest that in the future, after more studies and clinical trials, an engineered food-grade Lactobacillus strain may be useful as a vector for in situ production of PEP in the upper small intestine of CD patients.

Isolation and gut microbiota modulation of antibiotic-resistant probiotics from human feces

Antibiotic-resistant probiotics may be advantageous for antibiotic-induced gut microbiota imbalance. In this article, we aimed to isolate antibiotic-resistant bacteria as potential probiotics. Feces from 3 healthy adults and 2 infants were used to isolate the antibiotic-resistant bacteria. Then we established gut microbiota imbalance mice model by antibiotics treatment and used it to assess the effect of the probiotics. Finally, we identified 8 isolates, and 6 of them were used as probiotics cocktail. Number of anaerobe, lactobacilli, and Bifidobacterium in feces were higher in the probiotic group (9.47±0.35 log10CFU/g, 8.74±0.18 log10CFU/g, 7.24±0.38 log10CFU/g, respectively) compared with model group (P<0.05). Richness and diversity index of probiotic group (19.79±0.29 and 2.95±0.06, respectively) were larger than model group (P<0.05). Diarrhea and mucosal edema had been alleviated during probiotic treatment. Our results validated that bacteriotherapy was available to treat gut microbiota imbalance.

Cloning Vectors Based on Cryptic Plasmids Isolated from Lactic Acid Bacteria:Their Characteristics and Potential Applications in Biotechnology

Lactic acid bacteria (LAB) are Gram positive bacteria, widely distributed in nature, and industrially important as they are used in a variety of industrial food fermentations. The use of genetic engineering techniques is an effective means of enhancing the industrial applicability of LAB. However, when using genetic engineering technology, safety becomes an essential factor for the application of improved LAB to the food industry. Cloning and expression systems should be derived preferably from LAB cryptic plasmids that generally encode genes for which functions can be proposed, but no phenotypes can be observed. However, some plasmid-encoded functions have been discovered in cryptic plasmids originating from Lactobacillus, Streptococcus thermophilus, and Pediococcus spp. and can be used as selective marker systems in vector construction. This article presents information concerning LAB cryptic plasmids, and their structures, functions, and applications. A total of 134 cryptic plasmids collated are discussed.

Controlled Integration into the Lactococcus Chromosome of the pCI829-Encoded Abortive Infection Gene from Lactococcus lactis subsp. lactis UC811

The phage insensitivity gene of lactococcal plasmid pCI829 which encodes an abortive infection defense mechanism (Abi) was inserted into the Lactococcus lactis subsp. lactis CH919 chromosome by utilizing the integration plasmid pCI194, which contains 4.2 kb of homology with the conjugative transposon Tn919. Chloramphenicol-resistant transformants expressed phage insensitivity to the prolate-headed phage c2 and the small isometric-headed phage 712, and hybridization analysis indicated that transformants contained pCI194 integrated in single copy. The level of phage insensitivity expressed by the transformants was reduced from that observed when the abi gene was located on a replicating plasmid, as determined by plaque assay and burst size analysis. Amplification of the integrated structure after growth in increased concentrations of chloramphenicol resulted in an increase in the expression of phage insensitivity. Hybridization analysis revealed that while pCI194 was stably maintained in an integrated state over 100 generations in the absence of selective pressure, the ability to express phage insensitivity was lost. Hybridization analysis also revealed that DNA flanking the abi gene contains homology to the CH919 chromosome.

Degradation of Raw Starch by a Wild Amylolytic Strain of Lactobacillus plantarum

Lactobacillus plantarum A6, isolated from fermented cassava, can break down cassava raw starch that has not been subjected to preliminary physicochemical treatment. When the pH was kept at 6, the microorganism cultured in a bioreactor excreted a high alpha-amylase activity (60 U/ml). Synthesis of the enzyme occurred during the stationary phase and resulted in full hydrolysis of the cassava starch granules. This gave 41 g of lactic acid from 45 g of raw starch after 3 days of fermentation. Enzymatic attack was evident under scanning electron microscopy in the rougher appearance of the surface of starch granules and in the presence of large cavities in some of them. In contrast, when the pH was not regulated, only a small amount of alpha-amylase activity was produced (2 U/ml) and no decrease in the starch content of the medium was observed. However, under scanning electron microscopy, some granules displayed a rougher surface, which might have been the result of weak enzymatic attack.

D-lactic acid production from cellooligosaccharides and beta-glucan using L-LDH gene-deficient and endoglucanase-secreting Lactobacillus plantarum

In order to achieve direct fermentation of an optically pure D: -lactic acid from cellulosic materials, an endoglucanase from a Clostridium thermocellum (CelA)-secreting plasmid was introduced into an L: -lactate dehydrogenase gene (ldhL1)-deficient Lactobacillus plantarum (ldhL1) bacterial strain. CelA expression and its degradation of beta-glucan was confirmed by western blot analysis and enzyme assay, respectively. Although the CelA-secreting ldhL1 assimilated cellooligosaccharides up to cellohexaose (although not cellotetraose), the main end product was acetic acid, not lactic acid, due to the conversion of lactic acid to acetic acid. Cultivation under anaerobic conditions partially suppressed this conversion resulting in the production of 1.27 g/l of D: -lactic acid with a high optical purity of 99.5% from a medium containing 2 g/l of cellohexaose. Subsequently, D: -lactic acid fermentation from barley beta-glucan was carried out with the addition of Aspergillus aculeatus beta-glucosidase produced by recombinant Aspergillus oryzae and 1.47 g/l of D: -lactic was produced with a high optical purity of 99.7%. This is the first report of direct lactic acid fermentation from beta-glucan and a cellooligosaccharide that is a more highly polymerized sugar than cellotriose.

Coexpression of rumen microbial β-glucanase and xylanase genes in Lactobacillus reuteri

The aim of this study was to clone and coexpress two rumen fibrolytic enzyme genes in Lactobacillus reuteri. The ability of the genetically modified strain to degrade beta-glucan and xylan was evaluated. The Fibrobacter succinogenes beta-glucanase (1,3-1,4-beta-D: -glucan 4-glucanohydrolase [EC 3.2.1.73]) gene and the Neocallimastix patriciarum xylanase gene, xynCDBFV, were constructed to coexpress and secrete under control of the Lactococcus lactis lacA promoter and its secretion signal and then transformed into L. reuteri Pg4, a strain isolated from the gastrointestinal tract of broiler chickens. The transformed L. reuteri strain acquired the capacity to break down soluble beta-glucan and xylan. The introduction of the recombinant plasmids and production of beta-glucanase and xylanase did not affect cell growth. To the best of our knowledge, this is the first report of coexpression of rumen microbial fibrolytic enzyme genes in L. reuteri.

Heterologous expression of enterocin AS-48 in several strains of lactic acid bacteria

AIMS

Enterococcus faecalis produces a cationic and circular enterocin, AS-48, of 7149 Da, the genetic determinants of which are located within the pMB2 plasmid. We have compared enterocin AS-48 production by different enterococci species with that of other 'safe' lactic acid bacteris (LAB) (GRAS status) and looked into the subsequent application of this enterocin in food production.

METHODS AND RESULTS

In an effort to exploit this system for the heterologous expression of enterocin AS-48, a number of vectors containing the as-48 cluster were constructed and used to transform several LAB strains (genera Enterococcus, Lactococcus and Lactobacillus)

CONCLUSION

Heterologous production of enterocin AS-48 failed when bacteria other than those belonging to the genus Enterococcus were used as hosts, although expression of a partial level of resistance against AS-48 were always detected, ruling out the possibility of a lack of recognition of the enterococcal promoters.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our results reveal the special capacity of species from the genus Enterococcus to produce AS-48, an enterocin that requires a post-transcriptional modification to generate a circular peptide with a wide range of inhibitory activity against pathogenic and spoilage bacteria. Preliminary experiments in foodstuffs using nonvirulent enterococci with interesting functional properties reveal the possibility of a biotechnological application of these transformants.

Direct cloning of a xylanase gene from the mixed genomic DNA of rumen fungi and its expression in intestinal Lactobacillus reuteri

A relatively newly defined xylanase gene, xynR8, was obtained directly from a mixed DNA sample prepared from unpurified rumen fungal cultures by PCR amplification. The DNA sequence of xynR8 revealed that the gene was 884 bp in size and encoded amino acid sequences with a molecular weight of 27.9 kDa. XynR8 belonged to glycosyl hydrolase family 11, and the catalytic site residues were also found in its amino acid sequence. The main hydrolysis products of XynR8 were xylobiose, xylotriose and xylotetrose, which indicated that it belonged to the endoxylanases. The xynR8 gene was constructed so as to express and secrete under the control of the Lactococcus lactis lac A promoter and its secretion signal, and was transformed into L. reuteri Pg4, a strain isolated from the gastrointestinal tract of broiler chickens. The L. reuteri transformants harboring xynR8 not only acquired the capacity to break down xylan, but also maintained their high adhesion efficiency to mucin and mucus and their resistance to bile salts and acid.

Expression of rumen microbial fibrolytic enzyme genes in probiotic Lactobacillus reuteri

This study was aimed at evaluating the cloning and expression of three rumen microbial fibrolytic enzyme genes in a strain of Lactobacillus reuteri and investigating the probiotic characteristics of these genetically modified lactobacilli. The Neocallimastix patriciarum xylanase gene xynCDBFV, the Fibrobacter succinogenes beta-glucanase (1,3-1,4-beta-D-glucan 4-glucanohydrolase [EC 3.2.1.73]) gene, and the Piromyces rhizinflata cellulase gene eglA were cloned in a strain of L. reuteri isolated from the gastrointestinal tract of broilers. The enzymes were expressed and secreted under the control of the Lactococcus lactis lacA promoter and its secretion signal. The L. reuteri transformed strains not only acquired the capacity to break down soluble carboxymethyl cellulose, beta-glucan, or xylan but also showed high adhesion efficiency to mucin and mucus and resistance to bile salt and acid.

Optimization of technical conditions for the transformation of Lactobacillus acidophilus strains by electroporation

AIMS

To optimize the conditions for electroporating foreign plasmid DNA into Lactobacillus acidophilus ATCC 43121.

METHODS AND RESULTS

The conditions of electroporation were optimized to improve the transformation efficiency. Plasmid pNZ123 containing multicloning site and chloramphenicol resistance was employed to construct a cloning vector. The optimum electroporation conditions for the maximum transformation efficiency were a pulse strength of 12.5 kV cm(-1), a pulse number of 10, a pulse interval of 500 ms, and pNZ123 plasmid DNA concentration of 25 ng microl(-1). Under the optimum conditions the transformation efficiency of L. acidophilus ATCC 43121 was 1.84 +/- 0.13 x 10(4) (+/- standard error of measurements) CFU per mug of plasmid DNA. Other strains of L. acidophilus showed transformation efficiencies ranging from 1.38 +/- 0.02 x 10(4) to 9.32 +/- 0.54 x 10(4) under these conditions. A green fluorescent protein (GFP) was successfully expressed and detected by fluorescence microscopy when the pKU::slpA-GFP, pNZ123 containing GFP gene, was transformed in L. acidophilus ATCC 43121 under the optimum conditions.

CONCLUSIONS

The results suggest that electrical parameters, antibiotic concentration, and host specificity play important roles to determine transformation efficiency of lactobacilli. The optimum conditions for the transformation of L. acidophilus ATCC 43121 may be applied to improve transformation efficiency of other lactobacilli.

SIGNIFICANCE AND IMPACT OF THE STUDY

The optimized conditions for electrotransformation may provide a mean to improve the introduction of foreign DNA into L. acidophilus to be used as a vehicle for a heterologous protein expression.

Sequencing, characterization and transcriptional analysis of the histidine decarboxylase operon of Lactobacillus buchneri

The amplification of an internal fragment of the hdcA gene for histidine decarboxylase in Lactobacillus buchneri showed the gene to be located on the bacterial chromosome. Reverse PCR was then used to amplify both it and its adjacent genes. The histidine decarboxylase cluster was found to be composed of four genes: hdcC (expressed in Lactococcus lactis, the product of which is located in the membrane, suggesting it to be a histidine/histamine antiporter), hdcA (which encodes histidine decarboxylase), hdcB (of unknown function but co-transcribed as bicistronic mRNA together with hdcA) and hisS (the only copy of a gene encoding a histidyl-tRNA synthetase in Lb. buchneri). The expression of hisS depends on the histidine concentration of the growth medium, and it can be transcribed as monocistronic or hdcA-hdcB-hisS polycistronic mRNA.

Optimizing scale-up fermentation processes

There are many aims associated with the optimization of fermentation processes. Optimization is expected to increase the yield of the final product but the process must be compliant with good manufacturing practices, the available equipment and the expected final scale of operation. Dealing with genetically modified microorganisms that overproduce recombinant protein has the advantage that the vast majority of the processes use only three different species, namely Escherichia coli, Saccharomyces cerevisiae and Pichia pastoris. Standard processes for each organism are described in textbooks and serve as a basis for the development of a tailored process. This article outlines the general philosophy that we have devised to ensure an efficient approach of scaling up fermentation processes for biopharmaceutical purposes, in a multidisciplinary environment.

Integrative food-grade expression system based on the lactose regulon of Lactobacillus casei

The lactose operon from Lactobacillus casei is regulated by very tight glucose repression and substrate induction mechanisms, which made it a tempting candidate system for the expression of foreign genes or metabolic engineering. An integrative vector was constructed, allowing stable gene insertion in the chromosomal lactose operon of L. casei. This vector was based on the nonreplicative plasmid pRV300 and contained two DNA fragments corresponding to the 3' end of lacG and the complete lacF gene. Four unique restriction sites were created, as well as a ribosome binding site that would allow the cloning and expression of new genes between these two fragments. Then, integration of the cloned genes into the lactose operon of L. casei could be achieved via homologous recombination in a process that involved two selection steps, which yielded highly stable food-grade mutants. This procedure has been successfully used for the expression of the E. coli gusA gene and the L. lactis ilvBN genes in L. casei. Following the same expression pattern as that for the lactose genes, beta-glucuronidase activity and diacetyl production were repressed by glucose and induced by lactose. This integrative vector represents a useful tool for strain improvement in L. casei that could be applied to engineering fermentation processes or used for expression of genes for clinical and veterinary uses.

Generation of food-grade recombinant lactic acid bacterium strains by site-specific recombination

The construction of a delivery and clearing system for the generation of food-grade recombinant lactic acid bacterium strains, based on the use of an integrase (Int) and a resolvo-invertase (beta-recombinase) and their respective target sites (attP-attB and six, respectively) is reported. The delivery system contains a heterologous replication origin and antibiotic resistance markers surrounded by two directly oriented six sites, a multiple cloning site where passenger DNA could be inserted (e.g., the cI gene of bacteriophage A2), the int gene, and the attP site of phage A2. The clearing system provides a plasmid-borne gene encoding beta-recombinase. The nonreplicative vector-borne delivery system was transformed into Lactobacillus casei ATCC 393 and, by site-specific recombination, integrated as a single copy in an orientation- and Int-dependent manner into the attB site present in the genome of the host strain. The transfer of the clearing system into this strain, with the subsequent expression of the beta-recombinase, led to site-specific DNA resolution of the non-food-grade DNA. These methods were validated by the construction of a stable food-grade L. casei ATCC 393-derived strain completely immune to phage A2 infection during milk fermentation.

Expression of Bacillus subtilis phytase in Lactobacillus plantarum 755

Phytase enzymes can increase the nutritional value of food and feed by liberating inorganic phosphate from phytate, the major storage form of phosphorus in plants. The phytase (phyC) from Bacillus subtilis VTT E-68013 was expressed in Lactobacillus plantarum strain 755 using Lact. amylovorus alpha-amylase secretion signals. In an overnight cultivation in MRS medium containing cellobiose for induction of the alpha-amylase promoter, catalytically active phytase was secreted as a predominant extracellular protein. However, Western blot analysis revealed unprocessed and processed phytase in the cell fraction. Pulse chase experiments showed that the recombinant phytase was secreted at a slower rate in comparison to the native proteins of Lact. plantarum 755.

Transport of D-xylose in Lactobacillus pentosus, Lactobacillus casei, and Lactobacillus plantarum: evidence for a mechanism of facilitated diffusion via the phosphoenolpyruvate:mannose phosphotransferase system

We have identified and characterized the D-xylose transport system of Lactobacillus pentosus. Uptake of D-xylose was not driven by the proton motive force generated by malolactic fermentation and required D-xylose metabolism. The kinetics of D-xylose transport were indicative of a low-affinity facilitated-diffusion system with an apparent K(m) of 8.5 mM and a V(max) of 23 nmol min(-1) mg of dry weight(-1). In two mutants of L. pentosus defective in the phosphoenolpyruvate:mannose phosphotransferase system, growth on D-xylose was absent due to the lack of D-xylose transport. However, transport of the pentose was not totally abolished in a third mutant, which could be complemented after expression of the L. curvatus manB gene encoding the cytoplasmic EIIB(Man) component of the EII(Man) complex. The EII(Man) complex is also involved in D-xylose transport in L. casei ATCC 393 and L. plantarum 80. These two species could transport and metabolize D-xylose after transformation with plasmids which expressed the D-xylose-catabolizing genes of L. pentosus, xylAB. L. casei and L. plantarum mutants resistant to 2-deoxy-D-glucose were defective in EII(Man) activity and were unable to transport D-xylose when transformed with plasmids containing the xylAB genes. Finally, transport of D-xylose was found to be the rate-limiting step in the growth of L. pentosus and of L. plantarum and L. casei ATCC 393 containing plasmids coding for the D-xylose-catabolic enzymes, since the doubling time of these bacteria on D-xylose was proportional to the level of EII(Man) activity.

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.

Functional expression in Lactobacillus plantarum of xylP encoding the isoprimeverose transporter of Lactobacillus pentosus

The xylP gene of Lactobacillus pentosus, the first gene of the xylPQR operon, was recently found to be involved in isoprimeverose metabolism. By expression of xylP on a multicopy plasmid in Lactobacillus plantarum 80, a strain which lacks active isoprimeverose and D-xylose transport activities, it was shown that xylP encodes a transporter. Functional expression of the XylP transporter was shown by uptake of isoprimeverose in L. plantarum 80 cells, and this transport was driven by the proton motive force generated by malolactic fermentation. XylP was unable to catalyze transport of D-xylose.

Application of the extracellular alpha-amylase gene from Streptococcus bovis 148 to construction of a secretion vector for yogurt starter strains

Streptococcus thermophilus ATCC 19258, Lactobacillus delbrueckii subsp. bulgaricus T-11, and Lactococcus lactis subsp. lactis IL1403 were transformed with the alpha-amylase gene (amyA) from Streptococcus bovis 148 by using a wide host-range vector, and all the transformants secreted the alpha-amylase successfully. Since the promoter and the secretion signal of the amyA gene were functional in these strains, we constructed a secretion vector using the expression elements of amyA. Trials to secrete foreign enzymes in yogurt starter strains were performed using this novel secretion vector.

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.

Molecular characterization of the alpha-amylase genes of Lactobacillus plantarum A6 and Lactobacillus amylovorus reveals an unusual 3' end structure with direct tandem repeats and suggests a common evolutionary origin

The alpha-amylase gene (amyA) of Lactobacillus plantarum A6 was isolated from the genome by polymerase chain reaction with degenerated oligonucleotides, synthesized according to the tryptic peptide amino acid sequences of the purified enzyme. Nucleic acid sequence analysis revealed one open reading frame of 2739 bp encoding a 913 amino acid protein. The amylase appears to be divided into two equal parts. The N-terminal part has the typical characteristics of the well-known alpha-amylase family (65% identity with the alpha-amylase of Bacillus subtilis and 97% identity with the partial sequence available for the alpha-amylase of Lactobacillus amylovorus). The C-terminal part displays a fairly unusual structure. It consists of four direct tandem repeated sequences of 104 amino acids sharing 100% similarity. The complete nucleotide sequence of the alpha-amylase gene of L. amylovorus was also determined. An open reading frame of 2862 bp encoding a 954 amino acid protein was identified. Perfect homology between the two amyA genes was observed in the N-terminal region. The C-terminal part of L. amylovorus alpha-amylase also included tandem repeat units but striking differences were observed: (i) the addition of one repeat unit; (ii) a shorter, 91 amino acid repetition unit. These structural homologies suggest that both genes have a common ancestor and may have evolved independently by duplication with subsequent recombination and mutation.

Expression of Bacillus subtilis levanase gene in Lactobacillus plantarum and Lactobacillus casei

Two Lactobacillus-Escherichia coli shuttle vectors, harbouring the levanase gene from Bacillus subtilis under the control of its own promoter (pLPEW1) or behind the E. coli tac promoter (pESIEW2), were constructed. Lactobacillus plantarum showed the same growth characteristics on selective plates and in liquid media containing inulin, after transformation with either pLPEW1 or pESIEW2. L. plantarum transformed with pLPEW1 could be selected on inulin plates, indicating that levanase expression can be used as a food-grade selection system for Lactobacillus. Lactobacillus casei grew faster in inulin-containing medium than L. plantarum after transformation with pESIEW2, but did not grow when harbouring pLPEW1. Inulin-degrading activities of 90 mU/ml were found in culture medium of L. plantarum containing pLPEW1 or pESIEW2, and of 500 mU/ml in medium of L. casei (pESIEW2). Addition of 1 mM isopropyl beta-D-thiogalactoside to the culture medium had no effect on growth and levanase expression in L. plantarum (pESIEW2) and L. casei (pESIEW2) strains. Levanase produced by L. casei (pESIEW2) has a size of 75 kDa and 72 kDa, corresponding to that of unprocessed and mature B. subtilis levanase, respectively, suggesting that the protein produced is recognized and processed by a signal peptidase.

Phenotypically based taxonomy using API 50CH of lactobacilli from Nigerian ogi, and the occurrence of starch fermenting strains

One-hundred and twenty isolates of lactic acid bacteria isolated from ogi and three traditional cereal-based alcoholic beverages from Nigeria, together with 18 reference strains from Swedish sour doughs, and 50 type-and reference strains of mainly Lactobacillus, were phenotypically classified on their fermentation ability of 49 carbohydrates, including soluble starch. Data were examined by Jaccard Coefficient (SJ), Simple Matching Coefficient (SSM), and unweighted pair group algorithm with arithmetic averages (UPGMA). Seven major clusters were defined at the 82% SJ-similarity level (corresponds to the SSM-level of 91%). Three were identified as Lactobacillus plantarum or L. plantarum-like (together 41% of the ogi isolates). The others were obligately heterofermentative; Cluster 7 was identified as L. confusus (11% of the ogi isolates). Three minor clusters were identified as L. murinus, L. agilis or L. gallinarium, and Leuconostoc mesenteroides subsp. mesenteroides, respectively. The phenotype of the L. plantarum isolates varied within wide limits. Seventeen isolates possessed starch fermenting capacity. Nine of these were identified as L. plantarum or L. plantarum-like (isolated from ogi); one was identified as Leuconostoc mesenteroides subsp. mesenteroides, and the rest were unidentified non-clustering strains.