Increased exopolysaccharide production in Lactococcus lactis due to increased levels of expression of the NIZO B40 eps gene cluster

Nisin controlled homologous Over-expression of an exopolysaccharide biosynthetic glycosyltransferase gene for enhanced EPS production in Lactobacillus plantarum BR2

Glycosyltransferases synthesize a variety of exopolysaccharides (EPS) with different properties by altering the type of glycosidic linkage, degree of branching, length, mass, and conformation of the polymers. The genome analysis of an EPS-producing, Lactobacillus plantarum BR2 (Accession No: MN176402) showed twelve glycosyltransferase genes, and the gene BR2gtf (1116 bp), annotated as an EPS biosynthetic glycosyltransferase was cloned into the pNZ8148 vector. The recombinant pNZ8148 vector along with pNZ9530, a regulatory plasmid, were electroporated to L. plantarum BR2 for the over-expression of gtf gene under a nisin-controlled expression system and the glycosyltransferase activity of the recombinant and the wild-type strains were analysed. The recombinant strain showed 54.4% increase in EPS production with the maximum EPS production of 23.2 ± 0.5 g/L in a 5 L bioreactor study after 72 h of fermentation. This study shows an effective molecular strategy possibly to be adopted in lactic acid bacteria to enhance exopolysaccharide production.

Diverse Repertoire and Relationship of Exopolysaccharide Genes in Cold-Adapted Acinetobacter sp. CUI-P1 Revealed by Comparative Genome Analysis

This study focused on the exploration of microbial communities inhabiting extreme cold environments, such as the Passu and Pisan glaciers of Pakistan, and their potential utilization in industrial applications. Among the 25 initially screened strains, five were found to be suitable candidates for exopolysaccharide (EPS) production, with strain CUI-P1 displaying the highest yield of 7230.5 mg/L compared to the other four strains. The purified EPS from CUI-P1 was tested for its ability to protect probiotic bacteria and E. coli expressing green fluorescence protein (HriGFP) against extreme cold temperatures, and it exhibited excellent cryoprotectant and emulsification activity, highlighting its potential use in the biotechnological industry. Furthermore, the genome of Acinetobacter sp., CUI-P1 comprised 199 contigs, with a genome size of 10,493,143bp and a G + C content of 42%, and showed 98.197% nucleotide identity to the type genome of Acinetobacter baumannii ATCC 17978. These findings offer promising avenues for the application of EPS as a cryoprotectant, an essential tool in modern biotechnology.

Effects of galactosyltransferase on EPS biosynthesis and freeze-drying resistance of Lactobacillus acidophilus NCFM

Galactosyltransferase (GalT) is an important enzyme in synthesizing exopolysaccharide (EPS), the major polymer of biofilms protecting cells from severe conditions. However, the contribution to, and regulatory mechanism of GalT, in stressor resistance are still unclear. Herein, we successfully overexpressed GalT in Lactobacillus acidophilus NCFM by genetic engineering. The GalT activity and freeze-drying survival rate of the recombinant strain were significantly enhanced. The EPS yield also increased by 17.8%, indicating a positive relationship between freeze-drying resistance and EPS. RNA-Seq revealed that GalT could regulate the flux of the membrane transport system, pivotal sugar-related metabolic pathways, and promote quorum sensing to facilitate EPS biosynthesis, which enhanced freeze-drying resistance. The findings concretely prove that the mechanism of GalT regulating EPS biosynthesis plays an important role in protecting lactic acid bacteria from freeze-drying stress.

Expression of genes involved in exopolysaccharide synthesis in Lactiplantibacillus plantarum VAL6 under environmental stresses

Environmental factors can alter exopolysaccharide biosynthesis in lactic acid bacteria (LAB). To further clarify this potential relationship, the mRNA expression of genes involved in exopolysaccharide synthesis such as glmU, pgmB1, cps4E, cps4F, cps4J, and cps4H in Lactiplantibacillus plantarum VAL6 under different conditions including temperature, pH, sodium chloride (NaCl), and carbon dioxide (CO₂) intensification culture was studied. The transcriptomic data revealed that the exposure of L. plantarum VAL6 at pH 3 increased the expression level of cps4H but decreased the expression levels of pgmB1 and cps4E. Under pH 8, cps4F and cps4E were significantly upregulated, whereas pgmB1 was downregulated. Similarly, the expression levels of cps4F, cps4E, and cps4J increased sharply under stresses at 42 or 47 °C. In the case of NaCl stress, glmU, pgmB1, cps4J, and cps4H were downregulated in exposure to NaCl at 7 and 10% concentrations while cps4E and cps4F were upregulated at 1 h of 10%-NaCl treatment and at 5 h of 4%-NaCl treatment. Remarkably, CO₂ intensification culture stimulated the expression of all tested genes. In addition, simultaneous changes in expression of cps4E and cps4F under environmental challenges may elicit the possibility of an association between the two genes. These findings indicated that the expression level of eps genes is responsible for changes in the yield and monosaccharide composition of exopolysaccharides under environmental stresses.

Proteomic analysis reveals potential factors associated with enhanced EPS production in Streptococcus thermophilus ASCC 1275

Streptococcus thermophilus ASCC 1275 has two chain length determining genes - epsC and epsD- in its eps gene cluster, and produces two times more EPS in sucrose medium than that in glucose and lactose. Hence, we investigated the influence of sugars (glucose, sucrose and lactose), at log phase (5 h) and stationary phase (10 h), on the global proteomics of S. thermophilus 1275 to understand the differentially expressed proteins (DEPs) during EPS production using isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis. Among 98 DEPs in sucrose medium, most of them were mapped into EPS biosynthesis pathway and other related metabolisms. There was an upregulation of several proteins involved in sugar transport (phosphoenolpyruvate (PEP) phosphotransferase system), EPS assembly (epsG1D) and amino acid metabolism (methionine, cysteine/arginine metabolism) in sucrose medium. This study showed that increased EPS production in S. thermophilus 1275 requires a well-co-ordinated regulation of pathway involved in both EPS assembly and amino acid metabolism along with the availability of sugars. Thus, it provided valuable insights into the biosynthesis and regulation of EPS in S. thermophilus 1275, and potential gene targets for understanding high-EPS strains.

Enhanced Exopolysaccharide Production by Lactobacillus rhamnosus in Co-Culture with Saccharomyces cerevisiae

Lactobacillus strains are known to produce exopolysaccharides (EPS) with recognized health benefits (i.e. prebiotic and immunomodulation) but production is limited by low yields. Co-culture has been shown to improve metabolite productivity, particularly bacteriocins and EPS. Although lactic acid bacteria (LAB) and yeasts are found in several fermented products, the molecular mechanisms linked to the microbial interactions and their influences on EPS biosynthesis are unclear. The aim of the present study was to investigate the effect of co-culture on EPS production by three Lactobacillus rhamnosus strains (ATCC 9595, R0011, and RW-9595M) in association with Saccharomyces cerevisiae. Fermentation, in both mono and co-culture, was carried out and the expression of key LAB genes was monitored. After 48 h, results revealed that EPS production was enhanced by 39%, 49%, and 42% in co-culture for R0011, ATCC 9595, and RW-9595M, respectively. Each strain showed distinctive gene expression profiles. For a higher EPS production, higher EPS operon expression levels were observed for RW-9595M in co-culture. The construction of gene co-expression networks revealed common correlations between the expression of genes related to the EPS operons, sugar metabolism, and stress during EPS production and microbial growth for the three strains. Our findings provide insight into the positive influence of inter-kingdom interactions in stimulating EPS biosynthesis, representing progress toward the development of a bio-ingredient with broad industrial applications.

Systems Biology - A Guide for Understanding and Developing Improved Strains of Lactic Acid Bacteria

Lactic Acid Bacteria (LAB) are extensively employed in the production of various fermented foods, due to their safe status, ability to affect texture and flavor and finally due to the beneficial effect they have on shelf-life. More recently, LAB have also gained interest as production hosts for various useful compounds, particularly compounds with sensitive applications, such as food ingredients and therapeutics. As for all industrial microorganisms, it is important to have a good understanding of the physiology and metabolism of LAB in order to fully exploit their potential, and for this purpose, many systems biology approaches are available. Systems metabolic engineering, an approach that combines optimization of metabolic enzymes/pathways at the systems level, synthetic biology as well as in silico model simulation, has been used to build microbial cell factories for production of biofuels, food ingredients and biochemicals. When developing LAB for use in foods, genetic engineering is in general not an accepted approach. An alternative is to screen mutant libraries for candidates with desirable traits using high-throughput screening technologies or to use adaptive laboratory evolution to select for mutants with special properties. In both cases, by using omics data and data-driven technologies to scrutinize these, it is possible to find the underlying cause for the desired attributes of such mutants. This review aims to describe how systems biology tools can be used for obtaining both engineered as well as non-engineered LAB with novel and desired properties.

Relationship Between Putative eps Genes and Production of Exopolysaccharide in Lactobacillus casei LC2W

Lactobacillus casei LC2W, a probiotic strain, can produce exopolysaccharide (EPS) with anti-hypertensive bioactivity. The relationship between eps genes and EPS synthesis in LC2W due to unclear regulation mechanism of EPS biosynthesis was investigated. The several relevant genes in EPS biosynthetic gene cluster were deleted, overexpressed and complemented. The results suggested that glucose-1-phosphate thymidyltranseferase gene (LC2W_2179), uncharacterized EPS biosynthesis protein (LC2W_2188), and EPS biosynthesis protein (LC2W_2189) were related to EPS biosynthesis. EPS titer decreased 15, 13, and 21% when the three genes were deleted, respectively. When they were overexpressed, EPS titer increased 16, 10, and 18%. When they were complemented, EPS titer was similar to the wild-type strain. This work showed the three eps genes from LC2W played important roles on EPS production.

'Ropy' phenotype, exopolysaccharides and metabolism: Study on food isolated potential probiotics LAB

Lactic acid bacteria are fully recognized for their industrial applications among which the production and release of exopolysaccharides. In the present investigation, we screened fifteen Lactobacilli in order to find ropy strains, quantify exopolysaccharides and detect proteins specifically associated with the ropy-exopolysaccharide production. The highest ropy-exopolysaccharide producer (L. helveticus 6E8), was grown in stimulating and basal condition (10% and 2% lactose) and subjected to comparative proteomic analysis. The levels of 4 proteins were found significantly increased in the membrane fraction under stimulating conditions: a specific exopolysaccharide biosynthetic protein, a stress-induced protein, a protein involved in secretion and an ATP-synthase subunit. Conversely, several enzymes involved in anabolism and protein synthesis were decreased. These results suggest a general shift from growth to exopolysaccharide-mediated protection from the hyperosmotic environment. Due to the great interest in exopolysaccharides with novel features, the identification of these proteins could have implications for future improvements of industrial strains.

Altering textural properties of fermented milk by using surface-engineered Lactococcus lactis

Lactic acid bacteria are widely used for the fermentation of dairy products. While bacterial acidification rates, proteolytic activity and the production of exopolysaccharides are known to influence textural properties of fermented milk products, little is known about the role of the microbial surface on microbe-matrix interactions in dairy products. To investigate how alterations of the bacterial cell surface affect fermented milk properties, 25 isogenic Lactococcus lactis strains that differed with respect to surface charge, hydrophobicity, cell chaining, cell-clumping, attachment to milk proteins, pili expression and EPS production were used to produce fermented milk. We show that overexpression of pili increases surface hydrophobicity of various strains from 3-19% to 94-99%. A profound effect of different cell surface properties was an altered spatial distribution of the cells in the fermented product. Aggregated cells tightly fill the cavities of the protein matrix, while chaining cells seem to be localized randomly. A positive correlation was found between pili overexpression and viscosity and gel hardness of fermented milk. Gel hardness also positively correlated with clumping of cells in the fermented milk. Viscosity of fermented milk was also higher when it was produced with cells with a chaining phenotype or with cells that overexpress exopolysaccharides. Our results show that alteration of cell surface morphology affects textural parameters of fermented milk and cell localization in the product. This is indicative of a cell surface-dependent potential of bacterial cells as structure elements in fermented foods.

Improved Polysaccharide Production by Homologous Co-overexpression of Phosphoglucomutase and UDP Glucose Pyrophosphorylase Genes in the Mushroom Coprinopsis cinerea

Coprinopsis polysaccharides exhibit hypoglycemic and antioxidant activities. In this report, increases in polysaccharide production by homologous co-overexpression or individual homologous overexpression of phosphoglucomutase and UDP glucose pyrophosphorylase gene in Coprinopsis cinerea, which participate in polysaccharide biosynthesis. The transcription levels of the target genes were upregulated significantly in the oePGM-UGP strain when compared with the oePGM or oeUGP strain. The maximum intracellular polysaccharide content obtained in the oePGM-UGP strain was 1.49-fold higher than that of the WT strain, whereas a slight improvement in polysaccharide production was obtained in the oePGM and oeUGP strains. Extracellular polysaccharide production was enhanced by 75% in the oePGM-UGP strain when compared with that of the WT strain, whereas improvements of 30% and 16% were observed for the oePGM and oeUGP strains, respectively. These results show that multiple interventions in polysaccharide biosynthesis pathways of Basidiomycetes might improve polysaccharide yields when compared with that of single interventions.

Comparative mRNA-Seq Analysis Reveals the Improved EPS Production Machinery in Streptococcus thermophilus ASCC 1275 During Optimized Milk Fermentation

Exo-polysaccharide (EPS) produced by dairy starters plays critical roles in improving texture and functionalities of fermented dairy products. One of such high EPS producers, Streptococcus thermophilus ASCC 1275 (ST1275) was used as a model dairy strain to understand the stimulation of its EPS production under optimal milk fermentation conditions. The mRNA-seq analysis and targeted pathway analysis indicate that genes associated with lactose (milk sugar) catabolism, EPS assembly, proteolytic activity, and arginine/methionine/cysteine synthesis and transport in ST1275 were significantly up-regulated under the optimized conditions of pH 5.5, 40°C, or WPI supplementation compared to that of pH 6.5 and 37°C, respectively. This indicates that genes involved in above metabolisms cooperate together for improving EPS yield from ST1275. This study provides a global view map on potential targeted pathways and specific genes accounted for enhanced EPS production in Str. thermophilus and that could be modulated by fermentation conditions.

Exopolysaccharides produced by lactic acid bacteria: from health-promoting benefits to stress tolerance mechanisms

A wide range of lactic acid bacteria (LAB) is able to produce capsular or extracellular polysaccharides, with various chemical compositions and properties. Polysaccharides produced by LAB alter the rheological properties of the matrix in which they are dispersed, leading to typically viscous and "ropy" products. Polysaccharides are involved in several mechanisms such as prebiosis and probiosis, tolerance to stress associated to food process, and technological properties of food. In this paper, we summarize the beneficial properties of exopolysaccharides (EPS) produced by LAB with particular attention to prebiotic properties and to the effect of exopolysaccharides on the LAB-host interaction mechanisms, such as bacterial tolerance to gastrointestinal tract conditions, ability of ESP-producing probiotics to adhere to intestinal epithelium, their immune-modulatory activity, and their role in biofilm formation. The pro-technological aspect of exopolysaccharides is discussed, focusing on advantageous applications of EPS in the food industry, i.e., yogurt and gluten-free bakery products, since it was found that these microbial biopolymers positively affect the texture of foods. Finally, the involvement of EPS in tolerance to stress conditions that are commonly encountered in fermented beverages such as wine is discussed.

Exopolysaccharide production and ropy phenotype are determined by two gene clusters in putative probiotic strain Lactobacillus paraplantarum BGCG11

Lactobacillus paraplantarum BGCG11, a putative probiotic strain isolated from a soft, white, artisanal cheese, produces a high molecular-weight heteropolysaccharide, exopolysaccharide (EPS)-CG11, responsible for the ropy phenotype and immunomodulatory activity of the strain. In this study, a 26.4-kb region originating from the pCG1 plasmid, previously shown to be responsible for the production of EPS-CG11 and a ropy phenotype, was cloned, sequenced, and functionally characterized. In this region 16 putative open reading frames (ORFs), encoding enzymes for the production of EPS-CG11, were organized in specific loci involved in the biosynthesis of the repeat unit, polymerization, export, regulation, and chain length determination. Interestingly, downstream of the eps gene cluster, a putative transposase gene was identified, followed by an additional rfb gene cluster containing the rfbACBD genes, the ones most probably responsible for dTDP-L-rhamnose biosynthesis. The functional analysis showed that the production of the high-molecular-weight fraction of EPS-CG11 was absent in two knockout mutants, one in the eps and the other in the rfb gene cluster, as confirmed by size exclusion chromatography analysis. Therefore, both eps and rfb genes clusters are prerequisites for the production of high-molecular-weight EPS-CG11 and for the ropy phenotype of strain L. paraplantarum BGCG11.

EpsA is an essential gene in exopolysaccharide production in Lactobacillus johnsonii FI9785

Lactobacillus johnsonii FI9785 has an eps gene cluster which is required for the biosynthesis of homopolymeric exopolysaccharides (EPS)‐1 and heteropolymeric EPS‐2 as a capsular layer. The first gene of the cluster, epsA, is the putative transcriptional regulator. In this study we showed the crucial role of epsA in EPS biosynthesis by demonstrating that deletion of epsA resulted in complete loss of both EPS‐1 and EPS‐2 on the cell surface. Plasmid complementation of the epsA gene fully restored EPS production, as confirmed by transmission electron microscopy and nuclear magnetic resonance (NMR) analysis. Furthermore, this complementation resulted in a twofold increase in the expression levels of this gene, which almost doubled amounts of EPS production in comparison with the wild‐type strain. Analysis of EPS by NMR showed an increased ratio of the heteropolysaccharide to homopolysaccharide in the complemented strain and allowed identification of the acetylated residue in EPS‐2 as the (1,4)‐linked βGlcp unit, with the acetyl group located at O‐6. These findings indicate that epsA is a positive regulator of EPS production and that EPS production can be manipulated by altering its expression.

Impact of exopolysaccharide production on functional properties of some Lactobacillus salivarius strains

The aim of this work was to characterize functional properties of Lactobacillus salivarius strains isolated from chicken feces. Detection of genes responsible for exopolysaccharide (EPS) production revealed that all strains harbored a dextransucrase gene, but p-gtf gene was only detected in strain E4. Analysis of EPS production levels showed significant alterations among strains tested. Biofilm formation was found to be medium composition dependant, and there was a negative correlation with biofilm formation and EPS production. Autoaggregation properties and coaggregation of L. salivarius strains with chicken pathogens were appeared to be specific at strain level. An increment in bacterial adhesion to chicken gut explants was observed in L. salivarius strains with the reduction in EPS production levels. This study showed that strain-specific properties can determine the functional properties of L. salivarius strains, and the interference of these properties might be crucial for final selection of these strains for technological purposes.

Enhanced rhamnolipid production of Pseudomonas aeruginosa SG by increasing copy number of rhlAB genes with modified promoter

Increasing the copy number of rhlAB genes with a modified promoter efficiently enhanced the production of rhamnolipid by P. aeruginosa.

Characterization of an Ebosin derivative produced by heterologous gene replacement in Streptomyces sp. 139

BACKGROUND

Ebosin is a novel exopolysaccharide (EPS) produced by Streptomyces sp. 139 and evidenced to possess an anti-rheumatic arthritis activity in vivo. The Ebosin biosynthesis gene cluster (ste) consists of 27 ORFs and ste7 has previously been demonstrated to code for a fucosyltransferase, which plays an essential role in the formation of repeating sugar units during Ebosin production. Aiming to generate derivatives of Ebosin for better activity, we replaced ste7 with a gene encoding for a glucosyltransferase (gtf) from Streptococcus thermophilus.

RESULTS

This alteration resulted in a novel Ebosin derivative (EPS-7 g) with its monosaccharide composition dramatically changed, especially in the proportion of glucose which increased from 1.1% (Ebosin) to 84.01% (EPS-7 g). In an ELISA analysis, EPS-7 g exhibited a higher binding activity for IL-1R, as a competitor of interleukin-1, than that of Ebosin. It also exhibited a higher inhibitory effect on the activity of IL-1β-converting enzyme and production of IL-1β in fibroblast-like synoviocytes (FLS). In addition, experiments with acute inflamed mice induced by croton oil showed a significantly higher anti-inflammatory activity of EPS-7 g compared with Ebosin.

CONCLUSIONS

The new Ebosin derivative EPS-7 g is more bioactive than Ebosin evaluated by a series of experiments. This is the first report demonstrating a modification of EPS structure via heterologous gene replacement in Streptomyces.

Enhancement of Exopolysaccharide Production of Lactobacillus fermentum TDS030603 by Modifying Culture Conditions

To optimize culture conditions that enhance production of a highly viscous exopolysaccharide of Lactobacillus fermentum TDS030603, a chemically defined medium was examined. The best yield was found to be 199 ± 23 mg/l when 48-hr cultivation was microaerobically performed at 30°C in the chemically defined medium supplemented with 5% glucose and 1% ammonium citrate without pH control. In response to the optimized exopolysaccharide production, the mRNA expression levels of epsB, epsE, and epsG elevated significantly. Our results indicated that the optimal C/N ratio and/or microaerobic condition can alter the expression levels of several exopolysaccharide biosynthesis-related genes promoting the exopolysaccharide production yield.

Sugar source modulates exopolysaccharide biosynthesis in Bifidobacterium longum subsp. longum CRC 002

The effect of four sugars (glucose, galactose, lactose and fructose) on exopolysaccharide (EPS) production by Bifidobacterium longum subsp. longum CRC 002 was evaluated. More EPS was produced when CRC 002 was grown on lactose in the absence of pH control, with a production of 1080±120 mg EPS l−1 (P<0.01) after 24 h of incubation. For fructose, galactose and glucose, EPS production was similar, at 512±63, 564±165 and 616±93 mg EPS l−1, respectively. The proposed repeating unit composition of the EPS is 2 galactose to 3 glucose. The effect of sugar and fermentation time on expression of genes involved in sugar nucleotide production (galK, galE1, galE2, galT1, galT2, galU, rmlA, rmlB1 and rmlCD) and the priming glycosyltransferase (wblE) was quantified using real-time reverse transcription PCR. A significantly higher transcription level of wblE (9.29-fold) and the genes involved in the Leloir pathway (galK, 4.10-fold; galT1, 2.78-fold; and galE2, 4.95-fold) during exponential growth was associated with enhanced EPS production on lactose compared to glucose. However, galU expression, linking glucose metabolism with the Leloir pathway, was not correlated with EPS production on different sugars. Genes coding for dTDP-rhamnose biosynthesis were also differentially expressed depending on sugar source and growth phase, although rhamnose was not present in the composition of the EPS. This precursor may be used in cell wall polysaccharide biosynthesis. These results contribute to understanding the changes in gene expression when different sugar substrates are catabolized by B. longum subsp. longum CRC 002.

The Ser/Thr/Tyr phosphoproteome of Lactococcus lactis IL1403 reveals multiply phosphorylated proteins

Recent phosphoproteomics studies of several bacterial species have firmly established protein phosphorylation on Ser/Thr/Tyr residues as a PTM in bacteria. In particular, our recent reports on the Ser/Thr/Tyr phosphoproteomes of bacterial model organisms Bacillus subtilis and Escherichia coli detected over 100 phosphorylation events in each of the bacterial species. Here we extend our analyses to Lactococcus lactis, a lactic acid bacterium widely employed by the food industry, in which protein phosphorylation at Ser/Thr/Tyr residues was barely studied at all. Despite the lack of almost any prior evidence of Ser/Thr/Tyr protein phosphorylation in L. lactis, we identified a phosphoproteome of a size comparable to that of E. coli and B. subtilis, with 73 phosphorylation sites distributed over 63 different proteins. The presence of several multiply phosphorylated proteins, as well as over-representation of phosphothreonines seems to be the distinguishing features of the L. lactis phosphoproteome. Evolutionary comparison and the conservation of phosphorylation sites in different bacterial organisms indicate that a majority of the detected phosphorylation sites are species-specific, and therefore have probably co-evolved with the adaptation of the bacterial species to their present-day ecological niches.

Modelling strategies for the industrial exploitation of lactic acid bacteria

Lactic acid bacteria (LAB) have a long tradition of use in the food industry, and the number and diversity of their applications has increased considerably over the years. Traditionally, process optimization for these applications involved both strain selection and trial and error. More recently, metabolic engineering has emerged as a discipline that focuses on the rational improvement of industrially useful strains. In the post-genomic era, metabolic engineering increasingly benefits from systems biology, an approach that combines mathematical modelling techniques with functional-genomics data to build models for biological interpretation and--ultimately--prediction. In this review, the industrial applications of LAB are mapped onto available global, genome-scale metabolic modelling techniques to evaluate the extent to which functional genomics and systems biology can live up to their industrial promise.

In silico reconstruction of the metabolic pathways of Lactobacillus plantarum: comparing predictions of nutrient requirements with those from growth experiments

On the basis of the annotated genome we reconstructed the metabolic pathways of the lactic acid bacterium Lactobacillus plantarum WCFS1. After automatic reconstruction by the Pathologic tool of Pathway Tools (http://bioinformatics.ai.sri.com/ptools/), the resulting pathway-genome database, LacplantCyc, was manually curated extensively. The current database contains refinements to existing routes and new gram-positive bacterium-specific reactions that were not present in the MetaCyc database. These reactions include, for example, reactions related to cell wall biosynthesis, molybdopterin biosynthesis, and transport. At present, LacplantCyc includes 129 pathways and 704 predicted reactions involving some 670 chemical species and 710 enzymes. We tested vitamin and amino acid requirements of L. plantarum experimentally and compared the results with the pathways present in LacplantCyc. In the majority of cases (32 of 37 cases) the experimental results agreed with the final reconstruction. LacplantCyc is the most extensively curated pathway-genome database for gram-positive bacteria and is open to the microbiology community via the World Wide Web (www.lacplantcyc.nl). It can be used as a reference pathway-genome database for gram-positive microbes in general and lactic acid bacteria in particular.

Engineering metabolic highways in Lactococci and other lactic acid bacteria

Lactic acid bacteria (LAB) are widely used in industrial food fermentations and are receiving increased attention for use as cell factories for the production of food and pharmaceutical products. Glycolytic conversion of sugars into lactic acid is the main metabolic highway in these Gram-positive bacteria and Lactococcus lactis has become the model organism because of its small genome, genetic accessibility and simple metabolism. Here we discuss the metabolic engineering of L. lactis and the value of metabolic models compared with other LAB, with a particular focus on the food-grade production of metabolites involved in flavour, texture and health.