Home About us Contact
|
Home About us Contact | ||
|
|
||
Lactococcus Lactis (Lactococcu + lacti)
Terms modified by Lactococcus Lactis Selected AbstractsUniversal method for synthesis of artificial gel antibodies by the imprinting approach combined with a unique electrophoresis technique for detection of minute structural differences of proteins, viruses, and cells (bacteria).ELECTROPHORESIS, Issue 23 2006III: Gel antibodies against cells (bacteria) Abstract Artificial antibodies in the form of gel granules were synthesized from the monomers acrylamide and N,N'-methylenebisacrylamide by the imprinting method in the presence of Echerichia coli bacteria as template. The electrophoretic migration velocities of the gel antibodies (i),saturated with the antigen (Escherichia,coli MRE-600), (ii),freed of the antigen, and (iii),resaturated with bacteria, were determinated by electrophoresis in a rotating narrow-bore tube of 245,mm length and the 2.5 and 9.6,mm inner and outer diameters, respectively. Removal of bacteria from the gel antibodies was made by treatment with enzymes, followed by washing with SDS and buffer. Gel granules becoming charged by adsorption of bacteria move in an electrical field. We obtained a significant selectivity of gel antibodies for E.,coli MRE-600, since the granules did not interact with Lactococcus lactis; and when E.,coli BL21 bacteria were added to the gels selective for E.,coli MRE-600, a significant difference in the migration rate of the complexes formed with the two strains was observed indicating the ability of differentiation between the two strains. The gel antibodies can be used repeatedly. The new imprinting method for the synthesis of artificial gel antibodies against bioparticles described herein, and the classical electrophoretic analysis technique employed, thus represent , when combined , a new approach to distinguish between different types and strains of bacteria. The application area can certainly be extended to cover other classes of cells. [source] Contribution of exofacial thiol groups in the reducing activity of Lactococcus lactisFEBS JOURNAL, Issue 10 2010D. Michelon Lactococcus lactis can decrease the redox potential at pH 7 (Eh7) from 200 to ,200 mV in oxygen free Man,Rogosa,Sharpe media. Neither the consumption of oxidizing compounds or the release of reducing compounds during lactic acid fermentation were involved in the decrease in Eh7 by the bacteria. Thiol groups located on the bacterial cell surface appear to be the main components that are able to establish a greater exchange current between the Pt electrode and the bacteria. After the final Eh7 (,200 mV) was reached, only thiol-reactive reagents could restore the initial Eh7 value. Inhibition of the proton motive force showed no effect on maintaining the final Eh7 value. These results suggest that maintaining the exofacial thiol (,SH) groups in a reduced state does not depend on an active mechanism. Thiol groups appear to be displayed by membrane proteins or cell wall-bound proteins and may participate in protecting cells against oxidative stress. [source] The structural comparison of the bacterial PepX and human DPP-IV reveals sites for the design of inhibitors of PepX activityFEBS JOURNAL, Issue 8 2005Pascal Rigolet X-prolyl dipeptidyl aminopeptidases (X-PDAP) are enzymes catalysing the release of dipeptides from the amino termini of polypeptides containing a proline or an alanine at the penultimate position. Involved in various mammalian regulation processes, as well as in chronic human diseases, they have been proposed to play a role in pathogenicity for Streptococci. We compared the structure of X-PDAP from Lactococcus lactis (PepX) with its human counterpart DPP-IV. Despite very different overall folds, the residues most implicated for X-PDAP activity are conserved in the same positions and orientations in both enzymes, thus defining a structural signature for the X-PDAP specificity that crosses the species frontiers of evolution. Starting from this observation, we tested some inhibitors of DPP-IV on PepX activity, for which no specific inhibitor is known. We thus found that PepX was highly sensitive to valine-pyrrolidide with a KI of 9.3 µm, close to that reported in DPP-IV inhibition. We finally used the structure of PepX from L. lactis as a template for computer-based homology modeling of PepX from the pathogenic Streptococcus gordonii. Docking simulations of valine-pyrrolidide into the active site of PepX led to the identification of key residues for a rational drug design against PepX from Streptococci. These results could have applications in human health giving new perspectives to the struggle against pathogens. [source] Expression of the pyrG gene determines the pool sizes of CTP and dCTP in Lactococcus lactisFEBS JOURNAL, Issue 12 2004Casper M. Jųrgensen The pyrG gene from Lactococcus lactis encodes CTP synthase (EC 6.4.3.2), an enzyme converting UTP to CTP. A series of strains were constructed with different levels of pyrG expression by insertion of synthetic constitutive promoters with different strengths in front of pyrG. These strains expressed pyrG levels in a range from 3 to 665% relative to the wild-type expression level. Decreasing the level of CTP synthase to 43% had no effect on the growth rate, showing that the capacity of CTP synthase in the cell is in excess in a wild-type strain. We then studied how pyrG expression affected the intracellular pool sizes of nucleotides and the correlation between pyrG expression and nucleotide pool sizes was quantified using metabolic control analysis in terms of inherent control coefficients. At the wild-type expression level, CTP synthase had full control of the CTP concentration with a concentration control coefficient close to one and a negative concentration control coefficient of ,0.28 for the UTP concentration. Additionally, a concentration control coefficient of 0.49 was calculated for the dCTP concentration. Implications for the homeostasis of nucleotide pools are discussed. [source] Oral vaccination of mice against Helicobacter pylori with recombinant Lactococcus lactis expressing urease subunit BFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 3 2009Qing Gu Abstract To determine whether a protective immune response could be elicited by oral delivery of a recombinant live bacterial vaccine, Helicobacter pylori urease subunit B (UreB) was expressed for extracellular expression in food-grade bacterium Lactococcus lactis. The UreB-producing strains were then administered orally to mice, and the immune response to UreB was examined. Orally vaccinated mice produced a significant UreB-specific serum immunoglobulin G (IgG) response. Specific anti-UreB IgA responses could be detected in the feces of mice immunized with the secreting lactococcal strain. Mice vaccinated orally were significantly protected against gastric Helicobacter infection following a challenge with H. pylori strain SS1. In conclusion, mucosal vaccination with L. lactis expressing UreB produced serum IgG and UreB-specific fecal IgA, and prevented gastric infection with H. pylori. [source] A xylose-inducible expression system for Lactococcus lactisFEMS MICROBIOLOGY LETTERS, Issue 2 2004Anderson Miyoshi Abstract A new controlled production system to target heterologous proteins to cytoplasm or extracellular medium is described for Lactococcus lactis NCDO2118. It is based on the use of a xylose-inducible lactococcal promoter, PxylT. The capacities of this system to produce cytoplasmic and secreted proteins were tested using the Staphylococcus aureus nuclease gene (nuc) fused or not to the lactococcal Usp45 signal peptide. Xylose-inducible nuc expression is tightly controlled and resulted in high-level and long-term protein production, and correct targeting either to the cytoplasm or to the extracellular medium. Furthermore, this expression system is versatile and can be switched on or off easily by adding either xylose or glucose, respectively. These results confirm the potential of this expression system as an alternative and useful tool for the production of proteins of interest in L. lactis. [source] Heterologous gene expression in Lactococcus lactis; expression of the Azotobacter vinelandii algE6 gene product displaying mannuronan C-5 epimerase activityFEMS MICROBIOLOGY LETTERS, Issue 2 2003Janet M. Blatny Abstract The Azotobacter vinelandii mannuronan C-5 epimerases AlgE1,7 can be used to improve the properties of the commercially important polysaccharide alginate that is widely used in a variety of products, such as food and pharmaceuticals. Since lactic acid bacteria are generally regarded as safe, they are attractive candidates for production of the epimerases. A. vinelandii genes are GC-rich, in contrast to those of lactic acid bacteria, but we show here that significant expression levels of the epimerase AlgE6 can be obtained in Lactococcus lactis using the nisin-controlled expression system. A 1200-fold induction ratio was obtained resulting in an epimerase activity of 23,900 dpm mg,1 h,1, using a tritiated alginate substrate. The epimerase was detected by Western blotting and nuclear magnetic resonance spectroscopy analysis of its reaction product showed that the enzyme displayed catalytic properties similar to those produced in Escherichia coli. [source] Flavour formation by lactic acid bacteria and biochemical flavour profiling of cheese productsFEMS MICROBIOLOGY REVIEWS, Issue 3 2005Gerrit Smit Abstract Flavour development in dairy fermentations, most notably cheeses, results from a series of (bio)chemical processes in which the starter cultures provide the enzymes. Particularly the enzymatic degradation of proteins (caseins) leads to the formation of key-flavour components, which contribute to the sensory perception of dairy products. More specifically, caseins are degraded into peptides and amino acids and the latter are major precursors for volatile aroma compounds. In particular, the conversion of methionine, the aromatic and the branched-chain amino acids are crucial. A lot of research has focused on the degradation of caseins into peptides and free amino acids, and more recently, enzymes involved in the conversion of amino acids were identified. Most data are generated on Lactococcus lactis, which is the predominant organism in starter cultures used for cheese-making, but also Lactobacillus, Streptococcus, Propionibacterium and species used for surface ripening of cheeses are characterised in their flavour-forming capacity. In this paper, various enzymes and pathways involved in flavour formation will be highlighted and the impact of these findings for the development of industrial starter cultures will be discussed. [source] The long and winding road from the research laboratory to industrial applications of lactic acid bacteriaFEMS MICROBIOLOGY REVIEWS, Issue 3 2005Martin Bastian Pedersen Abstract Research innovations are constantly occurring in universities, research institutions and industrial research laboratories. These are reported in the scientific literature and presented to the scientific community in various congresses and symposia as well as through direct contacts and collaborations. Conversion of these research results to industrially useful innovations is, however, considerably more complex than generally appreciated. The long and winding road from the research laboratory to industrial applications will be illustrated with two recent examples from Chr. Hansen A/S: the implementation in industrial scale of a new production technology based on respiration by Lactococcus lactis and the introduction to the market of L. lactis strains constructed using recombinant DNA technology. [source] Screening for natural defence mechanisms of Lactococcus lactis strains isolated from traditional starter culturesINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 7 2007Andreja Mikli Summary Three different bacterial defence mechanisms were identified in the seventeen Lactococcus lactis isolates from starter cultures in three Slovenian dairy plants. Isolates MB18, KR7, PT4, PT13 and PT19 inhibited phage adsorption by means of exopolysaccharides production. The most extensive polysaccharides production was detected in PT19 isolate, which was susceptible only to phage ,PT19. Eight isolates exhibited nuclease activity, and seven of them were susceptible up to four phages out of thirteen from our collection. Eight isolates possessed the abiB gene, fourteen isolates abiH, two isolates abiJ and one isolate abiQ. Isolates PT27 and PT28 possessed AbiB, AbiH and AbiJ mechanisms as well as inhibition of phage adsorption. Isolate MB18, which was susceptible to one phage only, possessed the abiQ gene, nuclease activity and ability to prevent adsorption of most phages. Isolates PT67 and PT70, possessing only AbiH mechanism, were susceptible to only two phages. [source] Chemical and microbiological quality of Garris, Sudanese fermented camel's milk productINTERNATIONAL JOURNAL OF FOOD SCIENCE & TECHNOLOGY, Issue 3 2006Abdel Moneim El-Hadi Sulieman Summary In the present study, some of the chemical and microbiological characteristics of garris, a Sudanese traditionally fermented camel's milk product, were investigated. The chemical analyses included, pH, titrable acidity and ethanol contents. A total of 100 strains of lactic acid bacteria (LAB) were isolated from twenty samples of traditionally fermented household garris. The selected isolates were phenotypically characterized by their ability to ferment 49 carbohydrates using API 50 CHL kits and additional biochemical tests. LAB dominated the microflora of garris samples, and the major genera were Lactobacillus (74%), followed by Lactococcus (12%), Enterococcus (10%) and Leuconostocs (4%). The most predominant Lactobacillus species were identified as Lactobacillus paracasei ssp. paracasei (64 strains), L. fermentum (seven strains) and only three strains as L. plantarum. Most strains produced the enzymes that are relevant to cultured dairy product processing. The Lactococcus species were identified as Lactococcus lactis. The average pH value of the samples was 4.42 ± 0.21. The pH values were accompanied with increasing of titrable acidity which averaged 1.72 ± 0.04%. The relatively high amounts of ethanol detected in all samples (average 1.40 ± 0.03%) together with the high yeasts counts (6.0 ± 0.53 log10 cfu mL,1), indicated that the fermentation process of garris is a yeast-lactic fermentation. [source] Genotypic and technological characterization of Lactococcus lactis isolates involved in processing of artisanal Manchego cheeseJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2009P. Nieto-Arribas Abstract Aims:, Genotypic and technological characterization of wild lactococci isolated from artisanal Manchego cheese during the ripening process for selection of suitable starter cultures. Methods and Results:, A total of 114 isolates of lactococci were typed using randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR). Sixteen distinct RAPD-PCR patterns, at a similarity level of 73%, were obtained. On the basis of species-specific PCR reaction, the isolates were assigned to the species Lactococcus lactis subsp. lactis and Lactococcus lactis subsp. cremoris with L. lactis subsp. lactis being predominant at both dairies. Twenty-six isolates were technologically characterized to select those with the best properties. Most of them showed good technological properties although some could produce tyramine. Conclusions:, The presence of coincident genotypes at both dairies has been demonstrated, which would suggest that they are well adapted to the Manchego cheese environment. Interesting differences were found in the technological characterization and the potential role of autochthonous lactococci strains as starter culture has been displayed. Significance and Impact of the Study:, The great economic importance of Manchego cheese encouraged a deeper knowledge of its microbiota, to select strains with the best properties to use as starter cultures in industrial Manchego cheeses, preserving the autochthonous characteristics. [source] Use of induction promoters to regulate hyaluronan synthase and UDP-glucose-6-dehydrogenase of Streptococcus zooepidemicus expression in Lactococcus lactis: a case study of the regulation mechanism of hyaluronic acid polymerJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2009J.Z. Sheng Abstract Aims:, To determine the effects of the ratios of hyaluronan synthase expression level to precursor sugar UDP-GlcA biosynthesis ability on the molecular weight (MW) of hyaluronic acid (HA) in recombinant Lactococcus lactis. Methods and Results:, The genes szHasA (hyaluronan synthase gene) and szHasB (UDP-glucose-6-dehydrogenase gene) of Streptococcus zooepidemicus were introduced into L. lactis under the control of nisA promoter and lacA promoter respectively, resulting in a dual-plasmid controlled expression system. The effects of the ratios of hyaluronan synthase expression level to the precursor sugar UDP-GlcA biosynthesis ability under different induction concentration collocations with nisin and lactose on the MW of HA in recombinant L. lactis were determined. The results showed that the final weight-average molecular weight () of HA correlated with the relative ratios of HasA (hyaluronan synthase) expression level to the concentration of UDP-GlcA. Conclusions:, Regulating the relative ratios of HasA expression level to the precursor sugar biosynthesis ability was an efficient method to control the size of HA. Significance and Impact of the Study:, This study put forward a guide to establish an efficacious way to control the size of HA in fermentation. [source] Nisin Z inhibits the growth of Candida albicans and its transition from blastospore to hyphal formJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2008C. Le Lay Abstract Aims:, To investigate the efficacy of nisin Z, an antimicrobial peptide produced by certain strains of Lactococcus lactis against Candida albicans growth and transition. Methods and Results:,Candida albicans was cultured in the presence of various concentrations of nisin Z (1000, 500, and 100 ,g ml,1) for different time points. Candida albicans growth was determined using the Alamar Blue assay. The yeast's transition from blastospore to hyphal form was assessed through optical microscope observations. The effect of nisin Z on C. albicans ultrastructure was followed by scanning and transmission electron microscopy. Our results show that nisin Z inhibited C. albicans growth beginning at 500 ,g ml,1. This inhibition was both time- and dose-dependent. Nisin Z was also active against C. albicans transition by significantly inhibiting the transformation of C. albicans from the blastospore to hyphal form. Treatments with nisin Z lead to ultrastructural disturbances of C. albicans. Conclusion:, Our findings indicate that nisin Z significantly reduced C. albicans growth and transition. These effects may have occurred through ultrastructural modifications of this yeast. Significance and Impact of the Study:, For the first time, effect of nisin Z on C. albicans was investigated. These results therefore suggest that nisin Z may have antifungal properties, and could be used as an antifungal molecule. [source] Construction and evaluation of food-grade vectors for Lactococcus lactis using aspartate aminotransferase and , -galactosidase as selectable markersJOURNAL OF APPLIED MICROBIOLOGY, Issue 1 2006V.R. Sridhar Abstract Aims:, We report development of two food-grade cloning vectors for Lactococcus lactis, which utilize either a lactococcal aspartate aminotransferase gene (aspC), or Bifidobacterium longum, -galactosidase gene (aglL) as selectable markers. Methods and Results:, The theta-replicon of lactococcal plasmid, pW563, was combined with aspC and a multiple cloning site. When electroporated into L. lactis JLS400 (AspC,), the resulting vector, pSUW611 (3·9 kbp), restores ability of the mutant to grow in milk thus allowing for selection of the transformants. The vector is stable during 100 generations of nonselective growth (0·2% loss per generation). The second vector, pSUW711 (5·1 kbp), was constructed by exchanging aspC with aglL under the control of usp45 promoter. Lactococcus lactis transformed with pSUW711 produced distinctive colonies within 48,72 h on melibiose-containing plates. Expression of two Lactobacillus helveticus peptidases was attempted using these new vehicles. Introduction of pepN on pSUW611 and pSUW711 into L. lactis led to a sixfold, or 27-fold increase in aminopeptidase activity, respectively. However, no changes in endopeptidase activity were recorded upon transformation with pSUW611 carrying pepO2 under control of three different promoters. Attempts were also made to construct high copy variants of pSUW711. Conclusions:, The aspC and aglL can be employed as food-grade genetic markers for L. lactis. The vectors, pSUW611 and pSUW711, were successfully used to express Lact. helveticus PepN in L. lactis. Significance and Impact of the Study:, Two novel food-grade vectors were developed which provide simple and convenient selection and maintenance in L. lactis. [source] Characterization of dominant microbiota of a Ghanaian fermented milk product, nyarmie, by culture- and nonculture-based methodsJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2006M. Obodai Abstract Aims:, To characterize the predominant micro-organisms in a Ghanaian traditional fermented dairy product, nyarmie, made from cows' milk, using both culture- and nonculture-based methods. Methods and Results:, Samples of nyarmie were analysed from three production sites in Accra, by determining the counts on selective culture media. The microbial diversity occurring in nyarmie was also evaluated by 16S/18S ribosomal DNA PCR amplification and denaturing gradient gel electrophoresis. Results showed that nyarmie contained lactococci and lactobacilli in the range of 108 and 1010 CFU ml,1, respectively, and yeasts at around 107 CFU ml,1. The pH ranged between 3·49 and 4·25. The predominant lactic acid bacteria (LAB) in nyarmie were Leuconostocmesenteroides ssp. mesenteroides, Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, Lact.helveticus, Lact. delbrueckii ssp. lactis and Lactococcus lactis, while Saccharomyces cerevisiae was the predominant yeast species. Lactobacillus delbrueckii ssp. delbrueckii was not detected by cultivation but its predominance was revealed by PCR-DGGE analysis. Conclusions:, The flora in products from different producers varied in the LAB composition present and may result in variations in product quality. Significance and Impact of the Study:, Development and use of starter cultures for nyarmie may be beneficial in improving the consistency of product quality. [source] Antilisterial activity of lactic acid bacteria isolated from rigouta, a traditional Tunisian cheeseJOURNAL OF APPLIED MICROBIOLOGY, Issue 3 2004T. Ghrairi Abstract Aims:, Screening for lactic acid bacteria (LAB) producing bacteriocins and other antimicrobial compounds is of a great significance for the dairy industry to improve food safety. Methods and Results:, Six-hundred strains of LAB isolated from ,rigouta', a Tunisian fermented cheese, were tested for antilisterial activity. Eight bacteriocinogenic strains were selected and analysed. Seven of these strains were identified as Lactococcus lactis and produced nisin Z as demonstrated by mass spectrometry analysis of the purified antibacterial compound. Polymerase chain reaction experiments using nisin gene-specific primers confirmed the presence of nisin operon. Plasmid profiles analysis suggests the presence of, at least, three different strains in this group. MMT05, the eighth strain of this antilisterial collection was identified, at molecular level, as Enterococcus faecalis. The purified bacteriocin produced by this strain showed a molecular mass of 10 201·33 ± 0·85 Da. This new member of class III bacteriocins was termed enterocin MMT05. Conclusions:, Seven lactococcal strains producing nisin Z were selected and could be useful as bio-preservative starter cultures. Additional experiments are needed to evaluate the promising strain MMT05 as bio-preservative as Enterococci could exert detrimental or beneficial role in foods. Significance and Impact of the Study:, Only a few antibacterial strains isolated from traditional African dairy products were described. The new eight strains described herein contribute to the knowledge of this poorly studied environment and constitute promising strains for fermented food safety. [source] Integrated polymerase chain reaction-based procedures for the detection and identification of species and subspecies of the Gram-positive bacterial genus LactococcusJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2002Z.Y. Pu Aims:,Five species of the Gram-positive bacterial genus Lactococcus (Lactococcus lactis, L. garvieae, L. plantarum, L. piscium and L. raffinolactis) are currently recognized. The aim of this work was to develop a simple approach for the identification of these species, as well as to differentiate the industrially important dairy subspecies L. lactis subsp. lactis and L. lactis subsp. cremoris. Methods and Results:,Methods were devised based on specific polymerase chain reaction (PCR) amplifications that exploit differences in the sequences of the 16S ribosomal RNA genes of each species, followed by restriction enzyme cleavage of the PCR products. The techniques developed were used to characterize industrial cheese starter strains of L. lactis and the results were compared with biochemical phenotype and DNA sequence data. Conclusions:,The PCR primers designed can be used simultaneously, providing a simple scheme for screening unknown isolates. Strains of L. lactis show heterogeneity in the 16S ribosomal RNA gene sequence. Significance and Impact of the Study:,This work provides an integrated set of methods for differentiation and identification of lactococcal species associated with agricultural, veterinary, medical and processed food industries. [source] Autolytic phenotype of Lactococcus lactis strains isolated from traditional Tunisian dairy productsJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2002H. Ouzari Aims:,To evaluate the autolytic properties of Lactococcus lactis strains isolated from artisan Tunisian dairy products, their peptidoglycan hydrolase content and their activity spectrum. Methods and Results:,The autolytic phenotype of Lactococcus strains was evaluated under starvation conditions in potassium phosphate buffer. The results obtained highlighted a high degree of diversity among the strains analysed, allowing the identification of high and low autolytic Lactococcus lactis strains. Peptidoglycan hydrolase content was evaluated by renaturing SDS-PAGE using cells of Micrococcus lysodeikticus as a target for the enzymatic activity. A major activity band migrating at about 45 kDa was observed. The lytic activity, evaluated in the presence of different chemicals, was retained in 8% NaCl, 15 mmol l,1 CaCl2, and in a pH range between 5 and 9·5. The substrate specificity of peptidoglycan hydrolase from Lactococcus strains was evaluated in renaturing SDS-PAGE incorporating cells of different bacterial species. The major autolysin of Lactococcus lactis was active against cells of Lactococcus lactis subsp. lactis, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lactobacillus helveticus and Listeria monocytogenes. Conclusions:,Autolytic activity is widely distributed in Lactococcus lactis and the rate of autolysis is strain-dependent. The major peptidoglycan hydrolase showed a wide spectrum of activity against several lactic acid bacteria and bacterial species involved in food-related infection. Significance and Impact of the Study:,The autolytic phenotype of Lactococcus lactis strains isolated from Tunisian artisan dairy products has been determined, and the data obtained should allow the selection of strains of technological interest in the cheese-ripening process. [source] Genotypic and phenotypic heterogeneity among lactococci isolated from traditional Pecorino Sardo cheeseJOURNAL OF APPLIED MICROBIOLOGY, Issue 2 2000L. Mannu Twenty-nine Lactococcus lactis isolates from one traditional 24 h-old Pecorino Sardo cheese were characterized phenotypically, technologically and genotypically in order to assess the biodiversity within this wild microbial population. Two DNA-based techniques, plasmid profiling and PFGE, were used for the genetic typing of the isolates. All 29 isolates were characterized at strain level and eight different genotypes were recognized. In addition, by combining the results from plasmid profile analysis and PFGE, it was possible to identify closely related isolates probably belonging to the same clonal lineage. The dominant biotype was identified in the 24 h-old cheese, as were the strains believed to act as starters for the curd. Atypical lactococci, able to grow in 6·5% NaCl, were isolated. The results suggest that wild bacterial populations should be preserved in order to protect the traditional raw milk cheeses, and to select new starter strains for the dairy industry. [source] Genetically engineered normal flora for oral polypeptide delivery: Dose,absorption responseJOURNAL OF PHARMACEUTICAL SCIENCES, Issue 8 2009Gagan Kaushal Abstract Genetically modified Lactococcus lactis (L. lactis), a probiotic bacterium, able to secrete ,-lactamase (29 kDa), was used as a vector for the oral delivery of ,-lactamase to the rats. Three different doses of L. lactis were administered to the rats, and the resulted ,-lactamase oral bioavailability was studied, and compared to the solution form. The oral administration of 1.2,×,107, 3,×,107, and 8,×,107 colony-forming units of L. lactis led to 145, 209, and 364 mU of ,-lactamase absorbed, and the corresponding bioavailability was 8.7%, 15.5%, and 20.8% based on the in vitro production of ,-lactamase by L. lactis. The oral administration of 504 mU and 1008 mU ,-lactamase free solution resulted in 30 and 47 mU absorbed, a bioavailability of 5.9% and 4.7%, respectively. L. lactis significantly (p,<,0.01) increased the oral bioavailability compared to the free solution form. A significant (p,<,0.01) increase in the MAT value as compared to the solution, demonstrated that L. lactis can be used as a sustained delivery system. In conclusion, there is a linear relationship between L. lactis dose and these absorption PK parameters within L. lactis dose range of the current study. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:2573,2580, 2009 [source] Discrepancies between the phenotypic and genotypic characterization of Lactococcus lactis cheese isolatesLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2006M. De La Plaza Abstract Aims:, The use of randomly amplified polymorphic DNA (RAPD)-PCR fingerprinting and plasmid profiles to determine at the strain level, the similarity of Lactococcus lactis isolates obtained during sampling of traditional cheeses and to verify its correspondence to the selected phenotypic characteristics. Methods and Results:, A total of 45 L. lactis isolates were genotypically analysed by RAPD-PCR fingerprinting and plasmid patterns. Phenotypic traits used to compare strains were proteolytic, acidifying, aminotransferase (aromatic and branched chain aminotransferase) and , -ketoisovalerate decarboxylase (Kivd) activities. The results show that 23 isolates could be grouped in clusters that exhibited 100% identity in both their RAPD and plasmid patterns, indicating the probable isolation of dominant strains during the cheese sampling process. However, there were phenotypic differences between isolates within the same cluster that included the loss of relevant technological properties such as proteinase activity and acidifying capacity or high variation in their amino acid converting enzyme activities. Likewise, the analysis of a specific attribute, Kivd activity, indicated that 7 of 15 isolates showed no detectable activity despite the presence of the encoding (kivd) gene. Conclusion:, Phenotypic differences found between genotypically similar strains of L. lactis strains could be linked to differences in enzymatic expression. Significance and Impact of the Study:, Phenotypic analysis of L. lactis isolates should be considered when selecting strains with new cheese flavour forming capabilities. [source] Influence of pH drop on both nisin and pediocin production by Lactococcus lactis and Pediococcus acidilacticiLETTERS IN APPLIED MICROBIOLOGY, Issue 1 2003N.P. Guerra Abstract Aims: To develop a kinetic model for describing the specific effect of pH drop on nisin and pediocin production in whey. Methods and Results: The effect of pH drop on both bacteriocin productions was tested in non-buffered whey and whey buffered at initial pH 6·3 with 0·03, 0·10 and 0·25 mol l,1 of potassium hydrogen phthalate-NaOH. An accurate description of the experimental data of nisin and pediocin obtained at different pH drops is obtained with the proposed model. Conclusions: The proposed model was able to typify both bacteriocins as pH-dependent primary metabolites. Significance and Impact of the Study: The decisive role of pH drop for bacteriocin production on whey was demonstrated and modelled. This study contributes to a better understanding of underlying metabolic regulatory mechanisms, which could facilitate the optimization of bacteriocin production for upscaling. [source] Conditions for conjugative transposon transfer in Lactococcus lactisLETTERS IN APPLIED MICROBIOLOGY, Issue 5 2000G. Blaiotta Three different techniques for bacterial mating were applied to wild type and culture collection strains of Lactococcus lactis harbouring transposons: direct plate conjugation, filter mating and mating on milk agar. Efficiencies and frequencies of transfer were compared. Transconjugants were characterized by marker properties and molecular assays. Transposon-coded Suc+ Nis+ phenotype as well as Suc+ Bac+ Nis, phenotype were transferred with frequencies ranging between 10,9 and 10,6. Milk agar plate mating was the best technique for obtaining gene transfer events involving wild type lactococci. [source] Lactococcus lactis produces short-chain quinones that cross-feed Group B Streptococcus to activate respiration growthMOLECULAR MICROBIOLOGY, Issue 5 2008Lahcen Rezaļki Summary Quinones are essential components of the respiration chain that shuttle electrons between oxidoreductases. We characterized the quinones synthesized by Lactococcus lactis, a fermenting bacterium that activates aerobic respiration when a haem source is provided. Two distinct subgroups were characterized: Menaquinones (MK) MK-8 to MK-10, considered as hallmarks of L. lactis, are produced throughout growth. MK-3 and demethylMK-3 [(D)MK-3] are newly identified and are present only late in growth. Production of (D)MK-3 was conditional on the carbon sugar and on the presence of carbon catabolite regulator gene ccpA. Electron flux driven by both (D)MK fractions was shared between the quinol oxidase and extracellular acceptors O2, iron and, with remarkable efficiency, copper. Purified (D)MK-3, but not MK-8,10, complemented a menB defect in L. lactis. We previously showed that a respiratory metabolism is activated in Group B Streptococcus (GBS) by exogenous haem and MK, and that this activity is implicated in virulence. Here we show that growing lactococci donate (D)MK to GBS to activate respiration and stimulate growth of this opportunist pathogen. We propose that conditions favouring (D)MK production in dense microbial ecosystems, as present in the intestinal tract, could favour implantation of (D)MK-scavengers like GBS within the complex. [source] Identification of an essential gene responsible for d -Asp incorporation in the Lactococcus lactis peptidoglycan crossbridgeMOLECULAR MICROBIOLOGY, Issue 6 2006Patrick Veiga Summary Bacteria such as Lactococcus lactis have d -aspartate (d -Asp) or its amidated derivative d -asparagine (d -Asn), in their peptidoglycan (PG) interpeptide crossbridge. We performed a subtractive genome analysis to identify L. lactis gene yxbA, orthologues of which being present only in bacteria containing d -amino acids in their PG crossbridge, but absent from those that instead insert l -amino acids or glycine. Inactivation of yxbA required a complementing Streptococcus pneumoniae murMN genes, which express enzymes that incorporate l -Ser- l -Ala or l -Ala- l -Ala in the PG crossbridge. Our results show that (i) yxbA encodes d -Asp ligase responsible for incorporation of d -Asp in the PG crossbridge, and we therefore renamed it as aslA, (ii) it is an essential gene, which makes its product a potential target for specific antimicrobials, (iii) the absence of d -Asp may be complemented by l -Ser- l -Ala or l -Ala- l -Ala in the L. lactis PG, indicating that the PG synthesis machinery is not selective for the side-chain residues, and (iv) lactococcal strains having l -amino acids in their PG crossbridge display defects in cell wall integrity, but are able to efficiently anchor cell wall proteins, indicating relative flexibility of lactococcal transpeptidation reactions with respect to changes in PG side-chain composition. [source] Fibronectin-binding proteins of Staphylococcus aureus mediate activation of human platelets via fibrinogen and fibronectin bridges to integrin GPIIb/IIIa and IgG binding to the Fc,RIIa receptorMOLECULAR MICROBIOLOGY, Issue 1 2006J. Ross Fitzgerald Summary Staphylococcus aureus is a leading cause of infective endocarditis (IE). Platelet activation promoted by S. aureus resulting in aggregation and thrombus formation is an important step in the pathogenesis of IE. Here, we report that the fibrinogen/fibronectin-binding proteins FnBPA and FnBPB are major platelet-activating factors on the surface of S. aureus from the exponential phase of growth. Truncated derivatives of FnBPA, presenting either the fibrinogen-binding A domain or the fibronectin-binding BCD region, each promoted platelet activation when expressed on the surface of S. aureus or Lactococcus lactis, indicating two distinct mechanisms of activation. FnBPA-promoted platelet activation is mediated by fibrinogen and fibronectin bridges between the A domain and the BCD domains, respectively, to the low affinity form of the integrin GPIIb/IIIa on resting platelets. Antibodies recognizing the FnBPA A domain or the complex between the FnBPA BCD domains and fibronectin were essential for activation promoted by bacteria expressing the A domain or the BCD domain respectively. Activation was inhibited by a monoclonal antibody (IV-3) specific for the Fc,RIIa IgG receptor on platelets. We propose that the activation of quiescent platelets by bacteria expressing FnBPs involves the formation of a bridge between the bacterial cell and the platelet surface by (i) fibronectin and fibrinogen interacting with the low affinity form of GPIIb/IIIa and (ii) by antibodies specific to FnBPs that engage the platelet Fc receptor Fc,RIIa. Platelet activation by S. aureus clinical IE isolates from both the exponential and stationary phases of growth was completely inhibited by monoclonal antibody IV-3 suggesting that the IgG,Fc,RIIa interaction is of fundamental importance for platelet activation mediated by this organism. This suggests new avenues for development of therapeutics against vascular infections. [source] Conjugation mediates transfer of the Ll.LtrB group II intron between different bacterial speciesMOLECULAR MICROBIOLOGY, Issue 5 2004Kamila Belhocine Summary Some self-splicing group II introns (ribozymes) are mobile retroelements. These retroelements, which can insert themselves into cognate intronless alleles or ectopic sites by reverse splicing, are thought to be the evolutionary progenitors of the widely distributed eukaryotic spliceosomal introns. Lateral or horizontal transmission of introns (i.e. between species), although never experimentally demonstrated, is a well-accepted model for intron dispersal and evolution. Horizontal transfer of the ancestral bacterial group II introns may have contributed to the dispersal and wide distribution of spliceosomal introns present in modern eukaryotic genomes. Here, the Ll.LtrB group II intron from the Gram-positive bacterium Lactococcus lactis was used as a model system to address the dissemination of introns in the bacterial kingdom. We report the first experimental demonstration of horizontal transfer of a group II intron. We show that the Ll.LtrB group II intron, originally discovered on an L. lactis conjugative plasmid (pRS01) and within a chromosomally located sex factor in L. lactis 712, invades new sites using both retrohoming and retrotransposition pathways after its transfer by conjugation. Ll.LtrB lateral transfer is shown among different L. lactis strains (intraspecies) (retrohoming and retrotransposition) and between L. lactis and Enterococcus faecalis (interspecies) (retrohoming). These results shed light on long-standing questions about intron evolution and propagation, and demonstrate that conjugation is one of the mechanisms by which group II introns are, and probably were, broadly disseminated between widely diverged organisms. [source] Strong associations between gene function and codon usageAPMIS, Issue 9 2003ANDERS FUGLSANG The association between codon usage and gene function was analyzed in the complete genomes of Eschericia coli, Bacillus subtilis, Lactococcus lactis and Campylobacter jejuni, using the functional annotation provided by NCBI. Two distinctly different ways of quantifying codon usage were used in the analysis. By using contingency tables it was found that for most amino acids a highly significant association with gene function exists for all species, indicating that codon usage at the level of individual amino acids is generally closely coordinated with gene function. By computing the effective number of codons in the annotated genes and comparing the median values in groups of different gene functions it was shown for all species that codon bias gene by gene also differs. [source] The effect of Lactococcus lactis on the abundance of aeromonads in the rearing water of the goldfish, Carassius auratus (Linnaeus)AQUACULTURE RESEARCH, Issue 1 2009Haruo Sugita First page of article [source] | ||||||||||||||||||||||||||||