Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Lactococcus lactis”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,531 records · Page 85Linked to original sources
PubMed2002

The LcnC homologue cannot replace LctT in lacticin 481 export.

Lacticin 481 is produced by Lactococcus lactis subsp. lactis and belongs to subgroup AII of the lanthionine-containing bacteriocins. The putative homodimeric LctT involved in lacticin 481 production shares significant similarities with the 'LcnC' protein encoded by 'lcnC', located on the chromosome of the lactic acid bacterium, L. lactis IL1403. LctT and 'LcnC' belong to the recently defined family of AMS (ABC transporter maturation and secretion) proteins. Inactivation of the 'lcnC' gene demonstrates that it is not responsible for the weak lacticin 481 production observed in a strain expressing only the precursor peptide LctA, and the modification enzyme LctM. This result indicates that the two AMS proteins, 'LcnC' and LctT, are not interchangeable in the machinery of processing/export of lacticin 481.

ATP-Binding Cassette Transporters↗
PubMed1997

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.

Genetic Vectors↗
PubMed1999

A nisin bioassay based on bioluminescence.

A Lactococcus lactis subsp. lactis strain that can sense the bacteriocin nisin and transduce the signal into bioluminescence was constructed. By using this strain, a bioassay based on bioluminescence was developed for quantification of nisin, for detection of nisin in milk, and for identification of nisin-producing strains. As little as 0.0125 ng of nisin per ml was detected within 3 h by this bioluminescence assay. This detection limit was lower than in previously described methods.

Animals↗
PubMed1992

Genetic analysis of scrA and scrB from Streptococcus sobrinus 6715.

A DNA fragment containing scrA and scrB, which encode enzyme II of the phosphoenolpyruvate-dependent sucrose phosphotransferase system and sucrose-6-phosphate hydrolase, respectively, was isolated from a lambda gt10 genomic DNA library of Streptococcus sobrinus 6715. Both genes were located on a 4.2-kb DNA fragment which was maintained stably in Escherchia coli on low-copy-number vector pGB2. The recombinant E. coli clone expressed sucrose-hydrolytic activity on MacConkey agar base supplemented with raffinose or sucrose. Results from deletion analysis showed that the sucrose-metabolic activity was contained within a 3.5-kb region. The lactic acid bacterium Lactococcus lactis subsp. lactis LM0230, which is devoid of sucrose-metabolic activity, was used to study the enzyme activities encoded by scrA and scrB from S. sobrinus 6715. L. lactis transformants carrying the 4.2-kb S. sobrinus-derived DNA fragment on E. coli-Streptococcus shuttle vector pDL278 were able to grow at the expense of sucrose and exhibited enzyme II and sucrose-6-phosphate hydrolase activities. Results from hybridization studies and a comparison of the restriction endonuclease maps of the scrA- and scrB-containing chromosomal regions from S. mutans GS5 and S. sobrinus 6715 suggested considerable divergence.

DNA Probes↗
PubMed2005

Heterologously expressed bacterial and human multidrug resistance proteins confer cadmium resistance to Escherichia coli.

The human MDR1 gene is induced by cadmium exposure although no resistance to this metal is observed in human cells overexpressing hMDR1. To access the role of MDR proteins in cadmium resistance, human MDR1, Lactococcus lactis lmrA, and Oenococcus oeni omrA were expressed in an Escherichia coli tolC mutant strain which proved to be hypersensitive to cadmium. Both the human and bacterial MDR genes conferred cadmium resistance to E. coli up to 0.4 mM concentration. Protection was abolished by 100 microM verapamil. Quantification of intracellular cadmium concentration by atomic absorption spectrometry showed a reduced cadmium accumulation in cells expressing the MDR genes. Inside-out membrane vesicles of L. lactis overexpressing lmrA displayed an ATP-dependent (109)Cd(2+) uptake that was stimulated by glutathione. An evolutionary model is discussed in which MDR proteins have evolved independently from an ancestor protein displaying both organic xenobiotic- and divalent metal-extrusion abilities.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Augmented production of extracellular superoxide by blood isolates of Enterococcus faecalis.

To assess the frequency of extracellular superoxide (O-2) production by enterococci, multiple species were surveyed in a whole organism assay for their ability to reduce ferricytochrome c in a superoxide dismutase-inhibitable fashion. For stool and clinical enterococcal isolates and 12 type strains, only Enterococcus faecalis (87/91 isolates and ATCC 19433), Enterococcus faecium (5/13 isolates), Enterococcus casseliflavus (ATCC 25778), and Enterococcus gallinarum (ATCC 35038) produced extracellular O-2. Among 106 strains comprising 13 species of enteric gram-negative bacilli and gram-positive cocci, only Lactococcus lactis subspecies lactis produced extracellular O-2. Mean (+/-SE) rates of extracellular O-2 production in vitro by E . faecalis for isolates associated with bacteremia and endocarditis and for isolates from stool were 2.4+/-0.2, 1.9+/-0.2, 1.5+/-0.3 nmol of O-2 min(-1) 10(9) cfu(-1), respectively (P=.025, analysis of variance), suggesting an association between invasiveness and extracellular O-2 production.

Bacteremia↗
PubMed2002

Use of the alr gene as a food-grade selection marker in lactic acid bacteria.

Both Lactococcus lactis and Lactobacillus plantarum contain a single alr gene, encoding an alanine racemase (EC 5.1.1.1), which catalyzes the interconversion of D-alanine and L-alanine. The alr genes of these lactic acid bacteria were investigated for their application as food-grade selection markers in a heterologous complementation approach. Since isogenic mutants of both species carrying an alr deletion (Deltaalr) showed auxotrophy for D-alanine, plasmids carrying a heterologous alr were constructed and could be selected, since they complemented D-alanine auxotrophy in the L. plantarum Deltaalr and L. lactis Deltaalr strains. Selection was found to be highly stringent, and plasmids were stably maintained over 200 generations of culturing. Moreover, the plasmids carrying the heterologous alr genes could be stably maintained in wild-type strains of L. plantarum and L. lactis by selection for resistance to D-cycloserine, a competitive inhibitor of Alr (600 and 200 micro g/ml, respectively). In addition, a plasmid carrying the L. plantarum alr gene under control of the regulated nisA promoter was constructed to demonstrate that D-cycloserine resistance of L. lactis is linearly correlated to the alr expression level. Finally, the L. lactis alr gene controlled by the nisA promoter, together with the nisin-regulatory genes nisRK, were integrated into the chromosome of L. plantarum Deltaalr. The resulting strain could grow in the absence of D-alanine only when expression of the alr gene was induced with nisin.

Anti-Bacterial Agents↗
PubMed2002

Direct observation of bacterial exopolysaccharides in dairy products using confocal scanning laser microscopy.

The objective of this work was to develop a methodology for direct visualization of bacterial exopolysaccharides (EPS) in fully hydrated dairy products. The new method involved staining EPS with wheat germ agglutinin labeled with Alexa fluor 488 or staining with concanavalin A 488. Samples were observed using confocal scanning laser microscopy. Distribution of EPS produced by Lactococcus lactis (CHCC 3367), a combination of Streptococcus thermophilus (CHCC 3534) and Lactobacillus delbrueckii ssp. bulgaricus (CHCC 769) and Lactobacillus delbrueckii ssp. bulgaricus RR in milk was compared in stirred and unstirred fermented milk. The EPS and proteins were observed as distinct entities, with EPS present in the protein network pores. EPS was observed in greater amounts in milk fermented by the ropy L. lactis culture than in milk fermented by the less ropy strain of S. thermophilus. Stirring the fermented milk caused aggregation of EPS into more extended structures. The more ropy the culture, the longer and larger the strands formed during stirring. The method was also applied to Feta cheese made with an EPS-producing strain of S. thermophilus. EPS was observed in the cheese as thick sheets filling pores in the protein network.

Animals↗
PubMed1992

Functional reconstitution of membrane proteins in monolayer liposomes from bipolar lipids of Sulfolobus acidocaldarius.

Membranes of Sulfolobus acidocaldarius, an extreme thermophilic archaebacterium, are composed of unusual bipolar lipids. They consist of macrocyclic tetraethers with two polar heads linked by two hydrophobic C40 phytanyl chains which are thought to be arranged as a monolayer in the cytoplasmic membrane. Fractionation of a total lipid-extract from S. acidocaldarius yielded a lipid fraction which forms closed and stable unilamellar liposomes in aqueous media. Beef heart cytochrome c-oxidase could be functionally reconstituted in these liposomes. In the presence of reduced cytochrome c, a protonmotive force (delta p) across the liposomal membrane was generated of up to -92 mV. Upon fusion of these proteoliposomes with membrane vesicles of Lactococcus lactis, the delta p generated by cytochrome c-oxidase activity was capable to drive uphill transport of leucine. Electron microscopic analysis indicated that the tetraether lipids form a single monolayer liposome. The results demonstrate that tetraether lipids of archaebacteria can form a suitable matrix for the function of exogenous membrane proteins originating from a regular lipid bilayer.

Animals↗
PubMed1995

Characteristics of Tn5307 exchange and intergeneric transfer of genes associated with nisin production.

Transfer of the Lactococcus lactis 11454 nisin-sucrose conjugative transposon, Tn5307, was investigated to develop a methodology for conjugation of this element to other lactic acid bacteria. Tn5307 exchange was sensitive to temperature and pH but was not affected by protease or amylase treatments to donor cells. Moreover, conjugation studies demonstrated that the direct-plate method could be employed to rapidly identify LM2301 transconjugants able to transfer Tn5307 at least ten times more efficiently than 11454. Intergeneric transfer of nisin and sucrose genes between L. lactis and a dairy Enterococcus sp. was also investigated. Erythromycin-resistant Enterococcus sp. recipients were developed by electro-transformation with pGK13 or by conjugal introduction of the broad-host-range plasmid pAM beta 1. Matings between L. lactis 11454 and an Enterococcus sp. recipient that contained pAM beta 1 yielded sucrose-positive, nisin-immune transconjugants at a frequency of 2.3 x 10(-9) transconjugants per donor cfu. Agar-overlay assays for nisin production revealed that enterococcal transconjugants did not produce the bacteriocin, but DNA.DNA hybridization with a nisA-specific probe demonstrated that these bacteria had acquired the nisin structural gene.

Anti-Bacterial Agents↗
PubMed1999

An aminoacyl-tRNA synthetase paralog with a catalytic role in histidine biosynthesis.

In addition to their essential catalytic role in protein biosynthesis, aminoacyl-tRNA synthetases participate in numerous other functions, including regulation of gene expression and amino acid biosynthesis via transamidation pathways. Herein, we describe a class of aminoacyl-tRNA synthetase-like (HisZ) proteins based on the catalytic core of the contemporary class II histidyl-tRNA synthetase whose members lack aminoacylation activity but are instead essential components of the first enzyme in histidine biosynthesis ATP phosphoribosyltransferase (HisG). Prediction of the function of HisZ in Lactococcus lactis was assisted by comparative genomics, a technique that revealed a link between the presence or the absence of HisZ and a systematic variation in the length of the HisG polypeptide. HisZ is required for histidine prototrophy, and three other lines of evidence support the direct involvement of HisZ in the transferase function. (i) Genetic experiments demonstrate that complementation of an in-frame deletion of HisG from Escherichia coli (which does not possess HisZ) requires both HisG and HisZ from L. lactis. (ii) Coelution of HisG and HisZ during affinity chromatography provides evidence of direct physical interaction. (iii) Both HisG and HisZ are required for catalysis of the ATP phosphoribosyltransferase reaction. This observation of a common protein domain linking amino acid biosynthesis and protein synthesis implies an early connection between the biosynthesis of amino acids and proteins.

ATP Phosphoribosyltransferase↗
PubMed2001

The lactococcal secondary multidrug transporter LmrP confers resistance to lincosamides, macrolides, streptogramins and tetracyclines.

The active efflux of toxic compounds by (multi)drug transporters is one of the mechanisms that bacteria have developed to resist cytotoxic drugs. The authors describe the role of the lactococcal secondary multidrug transporter LmrP in the resistance to a broad range of clinically important antibiotics. Cells expressing LmrP display an increased resistance to the lincosamide, streptogramin, tetracycline and 14- and 15-membered macrolide antibiotics. The streptogramin antibiotic quinupristin, present in the fourth-generation antibiotic RP 59500, can inhibit LmrP-mediated Hoechst 33342 transport, but is not transported by LmrP, indicating that quinupristin acts as a modulator of LmrP activity. LmrP-expressing Lactococcus lactis cells in which a proton-motive force is generated accumulate significantly less tetracycline than control cells without LmrP expression. In contrast, LmrP-expressing and control cells accumulate equal amounts of tetracycline in the absence of metabolic energy. These findings demonstrate that the increased antibiotic resistance in LmrP-expressing cells is a result of the active extrusion of antibiotics from the cell.

Anti-Bacterial Agents↗
PubMed1990

Molecular cloning and DNA sequence of lacE, the gene encoding the lactose-specific enzyme II of the phosphotransferase system of Lactobacillus casei. Evidence that a cysteine residue is essential for sugar phosphorylation.

The gene coding for the lactose-specific Enzyme II of the Lactobacillus casei phosphoenolpyruvate-dependent phosphotransferase system, lacE, has been isolated by molecular cloning and expressed in Escherichia coli. The DNA sequence of the lacE gene and the deduced amino acid sequence are presented. The putative translation product comprises a hydrophobic protein of 577 amino acids with a calculated molecular mass of 62,350 Da. The deduced polypeptide has a high degree of sequence similarity with the corresponding lactose-specific enzymes II of Staphylococcus aureus and Lactococcus lactis. The sequence surrounding cysteine 483 was strongly conserved in the three proteins. The identity of the lacE product as the Enzyme IIlacL.casei was demonstrated by in vitro lactose phosphorylation assays using the protein expressed in E. coli. Single replacement of each of the histidine and cysteine residues by site-directed mutagenesis pointed to cysteine 483 as an amino acid residue essential for the phosphoryl group transfer reaction.

Base Sequence↗
PubMed1999

An improved method for screening alpha-acetolactate producing mutants.

Alpha-Acetolactate-deficient Lactococcus lactis ssp. lactis biovar. diacelylactis are utilised in several industrial processes for producing diacetyl and alpha-acetolactate. They can be selected by screening after random mutagenesis. We improved a previously described screening method [Monnet, C., Schmitt, P., Diviès, C., 1997. Appl. Environ. Microbiol. 63, 793-795], which makes it possible to screen up to 1000 colonies per agar plate, whereas the previous method allowed to screen only 60 colonies per agar plate. The new screening method facilitates selection of alpha-acetolactate-deficient mutants.

Filtration↗
PubMed2004

Regulation of lantibiotic lacticin 481 production at the transcriptional level by acid pH.

The lantibiotic lacticin 481 operon (lctAMTFEG) is mainly transcribed from P1 and P3, two promoters lying upstream of lctA. A weak additional promoter allows independent expression of the immunity genes (lctFEG). Lacticin 481 production by Lactococcus lactis is stimulated by the acidification due to lactic acid production, and by artificially lowering the pH of the medium. This regulation occurs at the transcriptional level, since P1 and P3 are both acid-induced. P1 is weaker but more tightly regulated than P3. As no specific regulator is encoded by the lacticin 481 operon, P1 and P3 are likely controlled by a general regulator.

Acids↗
PubMed2001

Growth of nisin-producing lactococci in cooked rice supplemented with soybean extract and its application to inhibition of Bacillus subtilis in rice miso.

Lactic acid fermentation of cooked rice and rice koji by supplementation with soybean extract (SBE) and its application to rice miso fermentation were investigated. By supplementing the cooked rice with SBE, lactic acid bacteria (LAB) grew well without any unfavorable effects on the rice such as off-flavor or coloration. Lactococcus lactis subsp. lactis IFO12007 (Lc. lactis, a producer of the bacteriocin nisin) proliferated at 10(8 to approximately 9) cells/g after 24 h of incubation and produced high activity of nisin. The fermented rice with Lc. lactis strongly inhibited not only Bacillus subtilis ATCC19659 but also the other Bacillus strains. While some strains of LAB markedly inhibited the growth of Asp. oryzae, resulting in failure of koji fermentation, Lc. lactis did not affect the growth of these molds. When Lc. lactis was used for rice miso fermentation as a lactic acid starter culture, Lc. lactis rapidly proliferated and produced high nisin activity of 6,400 IU/g, in the steamed rice, resulting in complete growth inhibition of B. subtilis, which had been inoculated at the beginning of the koji fermentation. The rice miso after 12 weeks of aging had a suitable pH, and favorable taste and color. Furthermore, hyposalting of rice miso could be done without difficulty by lactic acid fermentation of both rice and soybeans.

Bacillus subtilis↗
PubMed2002

Identification and characterization of phage-resistance genes in temperate lactococcal bacteriophages.

The sie2009 gene, which is situated between the genes encoding the repressor and integrase, on the lysogeny module of the temperate lactococcal bacteriophage Tuc2009, was shown to mediate a phage-resistance phenotype in Lactococcus lactis against a number of bacteriophages. The Sie2009 protein is associated with the cell membrane and its expression leaves phage adsorption, transfection and plasmid transformation unaffected, but interferes with plasmid transduction, as well as phage replication. These observations indicate that this resistance is as a result of DNA injection blocking, thus representing a novel superinfection exclusion system. A polymerase chain reaction (PCR)-based strategy was used to screen a number of lactococcal strains for the presence of other prophage-encoded phage-resistance systems. This screening resulted in the identification of two such systems, without homology to sie2009, which were shown to mediate a phage-resistance phenotype similar to that conferred by sie2009. To our knowledge, this is the first description of a phage-encoded super-infection exclusion/injection blocking mechanism in the genus Lactococcus.

Amino Acid Sequence↗
PubMed2000

[The production of antihypertensive peptides in beta-casein proteolysis].

Antihypertensive peptides were obtained after the proteolysis of beta-casein by starter cells Lactococcus lactis ssp. lactis and lactococci with pepsin or fromase. The peptides have shown the effect as inhibitors of angiotensin-converting enzyme. The strongest action the peptide obtained after the proteolysis of beta-casein by synergic action of lactococci with pepsin has shown. It demonstrates a capability of formation of such peptides directly in milk products during their making and maturation under the action of proteolytic system of lactic acid bacteria and milk clothing proteases.

Angiotensin-Converting Enzyme Inhibitors↗