Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Lactococcus”

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 973 records · Page 54Linked to original sources
PubMed1989

Transport of basic amino acids by membrane vesicles of Lactococcus lactis.

The uptake of the basic amino acids arginine, ornithine, and lysine was studied in membrane vesicles derived from cells of Lactococcus lactis which were fused with liposomes in which beef heart mitochondrial cytochrome c oxidase was incorporated as a proton motive force (PMF)-generating system. In the presence of ascorbate N,N,N'N'-tetramethylphenylenediamine-cytochrome c as the electron donor, these fused membranes accumulated lysine but not ornithine or arginine under aerobic conditions. The mechanism of energy coupling to lysine transport was examined in membrane vesicles of L. lactis subsp. cremoris upon imposition of an artificial electrical potential (delta psi) or pH gradient or both and in fused membranes of these vesicles with cytochrome c oxidase liposomes in which the delta psi and delta pH were manipulated with ionophores. Lysine uptake was shown to be coupled to the PMF and especially to the delta psi, suggesting a proton symport mechanism. The lysine carrier appeared to be specific for L and D isomers of amino acids with a guanidine or NH2 group at the C6 position of the side chain. Uptake of lysine was blocked by p-chloromercuribenzene sulfonic acid but not by maleimides. Counterflow of lysine could not be detected in L. lactis subsp. cremoris, but in the arginine-ornithine antiporter-containing L. lactis subsp. lactis, rapid counterflow occurred. Homologous exchange of lysine and heterologous exchange of arginine and lysine were mediated by this antiporter. PMF-driven lysine transport in these membranes was noncompetitively inhibited by arginine, whereas the uptake of arginine was enhanced by lysine. These observations are compatible with a model in which circulation of lysine via the lysine carrier and the arginine-ornithine antiporter leads to accumulation of arginine.

Amino Acids, Diamino↗
PubMed1989

A maturation protein is essential for production of active forms of Lactococcus lactis SK11 serine proteinase located in or secreted from the cell envelope.

The complete nucleotide sequence of a gene located immediately upstream of the Lactococcus lactis subsp. cremoris SK11 prtP gene encoding the cell envelope-attached proteinase was determined. This gene, designated prtM, was found to be transcribed from the same promotor region as was the proteinase gene but in the opposite direction. The prtM gene directed the expression in Escherichia coli of a protein with a size similar to the expected value of 33 kilodaltons, as deduced from the nucleotide sequence data. The derived amino acid sequence of the PrtM protein indicated the presence of a consensus lipoprotein signal sequence at the N terminus, which suggested that PrtM is a lipoprotein. Plasmids containing the prtM gene, the prtP gene, or both were constructed. Expression studies of L. lactis clones containing these plasmids showed that the prtM gene encodes a trans-acting activity involved in the maturation of cell envelope-located and -secreted forms of the SK11 proteinase.

Amino Acid Sequence↗
PubMed1989

Product of the Lactococcus lactis gene required for malolactic fermentation is homologous to a family of positive regulators.

Malolactic fermentation is a secondary fermentation that many lactic acid bacteria can carry out when L-malate is present in the medium. The activation of the malolactic system in Lactococcus lactis is mediated by a locus we call mleR. Induction of the genes necessary to perform malolactic fermentation occurs only in bacteria with a functional copy of mleR. The mleR gene consists of one open reading frame capable of coding for a protein with a calculated molecular mass of 33,813 daltons. The amino acid sequence of the predicted MleR gene product is homologous to that of positive activators in gram-negative bacteria: LysR, IlvY gene products of Escherichia coli, MetR, CysB of Salmonella typhimurium, AmpR of Enterobacter cloacae, NodD of Rhizobium sp., and TrpI of Pseudomonas aeruginosa.

Amino Acid Sequence↗
PubMed1990

Conjugal mobilization of streptococcal plasmid pMV158 between strains of Lactococcus lactis subsp. lactis.

pMV158, a non-self-transmissible plasmid encoding tetracycline resistance, was conjugally transferred from Enterococcus faecalis JH203 to Lactococcus lactis subsp. lactis IL1403. This transfer appeared to be dependent on the cotransfer of the conjugative plasmids pAM beta 1 or pIP501. Intraspecies conjugal transfer of pMV158 also occurred in strain IL1403. In contrast to the transfer from E. faecalis, transfer in IL1403 did not require the presence of a conjugative plasmid in the donor strain but, rather, appeared to be dependent on putative chromosomal functions in strain IL1403. The transfer of pMV158 from strain IL1403 required the presence of an active pMV158-encoded protein, which showed homology to the Pre (plasmid recombination enzyme) proteins encoded by several small plasmids extracted from Staphylococcus aureus, such as pT181.

Conjugation, Genetic↗
PubMed1990

Nucleotide sequence and expression in Escherichia coli of the Lactococcus lactis citrate permease gene.

The plasmid-encoded citrate determinant of the Lactococcus lactis subsp. lactis var. diacetylactis NCDO176 was cloned and functionally expressed in a Cit- Escherichia coli K-12 strain. From deletion derivative analysis, a 3.4-kilobase region was identified which encodes the ability to transport citrate. Analysis of proteins encoded by the cloned fragment in a T7 expression system revealed a 32,000-dalton protein band, which correlated with the ability of cells to transport citrate. Energy-dependent [1,5-14C]citrate transport was found with membrane vesicles prepared from E. coli cells harboring the citrate permease-expressing plasmid. The gene encoding citrate transport activity, citP, was located on the cloned fragment by introducing a site-specific mutation that abolished citrate transport and resulted in a truncated form of the 32,000-dalton expression product. The nucleotide sequence for a 2.2-kilobase fragment that includes the citP gene contained an open reading frame of 1,325 base pairs coding for a very hydrophobic protein of 442 amino acids, which shows no sequence homology with known citrate carriers.

Amino Acid Sequence↗
PubMed1990

Cloning, expression, and sequence determination of a bacteriophage fragment encoding bacteriophage resistance in Lactococcus lactis.

A number of host-encoded phage resistance mechanisms have been described in lactococci. However, the phage genome has not been exploited as a source of additional resistance determinants. A 4.5-kb BamHI-HindIII fragment of phage nck202.50 (phi 50) was subcloned in streptococcus-Escherichia coli shuttle plasmid pSA3 and introduced into Lactococcus lactis NCK203 and MG1363 by protoplast transformation. This cloned phage fragment directed a bacteriophage resistance phenotype designated Per (phage-encoded resistance). Both phi 50 and a distantly related phage, nck202.48 (phi 48), formed small plaques on strain NCK213 at a slightly reduced efficiency of plaquing on the Per+ host. The per locus was further reduced to a 1.4-kb fragment through in vitro deletion analysis. The 1.4-kb fragment was sequenced, and the Per phenotype was found to be associated with a ca. 500-bp region rich in direct and inverted repeats. We present evidence that the Per region contains a phage origin of replication which, in trans, may interfere with phage replication by titration of DNA polymerase or other essential replication factors. It was demonstrated that the Per+ phenotype is not a result of reduced adsorption or action of a restriction and modification system. Per+ activity was not detected against six independent phages which were previously shown to be sensitive to the Hsp+ mechanism. The mutually exclusive resistance mechanisms could be combined to confer resistance to both types of phages (Hsp resistant and Per resistant) in a single host. This is the first description in lactococci of a phage resistance phenotype, other than superinfection immunity, originating from a lactococcal phage genome.

Amino Acid Sequence↗
PubMed1990

Isolation and characterization of lipoteichoic acid, a cell envelope component involved in preventing phage adsorption, from Lactococcus lactis subsp. cremoris SK110.

The cell envelope of the phage-resistant Lactococcus lactis subsp. cremoris SK110 differed from its phage-sensitive variant by the presence of a galactosyl-containing component. This component was present in material obtained from SK110 by a mild alkali treatment. In a similar fraction extracted from SK112, no galactosyl-containing components were detected. With respect to gel permeation chromatography and electrophoretic mobility, identical characteristics of the alkali-extracted material and purified lipoteichoic acid (LTA) were measured. Chemical analysis of the latter component showed the absence of galactose in LTA isolated from SK112, whereas it was present in LTA obtained from SK110. In this paper, we propose that galactosyl-containing LTA is involved in preventing phage adsorption to L. lactis subsp. cremoris SK110.

Adsorption↗
PubMed1990

Simultaneous loss of N5-(carboxyethyl)ornithine synthase, nisin production, and sucrose-fermenting ability by Lactococcus lactis K1.

A spontaneous derivative of Lactococcus lactis subsp. lactis K1 (formerly Streptococcus lactis K1) lacking N5-(carboxyethyl)ornithine synthase (EC 1.5.1.24) was isolated. This mutant had also lost the abilities to ferment sucrose and to produce the antibiotic nisin. Hybridization studies indicate that these linked traits are encoded on the chromosome of L. lactis K1 and that they may be located on a conjugative transposon.

Amino Acid Oxidoreductases↗
PubMed1991

Lactococcin A, a new bacteriocin from Lactococcus lactis subsp. cremoris: isolation and characterization of the protein and its gene.

A new bacteriocin, termed lactococcin A (LCN-A), from Lactococcus lactis subsp. cremoris LMG 2130 was purified and sequenced. The polypeptide contained no unusual amino acids and showed no significant sequence similarity to other known proteins. Only lactococci were killed by the bacteriocin. Of more than 120 L. lactis strains tested, only 1 was found resistant to LCN-A. The most sensitive strain tested, L. lactis subsp. cremoris NCDO 1198, was inhibited by 7 pM LCN-A. By use of a synthetic DNA probe, lcnA was found to be located on a 55-kb plasmid. The lcnA gene was cloned and sequenced. The sequence data revealed that LCN-A is ribosomally synthesized as a 75-amino-acid precursor including a 21-amino-acid N-terminal extension. An open reading frame encoding a 98-amino-acid polypeptide was found downstream of and in the same operon as lcnA. We propose that this open reading frame encodes an immunity function for LCN-A. In Escherichia coli lcnA did not cause an LCN-A+ phenotype. L. lactis subsp. lactis IL 1403 produced small amounts of the bacteriocin and became resistant to LCN-A after transformation with a recombinant plasmid carrying lcnA. The other lactococcal strains transformed with the same recombinant plasmid became resistant to LCN-A but did not produce any detectable amount of the bacteriocin.

Amino Acid Sequence↗
PubMed1991

Replacement recombination in Lactococcus lactis.

In the pUC18-derived integration plasmid pML336 there is a 5.3-kb chromosomal DNA fragment that carries the X-prolyl dipeptidyl aminopeptidase gene (pepXP). The gene was inactivated by the insertion of an erythromycin resistance determinant into its coding sequence. Covalently closed circular DNA of pML336 was used for the electrotransformation of Lactococcus lactis. In 2% of the erythromycin-resistant transformants the pepXP gene was inactivated by a double-crossover event (replacement recombination) between pML336 and the L. lactis chromosome. The other transformants in which the pepXP gene had not been inactivated carried a Campbell-type integrated copy of the plasmid. Loss of part of the Campbell-type integrated plasmid via recombination between 1.6-kb nontandem repeats occurred with low frequencies that varied between less than 2.8 x 10(-6) and 8.5 x 10(-6), producing cells with a chromosomal structure like that of cells in which replacement recombination had taken place.

Chromosomes, Bacterial↗
PubMed1991

A membrane protein is required for bacteriophage c2 infection of Lactococcus lactis subsp. lactis C2.

Phage-resistant mutants, isolated from cultures of Lactococcus lactis subsp. lactis C2 infected with phage c2, did not form plaques but bound phage normally. The mutants were sensitive to another phage, sk1, although the number of plaques was reduced approximately 56% and the plaques were four times smaller. Binding to phage sk1 was reduced about 10%. Another group of phage-resistant mutants, isolated from cultures infected with phage sk1, bound normally to both phages c2 and sk1 but did not form plaques with either phage. Carbohydrate analyses by gas chromatography of the cell walls showed no significant differences in saccharide compositions between the wild-type and phage-resistant cells. However, a difference was observed in the interactions of the phage with the cytoplasmic membranes. Membranes from the wild-type cells, but not mutant cells, inactivated phage c2. Phage sk1 was not inactivated by membrane from either strain. Treatment of wild-type membranes with proteinase K eliminated the ability of the membrane to inactivate the phage, whereas treatment with mutanolysin had no effect. On the basis of this ability to inactivate the phage, a membrane protein was partially purified by gel filtration and ion-exchange chromatography. Under nondenaturing conditions, the phage-inactivating protein has an apparent Mr of approximately 350,000. The protein has an apparent subunit size of 32 kDa, which suggests that it normally exists as a multimer with 10 to 12 subunits or in association with other membrane components. It is proposed that this protein is required for phage c2 infection.

Bacterial Proteins↗
PubMed1991

Replication and temperature-sensitive maintenance functions of lactose plasmid pSK11L from Lactococcus lactis subsp. cremoris.

The replication region of pSK11L, the lactose plasmid of Lactococcus lactis subsp. cremoris (L. cremoris) SK11, was isolated on a 14.8-kbp PvuII fragment by shotgun cloning into an Escherichia coli vector encoding erythromycin resistance and selection for erythromycin-resistant transformants of L. lactis subsp. lactis (L. lactis) LM0230. Deletion analysis and Tn5 mutagenesis of the resulting plasmid (pKMP1) further localized the replication region to a 2.3-kbp ScaI-SpeI fragment. DNA sequence analysis of this 2.3-kbp fragment revealed a 1,155-bp open reading frame encoding the putative replication protein, Rep. The replication origin was located upstream of rep and consisted of an 11-bp imperfect direct repeat and a 22-bp sequence tandemly repeated three and one-half times. The overall organization of the pSK11L replicon was remarkably similar to that of pCI305, suggesting that pSK11L does not replicate by the rolling-circle mechanism. Like pSK11L, pKMP1 was unstable in L. lactis LM0230. Deletion analysis allowed identification of several regions which appeared to contribute to the maintenance of pKMP1 in L. lactis LM0230. pKMP1 was significantly more stable in L. cremoris EB5 than in L. lactis LM0230 at all of the temperatures compared. This stability was lost by deletion of a 3.1-kbp PvuII-XbaI fragment which had no effect on stability in L. lactis LM0230. Other regions affecting stability in L. cremoris EB5 but not in L. lactis LM0230 were also identified. Stability assays conducted at various temperatures showed that pKMP1 maintenance was temperature sensitive in both L. lactis LM0230 and L. cremoris EB5, although the plasmid was more unstable in L. lactis LM0230. The region responsible for the temperature sensitivity phenotype in L. lactis LM0230 was tentatively localized to a 1.2-kbp ClaI-HindIII fragment which was distinct from the replication region of pSK11L. Our results suggest that the closely related L. lactis and L. cremoris subspecies behave differently regarding maintenance of plasmids.

Amino Acid Sequence↗
PubMed1991

Physical map of the chromosome of Lactococcus lactis subsp. lactis DL11 and localization of six putative rRNA operons.

A physical map of the chromosome of Lactococcus lactis subsp. lactis DL11 was constructed by using the contour-clamped homogeneous electric field mode of pulsed-field gel electrophoresis in one- and two-dimensional separations to analyze restriction digests of high-molecular-weight genomic DNA. The map, which shows all the observed NotI and SmaI sites (six and 21, respectively) and 8 of approximately 30 SalI sites, is circular and yields a total size of 2.58 megabase pairs for the L. lactis subsp. lactis DL11 chromosome. By using rDNA from Mycoplasma capricolum to probe Southern blots of pulsed-and fixed-field digestion patterns, six putative rRNA operons were identified in L. lactis subsp. lactis DL11 and placed on the map of the chromosome. Five of these loci are clustered in a region representing only 20% of the chromosome. The presence of a SmaI site in each of the putative operons allowed the direction of transcription of each operon to be deduced.

Blotting, Southern↗
PubMed1992

The efflux of a fluorescent probe is catalyzed by an ATP-driven extrusion system in Lactococcus lactis.

Many bacteria, both gram positive and gram negative, extrude in an energy-dependent manner the fluorescent pH indicator 2',7'-bis-(2-carboxyethyl)-5[and -6]-carboxyfluorescein (BCECF) (D. Molenaar, T. Abee, and W. N. Konings, Biochim. Biophys. Acta 1115:75-83, 1991). This efflux was studied in detail in Lactococcus lactis, and several indications that a transport system is involved were found. This transport system is most likely driven by ATP or a related compound. The evidence is that BCECF extrusion (i) occurs against a BCECF gradient, (ii) is strictly correlated with ATP concentration and not with the proton motive force, and (iii) is inhibited by vanadate and to a lesser extent by N,N'-dicyclohexylcarbodiimide. Most convincingly, a UV mutant with a strongly reduced efflux rate was isolated. Such a mutant was isolated from a BCECF-loaded and lactose-energized population by selection of highly fluorescent cells in a flow cytometer-cell sorter. The physiological function of this extrusion system is unknown, but its characteristics classify it among the traffic ATPases.

Adenosine Triphosphate↗
PubMed1992

Isolation, characterization, and physiological role of the pyruvate dehydrogenase complex and alpha-acetolactate synthase of Lactococcus lactis subsp. lactis bv. diacetylactis.

The pyruvate dehydrogenase complex of Lactococcus lactis subsp. lactis bv. diacetylactis has a specific activity of 6.6 U/mg and a Km of 1 mM for pyruvate. The specific activities of E2 and E3 in the complex are 30 and 0.36 U/mg, respectively. The complex is very sensitive to NADH inhibition and consists of four subunits: E1 alpha (44 kDa), E1 beta (35 kDa), E2 (73 kDa), and E3 (60 kDa). The L. lactis alpha-acetolactate synthase has a specific activity of 103 U/mg and a Km of 50 mM for pyruvate. Thiamine pyrophosphate (Km = 3.2 microM) and divalent cations are essential for activity. The native enzyme measures 172 kDa and consists of 62-kDa monomers. The role of both enzymes in product formation is discussed in view of NADH inhibition and competition for pyruvate.

Acetolactate Synthase↗
PubMed1992

Transfer of Tn916 between Lactococcus lactis subsp. lactis strains is nontranspositional: evidence for a chromosomal fertility function in strain MG1363.

Lactococcus lactis subsp. lactis MG1363 can act as a conjugative donor of chromosomal markers. This requires a chromosomally located fertility function that we designate the lactococcal fertility factor (Laff). Using inter- and intrastrain crosses, we identified other L. lactis strains (LMO230 and MMS373) that appear to lack Laff. The selectable marker in our crosses was Tcr, carried by Tn916, a transposon present on the chromosome. The transfer of Tcr was not due to Tn916-encoded conjugative functions, because (i) L. lactis cannot act as a donor in Tn916-promoted conjugation (F. Bringel, G. L. Van Alstine, and J. R. Scott, Mol. Microbiol. 5:2983-2993, 1992) and (ii) transfer occurred when the Tcr marker was present in a Tn916 derivative containing a mutation, tra-641, that prevents Tn916-directed conjugation in any host. In addition, we isolated a strain in which Tn916 appears to be linked to Laff; this strain should be useful for further analysis of this fertility factor. In this strain, Tn916 is on the same 600-kb SmaI fragment as Clu, a fertility factor previously shown to promote lactose plasmid transfer in L. lactis. Thus, it is possible that Clu and Laff are identical.

Base Sequence↗
PubMed1992

Tryptophan biosynthesis genes in Lactococcus lactis subsp. lactis.

The Lactococcus lactis chromosomal region containing the seven structural genes required for tryptophan biosynthesis was characterized by cloning and sequencing. All of the trp genes were identified by the homology of their products with known Trp proteins from other organisms. The identification was confirmed for five genes by their ability to complement trp mutations in Escherichia coli. The seven structural genes are present in the order trpEGDCFBA and span a 7,968-bp segment. Each gene is preceded by a putative ribosome binding site complementary to the 3' end of the L. lactis 16S rRNA. Three pairs of genes (trpG-trpD, trpC-trpF, and trpB-trpA) overlap, and there is intercistronic spacing of 124, 46, and 585 bp between the trpE-trpG, trpD-trpC, and trpF-trpB gene pairs, respectively. No gene fusion was found. Upstream of the trp genes, a 457-bp noncoding DNA segment contains several regions fitting the consensus for gram-positive promoters and one region strongly resembling a transcription terminator. However, it seems unlikely that an attenuation mechanism similar to the one found in E. coli regulates tryptophan biosynthesis in L. lactis, since no potential leader peptide was detected. We propose that a mechanisms resembling that described in Bacillus spp. can regulate trp genes expression in L. lactis.

Amino Acid Sequence↗
PubMed1992

Histidine biosynthesis genes in Lactococcus lactis subsp. lactis.

The genes of Lactococcus lactis subsp. lactis involved in histidine biosynthesis were cloned and characterized by complementation of Escherichia coli and Bacillus subtilis mutants and DNA sequencing. Complementation of E. coli hisA, hisB, hisC, hisD, hisF, hisG, and hisIE genes and the B. subtilis hisH gene (the E. coli hisC equivalent) allowed localization of the corresponding lactococcal genes. Nucleotide sequence analysis of the 11.5-kb lactococcal region revealed 14 open reading frames (ORFs), 12 of which might form an operon. The putative operon includes eight ORFs which encode proteins homologous to enzymes involved in histidine biosynthesis. The operon also contains (i) an ORF encoding a protein homologous to the histidyl-tRNA synthetases but lacking a motif implicated in synthetase activity, which suggests that it has a role different from tRNA aminoacylation, and (ii) an ORF encoding a protein that is homologous to the 3'-aminoglycoside phosphotransferases but does not confer antibiotic resistance. The remaining ORFs specify products which have no homology with proteins in the EMBL and GenBank data bases.

Amino Acid Sequence↗