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 505 records · Page 28Linked to original sources
PubMed1994

Prevention of C-terminal autoprocessing of Lactococcus lactis SK11 cell-envelope proteinase by engineering of an essential surface loop.

The catalytic domain of the cell-envelope proteinase from Lactococcus lactis SK11 has various inserts, situated in external loops of the catalytic domain, compared with the related subtilisins. Protein engineering was employed to analyse the necessity and function of one of these extra loops (residues 205-219), that is predicted to be located in close proximity to the substrate-binding region and is susceptible to autoproteolysis. We constructed a deletion mutant which lacks 14 residues of this surface loop and subsequently introduced various insertion cassettes coding either for the original loop with three mutations (E205S/E218T/M219S: triple-mutant proteinase) or for neutral spacers (1, 4, 7 and 16 serine residues). Engineered proteinases were analysed for activity, (auto)processing, and cleavage specificity. The presence of residues 205-219 is shown to be essential for proteolytic activity, as only triple-mutant proteinase retained activity towards casein substrates. The triple-mutant proteinase was found to be defective in C-terminal autoprocessing, and subsequent release from the lactococcal cell envelope in a calcium-free medium, indicative of either an altered proteolytic specificity or altered accessibility of the processing site. The specificity change appears to be subtle, as only small differences were found between wild-type and triple-mutant proteinase in the breakdown of casein substrates.

Amino Acid Sequence↗
PubMed2001

Lactate dehydrogenase has no control on lactate production but has a strong negative control on formate production in Lactococcus lactis.

A series of mutant strains of Lactococcus lactis were constructed with lactate dehydrogenase (LDH) activities ranging from below 1% to 133% of the wild-type activity level. The mutants with 59% to 133% of lactate dehydrogenase activity had growth rates similar to the wild-type and showed a homolactic pattern of fermentation. Only after lactate dehydrogenase activity was reduced ninefold compared to the wild-type was the growth rate significantly affected, and the ldh mutants started to produce mixed-acid products (formate, acetate, and ethanol in addition to lactate). Flux control coefficients were determined and it was found that lactate dehydrogenase exerted virtually no control on the glycolytic flux at the wild-type enzyme level and also not on the flux catalyzed by the enzyme itself, i.e. on the lactate production. As expected, the flux towards the mixed-acid products was strongly enhanced in the strain deleted for lactate dehydrogenase. What is more surprising is that the enzyme had a strong negative control ( CLDHJF1 =-1.3) on the flux to formate at the wild-type level of lactate dehydrogenase. Furthermore, we showed that L. lactis has limited excess of capacity of lactate dehydrogenase, only 70% more than needed to catalyze the lactate flux in the wild-type cells.

Fermentation↗
PubMed2000

Pharmacokinetics of Lactobacillus plantarum NCIMB 8826, Lactobacillus fermentum KLD, and Lactococcus lactis MG 1363 in the human gastrointestinal tract.

OBJECTIVES: Genetically modified lactic acid bacteria may be a way to deliver vaccinal epitopes in the gastrointestinal tract. AIM: Three strains of lactic acid bacteria were studied for their pharmacokinetics in the human gastrointestinal tract. METHODS: The survival of the strains was studied up to the ileum in six subjects each, after ingestion of 150 g of fermented milk. The strains and their concentrations in the products were Lactobacillus fermentum KLD (107 cfu/g), Lactobacillus plantarum NCIMB 8826 (108 cfu/g), and Lactococcus lactis MG 1363 (108 cfu/g). Ileal fluid was aspirated by intestinal intubation and immediately cultured. L. plantarum NCIMB 8826, which was found in high concentrations in the ileum, was studied for its survival in the faeces after consumption of 150 g of fermented milk three times daily for 7 days. Faecal samples were collected for culture. RESULTS: The concentration of L. plantarum NCIMB 8826 in the ileum reached 108 cfu/mL after a single dose, with a survival of 7%. L. fermentum KLD and Lc. lactis MG 1363 had lower (0.5 and 1.0%, respectively) and shorter (4 h) survival in the ileum. During the 7-day ingestion period, L. plantarum NCIMB 8826 reached high concentrations (108 cfu/g) in the faeces, with a survival of 25 +/- 29%. None of the strains colonized. CONCLUSIONS: L. plantarum NCIMB 8826 has a promising pharmacokinetic profile as a candidate vaccine vehicle.

Adult↗
PubMed2000

Orientation specificity of the Lactococcus lactis Chi site.

BACKGROUND: In Escherichia coli, the Chi sequence modulates the activity of RecBCD, a powerful double-stranded (ds) DNA exonuclease/helicase. Chi attenuates RecBCD exonuclease activity and stimulates homologous recombination in an orientation-dependent manner. ChiEc is frequent and over-represented on its genome, which is thought to be related to its role in dsDNA break repair. We previously identified a Chi-like sequence (referred to as ChiLl) and an exonuclease/helicase in the Gram-positive bacterium Lactococcus lactis. ChiLl and RexAB are functional analogues of ChiEc and RecBCD. RESULTS: We report that ChiLl attenuates RexAB exonuclease activity and stimulates homologous recombination in an orientation-dependent manner. Analysis of ChiLl distribution on the L. lactis chromosome reveals that ChiLl is frequent, highly over-represented, and oriented with respect to the direction of replication. CONCLUSION: Our results show that a single orientation of ChiLl interacts with RexAB. The active orientation is preferentially found on the replication leading strand of the L. lactis genome, consistent with a primary role of ChiLl in repair of dsDNA breaks at the replication fork. We propose that orientation-dependence of Chi activity and over-representation of Chi sequences on bacterial genomes may be conserved properties of exonuclease/helicase-Chi couples. Other properties of the Chi sequence distribution on the genomes might reflect more specific characteristics of each couple and of the host.

Chromosome Inversion↗
PubMed1997

Note: genetic and biochemical characterization on nisin Z produced by Lactococcus lactis ssp. lactis biovar. diacetylactis UL 719.

The bacteriocin produced by Lactococcus lactis ssp. lactis biovar. diacetylactis UL 719 was purified and characterized. Two peaks exhibiting antimicrobial activity were obtained after purification. Primary structure of the peptide of major peak 2 was identical to that of nisin Z when determined by Edman degradation and confirmed by DNA sequence analysis. The molecular mass as determined by mass spectrometry was 3346.39 +/- 0.40 Da for peak 1 and 3330.39 +/- 0.27 Da for peak 2, which suggests that peak 1 may correspond to an oxidized form of nisin Z. The two purified peaks exhibiting antimicrobial activity appear to correspond with oxidized and native forms of nisin Z.

Amino Acid Sequence↗
PubMed1997

Presence of additional peptidases in Streptococcus thermophilus CNRZ 302 compared to Lactococcus lactis.

Streptococcus thermophilus is widely used in the dairy industry but little is known about its peptidase system. The aim of this study was to determine the biochemical and genetic characteristics of this system, and to compare it to the well known system of Lactococcus lactis. We separated the intracellular proteins of Strep. thermophilus CNRZ 302 and L. lactis NCDO 763 by ion-exchange chromatography and we detected the activity of the different types of peptidases. In both L. lactis and Strep. thermophilus strains, we showed 13 different peptidase activities with biochemical homologies between both species. Streptococcus thermophilus also possessed two peptidases which we did not find in L. lactis: an aminopeptidase and an oligopeptidase. We performed Southern blot experiments and among the eight peptidase genes tested, only the genes encoding the general aminopeptidases, pepC and pepN, were homologous between the L. lactis and Strep. thermophilus strains. Besides biochemical and genetic similarities, the peptidase systems of Strep. thermophilus and L. lactis thus differed by the presence of additional peptidases in Strep. thermophilus.

Blotting, Southern↗
PubMed1997

Isolation and characterization of nisin-producing Lactococcus lactis subsp. lactis from bean-sprouts.

Bacterial isolates from bean-sprouts were screened for anti-Listeria monocytogenes bacteriocins using a well diffusion method. Thirty-four of 72 isolates inhibited the growth of L. monocytogenes Scott A. One, HPB 1688, which had the biggest inhibition zone against L. monocytogenes Scott A, was selected for subsequent analysis. Both ribotyping and DNA sequencing of 16S ribosomal RNA gene demonstrated that the isolate was Lactococcus lactis subsp. lactis. Polymerase chain reaction and nucleotide sequencing revealed that the genomic DNA of the bean-sprout isolates contained a nisin Z structural gene. In MRS broth, bean-sprout isolate HPB 1688 survived at 3-4.5 degrees C for at least 20 d, grew at 4 degrees C and produced anti-listerial compounds at 5 degrees C. When co-cultured with L. monocytogenes in MRS broth, the isolate inhibited the growth of L. monocytogenes at 4 degrees C after 14 d and at 10 degrees C after 2 d. When co-inoculated with 10(2) cells g-1 of L. monocytogenes on fresh-cut ready-to-eat Caesar salad, L. lactis subsp. lactis (10(8) cells g-1) was able to reduce the number of L. monocytogenes by 1-1.4 logs after storage for 10 d at 7 zero and 10 degrees C. A bacteriocin-producing Enterococcus faecium was also able to reduce the numbers of L. monocytogenes on Caesar salad, but did not act synergistically when co-inoculated with L. lactis subsp. lactis.

Anti-Bacterial Agents↗
PubMed1998

Cell membrane integrity and lysis in Lactococcus lactis: the detection of a population of permeable cells in post-logarithmic phase cultures.

A method was developed that enabled an analysis of the proportion of permeable cells in a culture of Lactococcus lactis. This used the fluorescence of propidium iodide (PI) when in contact with DNA and the impermeability of the intact cell membrane to this compound. A permeability index was suggested that expresses the PI-induced fluorescence of a cell suspension as a percentage of the value obtained from wholly permeabilized cells after treatment with cetyltrimethylammonium bromide. This method was applied to the determination of cell permeability in death phase cultures. A large proportion of unlysed cells was freely permeable to PI, a finding that may have some significance for the investigation of the role of cell lysis in cheese maturation. This method is suggested as a useful addition to the techniques available for the study of cell damage in a variety of fields, and for the screening of cheese starter bacteria.

Bacteriolysis↗
PubMed2000

Influence of different substrate limitations on the yield, composition and molecular mass of exopolysaccharides produced by Lactococcus lactis subsp. cremoris in continuous cultures.

The type of substrate limitation had a remarkable influence on the molecular mass of exopolysaccharides (EPS) produced by Lactococcus lactis subsp. cremoris NIZO B40 and NIZO B891. Under glucose/energy limitation, the molecular mass was much smaller than under leucine or phosphate limitation, resulting in a marked decrease of the intrinsic viscosity of this EPS. The sugar composition of EPS produced by both strains, and the phosphate content of EPS produced by NIZO B40, were not affected by the type of nutrient limitation. Both strains produced comparable amounts of EPS under leucine and glucose limitation, but the efficiency of EPS production was highest under glucose limitation. The EPS yields of the phosphorylated B40 EPS as well as the unphosphorylated B891 EPS were reduced, with about 40% under conditions of phosphate limitation.

Carbohydrate Sequence↗
PubMed2000

Biological and molecular characterization of a two-peptide lantibiotic produced by Lactococcus lactis IFPL105.

The lactic acid bacterium Lactococcus lactis IFPL105 secretes a broad spectrum bacteriocin produced from the 46 kb plasmid pBAC105. The bacteriocin was purified to homogeneity by ionic and hydrophobic exchange and reverse-phase chromatography. Bacteriocin activity required the complementary action of two distinct peptides (alpha and beta) with average molecular masses of 3322 and 2848 Da, respectively. The genes encoding the two peptides were cloned and sequenced and were found to be identical to the ltnAB genes from plasmid pMRC01 of L. lactis DPC3147. LtnA and LtnB contain putative leader peptide sequences similar to the known 'double glycine' type. The predicted amino acid sequence of mature LtnA and LtnB differed from the amino acid content determined for the purified alpha and beta peptides in the residues serine, threonine, cysteine and alanine. Post-translational modification, and the formation of lanthionine or methyllanthionine rings, could partly explain the difference. Hybridization experiments showed that the organization of the gene cluster in pBAC105 responsible for the production of the bacteriocin is similar to that in pMRC01, which involves genes encoding modifying enzymes for lantibiotic biosynthesis and dual-function transporters. In both cases, the gene clusters are flanked by IS946 elements, suggesting an en bloc transposition. The findings from the isolation and molecular characterization of the bacteriocin provide evidence for the lantibiotic nature of the two peptides.

Amino Acid Sequence↗
PubMed2000

Isolation of a bacteriocin-producing Lactococcus lactis subsp. lactis and application to control Listeria monocytogenes in Moroccan jben.

AIM: Use of a bacteriocin-producing lactococcal strain to control Listeria monocytogenes in jben. METHODS AND RESULTS: A Lactococcus lactis strain isolated from lben was shown, by the spot technique, to produce a bacteriocin different from nisin. Inhibitory activity of the bacteriocin-producing strain against Listeria monocytogenes was investigated in jben, made from cow's milk fermented with the producer organism and contaminated with 104 or 107 cfu ml-1. Listeria counts were monitored during manufacture, and during conservation at room and at refrigeration temperatures. Results showed that the pathogen was reduced by 2.7 logarithmic units after 30 h of jben processing when the initial inoculum of 107 cfu ml(-1) was used. For the initial inoculum of 104 cfu ml(-1), the bacterium was completely eliminated at 24 h. Furthermore, the use of the bacteriocin-producing starter culture extended the shelf-life of jben by 5 days. CONCLUSIONS: In situ production of the lactococcal bacteriocin is an efficient biological means of controlling L. monocytogenes in jben and of allowing shelf-life extension. SIGNIFICANCE AND IMPACT OF THE STUDY: The proposed technology will essentially benefit minimally processed dairy products and those made with raw milk.

Antibiosis↗
PubMed2001

Nucleotide sequence and characterization of the cell envelope proteinase plasmid in Lactococcus lactis subsp. cremoris HP.

AIMS: The major cell envelope proteinase (lactocepin; EC 3.4.21.96) produced by Lactococcus lactis cheese starter bacteria is required for starter growth and acid production in milk. The aim of this study was to characterize a lactocepin plasmid from a L. lactis subsp. cremoris cheese starter strain. METHODS AND RESULTS: A restriction map of the lactocepin plasmid pHP003 from strain HP was constructed, fragments were cloned in Escherichia coli vectors, and the complete DNA sequence (13,433 bp) was determined. Among 120 industrial L. lactis starter strains screened, five contained the same specificity-type lactocepin as pHP003. The lactocepin gene in these strains was invariably linked with a partially-deleted abiB gene. CONCLUSION: The lactocepin specificity type of strain HP, conferred by a known configuration of key residues, is relatively uncommon. The gene is invariably linked with a partially deleted abiB gene on each lactocepin plasmid. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first complete sequence reported for a lactocepin plasmid, and provides the basis for better understanding, or manipulation, of lactocepin production.

Animals↗
PubMed2001

pH-controlled cell release and biomass distribution of alginate-immobilized Lactococcus lactis subsp. lactis.

AIMS: To investigate the growth and release of Lactococcus lactis subsp. lactis in gel beads and to affect rates of cell release by changing the growth conditions. METHODS AND RESULTS: The rate of release and the distribution of immobilized L. lactis subsp. lactis in alginate beads were studied in continuous fermentations for 48 h. A change in operating pH from 6.5 to 9.25 initially reduced the ratio of the rates of cell release to lactate production by almost a factor of 105. Compared with fermentations at pH 6.5, growth at pH 9.25 also increased the final internal bead biomass concentration by a factor of 5 and increased the final rate of lactate production by 25%. After 48 h, the ratio of the rates of cell release to lactate production was still 10 times lower than in fermentations at pH 6.5. CONCLUSIONS: A change in the operating pH from 6.5 to 9.25 reduced rates of cell release throughout 48 h of fermentation and increased the final rates of lactate production and internal bead biomass concentration. SIGNIFICANCE AND IMPACT OF THE STUDY: These data illustrate that diffusional limitations and corresponding pH gradients can be exploited in affecting the distribution of immobilized growing cells and their concomitant release.

Alginates↗
PubMed2002

Recombinant Lactococcus starters as a potential source of additional peptidolytic activity in cheese ripening.

AIMS: The aim of this study was to modulate the lactococcal proteolytic system for enhancement of the cheese ripening process. METHODS AND RESULTS: The genes encoding PepN, PepC, PepX and PepI peptidases of a highly proteolytic Lactobacillus helveticus strain were transferred into Lactococcus lactis in a food-grade cloning system. A comparison of the relative peptidase activities from the transformants with those from the untransformed host, determined in the conditions of maturing cheese, showed that an increase in peptidase activity could be achieved by introducing a selected peptidase gene from Lact. helveticus into L. lactis. CONCLUSIONS: Recombinant L. lactis starter strains, carrying a peptidase gene from Lact. helveticus, may have an important contribution to the proteolysis of maturing cheese by producing an additional peptidolytic enzyme activity. SIGNIFICANCE AND IMPACT OF THE STUDY: The results will be of importance in shortening the ripening period and production of special cheeses (e.g. reduced-fat cheeses) with improved characteristics.

Aminopeptidases↗
PubMed2002

Lactococcus lactis DPC5598, a plasmid-free derivative of a commercial starter, provides a valuable alternative host for culture improvement studies.

AIMS: To generate a plasmid-free derivative of an extensively used industrial starter strain Lactococcus lactis DPC4268, which could be used as a backbone strain for starter improvement programmes. METHODS AND RESULTS: DPC4268 containing four large plasmids was subjected to high temperature plasmid curing resulting in derivatives, each with a different plasmid complement of one, two or three different plasmids in addition to a plasmid-free derivative. Industrially relevant phenotypes were assigned to each plasmid on the basis of detailed phenotypic and genetic analyses and these were (a) proteinase activity (Prt, 60 kb) (b) lactose fermentation (Lac, 55 kb) (c) bacteriophage adsorption inhibition (Ads, 44 kb) and (d) type I restriction/modification (R/M, 40 kb). The plasmid-free variant of DPC4268 was shown to be transformable at frequencies comparable to the common laboratory strain L. lactis MG1614. Furthermore its genome was demonstrated to be significantly different from the laboratory strains L. lactis MG1614 and the recently sequenced L. lactis IL1403 genomes by pulsed-field gel electrophoresis. CONCLUSIONS: This study produced an easily transformable plasmid-free derivative which was genomically different from both MG1614 and IL1403. In addition, important plasmid-borne industrial traits, including two phage-resistance mechanisms, were identified in DPC4268. SIGNIFICANCE AND IMPACT OF THE STUDY: L. DPC4268 is a vitally important commercial strain used in the manufacture of Cheddar cheese. The generation of a plasmid-free derivative may provide an important backbone strain as a basis for future strain improvement purposes.

Bacteriophages↗
PubMed2002

The EstA esterase is responsible for the main capacity of Lactococcus lactis to synthesize short chain fatty acid esters in vitro.

AIMS: Esters of short-chain fatty acids and alcohols participate significantly in the overall flavour of foods. The capacity of the lactic acid bacterium Lactococcus lactis to synthesize such esters is known even though the enzymes involved in the process are not well identified. The objective of our work is to determine whether the esterase is responsible for the whole capacity of L. lactis to synthesize esters in vitro. METHODS AND RESULTS: A negative mutant for the esterase was constructed and its capacity to synthesize short chain fatty acid esters from different substrate couples was compared to that of the wild type. We observed that the esterase is responsible for the main ester synthesis activity of L. lactis in vitro. However, in the presence of some substrates, the esterase negative mutant still synthesizes low amounts of esters. CONCLUSIONS: In favourable environmental conditions, the L. lactis esterase is responsible for the main ester synthesizing activity, even though another pathway for ester synthesis probably exists. SIGNIFICANCE AND IMPACT OF THE STUDY: Since esters are potent aroma compounds, esterase is probably a key enzyme in the development of food flavour.

Bacterial Proteins↗
PubMed2003

Charged casein-derived oligopeptides competitively inhibit the transport of a reporter oligopeptide by Lactococcus lactis.

AIM: To study the effect of casein-derived peptides, accumulated during growth of Lactococcus lactis in milk, on its oligopeptide transport (Opp) function. METHODS AND RESULTS: This effect was estimated by analysing the ability of casein-derived peptides to compete for the transport of a reporter peptide by whole L. lactis cells. The transport of the reported peptide was monitored by determining the intracellular concentrations of the corresponding amino acids by means of reverse-phase high-performance liquid chromatography (HPLC). Uptake of the reporter peptide was competitively inhibited by casein-derived peptides. The competition was only because of charged casein-derived peptides, including anionic peptides. The design of specific pure peptides made it possible to evidence for a positive (or negative) influence exerted by the positively (or negatively) charged side chain of the N-terminal amino acid on the competition. CONCLUSIONS: Charged casein-derived peptides impaired the oligopeptide transport function of L. lactis. SIGNIFICANCE AND IMPACT OF THE STUDY: These results demonstrate an inhibition of Opp when too many peptides are produced by the proteinase. Peptide transport by Opp therefore represents a bottleneck for increasing the growth rate of L. lactis in milk.

Animals↗
PubMed1996

Splicing of a group II intron in a functional transfer gene of Lactococcus lactis.

A chromosomally located sex factor that controls conjugation in Lactococcus lactis 712 has been cloned and sequenced, leading to the discovery of an open reading frame with homology to the maturases of group II self-splicing introns. Reverse transcriptase polymerase chain reaction amplification was used to demonstrate that the intron was spliced out of mRNA in vivo, and sequence analysis revealed the site of splicing. The intron was inserted within a sex-factor gene which encodes a protein with homology to proteins involved in rolling-circle DNA replication. Gene-disruption experiments were used to demonstrate that this mobA gene was essential for sex-factor transfer and this suggests that intron splicing is a necessary part of the conjugation process. The sequence of the intron was modelled to produce a secondary structure that exhibited several features characteristic of the IIA subgroup. Here we report the characterization of a new group II intron in the Gram-positive bacterium L. lactis and demonstrate for the first time in bacteria both splicing in vivo and an active role for the gene carrying the intron.

Amino Acid Sequence↗