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At least 703 records · Page 39Linked to original sources
PubMed1994

Application of the ligase chain reaction to the detection of nisinA and nisinZ genes in Lactococcus lactis ssp. lactis.

This paper reports on the application of the ligase chain reaction (LCR) to the specific detection of variants of the nisin structural gene (nisinA and nisinZ) in nisin producing strains of Lactococcus lactis ssp lactis. The LCR assay was used to screen nisin producing strains to determine which form of the nisin structural gene they contained. This method of differentiating the nisin structural gene variants provides a useful alternative to the only other available genetic differentiation, that of sequencing the gene.

Base Sequence↗
PubMed1994

The immune response to Lactococcus lactis: implications for its use as a vaccine delivery vehicle.

The development of natural antibodies to Lactococcus lactis in three inbred strains of mice and the effect of inoculating L. lactis into these mice has been investigated. All animals developed detectable levels of natural (systemic and secretory) anti-lactococcal antibodies. Systemic anti-lactococcal antibodies were principally IgG in young mice. An increase in anti-lactococcal IgM occurred in all older animals. Inoculation of L. lactis strains MG1820 or MG1363 by the oral and parenteral routes induced systemic anti-lactococcal antibody responses in a dose-dependent fashion. The relative immunogenicity of individual bacterial proteins varied according to mouse strain and route of inoculation.

Animals↗
PubMed1994

Comparative analysis of gene expression in Streptococcus pneumoniae and Lactococcus lactis.

The pFL10 plasmid vector for translational fusions was constructed. pFL10 is based in the promiscuous pLS1 replicon and contains the pC194 cat gene deprived of its transcriptional promoter and Shine-Dalgarno (SD) sequence. Three promoters (Pcit, PpolA and PtetL) from Gram-positive bacteria, inserted in pFL10, were tested for their ability to drive transcription in Lactococcus lactis and Streptococcus pneumoniae. These promoters were coupled to the SD sequence of the lactococcal citP gene fused to the cat gene. Determination of the 5' ends of the three mRNAs by primer extension revealed the same start sites in both bacterial systems. However, it was observed a differential efficiency of promoter utilization by the RNA polymerases from the two hosts. The transcriptional behavior correlates with expression of the cat gene measured by determinations of chloramphenicol acetyltransferase (CAT) activity. Substitution of the SD of citP by that of the T7 phi 10 gene rendered a similar decrease of the CAT production in both bacterial systems.

Base Sequence↗
PubMed1995

Functional expression in Saccharomyces cerevisiae of the Lactococcus lactis mleS gene encoding the malolactic enzyme.

Malolactic fermentation, a crucial step in winemaking, results mostly in degradation by lactic acid bacteria of L-malic acid into L-lactic acid. This direct decarboxylation is catalysed by the malolactic enzyme. Recently we, and others, have cloned the mleS gene of Lactococcus lactis encoding malolactic enzyme. Heterologous expression of mleS in Saccharomyces cerevisiae was tested to perform simultaneously alcoholic and malolactic fermentations by yeast. mleS gene was cloned in a yeast multicopy vector under a strong promoter. Malolactic activity was present in crude extracts of recombinant yeasts. Malic acid degradation was tested during alcoholic fermentation in synthetic media and must. Yeasts expressing the mleS gene actually produced L-lactate from L-malate; nevertheless malate degradation was far from complete.

Base Sequence↗
PubMed1995

Construction of a food-grade host/vector system for Lactococcus lactis based on the lactose operon.

A plasmid-based food-grade vector system was developed for Lactococcus lactis by exploiting the genes for lactose metabolism. L. lactis MG5267 is a plasmid-free strain containing the entire lactose operon as a chromosomal insertion. The lacF gene was deleted from this strain by a double cross-over homologous recombination event. The lacF-deficient strain produced a Lac- phenotype on indicator agar. A cloned copy of the lacF gene expressed on a plasmid was capable of complementing the lacF-deficient strain resulting in a Lac+ phenotype. This stably maintained system fits the requirements of a self-selecting vector system and has the potential to be exploited in the food industry.

Base Sequence↗
PubMed1996

Characterization of an insertion sequence-like element identified in plasmid pCIT264 from Lactococcus lactis subsp. lactis biovar diacetylactis.

Plasmid pCIT264 from Lactococcus lactis subsp. lactis biovar diacetylactis (L. diacetylactis) contains an insertion sequence (IS)-like element located in the citrate utilization (citQRP) cluster. This 967-nucleotide long element is bounded by 17 bp perfect inverted repeats and contains an open reading frame (ORF1) composed of 296 codons, which could encode a transposase. Expression of the IS from pCIT264 generates two mRNAs of 2900 and 1900 nucleotides. The transcription is driven by the P3 promoter, composed of a -10 region located at the right end of the IS and of a -35 region positioned downstream of this element. The IS-like element (IS982) is present in seven copies in the L.diacetylactis genome. The copy present in pCIT264 is highly stable and does not promote rearrangements of the cit cluster. We suggest that the stable maintenance of the IS-like element in pCIT264 could be due to a translational control of the putative transposase by an antisense RNA.

Base Sequence↗
PubMed1996

Cloning and sequencing of the novel abortive infection gene abiH of Lactococcus lactis ssp. lactis biovar. diacetylactis S94.

A gene which encodes resistance by abortive infection (Abi+) to bacteriophage was cloned from Lactococcus lactis ssp. lactis biovar. diacetylactis S94. This gene was found to confer a reduction in efficiency of plating and plaque size for prolate-headed bacteriophage phi 53 (group I of homology) and total resistance to the small isometric-headed bacteriophage phi 59 (group III of homology). The cloned gene is predicted to encode a polypeptide of 346 amino acid residues with a deduced molecular mass of 41 455 Da. No homology with any previously described genes was found. A probe was used to determine the presence of this gene in two strains on 31 tested.

Bacterial Proteins↗
PubMed1996

Evidence for a role of NisT in transport of the lantibiotic nisin produced by Lactococcus lactis N8.

The biosynthesis, immunity and regulation of nisin, a lanthionine-containing antimicrobial peptide produced by Lactococcus lactis, is encoded by two gene clusters, nisA/ZBTCIPRK and nisFEG. The mutant strain LAC46 with a deletion in the translocator gene nisT could not secrete nisin but nisin activity was detected from cell lysates. The nisT mutation was complemented by a NisT-expression plasmid resulting in restored capacity to secrete nisin. These results demonstrate that NisT is the transport protein dedicated to translocate nisin and that dehydration and lanthionine formation in nisin maturation can occur independently of transport.

Anti-Bacterial Agents↗
PubMed1997

A novel plasmid-encoded phage abortive infection system from Lactococcus lactis biovar. diacetylactis.

A 16-kb plasmid (pND859) was identified from Lactococcus lactis biovar. diacetylactis UK12922 which encodes phage resistance to the small isometric phage 712 when tested in L. lactis LM0230. The gene encoding phage abortive infection, designated abi-859, was localized on a 1.2-kb region which consists of an open reading frame (ORF) of 846 bp preceded by a potential ribosome-binding site and a putative promoter region. A helix-turn-helix region typical of DNA-binding motifs was identified near the N-terminal of the abi-859 product, suggesting a possible interaction with the phage DNA.

Amino Acid Sequence↗
PubMed1998

Nucleotide sequence and analysis of the new chromosomal abortive infection gene abiN of Lactococcus lactis subsp. cremoris S114.

A 7.275-kb DNA fragment which encodes resistance by abortive infection (Abi+) to bacteriophage was cloned from Lactococcus lactis subsp. cremoris S114. The genetic determinant for abortive infection was subcloned from this fragment. This gene was found to confer a reduction in efficiency of plating and plaque size for prolate-headed bacteriophage phi 53 (group I homology) and for small isometric-headed bacteriophage phi 59 (group III homology). This new gene, termed abiN, is predicted to encode a polypeptide of 178 amino acid residues with a deduced molecular mass of 20,461 Da and an isoelectric point of 4.63. No homology with any previously described genes was found. A probe was used to determine the presence of this gene only in S114 from 31 strains tested.

Bacteriophages↗
PubMed1998

A PCR fingerprinting technique to distinguish isolates of Lactococcus lactis.

A fingerprinting technique similar to repetitive extragenic palindromic PCR was developed to identify strains of Lactococcus lactis. The method distinguishes closely related strains and discriminates among some with identical ldh sequences. The fingerprinting primer LL-Rep1 complements a moderately repeated sequence found in low G + C Gram-positive bacteria and may therefore prove useful for discriminating among strains of other low G + C Gram-positive species.

Base Composition↗
PubMed1998

Two methods for the genetic differentiation of Lactococcus lactis ssp. lactis and cremoris based on differences in the 16S rRNA gene sequence.

The 16S ribosomal RNA gene sequences of Lactococcus lactis ssp. lactis and ssp. cremoris differ by 9-10 bp (depending on strain), within the first 200 bp of the sequence. These differences were used to develop two methods of genetically differentiating lactis and cremoris strains. Primers to conserved sequences in the 16S rRNA gene were used in a PCR reaction to amplify fragments of the 16S rRNA gene. A single base difference at position 180 of the sequence was utilised to develop a ligase chain reaction to differentiate lactis and cremoris sequences. The second method involved digestion of the amplified fragments with restriction endonucleases specific for either the lactis or cremoris sequence. Resolution of the digested fragments on an agarose gel allowed the strains to be identified as genetically lactis or cremoris. This method was used to examine lactococci isolated from raw milk. Of 31 raw milk strains examined, 21 contained the cremoris 16S rRNA sequence, however, all 31 strains exhibited the phenotypic characteristics of the lactis subspecies.

Animals↗
PubMed1999

Pyruvate flux distribution in NADH-oxidase-overproducing Lactococcus lactis strain as a function of culture conditions.

The influence of growth conditions on product formation from glucose by Lactococcus lactis strain NZ9800 engineered for NADH-oxidase overproduction was examined. In aerobic batch cultures, a large production of acetoin and diacetyl was found at acidic pH under pH-unregulated conditions. However, pyruvate flux was mainly driven towards lactate production when these cells were grown under strictly pH-controlled conditions. A decreased NADH-oxidase overproduction accompanied the homolactic fermentation, suggesting that the cellular energy was used with preference to maintain cellular homeostasis rather than for NADH-oxidase overproduction. The end product formation and NADH-oxidase activity were also studied in cells grown in aerobic continuous cultures under acidic conditions. A homoacetic type of fermentation as well as a low NADH-oxidase overproduction were observed at low dilution rates. NADH-oxidase was efficiently overproduced as the dilution rate was increased and consequently metabolic flux through lactate dehydrogenase drastically decreased. Under these conditions the flux limitation via pyruvate dehydrogenase was relieved and this enzymatic complex accommodated most of the pyruvate flux. Pyruvate was also significantly converted to acetoin and diacetyl via alpha-acetolactate synthase. At higher dilution rates, acetate production declined and the cultures turned to mixed-acid fermentation. These results suggest that the need to maintain the cellular homeostasis influenced NADH-oxidase overproduction and consequently the end product formation from glucose in these engineered strains.

Aerobiosis↗
PubMed1999

Nisin independent induction of the nisA promoter in Lactococcus lactis during growth in lactose or galactose.

Nisin biosynthesis is autoregulated extracellularly by the mature and modified peptide. To investigate other regulatory effects on nisin biosynthesis, a transcription fusion of the nisA promoter from Lactococcus lactis ATCC 11454 to the promoterless lacZ gene from Streptococcus thermophilus was constructed. This fusion construct, pDOC99, expressed beta-galactosidase in L. lactis ATCC 11454 growing in M17 medium containing glucose (M17G). Consistent with the known model for transcription of nisA, pDOC99 did not express beta-galactosidase in the non-nisin producer, L. lactis LM0230 grown in M17G, unless the nisRK genes (cloned in pDOC23) were included in trans and nisin was added to the medium. Growth of this strain in M17 containing lactose or galactose, resulted in nisA transcription, even in the absence of exogenous nisin. This expression was independent of pDOC23. Furthermore, nisA transcription in L. lactis LM0230(pDOC99) grown in M17G could be induced by the addition of exogenous galactose, with maximum induction occurring at concentrations > 5 mM.

Galactose↗
PubMed1999

A comparative analysis of the citrate permease P mRNA stability in Lactococcus lactis biovar diacetylactis and Escherichia coli.

The role of ribonucleases in the control of gene expression remains unknown in lactic acid bacteria. In the present work, we analysed the expression of the citP gene, which encodes the lactococcal citrate permease P, through the stability of the citQRP messenger in both Lactococcus lactis biovar diacetylactis (L. diacetylactis) and Escherichia coli. The chemical half-life for citQRP mRNA observed in L. diacetylactis wild-type strain was abnormally long for bacteria. It was even longer than that detected in E. coli RNase E or RNase III mutant strains. A model of processing and fate of RNA species containing citP gene is presented.

Bacterial Proteins↗
PubMed1999

Expression of the mobM gene of the streptococcal plasmid pMV158 in Lactococcus lactis subsp. lactis.

The streptococcal plasmid pMV158 is not auto-transferable, but it can be mobilised between bacteria by the use of functions supplied by plasmids of the pIP501/pAM beta 1 family. Plasmid pMV158 encodes a protein, MobM, which is involved in its mobilisation. This process initiates when MobM specifically cleaves supercoiled pMV158 plasmid DNA at the origin of transfer, oriT. Plasmid pMV158 has been transferred to Lactococcus lactis by conjugation aided by plasmid pAM beta 1. In the lactococcal host, MobM-mediated specific pMV158-relaxed molecules were detected. The intracellular amount of MobM has been quantified by immunoblot analyses and shown to be about 3500 molecules per cell. In the same host, we have mapped the initiation point of transcription of mobM. Transcription of this gene is directed from a promoter with an extended--10 region which overlaps with the pMV158-oriT.

Bacterial Proteins↗