Showing papers on "Lactococcus lactis published in 1992"
TL;DR: A physiological link is proposed between sucrose fermentation capacity and nisin production ability and carbon source regulation appears to be a major control mechanism for nisinProduction.
Abstract: Summary: Nisin production by Lactococcus lactis subsp. lactis NIZO 22186 was studied in batch fermentation using a complex medium. Nisin production showed primary metabolite kinetics: nisin biosynthesis took place during the active growth phase and completely stopped when cells entered the stationary phase. A stringent correlation could be observed between the expression of the prenisin gene (nisA) and the synthesis of the post-translationally enzymically modified and processed mature nisin peptide. Moreover, it seemed likely that nisin had a growth control function. A physiological link is proposed between sucrose fermentation capacity and nisin production ability. Carbon source regulation appears to be a major control mechanism for nisin production.
276 citations
TL;DR: Results suggest that NisB is membrane associated and that nisin biosynthesis occurs at the cell membrane, and NisT may be involved in nisin transport.
Abstract: Nisin produced by Lactococcus lactis 6F3 is used as a food preservative and is the most important member of a group of peptide-antibiotics containing lanthionine bridges (lantibiotics) (N. Schnell, K.-D. Entian, U. Schneider, F. Gotz, H. Zahner, R. Kellner, and G. Jung, Nature [London] 333:276-278, 1988). Nisin is ribosomally synthesized, and its structural gene, nisA, encodes a prepeptide that is posttranslationally modified, revealing the active lantibiotic (C. Kaletta and K.-D. Entian, J. Bacteriol. 171:1597-1601, 1989). Adjacent to nisA, the additional genes nisB, nisT, and nisC were identified. Over their entire sequences, these genes were homologous to genes recently identified as important for the biosynthesis of lantibiotics, that is, subtilin from Bacillus subtilis ATCC 6633 and epidermin from Staphylococcus epidermidis Tu 3298. Genes nisB, nisT, and nisC corresponded to open reading frames of 993, 600, and 418 amino acid residues, respectively. The nisT open reading frame is homologous to proteins of the HlyB (hemolysin B protein of Escherichia coli) subfamily. Proteins of this subfamily are responsible for the secretion of a variety of compounds, including large polypeptides, polysaccharides, and anti-drug tumors, indicating that NisT may be involved in nisin transport. Northern (RNA) blot analysis revealed a 0.3-kb transcript for the nisA structural gene, and the transcriptional start point of the nisA gene was determined by primer extension. Additionally, a mRNA of at least 3 kb was identified by using a hybridization probe specific to nisB. Antibodies were raised against the NisB protein, and Western blot (immunoblot) analysis revealed a molecular weight of about 115 kDa, which is in accordance with the theoretical protein size of 117.5 kDa as calculated from the nisB open reading frame. Several amphipathic transmembrane alpha-helices indicated that NisB is associated with the membrane. This was confirmed by preparing L. lactis vesicles. The NisB protein was tightly associated with the vesicle fraction and was released by sodium dodecyl sulfate treatment only. These results suggest that NisB is membrane associated and that nisin biosynthesis occurs at the cell membrane. Images
217 citations
TL;DR: A novel, chromosomally located conjugative transposon in Lactococcus lactis, Tn5276, was identified and characterized and encodes the production of and immunity to nisin, a lanthionine-containing peptide with antimicrobial activity, and the capacity to utilize sucrose via a phosphotransferase system.
Abstract: A novel, chromosomally located conjugative transposon in Lactococcus lactis, Tn5276, was identified and characterized. It encodes the production of and immunity to nisin, a lanthionine-containing peptide with antimicrobial activity, and the capacity to utilize sucrose via a phosphotransferase system. Conjugal transfer of Tn5276 was demonstrated from L. lactis NIZO R5 to different L. lactis strains and a recombination-deficient mutant. The integration of Tn5276 into the plasmid-free strain MG1614 was analyzed by using probes based on the gene for the nisin precursor (nisA) and the gene for sucrose-6-phosphate hydrolase (sacA). The transposon inserted at various locations in the MG1614 chromosome and showed a preference for orientation-specific insertion into a single target site (designated site 1). By using restriction mapping in combination with field inversion gel electrophoresis and DNA cloning of various parts of the element including its left and right ends, a physical map of the 70-kb Tn5276 was constructed, and the nisA and sacA genes were located. The nucleotide sequences of Tn5276 junctions in donor strain NIZO R5 and in site 1 of an MG1614-derived transconjugant were determined and compared with that of site 1 in recipient strain MG1614. The results show that the A + T-rich ends of Tn5276 are flanked by a direct hexanucleotide repeat in both the donor and the transconjugant but that the element does not contain a clear inverted repeat.
204 citations
TL;DR: The development of an expression system for mutated nisin Z (nisZ) genes is reported, using nisin A producing L. lactis as a host and a double mutation was introduced in the nisZ gene, resulting in the simultaneous production of two mutant species.
199 citations
TL;DR: Addition of glucose or sucrose to both milk and ultrafiltrate markedly enhanced exopolysaccharide production and modified the monosaccharide composition with glucose becoming dominant.
198 citations
TL;DR: An overview is given of the current knowledge concerning gene expression in Lactococcus lactis and a general picture of gene expression signals in L. lactis emerges that shows considerable similarity to those observed in Escherichia coli and Bacillus subtilis.
Abstract: Lactic acid bacteria are of major economic importance, as they occupy a key position in the manufacture of fermented foods. A considerable body of research is currently being devoted to the development of lactic acid bacterial strains with improved characteristics, that may be used to make fermentations pass of more efficiently, or to make new applications possible. Therefore, and because the lactococci are designated 'GRAS' organisms ('generally recognized as safe') which may be used for safe production of foreign proteins, detailed knowledge of homologous and heterologous gene expression in these organisms is desired. An overview is given of our current knowledge concerning gene expression in Lactococcus lactis. A general picture of gene expression signals in L. lactis emerges that shows considerable similarity to those observed in Escherichia coli and Bacillus subtilis. This feature allowed the expression of a number of L. lactis-derived genes in the latter bacterial species. Several studies have indicated, however, that in spite of the similarities, the expression signals from E. coli, B. subtilis and L. lactis are not equally efficient in these three organisms.
188 citations
TL;DR: Amonium sulfate precipitations resulted in a 455-fold increase in total lacticin 481 activity and Amino acid composition analysis of purified lacticIn 481 revealed the presence of lanthionine residues, suggesting that lactic in 481 is a member of the lantibiotic family of antimicrobial peptides.
Abstract: Lacticin 481, a bacteriocin produced during the growth of Lactococcus lactis subsp. lactis CNRZ 481, was purified sequentially by ammonium sulfate precipitation, gel filtration, and preparative and analytical reversed-phase high-pressure liquid chromatography. Ammonium sulfate precipitations resulted in a 455-fold increase in total lacticin 481 activity. The entire purification protocol led to a 107, 506-fold increase in the specific activity of lacticin 481. On the basis of its electrophoretic pattern in sodium dodecyl sulfate-polyacrylamide gels, lacticin 481 appeared as a single peptide band of 1.7 kDa. However, dimers of 3.4 kDa also exhibiting lacticin activity were detected. Derivatives of the lacticin-producing strain which did not produce lacticin 481 (Bac-) were sensitive to this bacteriocin (Bacs) and failed to produce the 1.7-kDa band. Amino acid composition analysis of purified lacticin 481 revealed the presence of lanthionine residues, suggesting that lacticin 481 is a member of the lantibiotic family of antimicrobial peptides. Seven residues (K G G S G V I) were sequenced from the N-terminal portion of lacticin 481, and these did not shown any homology with nisin or other known bacteriocin sequences.
183 citations
TL;DR: The genes responsible for bacteriocin production and immunity in Lactococcus lactis subsp. lactis biovar diacetylactis WM4 were localized and characterized by DNA restriction fragment deletion, subcloning, and nucleotide sequence analysis.
Abstract: The genes responsible for bacteriocin production and immunity in Lactococcus lactis subsp. lactis biovar diacetylactis WM4 were localized and characterized by DNA restriction fragment deletion, subcloning, and nucleotide sequence analysis. The nucleotide sequence of a 5.6-kb AvaII restriction fragment revealed a cluster with five complete open reading frames (ORFs) in the same orientation. DNA and protein homology analyses, combined with deletion and Tn5 insertion mutagenesis, implicated four of the ORFs in the production of and immunity to lactococcin A. The last two ORFs in the cluster were the lactococcin A structural and immunity genes, lcnA and lciA. The two ORFs immediately upstream of lcnA and lciA were designated lcnC and lcnD, and the proteins that they encoded showed similarities to proteins of signal sequence-independent secretion systems. lcnC encodes a protein of 716 amino acids that could belong to the HlyB family of ATP-dependent membrane translocators. LcnC contains an ATP binding domain in a conserved C-terminal stretch of approximately 200 amino acids and three putative hydrophobic segments in the N terminus. The lcnD product, LcnD, of 474 amino acids, is essential for lactococcin A expression and shows structural similarities to HlyD and its homologs. On the basis of these results, a secretion apparatus that is essential for the full expression of active lactococcin A is postulated.
163 citations
TL;DR: Bacteriocin production in TYT media was comparable with that in M17 and MRS, which had a higher peptide content, and TYT30 allowed good production of enterocin 1146 and lactocin D while TYT11 proved acceptable for all the strains tested.
Abstract: The effect of tryptone, yeast extract, Tween 80 and initial pH on the production of enterocin 1146 and lactocin D, two bacteriocins produced by lactic acid bacteria, was studied in a basal buffered medium (tryptone-yeast extract-tween, TYT) using factorial experiments and empirical modelling. Production of enterocin 1146 was affected by pH, yeast extract and Tween 80 and to a lesser degree, by the initial pH of the medium. On the basis of the predictions of the models developed, three TYT media (TYT10, TYT11 and TYT30) were designed to maximize bacteriocin production while minimizing the amount of peptides in the medium. Growth and bacteriocin production by Enterococcus faecium DPC 1146 (enterocin 1146), Lactococcus lactis subsp. lactis biovar diacetylactis DPC 3286 (lactocin D) and Lact. lactis subsp. cremoris LMG2130 (lactococcin A) was compared in TYT media and seven other culture media (Elliker lactic broth, M17, M17 dialysate, MRS, tryptose phosphate, tryptone yeast extract broth, yeast glucose Lemco broth). Bacteriocin production in TYT media was comparable with that in M17 and MRS, which had a higher peptide content. TYT30 allowed good production of enterocin 1146 and lactocin D while TYT11 proved acceptable for all the strains tested.
153 citations
TL;DR: The pyruvate dehydrogenase complex of Lactococcus lactis subsp.
Abstract: The pyruvate dehydrogenase complex of Lactococcus lactis subsp lactis bv diacetylactis has a specific activity of 66 U/mg and a Km of 1 mM for pyruvate The specific activities of E2 and E3 in the complex are 30 and 036 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 = 32 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 Images
142 citations
TL;DR: Results showed that transcriptional regulation of the lac operon is mediated by the interaction between the LacR repressor, the lac promoter, and sequences in the noncoding region between the lacR and lacA genes.
Abstract: We determined the location, activity, and regulation of the promoter of the Lactococcus lactis 8-kb lactose operon (lacABCDFEGX), which encodes the enzymes of the lactose phosphotransferase system and the tagatose 6-phosphate pathway. The lac promoter sequence corresponds closely to the consensus promoter described for gram-positive bacteria and is located in a back-to-back configuration with the promoter of the divergently transcribed lacR gene, which encodes the LacR repressor. The transcription start sites used under induced (lactose) and noninduced (glucose) conditions were determined. The minimal promoter region that could be isolated on a single restriction fragment included sequences ranging from -75 to +42. The effect of the presence of flanking sequences and the lacR gene on promoter activity and regulation was studied in Escherichia coli and L. lactis strains by using transcriptional fusions with promoterless chloramphenicol acetyltransferase reporter genes. The results showed that transcriptional regulation of the lac operon is mediated by the interaction between the LacR repressor, the lac promoter, and sequences in the noncoding region between the lacR and lacA genes. Sequences flanking the minimal promoter region appeared to enhance lac promoter activity much more in L. lactis (5- to 38-fold) than in E. coli (1.3- to 5-fold). Images
TL;DR: The genes for biosynthesis of the branched-chain amino acids leucine, isoleucine and valine in Lactococcus lactis subsp. NCDO2118 were characterized by cloning, complementation in Escherichia coli and Bacillus subtilis, and nucleotide sequence analysis as discussed by the authors.
Abstract: The genes for biosynthesis of the branched-chain amino acids leucine, isoleucine, and valine in Lactococcus lactis subsp. lactis NCDO2118 were characterized by cloning, complementation in Escherichia coli and Bacillus subtilis, and nucleotide sequence analysis. Nine structural genes are clustered on a 12-kb DNA fragment in the order leuABCD ilvDBNCA. Upstream of these genes, the nucleotide sequence suggests the existence of regulation by transcriptional attenuation. Between the leuD and ilvD genes is an unexpected gene, encoding a protein which belongs to the ATP-binding cassette protein superfamily.
TL;DR: Several strains of Lactococcus lactis subsp. diacetylactis and Leuconostoc spp. were compared for product formation from citrate in milk cultures as discussed by the authors.
Abstract: Several strains of Lactococcus lactis subsp. lactis var. diacetylactis and Leuconostoc spp. were compared for product formation from citrate in milk cultures. Most strains produced acetoin and butanediol. Some strains derived from buffer starter cultures produced, in addition, α-acetolactate. Lactococcus lactis strain C17, which produced acetoin and butanediol but no α-acetolactate in culture, was compared physiologically with L. lactis strain Ru4, which produced only α-acetolactate. Activities of enzymes involved in citrate metabolism were almost identical in both strains, with the exception of α-acetolactate decarboxylase, which was missing in strain Ru4. The formation of α-acetolactate, acetoin and diacetyl was further analysed in cell-free extracts. α-Acetolactate synthase activity saturated at a high pyruvate concentration (100 mm). This is in agreement with the observed accumulation of pyruvate externally, and probably internally, during α-acetolactate, acetoin and butanediol production by L. lactis cells.
TL;DR: The extracellular polysaccharide obtained from slime-forming Lactococcus lactis subsp.
TL;DR: Arbitrarily primed polymerase chain reaction, with incorporation of either radioactive or fluorescent labels, was used as a rapid and sensitive method for obtaining genomic fingerprints of strains of Lactococcus lactis.
Abstract: Arbitrarily primed polymerase chain reaction, with incorporation of either radioactive or fluorescent labels, was used as a rapid and sensitive method for obtaining genomic fingerprints of strains of Lactococcus lactis. Closely related strains produced almost identical fingerprints. Fingerprints of other strains showed only some similarities. Images
TL;DR: The results indicate that strains of the two subspecies form two distinct groups and that the DNA sequence divergence between L. lactis and L. cremoris is estimated to be between 20 and 30%.
Abstract: Relatedness between Lactococcus lactis subsp. cremoris and L. lactis subsp. lactis was assessed by Southern hybridization analysis, with cloned chromosomal genes as probes. The results indicate that strains of the two subspecies form two distinct groups and that the DNA sequence divergence between L. lactis subsp. lactis and L. lactis subsp. cremoris is estimated to be between 20 and 30%. The previously used phenotypic criteria do not fully discriminate between the groups; therefore, we propose a new classification which is based on DNA homology. In agreement with this revised classification, the L. lactis subsp. lactis and L. lactis subsp. cremoris strains from our collection have distinct phage sensitivities.
TL;DR: Nisin-resistant Leuconostoc mesenteroides was evaluated to demonstrate that nisin levels produced in mixed culture were sufficient to retard the onset of the growth of nisin-sensitive, homofermentative Lactobacillus plantarum ATCC 14917.
Abstract: Nisin-resistant Leuconostoc mesenteroides NCK293 and nisin-producing Lactococcus lactis subsp. lactis NCK401 were evaluated separately and in combination for growth and nisin production in a model sauerkraut fermentation. Strains were genetically marked and selectively enumerated by using antibiotic-containing media. The growth and survival of L. mesenteroides were similar in the presence and absence of Lactococcus lactis subsp. lactis. The growth of Lactococcus lactis subsp. lactis was not inhibited, although the maximum cell density was reduced and the population decline was more pronounced in the presence of L. mesenteroides. Nisin was detected within 24 h, and levels were relatively constant over the 12-day test period. The maximum cell populations and nisin level achieved could be altered by changing the initial cell ratios of L. mesenteroides and lactococcus lactis subsp. lactis. Isogenic nisin-producing and nisin-negative Lactococcus lactis subsp. lactis derivatives were used in combination with nisin-resistant L. mesenteroides to demonstrate that nisin levels produced in mixed culture were sufficient to retard the onset of the growth of nisin-sensitive, homofermentative Lactobacillus plantarum ATCC 14917.
TL;DR: The gene encoding the cell-envelope-associated proteinase of Lactobacillus paracasei subsp.
Abstract: The gene encoding the cell-envelope-associated proteinase of Lactobacillus paracasei subsp. paracasei NCDO 151 (formerly Lactobacillus casei NCDO 151) was cloned and sequenced. The gene was located on the chromosome and encoded a polypeptide of 1902 amino acids. The proteinase is N-terminally cleaved upon maturation. It shows extensive homology to the Lactococcus lactis subsp. cremoris Wg2 proteinase. Similar to the situation in Lactococcus, a maturation gene was found upstream of the proteinase gene. The cloned proteinase gene was expressed in Lactobacillus plantarum. However, no expression was observed when the gene was cloned in Lactococcus lactis.
TL;DR: The microflora of a white-brined cheese made from raw goat milk was studied during a 90-day ripening period, with low pH levels and high NaCl content affected the growth of most microbial groups resulting in considerably lower counts at 3 months.
TL;DR: Two strains of lactic acid bacteria, D53 and 23, identified as Lactococcus lactis by DNA-DNA hybridizations, produced heat stable bacteriocins which were resistant to trypsin and pepsin, but were inactivated by alpha-chymotrypsins and proteinase K.
TL;DR: The structure of the exopolysaccharide of Lactococcus lactis subsp.
TL;DR: This work investigated the inhibitor(s) produced by P. jensenii P126 (ATCC 4872) and classification of the inhibitor as a bacteriocin is supported by its proteinaceous nature and its bactericidal activity against L. delbrueckii subsp.
Abstract: The genus Propionibacterium includes cutaneous species typically found on human skin and the dairy or classical species (Propionibacterium freudenreichii, P. jensenii, P. thoenii, and P. acidipropionici) used industrially for the production of Swiss cheese and propionic acid. Grinstead (1989, M.S. thesis, Iowa State University, Ames) has previously observed that some dairy propionibacteria inhibit other species in the classical grouping. We further investigated the inhibitor(s) produced by P. jensenii P126 (ATCC 4872). An antagonist(s) from anaerobic agar cultures of P126 strongly inhibited two closely related strains of propionibacteria, P. acidipropionici P5 and P. jensenii P54, and Lactobacillus bulgaricus NCDO 1489, Lactobacillus delbrueckii subsp. lactis ATCC 4797, Lactococcus cremoris NCDO 799, and Lactococcus lactis subsp. lactis C2. The inhibitor, designated jenseniin G, was active at pH 7.0; inactivated by treatment with pronase E, proteinase K, and type 14 protease; insensitive to catalase; and stable to freezing, cold storage (4 degrees C, 3 days), and heat (100 degrees C, 15 min). Classification of the inhibitor as a bacteriocin is supported by its proteinaceous nature and its bactericidal activity against L. delbrueckii subsp. lactis ATCC 4797. The lack of detectable plasmids suggests a chromosomal location for the determinant(s) of jenseniin G.
TL;DR: Two Lactococcus lactis subsp.
Abstract: Two Lactococcus lactis subsp lactis strains, NCK400 and LJH80, isolated from a commercial sauerkraut fermentation were shown to produce nisin LJH80 was morphologically unstable and gave rise to two stable, nisin-producing (Nip+) derivatives, NCK318-2 and NCK318-3 NCK400 and derivatives of LJH80 exhibited identical morphological and metabolic characteristics, but could be distinguished on the basis of plasmid profiles and genomic hybridization patterns to a DNA probe specific for the iso-ISS1 element, IS946 NCK318-2 and NCK318-3 harbored two and three plasmids, respectively, which hybridized with IS946 Plasmid DNA was not detected in NCK400, and DNA from this strain failed to hybridize with IS946 Despite the absence of detectable plasmid DNA in NCK400, nisin-negative derivatives (NCK402 and NCK403) were isolated after repeated transfer in broth at 37 degrees C Nisin-negative derivatives concurrently lost the ability to ferment sucrose and became sensitive to nisin A 4-kbp HindIII fragment containing the structural gene for nisin (spaN), cloned from L lactis subsp lactis ATCC 11454, was used to probe genomic DNA of NCK318-2, NCK318-3, NCK400, and NCK402 digested with EcoRI or HindIII The spaN probe hybridized to an 88-kbp EcoRI fragment and a 10-kbp HindIII fragment in the Nip+ sauerkraut isolates, but did not hybridize to the Nip- derivative, NCK402 A different hybridization pattern was observed when the same probe was used against Nip+ L lactis subsp lactis ATCC 11454 and ATCC 7962 These phenotypic and genetic data confirmed that unique Nip+ L lactis subsp lactis strains were isolated from fermenting sauerkraut
TL;DR: The evidence is that BCECF extrusion is strictly correlated with ATP concentration and not with the proton motive force, and is inhibited by vanadate and to a lesser extent by N,N'-dicyclohexylcarbodiimide.
Abstract: 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.
TL;DR: 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 as discussed by the authors.
Abstract: 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.
TL;DR: Following chromosomal rearrangements in this region involving a newly discovered insertion element (IS905) generated a strain that was deficient in the nisA gene product but expressed those nisin determinants necessary for prenisin maturation, secretion, and immunity.
Abstract: Thenisin-producing Lactococcus lactis strain F15876hasbeenmodified anddeveloped foruse as an expression system forengineered nisin variants. Insertional inactivation oftheresident nisAgenehada polar effect on downstream genes,including those involved innisin immunity. However, subsequent chromosomal rearrangements inthis region involving a newlydiscovered insertion element (IS905) generated a strain that was deficient inthenisAgene product butexpressed thosenisin determinants necessaryforprenisin maturation, secretion, andimmunity. Complementation ofthelesion inthenisAgene byplasmid-encoded nisA genescontaining site-specific mutations resulted intheexclusive production ofaltered nisins containing specific aminoacidsubstitutions. Nisin isahighly modified peptide antibiotic produced by certain strains ofLactococcus lactis. Itisofgreat interest to thefoodindustry because ofitsefficient antimicrobial activityagainst awiderangeofgram-positive organisms, includingmanyspoilage bacteria andfoodpathogens suchas Listeria, Clostridium, andBacillus species (12, 25). Nisinisamemberofthefamily ofantibiotics termed lantibiotics. Theseunusual polycyclic peptides sharethe structural features ofdehydro residues andintrachain sulfide bridges forming lanthionine andI-methyllanthionine rings.
TL;DR: This review summarizes the recent developments in understanding the structure of nisin, the genetics of its production, and its mode of action and describes the most highly characterized bacteriocin produced by lactic acid bacteria.
TL;DR: The nucleotide sequence of the pepN gene from Lactococcus lactis encoding a zinc‐metallo aminopeptidase has been determined and a highly conserved area was identified which has similarity with the active site of thermolysin.
TL;DR: Quarg cheese was succesfully produced in 5 h with the immobilized freeze-dried (IFD) culture, but sensory evaluation confirmed a significant texture difference between cheeses made with free or IFD cultures.
TL;DR: The fifth phage resistance factor from the prototype phage-insensitive strain Lactococcus lactis subsp.
Abstract: The fifth phage resistance factor from the prototype phage-insensitive strain Lactococcus lactis subsp. lactis ME2 has been characterized and sequenced. The genetic determinant for Prf (phage resistance five) was subcloned from the conjugative plasmid pTN20, which also encodes a restriction and modification system. Typical of other abortive resistance mechanisms, Prf reduces the efficiency of plaquing to 10(-2) to 10(-3) and decreases the plaque size and burst size of the small isometric-headed phage p2 in L. lactis subsp. lactis LM0230. However, normal-size plaques occurred at a frequency of 10(-4) and contained mutant phages that were resistant to Prf, even after repeated propagation through a sensitive host. Prf does not prevent phage adsorption or promote restriction and modification activities, but 90% of Prf+ cells infected with phage p2 die. Thus, phage infections in Prf+ cells are aborted. Prf is effective in both L. lactis subsp. lactis and L. lactis subsp. cremoris strains against several small isometric-headed phages but not against prolate-headed phages. The Prf determinant was localized by Tn5 mutagenesis and subcloning. DNA sequencing identified a 1,056-nucleotide structural gene designated abiC. Prf+ expression was obtained when abiC was subcloned into the lactococcal expression vector pMG36e. abiC is distinct from two other lactococcal abortive phage resistance genes, abiA (Hsp+, from L. lactis subsp. lactis ME2) and abi416 (Abi+, from L. lactis subsp. lactis IL416). Unlike abiA, the action of abiC does not appear to affect DNA replication. Thus, abiC represents a second abortive system found in ME2 that acts at a different point of the phage lytic cycle.