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PubMed2000

Viscoelastic properties of an exocellular polysaccharide produced by a Lactococcus lactis.

The viscoelastic properties of a well-characterized exocellular polysaccharide (EPS) produced by the lactic acid bacterium Lactococcus lactis subsp. cremoris strain B40 were investigated. Dynamic rheological measurements were made as a function of frequency and EPS concentration. The bead-spring model of Rouse could reasonably describe the dynamic properties. Concentrated EPS solutions have a significant elasticity (G' > G") at high frequencies. The relatively high G' values at high concentrations and high frequencies are indicative of significant normal stress differences, and we put forward a hypothesis that suggests that these normal stresses may explain the contribution of EPSs to the ropy behavior of yogurts.

Algorithms↗
PubMedDate not supplied

Fusion to a carrier protein and a synthetic propeptide enhances E7 HPV-16 production and secretion in Lactococcus lactis.

An inducible system to improve and stabilize the production of an extremely labile protein (E7 antigen of human papillomavirus type 16) was developed in the food-grade bacterium Lactococcus lactis. A protein carrier, the staphylococcal nuclease Nuc, was fused either to N- or C-termini of E7 protein, and the resulting hybrid proteins were rescued from intracellular proteolysis but poorly secreted by L. lactis. A synthetic propeptide (LEISSTCDA) was then fused and significantly improved the secretion efficiency of the hybrid protein Nuc-E7 by L. lactis.

Carrier Proteins↗
PubMed2002

Proteolysis in Hispánico cheese manufactured using a mesophilic starter, a thermophilic starter, and bacteriocin-producing Lactococcus lactis subsp. lactis INIA 415 adjunct culture.

Lactococcus lactis subsp. lactis INIA 415, a strain harboring the structural genes of bacteriocins nisin Z and lacticin 481, was used as adjunct culture in the manufacture of Hispánico cheese with a mesophilic starter and a thermophilic starter of high aminopeptidase activity. Addition of the bacteriocin producer promoted early lysis of mesophilic and thermophilic starter bacteria. Extracellular aminopeptidase activity in 7-day-old cheese made using mesophilic and thermophilic starters plus bacteriocin producer was 3.0-fold the level reached in cheese made without the bacteriocin producer. Proteolysis in cheese made with mesophilic and thermophilic starters plus bacteriocin-producing adjunct culture after 25 days of ripening was 1.5-fold the level reached in cheese made without the bacteriocin producer, and the level of total free amino acids was 2.9-fold the level found in cheese made without the bacteriocin producer. Cheese made with mesophilic and thermophilic starters plus bacteriocin producer received the highest scores for flavor quality and flavor intensity and reached in 25 days the flavor intensity score of a 75-day-old cheese made without the bacteriocin producer.

Amino Acids↗
PubMed2002

Volatile compounds in Hispánico cheese manufactured using a mesophilic starter, a thermophilic starter, and bacteriocin-producing Lactococcus lactis subsp. lactis INIA 415.

The effect of the addition of Lactococcus lactis subsp. lactis INIA 415, a strain harboring the structural genes of nisin Z and lacticin 481, on the formation of volatile compounds in Hispánico cheese manufactured with a mesophilic starter or with the mesophilic starter and a thermophilic starter was investigated. Addition of bacteriocin-producing L. lactis subsp. lactis INIA 415 to milk enhanced the formation of 2-methyl-propanal, 2-methylbutanal, 3-methylbutanal, 2-methyl-1-propanol, 3-methyl-1-butanol, 1-octanol, 2-butanone, and 2,3-butanedione. On the other hand, addition of thermophilic starter enhanced the formation of acetaldehyde, ethanol, 3-methyl-2-buten-1-ol, ethyl butanoate, ethyl hexanoate, 2-butanone, and 2,3-butanedione in Hispánico cheese. Stepwise discriminant analysis using the relative abundances of volatile compounds classified cheeses by type of starter, with function 1 related to thermophilic starter and function 2 to bacteriocin producer.

Alcohols↗
PubMed2005

Esterified whey proteins can protect Lactococcus lactis against bacteriophage infection. Comparison with the effect of native basic proteins and L-polylysines.

Inhibitory action of basic esterified milk whey proteins [methylated (Met) or ethylated (Et) beta-lactoglobulin (BLG) and alpha-lactalbumin (ALA)], basic native proteins (chicken egg white lysozyme and calf thymus histone), and basic protein-like substances (L-polylysines) against the activity and replication of lactococcal bacteriophages (bIL66, bIL67, and bIL170) was tested. Chemical interactions of these proteins with phage DNA were determined as well as their protective effect on the growth of a laboratory plasmid-cured Lactococcus lactis subjected to an infection by the bacteriophages. All the proteins studied showed inhibitory activity against the three bacteriophages as tested by marked reduction of their lytic activities and decreasing the replication of studied phages. Histone and Met-BLG were more active toward bIL66 and bIL67, respectively, while both proteins were highly and equally active toward bIL170. Lysozyme showed lower antiviral activity. Antiviral activity of Et-BLG was a little bit lower than that observed in the case of the Met derivative. Esterified ALA also showed considerable but slightly lower antiviral activity as compared to other proteins. L-polylysines also showed an antiviral effect against the three bacteriophages studied, their influence being highly dependent on their molecular size. The best effective size of L-polylysines was in the range 15-70 kDa. Replication of bIL67 was inhibited by the presence of esterified ALA or BLG and native basic proteins. Complete inhibition of replication of bIL67 occurred when using polylysines with molecular masses in the ranges 4-15, 15-30, and 30-70 kDa, while protein-like substrates with lower molecular masses had only a slight effect. The presence of histone and Met-BLG at a concentration of 0.13 mg/mL in the incubation medium protected L. lactis against lysis when it was subjected to an infection by bIL67 (10(5) pfu/mL). The same action was achieved by l-polylysine (15-30 kDa) used at a concentration of 0.03 mg/mL in the incubation medium.

Bacteriophages↗
PubMed2002

Time dependent responses of glycolytic intermediates in a detailed glycolytic model of Lactococcus lactis during glucose run-out experiments.

Glucose addition and subsequent run-out experiments were compared to simulations with a detailed glycolytic model of Lactococcus lactis. The model was constructed largely on bases of enzyme kinetic data taken from literature and not adjusted for the specific simulations shown here. Upon glucose depletion a rapid increase in PEP, inorganic phosphate and a gradual decrease in fructose 1,6-bisphosphate (FBP) were measured and predicted by simulation. The dynamic changes in these and other intermediate concentrations as measured in the experiments were well predicted by the kinetic model.

Adenosine Triphosphate↗
PubMed2002

How to distinguish between the vacuum cleaner and flippase mechanisms of the lmrA multi-drug transporter in Lactococcus lactis.

A numerical model of the LmrA multi-drug transport system of Lactococcus lactis is used to explore the possibility of distinguishing experimentally between two putative transport mechanisms, i.e., the vacuum-cleaner and the flippase mechanisms. This comparative model also serves as an example of numerical simulation with the scripting language Python and its scientific add-on Scipy.

Bacterial Proteins↗
PubMed2003

Lacticin 3147 favours isoleucine transamination by Lactococcus lactis IFPL359 in a cheese-model system.

The bacteriocin, lacticin 3147, increased isoleucine transamination by Lactococcus lactis IFPL359 in a cheese model system. The formation of alpha-keto-beta-methyl-n-valeric acid and 2-hydroxy-3-methyl-valeric acid increased by three times in cheese slurries at 12 degrees C and cheese aroma intensity increased as well, which corresponded with a higher 2-methylbutanal formation.

Amino Acids↗
PubMed2004

Simple one-step purification of nisin Z from unclarified culture broth of Lactococcus lactis subsp. lactis A164 using expanded bed ion exchange chromatography.

A simple one-step purification method, using expanded bed, ion-exchange chromatography, for the fractionation of nisin Z produced by Lactococcus lactis subsp. lactis A164 was developed. The highest dynamic binding capacity (0.92) of the adsorbent was obtained at a superficial velocity of 367 cm h(-1), resulting in approx. 2.7-fold bed expansion. The range of pH for the maximum adsorption was 3-4. The isocratic elution with 0.15 M NaCl led to approx. >90% recovery. Single-step purification of nisin Z from unclarified A164 culture broth resulted in 31-fold purification with a 90% yield.

Bacterial Proteins↗
PubMed1999

Conversion of Lactococcus lactis from homolactic to homoalanine fermentation through metabolic engineering.

We report the engineering of Lactococcus lactis to produce the amino acid L-alanine. The primary end product of sugar metabolism in wild-type L. lactis is lactate (homolactic fermentation). The terminal enzymatic reaction (pyruvate + NADH-->L-lactate + NAD+) is performed by L-lactate dehydrogenase (L-LDH). We rerouted the carbon flux toward alanine by expressing the Bacillus sphaericus alanine dehydrogenase (L-AlaDH; pyruvate + NADH + NH4+ -->L-alanine + NAD+ + H2O). Expression of L-AlaDH in an L-LDH-deficient strain permitted production of alanine as the sole end product (homoalanine fermentation). Finally, stereospecific production (>99%) of L-alanine was achieved by disrupting the gene encoding alanine racemase, opening the door to the industrial production of this stereoisomer in food products or bioreactors.

Alanine↗
PubMed1997

Oral vaccination of mice against tetanus with recombinant Lactococcus lactis.

To determine whether a protective immune response could be elicited by oral delivery of a recombinant bacterial vaccine, tetanus toxin fragment C (TTFC) was expressed constitutively in Lactococcus lactis and administered orally to C57 BL/6 mice. The antibody titers elicited were lower than those following intranasal immunization (a route already known to result in high-level systemic anti-TTFC immune responses) but the protective efficacy was the same order of magnitude. The serum antibody isotypes elicited were predominantly IgG1 and IgG2a. TTFC-specific fecal IgA responses could be detected following oral or intranasal immunization. Chemically killed lactococci administered via the intranasal route were also able to elicit serum antibody responses of similar levels and kinetics to those induced by live bacteria.

Administration, Intranasal↗
PubMed1997

Food-grade controlled lysis of Lactococcus lactis for accelerated cheese ripening.

An attractive approach to accelerate cheese ripening is to induce lysis of Lactococcus lactis starter strains for facilitated release of intracellular enzymes involvement in flavor formation. Controlled expression of the lytic genes lytA and lytH, which encode the lysin and the holin proteins of the lactococcal bacteriophage phi US3, respectively, was accomplished by application of a food-grade nisin-inducible expression system. Simultaneous production of lysin and holin is essential to obtain efficient lysis and concomitant release of intracellular enzymes as exemplified by complete release of the debittering intracellular aminopeptidase N. Production of holin alone leads to partial lysis of the host cells, whereas production of lysin alone does not cause significant lysis. Model cheese experiments in which the inducible holinlysin overproducing strain was used showed a fourfold increase in release of L-Lactate dehydrogenase activity into the curd relative to the control strain and the holin-overproducing strain, demonstrating the suitability of the system for cheese applications.

Bacterial Proteins↗
PubMed2003

Biological containment of genetically modified Lactococcus lactis for intestinal delivery of human interleukin 10.

Genetically modified Lactococcus lactis secreting interleukin 10 provides a therapeutic approach for inflammatory bowel disease. However, the release of such genetically modified organisms through clinical use raises safety concerns. In an effort to address this problem, we replaced the thymidylate synthase gene thyA of L. lactis with a synthetic human IL10 gene. This thyA- hIL10+ L. lactis strain produced human IL-10 (hIL-10), and when deprived of thymidine or thymine, its viability dropped by several orders of magnitude, essentially preventing its accumulation in the environment. The biological containment system and the bacterium's capacity to secrete hIL-10 were validated in vivo in pigs. Our approach is a promising one for transgene containment because, in the unlikely event that the engineered L. lactis strain acquired an intact thyA gene from a donor such as L. lactis subsp. cremoris, the transgene would be eliminated from the genome.

Amino Acid Sequence↗
PubMed2001

Nisin production from Lactococcus lactis A.T.C.C. 7962 using supplemented whey permeate.

The influence of pH control and aeration (20% dissolved oxygen) on nisin production in a supplemented cheese whey permeate was examined during batch fermentation with Lactococcus lactis subsp. lactis A.T.C.C. 7962. A maximum nisin activity of 5280 i.u./ml of medium was observed in the raw extract of nisin after 9 h of fermentation with a constant pH at 4.9. However, the fermentation was continued until 24 h, when a decrease in the nisin activity was observed. The pH control did not influence the nisin production and aeration of the culture medium increased cell growth (biomass) but not nisin activity. The yeast Kluyveromyces marxianus, used as an alternative method to control pH, has not been efficient.

Animals↗
PubMed2002

Production of bacteriocins from Lactococcus lactis subsp. lactis CECT 539 and Pediococcus acidilactici NRRL B-5627 using mussel-processing wastes.

The growth and bacteriocin production by Lactococcus lactis subsp. lactis CECT 539 and Pediococcus acidilactici NRRL B-5627 were investigated on mussel-processing wastes. Both bacteriocin productions were satisfactorily modelled using a modified form of the Luedeking and Piret expression, which includes a term for the influence of the pH reduction rate. Experimental data from cultures buffered at different initial concentrations (0, 0.03, 0.10 and 0.25 M) of both bacteria were used to fit and verify the model. The influence of total sugars, nitrogen, phosphorus and buffer concentration on nisin and pediocin production was also studied using response-surface methodology and empirical modelling. Enhanced nisin production (33 BU/ml) was achieved in media buffered with 0.10 M potassium hydrogen phthalate/NaOH. However, the highest levels of pediocin (368 BU/ml) were obtained in the non-buffered media.

Animals↗
PubMed2003

Enhancement of nisin production by Lactococcus lactis in periodically re-alkalized cultures.

Synthesis of nisin as well as biomass production by Lactococcus lactis subsp. lactis CECT (Colección Española de Cultivos Tipo) 539 on both hydrolysed mussel-processing waste and whey medium were followed in three fixed volume fed-batch fermentations, with re-alkalization cycles. The two cultures on mussel-processing waste (MPW) were fed with a 240 g/l concentrated glucose and with a concentrated MPW (about 100 g of glucose/l). The culture on whey was fed with a mixture of concentrated whey (48 g of total sugars/l) and a 400 g/l concentrated lactose. The three cultures were mainly characterized with higher nisin titres [49.7, 109.6 and 124.7 bacteriocin activity units (AU)/ml respectively] compared with the batch process on de Man, Rogosa and Sharpe [(1960) J. Appl. Bacteriol. 23, 130-135] medium (49.6 AU/ml), MPW (9.5 AU/ml) and whey (22.5 AU/ml) [1 AU/ml is the amount of antibacterial compound needed to obtain 50% growth inhibition (LD50) compared with control tubes]. In the three fed-batch cultures a shift from homolactic to mixed-acid fermentation was observed, and other products (acetic acid, butane-2,3-diol or ethanol) in addition to lactic acid were detectable in the medium. However, their contributions to the total antibacterial activity of the post-incubates (the cell-free culture supernatant obtained at the end of the fermentation process) of L. lactis CECT 539 against Carnobacterium piscicola CECT 4020 were very low.

Animals↗
PubMed1991

Specificity of two genetically related cell-envelope proteinases of Lactococcus lactis subsp. cremoris towards alpha s1-casein-(1-23)-fragment.

The specificity of two genetically related cell-envelope serine proteinases (PI-type and PIII-type) of Lactococcus lactis subsp. cremoris towards the alpha s1-casein-(1-23)-fragment, an important intermediate product of primary chymosin-directed proteolysis in cheese, has been established. Both enzymes showed, at pH 6.5 and under relatively low-ionic-strength conditions, a characteristic, mutually different, cleavage pattern that seems, in the first instance, to be determined by the charge N-terminal to the cleaved bond. With Pi, three cleavage sites were found in the N-terminal positively charged part of the peptide and, with PIII, three sites were found in the C-terminal negatively charged part. Comparison of the specific cleavage sites in this peptide and those in beta-casein revealed similarities with respect to the different residues which can occur N-terminally to the cleaved bond. The properties of these substrate residues match with the structural and various interactive features of the respective binding regions of the enzymes predicted on the basis of a close sequence similarity of the lactococcal proteinases with the subtilisin family. A hydrophobic interaction and/or hydrogen-bridge formation seems to govern the binding of the first amino acid residue N-terminal to the scissile bond. The more distantly N-terminally positioned sequence of residues apparently is attracted electrostatically by a negative charge in the binding region of PI and by a positive charge in that of PIII, provided that the opposite charge is is present at the appropriate position in this sequence. Hence a specific electrostatic binding may occur; additionally, hydrophobic interaction and/or hydrogen-bond formation is important.

Amino Acid Sequence↗