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PubMed2006

Artisanal and experimental Pecorino Siciliano cheese: microbial dynamics during manufacture assessed by culturing and PCR-DGGE analyses.

Traditional artisanal Pecorino Siciliano (PS) cheeses, and two experimental PS cheeses were manufactured using either raw or pasteurised ewes' milk with the addition of starter cultures. The bacterial diversity and dynamics of the different cheese types were evaluated both by culturing and characterisation of isolates, and a culture-independent approach based on the 16S ribosomal RNA (rRNA) gene. Following cultivation, artisanal and experimental cheese types showed similar microbial counts, and isolates belonging to Lactococcus lactis, Streptococcus thermophilus, Enterococcus faecalis and Leuconostoc mesenteroides were identified by phenotypic characterisation and comparison of the restriction fragment length polymorphism (RFLP) of the 16S rRNA gene to that of reference species. The culture-independent fingerprinting technique PCR and denaturing gradient gel electrophoresis (DGGE) of V6 to V8 regions of the 16S rRNA gene of samples taken during artisanal PS cheese manufacture, from raw milk to the ripened cheese, indicated relevant shifts in the microbial community structure. The dominance of Streptococcus bovis and Lactococcus lactis species in the traditional artisanal PS was revealed by 16S rRNA gene sequencing. Comparison of DGGE profiles of samples from milk to ripened cheese, derived from artisanal procedure and the two experimental PS cheeses during production showed similar trends with the presence of intense bands in common. Nevertheless, the profiles of several artisanal cheeses from different farms appeared more diverse, and these additional species are probably responsible for the generally superior flavour and aroma development of traditional PS cheese.

Animals↗
PubMed2001

Nisin-producing organisms during traditional 'Fior di latte' cheese-making monitored by multiplex-PCR and PFGE analyses.

In this work we studied using different molecular methods the population dynamics of nisin-producing organisms and the persistence of such organisms within a complex ecosystem, 'Fior di latte' cheese, a traditional high-moisture pasta filata cheese. Using the primers targeting the eubacterial 16S-23S rRNA spacer region, together with those amplifying the nisA or nisZ gene, we were able to provide a rapid species identification of the isolates. Inhibitors of Lactococcus lactis subsp. lactis DSM 20481T used as indicator occurred during the whole process of cheese manufacture as a significant part of lactic microflora; however, only 12 among 109 isolates of bacteriocin producers were nisin producers. Amplification of the nisA or nisZ gene, using DNA extracted directly from dairy samples as templates, showed that the nisin structural gene was detected during cheese-making from milk samples up to the end of curd ripening but not in the final cheese. In order to monitor nisin-producing strains during cheese manufacturing, the 12 Lactococcus lactis nis+ strains were analysed by low frequency restriction fragment and PFGE. Nine isolates among the 12 nisin-producers exhibited an unique and distinct DNA banding pattern and are considered to be genetically diverse. The other three isolates from curd after ripening showed the same restriction pattern and could be the same strain. In fact, it was also isolated 2 months after the first analysis of cheese-making of 'Fior di latte'.

Bacteriocins↗
PubMed2004

New Lactococcus strain with immunomodulatory activity: enhancement of Th1-type immune response.

Few studies exist dealing with the probiotic activity of lactococci, which are commonly used as starter bacteria in the manufacture of many kinds of fermented dairy products. Fifteen strains of the genus Lactococcus were examined for their probiotic activities, such as immunomodulatory effects. Six strains induced the production of cytokines (IL-12, IL-6, and TNF-alpha) in macrophage-like cell line J774.1, and the highest induction was observed with Lactococcus lactis subsp. lactis G50. The cytokine induction in the J774.1 cell line was almost entirely sustained after heat-killing of the strain. Spleen cells from BALB/c mice fed G50 culture produced more IL-12 and IFN-gamma and slightly less IL-4 and IL-6 than the control (i.e., without strain G50), indicating that strain G50 can enhance Th1-type immune response in vivo. The effect of the oral administration of strain G50 on antibody response in mice was also investigated. Mice were immunized with ovomucoid (OVM), a potent egg allergen, and the antibody level in the serum was then determined. The total IgE antibody level in the group treated with strain G50 was significantly lower than that of the control. The response of OVM-specific IgG1 and IgE antibodies tended to be low in the group that was administered strain G50, compared with the response of the control group. These results suggest that strain G50 has an ability to suppress the Th2 response. Thus, Lactococcus lactis subsp. lactis G50 is a potential probiotic strain for the suppression of hypersensitive reactions caused by the Th2 response.

Animals↗
PubMed2004

Isolation, identification, and selection of lactic acid bacteria from alfalfa sprouts for competitive inhibition of foodborne pathogens.

Several studies have investigated the control of pathogens on alfalfa sprouts, and some treatments have been shown to be effective in reducing pathogen populations. However, control methods investigated thus far only provide pathogen control at a given point in the sprouting process and can affect germination. Competitive inhibition of pathogens with lactic acid bacteria might provide pathogen control throughout the sprouting process and up to consumption. The purpose of this study was to isolate and identify lactic acid bacteria from alfalfa sprouts to inhibit the growth of foodborne pathogens. Fifty-eight lactic acid bacteria isolates were obtained from alfalfa seeds and sprouts. These isolates were evaluated for inhibitory action against Salmonella enterica, Escherichia coli O157:H7, and Listeria monocytogenes by agar spot tests. All pathogens were inhibited by 32 (55%) of the isolates, S. enterica by 56 (97%), E. coli O157:H7 by 49 (84%), and L. monocytogenes by 41 (71%). The isolates were identified by the Analytical Profile Index evaluation of carbohydrate utilization. Isolates obtained from a sample of alfalfa seeds and identified as Lactococcus lactis subsp. lactis showed zones of inhibition of 4.0 mm or greater for all pathogens. One of these isolates, Lactococcus lactis subsp. lactis (L7), and an isolate previously obtained, Pediococcus acidilactici (D3), were evaluated for competitive inhibition of S. enterica, E. coli O157:H7, and L. monocytogenes in deMan Rogosa Sharpe agar and broth. Pathogen populations were significantly reduced by day 5. The selected isolates will be further evaluated in future studies for inhibitory action toward S. enterica, E. coli O157:H7, and L. monocytogenes during sprouting.

Antibiosis↗
PubMed2001

Chemical and microbiological characterisation of kefir grains.

Chemical and microbiological composition of four Argentinean kefir grains from different sources as well as characteristics of the corresponding fermented milk were studied. Kefir grains CIDCA AGK1, AGK2 and AGK4 did not show significant differences in their chemical and microbiological composition. In contrast, protein and yeast content of AGK3 was higher than in the other grains. Although grain microflora comprised lactobacilli, lactococcus, acetic acid bacteria and yeast, we found an important difference regarding species. Lactococcus lactis subsp. lactis, Lactobacillus kefir, Lactobacillus plantarum, Acetobacter and Saccharomyces were present in all types of kefir grain. While Leuconostoc mesenteroides was only isolated from grains CIDCA AGK1 and Lactococcus lactis subsp. lactis biovar diacetylactis, Lactobacillus parakefir and Kluyveromyces marxianus were only isolated from CIDCA AGK2 grains. All grains produced acid products with pH between 3.5 and 4.0. The apparent viscosity of AGK1 fermented milk was greater than the product obtained with AGK4. All fermented milks had inhibitory power towards Escherichia coli but AGK1 and AGK2 supernatants were able to halt the bacterial growth for at least 25 h. Grain weight increment in AGK1, AGK2 and AGK3 during growth in milk did not show significant differences. Despite their fermenting activity, AGK4 grains did not increase their weight.

Acetobacter↗
PubMed2001

Characterization of the lactic acid bacteria in ewe's milk and cheese from northwest Argentina.

Indigenous lactic acid bacteria in ewe's milk and artisanal cheese were studied in four samples of fresh raw milk and four 1-month-old cheeses from the provinces of northwest Argentina. Mean growth counts on M17, MRS, and MSE agar media did not show significant differences (P < 0.05) in raw milk and cheeses. Isolates of lactic acid bacteria from milk were identified as Enterococcus (48%), lactococci (14%), leuconostocs (8%), and lactobacilli (30%). All lactococci were identified as Lactococcus lactis (subsp. lactis and subsp. cremoris). Lactobacilli were identified as Lactobacillus plantarum (92%) and Lactobacillus acidophilus (8%). Enterococci (59%) and lactobacilli (41%) were isolated from cheeses. L. plantarum (93%), L. acidophilus (5%), and Lactobacillus casei (2%) were most frequently isolated. L. lactis subsp. lactis biovar diacetylactis strains were considered as fast acid producers. L. lactis subsp. cremoris strains were slow acid producers. L. plantarum and L. casei strains identified from the cheeses showed slow acid production. The majority of the lactobacilli and Lactococcus lactis strains utilized citrate and produced diacetyl and acetoin in milk. Enzyme activities (API-ZYM tests) of lactococci were low, but activities of L. plantarum strains were considerably higher. The predominance of L. plantarum in artisanal cheese is probably important in the ripening of these cheeses due to their physiological and biochemical characteristics.

Animals↗
PubMed2003

Bacterial community structure and location in Stilton cheese.

The microbial diversity occurring in Stilton cheese was evaluated by 16S ribosomal DNA analysis with PCR-denaturing gradient gel electrophoresis. DNA templates for PCR experiments were directly extracted from the cheese as well as bulk cells harvested from a variety of viable-count media. The variable V3 and V4-V5 regions of the 16S genes were analyzed. Closest relatives of Lactococcus lactis, Enterococcus faecalis, Lactobacillus plantarum, Lactobacillus curvatus, Leuconostoc mesenteroides, Staphylococcus equorum, and Staphylococcus sp. were identified by sequencing of the DGGE fragments. Fluorescently labeled oligonucleotide probes were developed to detect Lactococcus lactis, Lactobacillus plantarum, and Leuconostoc mesenteroides in fluorescence in situ hybridization (FISH) experiments, and their specificity for the species occurring in the community of Stilton cheese was checked in FISH experiments carried out with reference cultures. The combined use of these probes and the bacterial probe Eub338 in FISH experiments on Stilton cheese sections allowed the assessment of the spatial distribution of the different microbial species in the dairy matrix. Microbial colonies of bacteria showed a differential location in the different parts of the cheese examined: the core, the veins, and the crust. Lactococci were found in the internal part of the veins as mixed colonies and as single colonies within the core. Lactobacillus plantarum was detected only underneath the surface, while Leuconostoc microcolonies were homogeneously distributed in all parts observed. The combined molecular approach is shown to be useful to simultaneously describe the structure and location of the bacterial flora in cheese. The differential distribution of species found suggests specific ecological reasons for the establishment of sites of actual microbial growth in the cheese, with implications of significance in understanding the ecology of food systems and with the aim of achieving optimization of the fermentation technologies as well as preservation of traditional products.

Cheese↗
PubMed1999

Distribution of plasmid-borne stress protein genes in Streptococcus thermophilus and other lactic acid bacteria.

The presence of heat stress protein genes (hsp) was tested by Southern hybridization analysis in total DNA extracts from species of the genus Streptococcus (47 strains), Lactobacillus (34 strains), Lactococcus (24 strains), and Leuconostoc (5 strains). The biotinylated hsp16.4 probe prepared from an ORF2 fragment of pER341 (2.8 kb) tested positively with restricted DNA extracts of seven Streptococcus thermophilus strains and a single strain of Lactococcus lactis subsp. cremoris. In all positive S. thermophilus strains, the hsp was located on plasmids ranging from ca. 2.8 kb to 11 kb in size, while hsp was present in a 7.5-kb plasmid in Lactococcus lactis subsp. cremoris. Southern blots with a rep probe showed that all hsp16.4+ plasmids in S. thermophilus strains also shared homology with the replication function (rep) of pER341, suggesting the common origin of these plasmids.

Bacterial Proteins↗
PubMed1996

Genetic organization of the mle locus and identification of a mleR-like gene from Leuconostoc oenos.

Characterization of the mle locus harboring the malolactic enzyme gene mleA and malate permease gene mleP from Leuconostoc oenos was completed in this study by mRNA analysis. Northern (RNA) blot experiments revealed a 2.6-kb transcript, suggesting an operon structure harboring mleA and mleP genes. Primer extension analysis showed that the mle operon has a single transcription start site located 17 nucleotides upstream of the ATG translation start site for the mleA gene. We found sequences, TTGACT and TATGAT (which are separated by 18 bp), that are closely related to the gram-positive and Escherichia coli consensus promoter sequences. Upstream of the mleA gene, an 894-bp open reading frame that transcribed divergently from the mle operon was found. Sequence analysis and expression in E. coli minicells suggest that this open reading frame encodes a polypeptide with an apparent molecular mass of 34 kDa belonging to the LysR-type regulatory protein family. Protein comparisons showed the highest level of identity with the MleR regulatory protein from Lactococcus lactis, which is involved in the expression of the malolactic genes in the presence of L-malate. However, the MleR-like protein of L. oenos seems different from the protein of Lactococcus lactis, since no regulation of the malolactic enzyme by L-malate was effective under our experimental conditions.

Amino Acid Sequence↗
PubMed1996

Genomic organization of lactic acid bacteria.

Current knowledge of the genomes of the lactic acid bacteria, Lactococcus lactis and Streptococcus thermophilus, and members of the genera Lactobacillus, Leuconostoc, Pediococcus and Carnobacterium, is reviewed. The genomes contain a chromosome within the size range of 1.8 to 3.4 Mbp. Plasmids are common in Lactococcus lactis (most strains carry 4-7 different plasmids), some of the lactobacilli and pediococci, but they are not frequently present in S. thermophilus, Lactobacillus delbrueckii subsp. bulgaricus or the intestinal lactobacilli. Five IS elements have been found in L. lactis and most strains carry multiple copies of at least two of them; some strains also carry a 68-kbp conjugative transposon. IS elements have been found in the genera Lactobacillus and Leuconostoc, but not in S. thermophilus. Prophages are also a normal component of the L. lactis genome and lysogeny is common in the lactobacilli, however it appears to be rare in S. thermophilus. Physical and genetic maps for two L. lactis subsp. lactis strains, two L. lactis subsp. cremoris strains and S. thermophilus A054 have been constructed and each reveals the presence of six rrn operons clustered in less than 40% of the chromosome. The L. lactis subsp. cremoris MG1363 map contains 115 genetic loci and the S. thermophilus map has 35. The maps indicate significant plasticity in the L. lactis subsp. cremoris chromosome in the form of a number of inversions and translocations. The cause(s) of these rearrangements is (are) not known. A number of potentially powerful genetic tools designed to analyse the L. lactis genome have been constructed in recent years. These tools enable gene inactivation, gene replacement and gene recovery experiments to be readily carried out with this organism, and potentially with other lactic acid bacteria and Gram-positive bacteria. Integration vectors based on temperate phage attB sites and the random insertion of IS elements have also been developed for L. lactis and the intestinal lactobacilli. In addition, a L. lactis sex factor that mobilizes the chromosome in a manner reminiscent to that seen with Escherichia coli Hfr strains has been discovered and characterized. With the availability of this new technology, research into the genome of the lactic acid bacteria is poised to undertake a period of extremely rapid information accrual.

Bacteriophages↗
PubMed1998

Evolution of Streptococcus thermophilus bacteriophage genomes by modular exchanges followed by point mutations and small deletions and insertions.

Comparative sequence analysis of 40% of the genomes from two prototype Streptococcus thermophilus bacteriophages (lytic group I phage phi Sfi19 and the cos site containing temperate phage phi Sfi21) suggested two processes in the evolution of their genomes. In a first evolutionarily distant phase the basic genome structure was apparently constituted by modular exchanges. Over the 17-kb-long DNA segment analyzed in the present report, we observed clusters of genes with similarity to genes from Leuconostoc oenos phage L10, Lactococcus lactis phage BK5-T, and Streptococcus pneumoniae phage Dp-1. A chimeric protein was predicted for orf 1291 which showed similarity to both phage BK5-T and phage Dp-1 proteins. The very large orf 1626 gene product showed similarity to two adjacent genes from the Lactobacillus delbrueckii phage LL-H and further phage proteins (Lactococcus lactis, Bacillus subtills). The similarities were localized to distinct parts of this apparently multifunctional protein. The putative phi Sfi19 lysin showed similarity to both lysins of phages and cellular enzymes. In a second, evolutionarily more recent, phase the S, thermophilus phage genomes apparently diversified by point mutations and small deletions/insertions. Over the investigated 17-kb DNA region phi Sfi19 differed from phi Sfi21 by 10% base pair changes, the majority of which were point mutations (mainly at the third codon position), while a third of the base pair differences were contributed by small deletions/insertions. The base pair changes were unevenly distributed. Over the Leuconostoc phage-related DNA the change rate was high, while over the Lactococcus and S. pneumoniae phage-related DNA the change rate was low. We speculate that the degree of base pair change could provide relative time scales for the modular exchange reactions observed in S. thermophilus phages.

Amino Acid Sequence↗
PubMed2006

Production of a heterologous nonheme catalase by Lactobacillus casei: an efficient tool for removal of H2O2 and protection of Lactobacillus bulgaricus from oxidative stress in milk.

Lactic acid bacteria (LAB) are generally sensitive to H2O2, a compound that they can paradoxically produce themselves, as is the case for Lactobacillus bulgaricus. Lactobacillus plantarum ATCC 14431 is one of the very few LAB strains able to degrade H2O2 through the action of a nonheme, manganese-dependent catalase (hereafter called MnKat). The MnKat gene was expressed in three catalase-deficient LAB species: L. bulgaricus ATCC 11842, Lactobacillus casei BL23, and Lactococcus lactis MG1363. While the protein could be detected in all heterologous hosts, enzyme activity was observed only in L. casei. This is probably due to the differences in the Mn contents of the cells, which are reportedly similar in L. plantarum and L. casei but at least 10- and 100-fold lower in Lactococcus lactis and L. bulgaricus, respectively. The expression of the MnKat gene in L. casei conferred enhanced oxidative stress resistance, as measured by an increase in the survival rate after exposure to H2O2, and improved long-term survival in aerated cultures. In mixtures of L. casei producing MnKat and L. bulgaricus, L. casei can eliminate H2O2 from the culture medium, thereby protecting both L. casei and L. bulgaricus from its deleterious effects.

Animals↗
PubMed1999

Study of the possible mechanisms involved in the mucosal immune system activation by lactic acid bacteria.

The induction of a mucosal immune response is not easy due to the development of oral tolerance, but under some conditions, bacteria can activate this immune system. Antigens administered orally can interact with M cells of Peyer's patches or bind to the epithelial cells. We have demonstrated that certain lactic acid bacteria are able to induce specific secretory immunity, and others will enhance the gut inflammatory immune response. The aim of this work was to establish the reason for these different behaviors and to define possible mechanisms involved in the interaction of lactic acid bacteria at the intestinal level. We studied IgA+ and IgM+ B cells comparatively in bronchus and intestine and CD4+ T cells and IgA anti-lactic acid bacteria antibodies in the intestinal fluid, induced by oral administration of Lactobacillus casei, Lb. delbrueckii ssp. bulgaricus, Lb. acidophilus, Lb. plantarum, Lb. rhamnosus, Lactococcus lactis, and Streptococcus salivarius ssp. thermophilus. The increase in the IgA+ B cells in the bronchus means that these lactic acid bacteria were able to induce the IgA cycle by interaction with M cells from Peyer's patches or intestinal epithelial cells. The IgM+ cells increased when the stimulus did not induce the switch from IgM+ to IgA+. The increase in the CD4+ cells suggests interaction of Peyer's patches and enhancement of the B- and T-cell migration. The anti-lactic acid bacteria antibody is related to the processing and presentation of the microorganisms to the immune cells. We demonstrated that Lb. casei and Lb. plantarum were able to interact with Peyer's patch cells and showed an increase in IgA-, CD4+ cells, and antibodies specific for the stimulating strain. Lactobacillus acidophilus induced gut mucosal activation by interaction with the epithelial cells without increase in the immune cells associated with the bronchus. Although Lb. rhamnosus and Strep. salivarius ssp. thermophilus interact with epithelial cells, they also induced an immune response against their epitopes. Lactococcus lactis and Lb. delbrueckii ssp. bulgaricus induced an increase of IgA+ cells entering the IgA cycle but not CD4+ cells; thus, these bacteria would have been bound to epithelial cells that activated B lymphocytes without processing and presenting of their epitopes. We did not determine specific antibodies against Lc. lactis or Lb. bulgaricus.

Animals↗
PubMed1997

The lac operon of Lactobacillus casei contains lacT, a gene coding for a protein of the Bg1G family of transcriptional antiterminators.

The 5' region of the lac operon of Lactobacillus casei has been investigated. An open reading frame of 293 codons, designated lacT, was identified upstream of lacE. The gene product encoded by lacT is related to the family of transcriptional antiterminator proteins, which includes BglG from Escherichia coli, ArbG from Erwinia chrysanthemi, SacT, SacY, and LicT from Bacillus subtilis, and BglR from Lactococcus lactis. Amino acid sequence identities range from 35 to 24%, while similarities range from 56 to 47%. The transcriptional start site of the lac operon was identified upstream of lacT. The corresponding mRNA would contain in the 5' region a sequence with high similarity to the consensus RNA binding site of transcriptional antiterminators overlapping a sequence capable of folding into a structure that resembles a rho-independent terminator. LacT was shown to be active as an antiterminator in a B. subtilis test system using the sacB target sequence. lacT directly precedes lacEGF, the genes coding for enzyme IICB, phospho-beta-galactosidase, and enzyme IIA, and these genes are followed by a sequence that appears to encode a second rho-independent transcription terminator-like structure. Northern hybridizations with probes against lacT, lacE, and lacF revealed transcripts of similar sizes for the lac mRNAs of several L. casei strains. Since the length of the lac mRNA is just sufficient to contain lacTEGF, we conclude that the lac operon of L. casei does not contain the genes of the accessory tagatose-6-phosphate pathway as occurs in the lac operons of Lactococcus lactis, Streptococcus mutans, or Staphylococcus aureus.

Amino Acid Sequence↗
PubMed2000

Requirement of autolytic activity for bacteriocin-induced lysis.

The bacteriocin produced by Lactococcus lactis IFPL105 is bactericidal against several Lactococcus and Lactobacillus strains. Addition of the bacteriocin to exponential-growth-phase cells resulted in all cases in bacteriolysis. The bacteriolytic response of the strains was not related to differences in sensitivity to the bacteriocin and was strongly reduced in the presence of autolysin inhibitors (Co(2+) and sodium dodecyl sulfate). When L. lactis MG1363 and its derivative deficient in the production of the major autolysin AcmA (MG1363acmADelta1) were incubated with the bacteriocin, the latter did not lyse and no intracellular proteins were released into the medium. Incubation of cell wall fragments of L. lactis MG1363, or of L. lactis MG1363acmADelta1 to which extracellular AcmA was added, in the presence or absence of the bacteriocin had no effect on the speed of cell wall degradation. This result indicates that the bacteriocin does not degrade cell walls, nor does it directly activate the autolysin AcmA. The autolysin was also responsible for the observed lysis of L. lactis MG1363 cells during incubation with nisin or the mixture of lactococcins A, B, and M. The results presented here show that lysis of L. lactis after addition of the bacteriocins is caused by the resulting cell damage, which promotes uncontrolled degradation of the cell walls by AcmA.

Bacteriocins↗
PubMed2000

[Construction of genomic library from L. lactis AL2 and isolation of entire nisin biosynthesis gene cluster].

A total DNA library of Lactococcus lactis AL2 with high yield of nisin was successfully constructed using lambda EMBL3 as vector. 3900 plaques were obtained, which is much more than the required number of recombinants that represents an entire L. lactis genome according to Clarke and Carbon formula. Southern hybridization, PCR amplification and DNA sequencing revealed that the entire nisin biosynthesis gene cluster was isolated from the constructed library.

Base Sequence↗
PubMed1996

Genes responsible for nisin synthesis, regulation and immunity form a regulon of two operons and are induced by nisin in Lactoccocus lactis N8.

Nisin is a small post-translationally modified lanthionine-containing peptide (lantibiotic) produced by certain Lactococcus lactis strains which has a high antimicrobial activity against several pathogenic Gram-positive bacteria. Northern blots and RT/PCR analysis of the nisin-producing strain N8 revealed that the nisZBTCIPRKFEG gene cluster, responsible for nisin biosynthesis, immunity and regulation, consists of two operons, nisZBTCIPRK and nisFEG. The promoter of the nisFEB operon was mapped. The -35 to -1 region upstream of the transcription start of the nisFEG promoter showed 73% identity with the corresponding region upstream of the nisA and nisZ gene. In contrast to earlier reports, nisin was found to be secreted during the early stages of growth was well as later in the growth cycle. The secreted nisin was adsorbed on the surface of the cells and was released to the medium during mid-exponential growth, when the pH in the medium fell below 5.5. In nisZB antisense and nisT deletion mutant strains constructed in this study the transcription of the nisin operons, nisin production and immunity were lost. Provision of external nisin restored the transcription of both operons in the mutant strains, showing that the operons are coordinately regulated by mature nisin. Nisin induction of the mutant strains also resulted in an increased amount of the NisI protein and an increase in the level of immunity. Induction using higher concentrations of nisin yielded a higher level of immunity. These results showed that the nisin promoters are under positive control in an autoregulatory manner and that antimicrobial peptides can also function as signal molecules.

Base Sequence↗
PubMed2005

Parameter estimation in modulated, unbranched reaction chains within biochemical systems.

Modern biology is increasingly developing techniques for measuring time series of global gene expression and of many simultaneous proteins or metabolites. These data contain valuable information on the dynamics of cells, which has to be extracted with computational means. Given a suitable mathematical model, this extraction is in principle a straightforward regression task, but the complexity and nonlinearity of the differential equations that describe biological systems cause severe difficulties when the systems are of realistic size. We propose a method of stepwise regression that can be applied effectively to linear portions of pathways. The method may be combined with other estimation methods and either directly yields reasonable parameter estimates or at least provides appropriate start values for subsequent nonlinear search algorithms. We illustrate the method with the analysis of in vivo NMR data describing the dynamics of glycolytic metabolites in Lactococcus lactis.

Algorithms↗