In vitro colonisation of the distal colon by Akkermansia muciniphila is largely mucin and pH dependent

Host mucin is the main constituent of the mucus layer that covers the gut epithelium of the host, and an important source of glycans for the bacteria colonising the intestine. Akkermansia muciniphila is a mucin-degrading bacterium, abundant in the human gut, that is able to produce acetate and propionate during this degradation process. A. muciniphila has been correlated with human health in previous studies, but a mechanistic explanation is lacking. In this study, the main site of colonisation was characterised alongside additional conditions, such as differences in colon pH, prebiotic supplementation and variable mucin supply. To overcome the limitations of in vivo studies concerning variations in mucin availability and difficult access to proximal regions of the colon, a dynamic in vitro gut model (SHIME) was used. In this model, A. muciniphila was found to colonise the distal colon compartment more abundantly than the proximal colon ((±8 log copies/ml compared to ±4 log copies/ml) and the preference for the distal compartment was found to be pH-dependent. The addition of mucin caused a specific increase of A. muciniphila (±4.5 log increase over two days), far exceeding the response of other bacteria present, together with an increase in propionate. These findings suggest that colonisation and mucin degradation by A. muciniphila is dependent on pH and the concentration of mucin. Our results revealed the preference of A. muciniphila for the distal colon environment due to its higher pH and uncovered the quick and stable response of A. muciniphila to mucin supplementation.

Interaction of mouse splenocytes and macrophages with bacterial strains in vitro: the effect of age in the immune response

Probiotics influence the immune system, both at the local and systemic level. Recent findings suggest the relation between microbiota and the immune system alters with age. Our objective was to address direct effects of six bacterial strains on immune cells from young and aged mice: Lactobacillus plantarum WCFS1, Lactobacillus casei BL23, Lactococcus lactis MG1363, Bifidobacterium breve ATCC15700, Bifidobacterium infantis ATCC15697, and Akkermansia muciniphila ATCC BAA-835. We used splenocytes and naïve or interferon-γ-stimulated bone marrow-derived macrophages (BMDM) as responder populations. All tested bacterial strains induced phenotypic and cytokine responses in splenocytes and BMDM. Based on magnitude of the cellular inflammatory response and cytokine profiles, two subgroups of bacteria were identified, i.e. L. plantarum and L. casei versus B. breve, B. infantis, and A. muciniphila. The latter group of bacteria induced high levels of cytokines produced under inflammatory conditions, including tumour necrosis factor (TNF), interleukin (IL)-6 and IL-10. Responses to L. lactis showed features of both subgroups. In addition, we compared responses by splenocytes and BMDM derived from young mice to those of aged mice, and found that splenocytes and BMDM derived from aged mice had an increased IL-10 production and dysregulated IL-6 and TNF production compared to young immune cells. Overall, our study shows differential inflammatory responses to distinct bacterial strains, and profound age-dependent effects. These findings, moreover, support the view that immune environment importantly influences bacterial immune effects.

Stimulation of colonic motility by oral PEG electrolyte bowel preparation assessed by MRI: comparison of split vs single dose

BACKGROUND

Most methods of assessing colonic motility are poorly acceptable to patients. Magnetic resonance imaging (MRI) can monitor gastrointestinal motility and fluid distributions. We predicted that a dose of oral polyethylene glycol (PEG) and electrolyte solution would increase ileo-colonic inflow and stimulate colonic motility. We aimed to investigate the colonic response to distension by oral PEG electrolyte in healthy volunteers (HVs) and to evaluate the effect of single 2 L vs split (2 × 1 L) dosing.

METHODS

Twelve HVs received a split dose (1 L the evening before and 1 L on the study day) and another 12 HVs a single dose (2 L on the main study day) of PEG electrolyte. They underwent MRI scans, completed symptom questionnaires, and provided stool samples. Outcomes included small bowel water content, ascending colon motility index, and regional colonic volumes.

KEY RESULTS

Small bowel water content increased fourfold from baseline after ingesting both split (p = 0.0010) and single dose (p = 0.0005). The total colonic volume increase from baseline was smaller for the split dose at 35 ± 8% than for the single dose at 102 ± 27%, p = 0.0332. The ascending colon motility index after treatment was twofold higher for the single dose group (p = 0.0103).

CONCLUSIONS & INFERENCES

Ingestion of 1 and 2 L PEG electrolyte solution caused a rapid increase in the small bowel and colonic volumes and a robust rise in colonic motility. The increase in both volumes and motility was dose dependent. Such a challenge, being well-tolerated, could be a useful way of assessing colonic motility in future studies.

Bifidobacterium breve - HT-29 cell line interaction: modulation of TNF-α induced gene expression

To provide insight in the molecular basis for intestinal host-microbe interactions, we determined the genome-wide transcriptional response of human intestinal epithelial cells following exposure to cells of Bifidobacterium breve. To select an appropriate test system reflecting inflammatory conditions, the responsiveness to TNF-α was compared in T84, Caco-2 and HT-29 cells. The highest TNF-α response was observed in HT-29 cells and this cell line was selected for exposure to the B. breve strains M-16V, NR246 and UCC2003. After one hour of bacterial pre-incubation followed by two hours of additional TNF-α stimulation, B. breve M-16V (86%), but to a much lesser extent strains NR246 (50%) or UCC2003 (32%), showed a strain-specific reduction of the HT-29 transcriptional response to the inflammatory treatment. The most important functional groups of genes that were transcriptionally suppressed by the presence of B. breve M-16V, were found to be involved in immune regulation and apoptotic processes. About 54% of the TNF-α induced genes were solely suppressed by the presence of B. breve M-16V. These included apoptosis-related cysteine protease caspase 7 (CASP7), interferon regulatory factor 3 (IRF3), amyloid beta (A4) precursor proteinbinding family A member 1 (APBA1), NADPH oxidase (NOX5), and leukemia inhibitory factor receptor (LIFR). The extracellular IL-8 concentration was determined by an immunological assay but did not change significantly, indicating that B. breve M-16V only partially modulates the TNF-α pathway. In conclusion, this study shows that B. breve strains modulate gene expression in HT-29 cells under inflammatory conditions in a strain-specific way.

Polymerase chain reaction and denaturing gradient gel electrophoresis monitoring of fecal bifidobacterium populations in a prebiotic and probiotic feeding trial

A culture-independent approach based on genus-specific PCR and denaturing gradient gel electrophoresis (DGGE) was used to monitor qualitative changes in fecal bifidobacterial communities in a human feeding trial. DNA was extracted directly from feces and bifidobacterial 16S rDNA sequences were amplified using genus-specific PCR. The PCR fragments were subsequently separated in a sequence-specific manner by DGGE in order to obtain a profile of bifidobacterial fragments. The DGGE profiles revealed that in general, administration for two weeks of galactooligosaccharide and/or Bifidobacterium lactis Bb-12 (8 g and 3 x 10(10) cfu per day, respectively) did not affect the qualitative composition of the indigenous Bifidobacterium population, while B. lactis Bb-12 transiently colonised the gut.

Response of a soil bacterial community to grassland succession as monitored by 16S rRNA levels of the predominant ribotypes

The composition of predominant soil bacteria during grassland succession was investigated in the Dutch Drentse A area. Five meadows, taken out of agricultural production at different time points, and one currently fertilized plot represented different stages of grassland succession. Since fertilization and agricultural production were stopped, the six plots showed a constant decline in the levels of nutrients and vegetation changes. The activity of the predominant bacteria was monitored by direct ribosome isolation from soil and temperature gradient gel electrophoresis of reverse transcription (RT)-PCR products generated from bacterial 16S rRNA. The amounts of 16S rRNA of 20 predominant ribosome types per gram of soil were monitored via multiple competitive RT-PCR in six plots at different succession stages. These ribosome types mainly represented Bacillus and members of the Acidobacterium cluster and the alpha subclass of the class Proteobacteria. The 20 16S rRNA molecules monitored represented approximately half of all bacterial soil rRNA which was estimated by dot blot hybridizations of soil rRNA with the Bacteria probe EUB338. The grasslands showed highly reproducible and specific shifts of bacterial ribosome type composition. The total bacterial ribosome level increased during the first years after agricultural production and fertilization stopped. This correlated with the collapse of the dominant Lolium perenne population and an increased rate of mineralization of organic matter. The results indicate that there is a true correlation between the total activity of the bacterial community in soil and the amount of bacterial ribosomes.

Utilisation of saccharides in extruded domestic organic waste by Clostridium acetobutylicum ATCC 824 for production of acetone, butanol and ethanol

Domestic organic waste (DOW) collected in The Netherlands was analysed and used as substrate for acetone, butanol and ethanol (ABE) production. Two different samples of DOW, referred to as fresh DOW and dried DOW, were treated by extrusion in order to expand the polymer fibres present and to obtain a homogeneous mixture. The extruded material was analysed with respect to solvent and hot water extractives, uronic acids, lignin, sugars and ash. The total sugar content in the polymeric fractions of the materials varied from 27.7% to 39.3% (w/w), in which glucose represented the 18.4 and 25.1% of the materials, for fresh and dried DOW, respectively. The extruded fresh DOW was used as substrate for the ABE fermentation by the solventogenic strain Clostridium acetobutylicum ATCC 824. This strain was grown on a suspension of 10% (w/v) DOW in demineralised water without further nutrient supplement. This strain produced 4 g ABE/100 g extruded DOW. When C. acetobutylicum ATCC 824 was grown on a suspension of 10% (w/v) DOW hydrolysed by a combination of commercial cellulases and beta-glucosidases, the yield of solvents increased to 7.5 g ABE/100 g extruded DOW. The utilisation of sugar polymers in both hydrolysed and non-hydrolysed DOW was determined, showing that only a small proportion of the polymers had been consumed by the bacteria. These results indicate that growth and ABE production on DOW is mainly supported by soluble saccharides in the medium.

Deletion of various carboxy-terminal domains of Lactococcus lactis SK11 proteinase: effects on activity, specificity, and stability of the truncated enzyme

The Lactococcus lactis SK11 cell envelope proteinase is an extracellular, multidomain protein of nearly 2,000 residues consisting of an N-terminal serine protease domain, followed by various other domains of largely unknown function. Using a strategy of deletion mutagenesis, we have analyzed the function of several C-terminal domains of the SK11 proteinase which are absent in cell envelope proteinases of other lactic acid bacteria. The various deletion mutants were functionally expressed in L. lactis and analyzed for enzyme stability, activity, (auto)processing, and specificity toward several substrates. C-terminal deletions of first the cell envelope W (wall) and AN (anchor) domains and then the H (helix) domain leads to fully active, secreted proteinases of unaltered specificity. Gradually increasing the C-terminal deletion into the so-called B domain leads to increasing instability and autoproteolysis and progressively less proteolytic activity. However, the mutant with the largest deletion (838 residues) from the C terminus and lacking the entire B domain still retains proteolytic activity. All truncated enzymes show unaltered proteolytic specificity toward various substrates. This suggests that the main role played by these domains is providing stability or protection from autoproteolysis (B domain), spacing away from the cell (H domain), and anchoring to the cell envelope (W and AN domains). In addition, this study allowed us to more precisely map the main C-terminal autoprocessing site of the SK11 proteinase and the epitope for binding of group IV monoclonal antibodies.

Molecular characterization of the Lactococcus lactis ptsHI operon and analysis of the regulatory role of HPr

The Lactococcus lactis ptsH and ptsI genes, encoding the general proteins of the phosphoenolpyruvate-dependent phosphotransferase system, HPr and enzyme I, respectively, were cloned, and the regulatory role of HPr was studied by mutational analysis of its gene. A promoter sequence was identified upstream of the ptsHI operon, and the transcription start site was mapped by primer extension. The results of Northern analyses showed the presence of two glucose-inducible transcripts, one of 0.3 kb containing ptsH and a second of 2.0 kb containing both ptsH and ptsI. Disruption of the ptsH and ptsI genes in strain NZ9800 resulted in a reduced growth rate at the expense of glucose, but no growth at the expense of sucrose and fructose, confirming the dominant role of the phosphotransferase system in the uptake of these sugars in L. lactis. Complementation of the ptsH and ptsI mutants with the intact genes under the control of a regulated promoter resulted in the restoration of the wild-type phenotype. The role of HPr(Ser-P) in the recently established CcpA-mediated control of galactose metabolism as well as glycolysis was analyzed by producing an HPr mutant carrying an aspartic acid on residue 46 which mimicks a phosphorylated serine. The results of these experiments demonstrated the role of HPr(Ser-P) as corepressor in the catabolite repression of the gal operon. Furthermore, we show for the first time that HPr(Ser-P) functions as a coactivator in the CcpA-mediated catabolite activation of the pyruvate kinase and L-lactate dehydrogenase genes.

In situ detection of an uncultured predominant bacillus in Dutch grassland soils

Uncultured predominant Bacillus ribotype DA001 in Dutch Drentse A grassland soils, as revealed by its 16S rRNA sequence, was detected in soil by fluorescent whole-cell in situ hybridization. A prominent rod-shaped cell type was identified in bacterial suspensions prepared from soil by a multiple 16S rRNA probing approach.

Quantification of 16S rRNAs in complex bacterial communities by multiple competitive reverse transcription-PCR in temperature gradient gel electrophoresis fingerprints

A novel approach was developed to quantify rRNA sequences in complex bacterial communities. The main bacterial 16S rRNAs in Drentse A grassland soils (The Netherlands) were amplified by reverse transcription (RT)-PCR with bacterium-specific primers and were separated by temperature gradient gel electrophoresis (TGGE). The primer pair used (primers U968-GC and L1401) was found to amplify with the same efficiency 16S rRNAs from bacterial cultures containing different taxa and cloned 16S ribosomal DNA amplicons from uncultured soil bacteria. The sequence-specific efficiency of amplification was determined by monitoring the amplification kinetics by kinetic PCR. The primer-specific amplification efficiency was assessed by competitive PCR and RT-PCR, and identical input amounts of different 16S rRNAs resulted in identical amplicon yields. The sequence-specific detection system used for competitive amplifications was TGGE, which also has been found to be suitable for simultaneous quantification of more than one sequence. We demonstrate that this approach can be applied to TGGE fingerprints of soil bacteria to estimate the ratios of the bacterial 16S rRNAs.

Temperature gradient gel electrophoresis analysis of 16S rRNA from human fecal samples reveals stable and host-specific communities of active bacteria

The diversity of the predominant bacteria in the human gastrointestinal tract was studied by using 16S rRNA-based approaches. PCR amplicons of the V6 to V8 regions of fecal 16S rRNA and ribosomal DNA (rDNA) were analyzed by temperature gradient gel electrophoresis (TGGE). TGGE of fecal 16S rDNA amplicons from 16 individuals showed different profiles, with some bands in common. Fecal samples from two individuals were monitored over time and showed remarkably stable profiles over a period of at least 6 months. TGGE profiles derived from 16S rRNA and rDNA amplicons showed similar banding patterns. However, the intensities of bands with similar mobilities differed in some cases, indicating a different contribution to the total active fraction of the prominent fecal bacteria. Most 16S rRNA amplicons in the TGGE pattern of one subject were identified by cloning and sequence analysis. Forty-five of the 78 clones matched 15 bands, and 33 clones did not match any visible band in the TGGE pattern. Nested PCR of amplified 16S rDNA indicated preferential amplification of a sequence corresponding to 12 of the 33 nonmatching clones with similar mobilities in TGGE. The sequences matching 15 bands in the TGGE pattern showed 91.5 to 98.7% homology to sequences derived from different Clostridium clusters. Most of these were related to strains derived from the human intestine. The results indicate that the combination of cloning and TGGE analysis of 16S rDNA amplicons is a reliable approach to monitoring different microbial communities in feces.

Syntrophobacter fumaroxidans sp. nov., a syntrophic propionate-degrading sulfate-reducing bacterium

A syntrophic propionate-oxidizing bacterium, strain MPOBT, was isolated from a culture enriched from anaerobic granular sludge. It oxidized propionate syntrophically in co-culture with the hydrogen- and formate-utilizing Methanospirillum hungateii, and was able to oxidize propionate and other organic compounds in pure culture with sulfate or fumarate as the electron acceptor. Additionally, it fermented fumarate. 16S rRNA sequence analysis revealed a relationship with Syntrophobacter wolinii and Syntrophobacter pfennigii. The G + C content of its DNA was 60.6 mol%, which is in the same range as that of other Syntrophobacter species. DNA-DNA hybridization studies showed less than 26% hybridization among the different genomes of Syntrophobacter species and strain MPOBT. This justifies the assignment of strain MPOBT to the genus Syntrophobacter as a new species. The name Syntrophobacter fumaroxidans is proposed; strain MPOBT (= DSM 10017T) is the type strain.

Stabilization of Enzymes against Thermal Stress and Freeze-Drying by Mannosylglycerate

2-O-(beta)-Mannosylglycerate, a solute that accumulates in some (hyper)thermophilic organisms, was purified from Pyrococcus furiosus cells, and its effect on enzyme stabilization in vitro was assessed. Enzymes from hyperthermophilic, thermophilic, and mesophilic sources were examined. The thermostabilities of alcohol dehydrogenases from P. furiosus and Bacillus stearothermophilus and of glutamate dehydrogenases from Thermotoga maritima and Clostridium difficile were improved to a significant extent when enzyme solutions were incubated at supraoptimal temperatures in the presence of 2-O-(beta)-mannosylglycerate, but no effect on the thermostability of glutamate dehydrogenase from P. furiosus was detected. On the other hand, there was a remarkable effect on the thermal stabilities of rabbit muscle lactate dehydrogenase, baker's yeast alcohol dehydrogenase, and bovine liver glutamate dehydrogenase, which were used as model systems to evaluate stabilization of enzymes of mesophilic origin. For all of the enzymes examined and at the highest temperatures tested, 2-O-(beta)-mannosylglycerate was a better thermoprotectant than trehalose. The stabilizing effect exerted by 2-O-(beta)-mannosylglycerate on enzymes suggests a role for this compound as a protein thermostabilizer under physiological conditions. 2-O-(beta)-Mannosylglycerate was also effective in the protection of enzymes against stress imposed by freeze-drying, with its protecting effect being similar to or better than that exerted by trehalose. The data show 2-O-(beta)-mannosylglycerate to be a potential enzyme stabilizer in biotechnological applications.

Crystallization and preliminary structural studies of lactose-specific enzyme IIA from Lactococcus lactis

Lactose-specific enzyme IIA of the phosphoenol:pyruvate-dependent sugar phosphotransferase system from Lactococcus lactis has been crystallized in phosphate buffer. The crystals belong to space group P4(1)2(1)2 or its enantiomorph P4(3)2(1)2 with unit-cell axes a = b = 90.9 and c = 82.4 A. The packing parameter (Matthews parameter) V(m) of 2.48 A(3) Da(-1) is consistent with one trimer per asymmetric unit and non-crystallographic threefold symmetry has been confirmed by calculating a self-rotation function. The crystals diffract X-rays to at least 2.3 A resolution, are stable in an X-ray beam and are therefore appropriate for structure determination. Native data to 2.3 A resolution have been collected using a MAR image-plate system at a synchrotron source. One isomorphous heavy-atom derivative has been identified and the presence of an isomorphous signal in the data has been confirmed by Patterson methods.

Characterization of plasmid-encoded citrate permease (citP) genes from Leuconostoc species reveals high sequence conservation with the Lactococcus lactis citP gene

The citrate permease determinant (citP) in several Leuconostoc strains was demonstrated to be plasmid encoded by curing experiments and hybridization studies with a DNA fragment containing the citP gene from Lactococcus lactis subsp. lactis biovar diacetylactis NCDO176. Cloning and nucleotide sequence analysis of Leuconostoc lactis NZ6070 citP revealed almost complete identity to lactococcal citP.

Phylogenetic evidence for transfer of pentachlorophenol-mineralizing Rhodococcus chlorophenolicus PCP-I(T) to the genus Mycobacterium

We determined the nucleotide sequence of a 16S rRNA gene of Rhodococcus chlorophenolicus PCP-I(T) (= DSM 43826T) (T = type strain). Sequence comparisons revealed that there was a close relationship between strain PCP-I(T) and strains belonging to the genus Mycobacterium. The sequence data were used to construct a phylogenetic tree, which showed that Mycobacterium chubuense is the closest relative of strain PCP-I(T). We propose that strain PCP-I(T) should be transferred to the genus Mycobacterium and renamed Mycobacterium chlorophenolicum PCP-I(T) comb. nov.

Characterization of the nisin gene cluster nisABTCIPR of Lactococcus lactis. Requirement of expression of the nisA and nisI genes for development of immunity

The nisin gene cluster nisABTCIPR of Lactococcus lactis, located on a 10-kbp DNA fragment of the nisin-sucrose transposon Tn5276, was characterized. This fragment was previously shown to direct nisin-A biosynthesis and to contain the nisP and nisR genes, encoding a nisin leader peptidase and a positive regulator, respectively [van der Meer, J. R., Polman, J., Beerthuyzen, M. M., Siezen, R. J., Kuipers, O. P. & de Vos, W. M. (1993) J. Bacteriol. 175, 2578-2588]. Further sequence analysis revealed the presence of four open-reading frames, nisB, nisT, nisC and nisI, downstream of the structural gene nisA. The nisT, nisC and nisI genes were subcloned and expressed individually in Escherichia coli, using the T7-RNA-polymerase system. This resulted in the production of radiolabelled proteins with sizes of 45 kDa (NisC) and 32 kDa (NisI). The nisT gene product was not detected, possibly because of protein instability. The deduced amino acid sequence of NisI contained a consensus lipoprotein signal sequence, suggesting that this protein is a lipid-modified extracellular membrane-anchored protein. Expression of nisI in L. lactis provided the cells with a significant level of protection against exogenously added nisin, indicating that NisI plays a role in the immunity mechanism. In EDTA-treated E. coli cells, expression of nisI conferred up to a 170-fold increase in immunity against nisin A compared to controls. Moreover, a lactococcal strain deficient in nisin-A production, designated NZ9800, was created by gene replacement of nisA by a truncated nisA gene and was 10-fold less resistant to nisin A than the wild-type strain. A wild-type immunity level to nisin and production of nisin was obtained in strain NZ9800 harboring complementing nisA and nisZ plasmids. Transcription analyses of several L. lactis strains indicated that an expression product of the nisA gene, together with NisR, is required for the activation of nisA transcription.

Characterization of the Lactococcus lactis nisin A operon genes nisP, encoding a subtilisin-like serine protease involved in precursor processing, and nisR, encoding a regulatory protein involved in nisin biosynthesis

Biosynthesis of the lantibiotic peptide nisin by Lactococcus lactis NIZO R5 relies on the presence of the conjugative transposon Tn5276 in the chromosome. A 12-kb DNA fragment of Tn5276 including the nisA gene and about 10 kb of downstream DNA was cloned in L. lactis, resulting in the production of an extracellular nisin precursor peptide. This peptide reacted with antibodies against either nisin A or the synthetic leader peptide, suggesting that it consisted of a fully modified nisin with the nisin leader sequence still attached to it. This structure was confirmed by N-terminal sequencing and 1H-nuclear magnetic resonance analysis of the purified peptide. Deletion studies showed that the nisR gene is essential for the production of this intermediate. The deduced amino acid sequence of the nisR gene product indicated that the protein belongs to the family of two-component regulators. The deduced amino acid sequence of NisP, the putative product of the gene upstream of nisR, showed an N-terminal signal sequence, a catalytic domain with a high degree of similarity to those of subtilisin-like serine proteases, and a putative C-terminal membrane anchor. Cell extracts of Escherichia coli overexpressing nisP were able to cleave the nisin precursor peptide, producing active, mature nisin. A similar activation was obtained with whole cells but not with membrane-free extracts of L. lactis strains carrying Tn5276 in which the nisA gene had been inactivated. The results indicate that the penultimate step in nisin biosynthesis is secretion of precursor nisin without cleavage of the leader peptide, whereas the last step is the cleavage of the leader peptide sequence from the fully maturated nisin peptide.

DNA relatedness among some thermophilic members of the genus Methanobacterium: emendation of the species Methanobacterium thermoautotrophicum and rejection of Methanobacterium thermoformicicum as a synonym of Methanobacterium thermoautotrophicum

DNA reassociation was used to determine levels of relatedness among four thermophilic Methanobacterium strains that are able to use formate and between these organisms and two representative strains of Methanobacterium thermoautotrophicum, strain delta HT (= DSM 1053T = ATCC 29096T) (T = type strain) and strain Marburg (= DSM 2133). Three homology groups were delineated, and these groups coincided with the clusters identified by antigenic fingerprinting. The first group, which had levels of cross hybridization that ranged from 73 to 99%, included M. thermoautotrophicum delta HT, Methanobacterium thermoformicicum Z-245, Methanobacterium sp. strain THF, and Methanobacterium sp. strain FTF. The second and third groups were each represented by only one strain, Methanobacterium sp. strain CB-12 and M. thermoautotrophicum Marburg, respectively (cross-hybridization levels, 13 to 30 and 29 to 33%, respectively). Our results indicate that the name M. thermoformicicum should be rejected as it is a synonym of M. thermoautotrophicum. The taxonomic positions of strains Marburg and CB-12 need further investigation.

Characterization of the novel nisin-sucrose conjugative transposon Tn5276 and its insertion in Lactococcus lactis

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.

Proteinase overproduction in Lactococcus lactis strains: regulation and effect on growth and acidification in milk

Multicopy plasmids that contained the complete of 3'-deleted forms of the proteinase (prtP) gene of Lactococcus lactis subsp. cremoris SK11 under the control of different promoters were constructed and introduced into Prt- lactococcal strains. The production and location of the SK11 proteinase was determined in different hosts grown in industrial and laboratory media. In spite of the 10-fold-higher copy number of the prt genes, no overproduction of proteinase was observed in strain SK1128, a Prt- derivative of L. lactis subsp. cremoris SK112. In contrast, an approximately threefold overproduction of the cell envelope-located or fully secreted proteinase was found in strain MG1820 compared with that of its parental strain L. lactis subsp. lactis SH4109. In all strains proteinase production appeared to be regulated by the medium composition. Highest proteinase production of the SK11 derivatives was found in milk, in contrast to derivatives of SH4109 that produced most proteinase in whey permeate medium. Analysis of single strains with different levels of proteinase production or mixed cultures containing various ratios of Prt+ and Prt- cells indicated that the amount of proteinase produced per cell or culture determines the specific growth rate in milk. Overproduction of cell envelope-located or secreted proteinase in strain MG1820 resulted in a 20%-higher specific growth and acidification rate in milk compared with that in the wild-type strain SH4109. These results indicate that the growth of lactococci in milk is limited by the caseinolytic activity of the proteinase.

Structure and expression of the Lactococcus lactis gene for phospho-beta-galactosidase (lacG) in Escherichia coli and L. lactis

The Lactococcus lactis subsp. lactis 712 lacG gene encoding phospho-beta-galactosidase was isolated from the lactose mini-plasmid pMG820 and cloned and expressed in Escherichia coli and L. lactis. The low phospho-beta-galactosidase activity in L. lactis transformed with high-copy-number plasmids containing the lacG gene contrasted with the high activity found in L. lactis containing the original, low-copy-number lactose plasmid pMG820, and indicated that the original lactose promoter was absent from the cloned DNA. In E. coli the phospho-beta-galactosidase could be overproduced using the strong inducible lambda PL promoter, which allowed a rapid purification of the active enzyme. The complete nucleotide sequence of the L. lactis lacG gene and its surrounding regions was determined. The deduced amino acid sequence was confirmed by comparison with the amino acid composition of the purified phospho-beta-galactosidase and its amino-terminal sequence. This also allowed the exact positioning of the lacG gene and identification of its characteristic Gram-positive translation initiation signals. The homologous expression data and the sequence organization of the L. lactis lacG gene indicate that the gene is organized into a large lactose operon which contains an intergenic promoter located in an inverted repeat immediately preceding the lacG gene. The organization and sequence of the L. lactis lacG gene were compared with those of the highly homologous lacG gene from Staphylococcus aureus. A remarkable bias for leucine codons was observed in the lacG genes of these two species. Heterogramic homology was observed between the deduced amino acid sequence of the L. lactis phospho-beta-galactosidase, that of the functionally analogous E. coli phospho-beta-glucosidase, and that of an Agrobacterium beta-glucosidase (cellobiase).

Plasmid transformation by electroporation of Leuconostoc paramesenteroides and its use in molecular cloning

In this report, we demonstrate the utility of electroporation as an efficient method for genetic transformation of Leuconostoc paramesenteroides. We optimized several factors which determine the transformation frequency, resulting in transformation efficiencies of up to 4 x 10(3) transformants per micrograms of pNZ12 DNA, which contains the promiscuous Lactococcus lactis pSH71 replicon. Slightly lower efficiencies were obtained with a deletion derivative of the broad-host-range plasmid pAM beta 1. These plasmids could be stably maintained in L. paramesenteroides NZ6009 for more than 100 generations, even in the absence of selective pressure. In order to show the use of the developed host-vector system, we cloned the Lactococcus lactis gene encoding phospho-beta-galactosidase in L. paramesenteroides. Expression of this heterologous gene in L. paramesenteroides under control of Lactococcus lactis expression signals was evident from the presence, in transformants, of phospho-beta-galactosidase activity and a specific phospho-beta-galactosidase protein band on Western blots (immunoblots). In addition, we transformed a lactose-deficient derivative of L. paramesenteroides with a plasmid carrying a Lactococcus lactis-Escherichia coli lacZ gene fusion. The resulting transformants synthesized high levels of beta-galactosidase, indicating the efficiency of heterologous gene expression signals in L. paramesenteroides.

Molecular cloning of lactose genes in dairy lactic streptococci: the phospho-beta-galactosidase and beta-galactosidase genes and their expression products

The mesophilic (S. lactis and S. cremoris) and thermophilic (S. thermophilus) dairy lactic streptococci, which are used in industrial dairy fermentations, contain two different lactose hydrolysing enzymes, a phospho-beta-galactosidase and a beta-galactosidase. The central role of these enzymes in the pathways used for lactose transport and degradation is discussed along with their properties and distributions in lactic streptococci. In addition, recent results on the cloning, expression and sequence organization of the genes for the mesophilic phospho-beta-galactosidase and thermophilic beta-galactosidase are reviewed. Original data are presented concerning heterologous gene expression in the study of lactose hydrolysis in lactic streptococci. These include 1) the purification of the S. lactis phospho-beta-galactosidase from an overproducing Escherichia coli, and 2) the expression of the E. coli beta-galactosidase (lacZ) gene in S. lactis employing a lactic streptococcal expression vector.