Seroprevalence of Infection by Borrelia Species Responsible for Lyme Disease in the French Alps: Analysis of 27,360 Serology Tests, 2015-2020

Objectives: Lyme borreliosis incidence is increasing in several areas; moreover, it has recently gained the public's attention. Apart from erythema migrans, Lyme disease diagnosis relies (among others) on serology test; however, the prevalence of positive enzyme-linked immunosorbent assay (ELISA) and western blot (WB) assay has been poorly studied in the general population. We aimed to approach the seroprevalence of infection by Borrelia species responsible for Lyme disease in the French Isere department using city laboratories data. Patients and Methods: We retrieved all serological tests for Borrelia species responsible for Lyme disease performed in the two main networks of city laboratories between 2015 and 2020. All patients with both ELISA and WB IgG were considered seropositive. Results: We analyzed 27,360 tests (ELISA/ELISA+WB). Mean age was 50.9 ± 20.3 years (ranges: 0-101), with 57.1% females. Overall, 11.7% had IgG detected by ELISA, and 4.7% had IgG detected by both ELISA and WB assay. Seropositive status was more frequent in males (7.0% vs. 2.9%, p < 0.001). Seropositivity rate increased with age after a first peak in childhood; men aged 61-70 years had the highest seropositivity rate (10.3%). In addition, seropositivity rate was higher in persons from a rural area. In multivariate analysis, older age, male gender and living in a rural area were independently associated with seropositivity. Seropositivity rate was stable on the 2017-2020 period. Conclusion: The seroprevalence of infection by Borrelia species responsible for Lyme disease is high in Isere; this probably reduces the predictive positive value for Lyme disease of ELISA and WB IgG, suggesting that this serological test should not be performed for nonspecific symptoms.

Prevalence of SARS-CoV-2 antibodies in France: results from nationwide serological surveillance

Assessment of the cumulative incidence of SARS-CoV-2 infections is critical for monitoring the course and extent of the COVID-19 epidemic. Here, we report estimated seroprevalence in the French population and the proportion of infected individuals who developed neutralising antibodies at three points throughout the first epidemic wave. Testing 11,000 residual specimens for anti-SARS-CoV-2 IgG and neutralising antibodies, we find nationwide seroprevalence of 0.41% (95% CI: 0.05-0.88) mid-March, 4.14% (95% CI: 3.31-4.99) mid-April and 4.93% (95% CI: 4.02-5.89) mid-May 2020. Approximately 70% of seropositive individuals have detectable neutralising antibodies. Infection fatality rate is 0.84% (95% CI: 0.70-1.03) and increases exponentially with age. These results confirm that the nationwide lockdown substantially curbed transmission and that the vast majority of the French population remained susceptible to SARS-CoV-2 in May 2020. Our study shows the progression of the first epidemic wave and provides a framework to inform the ongoing public health response as viral transmission continues globally.

Prevalence of SARS-CoV-2 antibodies in France: results from nationwide serological surveillance

Assessment of the cumulative incidence of SARS-CoV-2 infections is critical for monitoring the course and extent of the COVID-19 epidemic. Here, we report estimated seroprevalence in the French population and the proportion of infected individuals who developed neutralising antibodies at three points throughout the first epidemic wave. Testing 11,000 residual specimens for anti-SARS-CoV-2 IgG and neutralising antibodies, we find nationwide seroprevalence of 0.41% (95% CI: 0.05-0.88) mid-March, 4.14% (95% CI: 3.31-4.99) mid-April and 4.93% (95% CI: 4.02-5.89) mid-May 2020. Approximately 70% of seropositive individuals have detectable neutralising antibodies. Infection fatality rate is 0.84% (95% CI: 0.70-1.03) and increases exponentially with age. These results confirm that the nationwide lockdown substantially curbed transmission and that the vast majority of the French population remained susceptible to SARS-CoV-2 in May 2020. Our study shows the progression of the first epidemic wave and provides a framework to inform the ongoing public health response as viral transmission continues globally.

Quorum-sensing regulators in Gram-positive bacteria: 'cherchez le peptide'

Gram-positive bacteria can regulate gene expression at the population level via a mechanism known as quorum sensing. Oligopeptides serve as the signaling molecules; they are secreted and then are either detected at the bacterial surface by two-component systems or reinternalized via an oligopeptide transport system. In the latter case, imported peptides interact with cognate regulators (phosphatases or transcriptional regulators) that modulate the expression of target genes. These regulators help control crucial functions such as virulence, persistence, conjugation and competence and have been reported in bacilli, enterococci and streptococci. They form the rapidly growing RRNPP group. In this issue of Molecular Microbiology, Hoover et al. (2015) highlight the group's importance: they have identified a new family of regulators, Tprs (Transcription factor regulated by a Phr peptide), which work with internalized Phr-like peptides. The mechanisms underlying the expression of the genes that encode these internalized peptides are poorly documented. However, Hoover et al. (2015) have provided a new insight: an environmental molecule, glucose, can inhibit expression of the Phr-like peptide gene via catabolic repression. This previously undescribed regulatory pathway, controlling the production of a bacteriocin, might influence Streptococcus pneumonia's fitness in the nasopharynx, where galactose is present.

Response of S. thermophilus LMD-9 to bacitracin: involvement of a BceRS/AB-like module and of the rhamnose-glucose polysaccharide synthesis pathway

Streptococcus thermophilus is a lactic acid bacterium of major importance to the dairy industry as it is found in numerous cheeses and is one of the two bacterial species involved in the fermentation of yogurt. Bacterial two-component signal transduction systems (TCSs) play important roles in the process of bacterial environmental adaptation. S. thermophilus LMD-9 possesses eight such TCS systems; however, their functions have thus far been only poorly investigated. Here, we focused on two of the TCSs in LMD-9, TCS06 and TCS07, whose encoding genes are located close to each other on the chromosome, and are associated with those of ABC transporters. TCS06 homologs are frequently found in Lactobacillales, but their function has not yet been determined, while TCS07 and its upstream potential ABC transporter are homologous to the BceRS/AB system, which is involved in bacitracin resistance in Bacillus and Streptococcus species. To investigate the function(s) of TCS06 and TCS07, we constructed and characterized deletion mutants and performed transcriptional analysis in the presence and absence of bacitracin. We show here that both TCS06 and TCS07 regulate the genes in their close vicinity, in particular those encoding ABC transporters. We propose that the response of S. thermophilus to bacitracin includes i) a bacitracin export system, regulated by TCS07 and constituting a BceRS/AB-like detoxification module, and ii) the modification of cell-envelope properties via modulation of rhamnose-glucose polysaccharide synthesis, at least partially regulated by TCS06.

Rgg proteins associated with internalized small hydrophobic peptides: a new quorum-sensing mechanism in streptococci

We identified a genetic context encoding a transcriptional regulator of the Rgg family and a small hydrophobic peptide (SHP) in nearly all streptococci and suggested that it may be involved in a new quorum-sensing mechanism, with SHP playing the role of a pheromone. Here, we provide further support for this hypothesis by constructing a phylogenetic tree of the Rgg and Rgg-like proteins from Gram-positive bacteria and by studying the shp/rgg1358 locus of Streptococcus thermophilus LMD-9. We identified the shp1358 gene as a target of Rgg1358, and used it to confirm the existence of the steps of a quorum-sensing mechanism including secretion, maturation and reimportation of the pheromone into the cell. We used surface plasmon resonance to demonstrate interaction between the pheromone and the regulatory protein and performed electrophoretic mobility shift assays to assess binding of the transcriptional regulator to the promoter regions of its target genes. The active form of the pheromone was identified by mass spectrometry. Our findings demonstrate that the shp/rgg1358 locus encodes two components of a novel quorum-sensing mechanism involving a transcriptional regulator of the Rgg family and a SHP pheromone that is detected and reimported into the cell by the Ami oligopeptide transporter.

Inhibitory effect of αS1- and αS2-casein hydrolysates on angiotensin I-converting enzyme in human endothelial cells in vitro, rat aortic tissue ex vivo, and renovascular hypertensive rats in vivo

A great number of milk-derived peptides have been shown to exhibit angiotensin converting enzyme (ACE) inhibitory properties and thus potential utility in the regulation of blood pressure. The present work aimed to investigate the effects of 2 milk trypsin hydrolysates from alpha(S1)- and alpha(S2)-casein (CH1 and CH2, respectively) on ACE activity evaluated in human umbilical vein endothelial cells (HUVEC) in vitro, rat aortic tissues ex vivo, and renovascular hypertensive rat in vivo. Incubation of HUVEC and rat aortic tissues with CH1 or CH2 induced a concentration-dependent inhibition of hydrolysis of the ACE substrate hippuryl-histidyl-leucine (HHL), the hydrolysates being much less potent than perindopril (an ACE inhibitor). However, in contrast to perindopril, CH1 and CH2 failed to modify angiotensin I-induced aortic ring vasoconstriction. The HPLC profiles of rat plasma after intragastric administration were variable among individuals but none of the observed peaks corresponded to peptides comprising CH1 or CH2 or to fragments of these peptides. During 4 wk of cardiovascular monitoring, in hydrolysate-fed renovascular hypertensive rats, systolic blood pressure weakly decreased compared with the control group. However, the CH1-fed hypertensive rats exhibited a decrease of heart rate during the nocturnal period of activity. To conclude, our results show that CH1 and CH2 inhibited ACE activity in HUVEC and rat aortic tissue but failed to antagonize the aortic-constricting effects of the natural agonist angiotensin I. Moreover, we demonstrated that CH1, to a greater extent than CH2, can slightly affect cardiovascular parameters although the ingested bioactive peptides could not be detected in the blood.

Bacterial oligopeptide-binding proteins

This review focuses on bacterial oligopeptide-binding proteins, which form part of the oligopeptide transport system belonging to the ATP-binding cassette family of transporters. Depending on the bacterial species, these binding proteins (OppA) capture peptides ranging in size from 2 to 18 amino acids from the environment and pass them on to the other components of the oligopeptide transport system for internalisation. Bacteria have developed several strategies to produce these binding proteins, which are periplasmic in Gram- bacteria and membrane-anchored in Gram+, with a higher stoichiometry (probably necessary for efficient transport) than the other components in the transport system. The expression of OppA-encoding genes is clearly modulated by external factors, especially nitrogen compounds, but the mechanisms of regulation are not always clear. The best-understood roles played by OppAs are internalisation of peptides for nutrition and recycling of muropeptides. It has, however, recently become clear that OppAs are also involved in sensing the external medium via specific or non-specific peptides.

Angiotensin I-converting-enzyme-inhibitory and antibacterial peptides from Lactobacillus helveticus PR4 proteinase-hydrolyzed caseins of milk from six species

Sodium caseinates prepared from bovine, sheep, goat, pig, buffalo or human milk were hydrolyzed by a partially purified proteinase of Lactobacillus helveticus PR4. Peptides in each hydrolysate were fractionated by reversed-phase fast-protein liquid chromatography. The fractions which showed the highest angiotensin I-converting-enzyme (ACE)-inhibitory or antibacterial activity were sequenced by mass spectrum and Edman degradation analyses. Various ACE-inhibitory peptides were found in the hydrolysates: the bovine alpha(S1)-casein (alpha(S1)-CN) 24-47 fragment (f24-47), f169-193, and beta-CN f58-76; ovine alpha(S1)-CN f1-6 and alpha(S2)-CN f182-185 and f186-188; caprine beta-CN f58-65 and alpha(S2)-CN f182-187; buffalo beta-CN f58-66; and a mixture of three tripeptides originating from human beta-CN. A mixture of peptides with a C-terminal sequence, Pro-Gly-Pro, was found in the most active fraction of the pig sodium caseinate hydrolysate. The highest ACE-inhibitory activity of some peptides corresponded to the concentration of the ACE inhibitor (S)-N-(1-[ethoxycarbonyl]-3-phenylpropyl)-ala-pro maleate (enalapril) of 49.253 micro g/ml (100 micro mol/liter). Several of the above sequences had features in common with other ACE-inhibitory peptides reported in the literature. The 50% inhibitory concentration (IC(50)) of some of the crude peptide fractions was very low (16 to 100 micro g/ml). Some identified peptides were chemically synthesized, and the ACE-inhibitory activity and IC(50)s were confirmed. An antibacterial peptide corresponding to beta-CN f184-210 was identified in human sodium caseinate hydrolysate. It showed a very large spectrum of inhibition against gram-positive and -negative bacteria, including species of potential clinical interest, such as Enterococcus faecium, Bacillus megaterium, Escherichia coli, Listeria innocua, Salmonella spp., Yersinia enterocolitica, and Staphylococcus aureus. The MIC for E. coli F19 was ca. 50 micro g/ml. Once generated, the bioactive peptides were resistant to further degradation by proteinase of L. helveticus PR4 or by trypsin and chymotrypsin.

Regulation of branched-chain amino acid biosynthesis by alpha-acetolactate decarboxylase in Streptococcus thermophilus

AIMS

To demonstrate the presence of an active alpha-acetolactate decarboxylase in Streptococcus thermophilus and to investigate its physiological function.

METHODS AND RESULTS

Streptococcus thermophilus CNRZ385 contains a gene encoding an alpha-acetolactate decarboxylase. Comparison of the production of alpha-acetolactate and its decarboxylation products, by the parent strain and an alpha-acetolactate decarboxylase-deficient mutant, demonstrated the presence of a control of the pool of alpha-acetolactate by valine, leucine and isoleucine. This control occurs via an allosteric activation of the alpha-acetolactate decarboxylase. Cell-free extracts of S. thermophilus were not able to decarboxylate the isoleucine precursor alpha-acetohydroxybutyrate.

CONCLUSIONS

These results strongly suggest that one of the physiological functions of the alpha-acetolactate decarboxylase in S. thermophilus is to regulate leucine and valine biosynthesis by diverting the flux of alpha-acetolactate towards acetoin when the branched-chain amino acids are present at a high concentration.

SIGNIFICANCE AND IMPACT OF THE STUDY

Regulation of branched-chain amino acid biosynthesis by alpha-acetolactate decarboxylase may occur in several other micro-organisms and explain some of their growth properties.

The EstA esterase is responsible for the main capacity of Lactococcus lactis to synthesize short chain fatty acid esters in vitro

AIMS

Esters of short-chain fatty acids and alcohols participate significantly in the overall flavour of foods. The capacity of the lactic acid bacterium Lactococcus lactis to synthesize such esters is known even though the enzymes involved in the process are not well identified. The objective of our work is to determine whether the esterase is responsible for the whole capacity of L. lactis to synthesize esters in vitro.

METHODS AND RESULTS

A negative mutant for the esterase was constructed and its capacity to synthesize short chain fatty acid esters from different substrate couples was compared to that of the wild type. We observed that the esterase is responsible for the main ester synthesis activity of L. lactis in vitro. However, in the presence of some substrates, the esterase negative mutant still synthesizes low amounts of esters.

CONCLUSIONS

In favourable environmental conditions, the L. lactis esterase is responsible for the main ester synthesizing activity, even though another pathway for ester synthesis probably exists.

SIGNIFICANCE AND IMPACT OF THE STUDY

Since esters are potent aroma compounds, esterase is probably a key enzyme in the development of food flavour.

Cell-wall proteinases PrtS and PrtB have a different role in Streptococcus thermophilus/Lactobacillus bulgaricus mixed cultures in milk

The manufacture of yoghurt relies on the simultaneous utilization of two starters: Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus). A protocooperation usually takes place between the two species, which often results in enhanced milk acidification and aroma formation compared to pure cultures. Cell-wall proteinases of Lactococcus lactis and lactobacilli have been shown to be essential to growth in milk in pure cultures. In this study, the role of proteinases PrtS from S. thermophilus and PrtB from Lb. bulgaricus in bacterial growth in milk was evaluated; a negative mutant for the prtS gene of S. thermophilus CNRZ 385 was constructed for this purpose. Pure cultures of S. thermophilus CNRZ 385 and its PrtS-negative mutant were made in milk as well as mixed cultures of S. thermophilus and Lb. bulgaricus: S. thermophilus CNRZ 385 or its PrtS-negative mutant was associated with several strains of Lb. bulgaricus, including a PrtB-negative strain. The pH and growth of bacterial populations of the resulting mixed cultures were followed, and the Lactobacillus strain was found to influence both the extent of the benefit of Lb. bulgaricus/S. thermophilus association on milk acidification and the magnitude of S. thermophilus population dominance at the end of fermentation. In all mixed cultures, the sequential growth of S. thermophilus then of Lb. bulgarius and finally of both bacteria was observed. Although proteinase PrtS was essential to S. thermophilus growth in milk in pure culture, it had no effect on bacterial growth and thus on the final pH of mixed cultures in the presence of PrtB. In contrast, proteinase PrtB was necessary for the growth of S. thermophilus, and its absence resulted in a higher final pH. From these results, a model of growth of both bacteria in mixed cultures in milk is proposed.

Branched-chain amino acid biosynthesis is essential for optimal growth of Streptococcus thermophilus in milk

Lactic acid bacteria are nutritionally demanding bacteria which need, among other things, amino acids for optimal growth. We identified the branched-chain amino acid (BCAA) biosynthesis pathway as an essential pathway for optimal growth of Streptococcus thermophilus in milk. Through random insertional mutagenesis, we isolated and characterized two mutants for which growth in milk is affected as a consequence of ilvB and ilvC gene interruptions. This situation demonstrates that the BCAA biosynthesis pathway is active in S. thermophilus. BCAA biosynthesis is necessary but not sufficient for optimal growth of S. thermophilus and is subject to retro-inhibition processes. The specificity of the BCAA biosynthesis pathway in S. thermophilus lies in the independent transcription of the ilvC gene encoding a keto acid reductoisomerase acting on acetolactate at the junction of the BCAA and acetoin biosynthesis pathways. The possible advantages for S. thermophilus of keeping this biosynthesis pathway active could be linked either to adaptation of the organism to milk, which is different than that of other dairy bacteria, or to the role of the pathway in maintaining the internal pH.

Streptococcus thermophilus cell wall-anchored proteinase: release, purification, and biochemical and genetic characterization

Streptococcus thermophilus CNRZ 385 expresses a cell envelope proteinase (PrtS), which is characterized in the present work, both at the biochemical and genetic levels. Since PrtS is resistant to most classical methods of extraction from the cell envelopes, we developed a three-step process based on loosening of the cell wall by cultivation of the cells in the presence of glycine (20 mM), mechanical disruption (with alumina powder), and enzymatic treatment (lysozyme). The pure enzyme is a serine proteinase highly activated by Ca(2+) ions. Its activity was optimal at 37 degrees C and pH 7.5 with acetyl-Ala-Ala-Pro-Phe-paranitroanilide as substrate. The study of the hydrolysis of the chromogenic and casein substrates indicated that PrtS presented an intermediate specificity between the most divergent types of cell envelope proteinases from lactococci, known as the PI and PIII types. This result was confirmed by the sequence determination of the regions involved in substrate specificity, which were a mix between those of PI and PIII types, and also had unique residues. Sequence analysis of the PrtS encoding gene revealed that PrtS is a member of the subtilase family. It is a multidomain protein which is maturated and tightly anchored to the cell wall via a mechanism involving an LPXTG motif. PrtS bears similarities to cell envelope proteinases from pyogenic streptococci (C5a peptidase and cell surface proteinase) and lactic acid bacteria (PrtP, PrtH, and PrtB). The highest homologies were found with streptococcal proteinases which lack, as PrtS, one domain (the B domain) present in cell envelope proteinases from all other lactic acid bacteria.

Genetic characterization of pepP, which encodes an aminopeptidase P whose deficiency does not affect Lactococcus lactis growth in milk, unlike deficiency of the X-prolyl dipeptidyl aminopeptidase

We sequenced the pepP gene of Lactococcus lactis, which encodes an aminopeptidase P (PepP), and demonstrated that the X-prolyl dipeptidyl aminopeptidase PepX plays a more important role than PepP in nitrogen nutrition. PepP shares homology with methionine aminopeptidases and could play a role in the maturation of nascent proteins.

Duplication of the pepF gene and shuffling of DNA fragments on the lactose plasmid of Lactococcus lactis

The gene corresponding to the lactococcal oligopeptidase PepF1 (formerly PepF [V. Monnet, M. Nardi, A. Chopin, M.-C. Chopin, and J.-C. Gripon, J. Biol. Chem. 269:32070-32076, 1994]) is located on the lactose-proteinase plasmid of Lactococcus lactis subsp. cremoris NCDO763. Use of the pepF1 gene as a probe with different strains showed that pepF1 is present on the chromosome of Lactococcus lactis subsp. lactis IL1403, whereas there is a second, homologous gene, pepF2, on the chromosome of strain NCDO763. From hybridization, PCR amplification, and sequencing experiments, we deduced that (i) pepF1 and pepF2 exhibit 80% identity and encode two proteins which are 84% identical and (ii) pepF2 is included in an operon composed of three open reading frames and is transcribed from two promoters. The protein, encoded by the gene located downstream of pepF2, shows significant homology with methyltransferases. Analysis of the sequences flanking pepF1 and pepF2 indicates that only a part of the pepF2 operon is present on the plasmid of strain NCDO763, while the operon is intact on the chromosome of strain IL1403. Traces of several recombination events are visible on the lactose-proteinase plasmid. This suggests that the duplication of pepF occurred by recombination from the chromosome of an L. lactis subsp. lactis strain followed by gene transfer. We discuss the possible functions of PepF and the role of its amplification.

Presence of additional peptidases in Streptococcus thermophilus CNRZ 302 compared to Lactococcus lactis

Streptococcus thermophilus is widely used in the dairy industry but little is known about its peptidase system. The aim of this study was to determine the biochemical and genetic characteristics of this system, and to compare it to the well known system of Lactococcus lactis. We separated the intracellular proteins of Strep. thermophilus CNRZ 302 and L. lactis NCDO 763 by ion-exchange chromatography and we detected the activity of the different types of peptidases. In both L. lactis and Strep. thermophilus strains, we showed 13 different peptidase activities with biochemical homologies between both species. Streptococcus thermophilus also possessed two peptidases which we did not find in L. lactis: an aminopeptidase and an oligopeptidase. We performed Southern blot experiments and among the eight peptidase genes tested, only the genes encoding the general aminopeptidases, pepC and pepN, were homologous between the L. lactis and Strep. thermophilus strains. Besides biochemical and genetic similarities, the peptidase systems of Strep. thermophilus and L. lactis thus differed by the presence of additional peptidases in Strep. thermophilus.

An aminopeptidase P from Lactococcus lactis with original specificity

An aminopeptidase P (E.C. 3.4.11.9) that cleaves the Arg-1-Pro-2 bond of bradykinin has been isolated for the first time from Lactococcus lactis. The peptidase was purified to homogeneity in a 3-step procedure and characterized. It is a monomeric metalloenzyme with a 43 kDa molecular mass, activated by Mn2+ and inhibited by DTT. It differs from the majority of aminopeptidases P already described by displaying a specificity for X-Pro-Pro N-terminal and probably an extended binding site that could accommodate amino acid residues beyond the P'2 position of the substrate.

Biochemical and genetic characterization of PepF, an oligopeptidase from Lactococcus lactis

Lactococcus lactis possesses a complex proteolytic system which is essential for its growth in milk. We characterized one of the peptidases of this system, oligopeptidase PepF, together with its structural gene. PepF hydrolyzed peptides containing between 7 and 17 amino acids with a rather wide specificity. It was purified to homogeneity. The N-terminal sequences of PepF and of peptides resulting from tryptic digestion of PepF were determined and used to design degenerate oligonucleotides which served to amplify a DNA fragment internal to pepF. This fragment was used as a probe to screen a lactococcal genomic library in Escherichia coli and to clone the entire gene pepF. The gene coded for a 70 kDa protein and was located on a 55-kilobase lactose-protease plasmid. A motif His-Glu-X-X-His, characteristic of metallopeptidases was evidenced. Two regions of PepF were found similar, first to a stretch of 43 amino acids around the zinc-binding site of several other peptidases, second to a stretch of 33 amino acids well conserved among creatine and arginine kinases. Preliminary results suggest the presence of a second copy of pepF.

Purification and characterization of a general aminopeptidase (St-PepN) from Streptococcus salivarius ssp. thermophilus CNRZ 302

A general aminopeptidase (St-PepN) was purified from an intracellular extract of Streptococcus salivarius ssp. thermophilus CNRZ 302 by ion-exchange chromatography and hydrophobic interaction chromatography. Gel electrophoresis of the purified enzyme in denaturing or nondenaturating conditions showed a single protein band. The enzyme is a monomer with a molecular mass of 97 kDa. Its activity is maximal at pH 7 and 36 degrees C and is completely abolished by CuCl2 and ZnCl2. The enzyme is strongly inhibited by metal-chelating reagents, such as EDTA and o-phenanthroline, which suggests that St-PepN is a metalloenzyme. The enzyme showed activity toward p-nitroanilide derivatives or dipeptides and tripeptides and showed a preference for hydrophobic or basic amino acids at the N-terminal position. Longer peptide chains, such as the B-chain of insulin, glucagon, or peptides generated by the hydrolysis of caseins, were degraded, too. The sequence of the first 21 residues of the mature enzyme was determined and showed high homology with that of the aminopeptidase PepN isolated from Lactococcus lactis ssp. cremoris Wg2. The properties of the enzyme are compared with those of corresponding enzymes of other species of lactic acid bacteria.

Substrate specificity of the cell envelope-located proteinase of Lactococcus lactis subsp. lactis NCDO 763

1. The specificity of the cell envelope-located proteinase of Lactococcus lactis subsp. lactis NCDO 763 towards caseins has been submitted to a statistical study. Positive and negative relations have been evidenced between several amino acids and positions P6 to P'2 of the cleaved bonds. 2. Fragment 1-23 of alpha s1 and oxidized B chain of insulin are well cleaved by the proteinase while CMP (fragment 106-169 of kappa-casein) is a poor substrate. 3. Comparison with other cell envelope-located proteinase has been done. The enzyme of the strain 763 hydrolyses alpha s1-casein and fragment 1-23 of alpha s1-casein as the enzyme of the strain Sk11 and beta-casein as the enzyme of the strain Wg2. 4. The specificity of these proteinases and the comparison of their amino acid sequences let us postulate a more complex substrate binding area for these lactococcal proteinases than for the subtilisin.

[Function of polynuclear neutrophils in patients with juvenile periodontitis and rapidly progressing periodontitis]

It is generally assumed that early onset forms of periodontal disease (including Juvenile and Rapidly Progressive Periodontitis) are associated with a defect in neutrophil behaviour. We have investigated neutrophil functions in patients with Juvenile (J.P.) and Rapidly Progressive Periodontitis (R.P.P.). In the group of J.P. patients the directed mobility (FMLP and zymosan activated plasma) is significantly decreased. The superoxide generation in response to FMLP decreases while the PMA response is normal. In the group of R.P.P. patients no significant abnormality has been reported.

Purification and Characterization of an Aminopeptidase from Lactococcus lactis subsp. cremoris AM2

An aminopeptidase was purified from cell extracts of Lactococcus lactis subsp. cremoris AM2 by ion-exchange chromatography. After electrophoresis of the purified enzyme in the presence or absence of sodium dodecyl sulfate, one protein band was detected. The enzyme was a 300-kilodalton hexamer composed of identical subunits not linked by disulfide bridges. Activity was optimal at 40°C and pH 7 and was inhibited by classical thiol group inhibitors. The aminopeptidase hydrolyzed naphthylamide-substituted amino acids, as well as dipeptides and tripeptides. Longer protein chains such as the B chain of insulin were hydrolyzed, but at a much slower rate. The Michaelis constant ( K m ) and the maximal rate of hydrolysis ( V max ) were, respectively, 4.5 mM and 3,600 pkat/mg for the substrate l -histidyl-β-naphthylamide. Amino acid analysis showed that the enzyme contained low levels of hydrophobic residues. The partial N-terminal sequence of the first 19 residues of the mature enzyme was determined. Polyclonal antibodies were obtained from the purified enzyme, and after immunoblotting, there was no cross-reaction between these antibodies and other proteins in the crude extract.

Purification and characterization of a cell wall proteinase from Streptococcus lactis NCDO 763

A proteinase was purified from a cell wall extract of a culture of Streptococcus lactis NCDO 763 grown in skim milk. Being active at a low pH (at pH 4.8 on haemoglobin and pH 6.0-6.5 on casein) and completely inhibited by diisopropylfluorophosphate, it was considered to be a serine proteinase partly inhibited by EDTA; the mol. wt was approximately 80,000.