HtrA is the unique surface housekeeping protease in Lactococcus lactis and is required for natural protein processing

Cell wall structure and function in lactic acid bacteria

The cell wall of Gram-positive bacteria is a complex assemblage of glycopolymers and proteins. It consists of a thick peptidoglycan sacculus that surrounds the cytoplasmic membrane and that is decorated with teichoic acids, polysaccharides, and proteins. It plays a major role in bacterial physiology since it maintains cell shape and integrity during growth and division; in addition, it acts as the interface between the bacterium and its environment. Lactic acid bacteria (LAB) are traditionally and widely used to ferment food, and they are also the subject of more and more research because of their potential health-related benefits. It is now recognized that understanding the composition, structure, and properties of LAB cell walls is a crucial part of developing technological and health applications using these bacteria. In this review, we examine the different components of the Gram-positive cell wall: peptidoglycan, teichoic acids, polysaccharides, and proteins. We present recent findings regarding the structure and function of these complex compounds, results that have emerged thanks to the tandem development of structural analysis and whole genome sequencing. Although general structures and biosynthesis pathways are conserved among Gram-positive bacteria, studies have revealed that LAB cell walls demonstrate unique properties; these studies have yielded some notable, fundamental, and novel findings. Given the potential of this research to contribute to future applied strategies, in our discussion of the role played by cell wall components in LAB physiology, we pay special attention to the mechanisms controlling bacterial autolysis, bacterial sensitivity to bacteriophages and the mechanisms underlying interactions between probiotic bacteria and their hosts.

Exploiting the peptidoglycan-binding motif, LysM, for medical and industrial applications

The lysin motif (LysM) was first identified by Garvey et al. in 1986 and, in subsequent studies, has been shown to bind noncovalently to peptidoglycan and chitin by interacting with N-acetylglucosamine moieties. The LysM sequence is present singly or repeatedly in a large number of proteins of prokaryotes and eukaryotes. Since the mid-1990s, domains containing one or more of these LysM sequences originating from different LysM-containing proteins have been examined for purely scientific reasons as well as for their possible use in various medical and industrial applications. These studies range from detecting localized binding of LysM-containing proteins onto bacteria to actual bacterial cell surface analysis. On a more applied level, the possibilities of employing the LysM domains for cell immobilization, for the display of peptides, proteins, or enzymes on (bacterial) surfaces as well as their utility in the development of novel vaccines have been scrutinized. To serve these purposes, the chimeric proteins containing one or more of the LysM sequences have been produced and isolated from various prokaryotic and eukaryotic expression hosts. This review gives a succinct overview of the characteristics of the LysM domain and of current developments in its application potential.

Utilization of (15)N-labelled yeast hydrolysate in Lactococcus lactis IL1403 culture indicates co-consumption of peptide-bound and free amino acids with simultaneous efflux of free amino acids

Lactococcus lactis subsp. lactis IL1403 was grown in medium containing unlabelled free amino acids and (15)N-labelled yeast hydrolysate to gain insight into the role of peptides as a source of amino acids under conditions where free amino acids are abundant. A mathematical model was composed to estimate the fluxes of free and peptide-derived amino acids into and out of the intracellular amino acid pool. We observed co-consumption of peptides and free amino acids and a considerable efflux of most free amino acids during growth. We did not observe significant differences between the peptide consumption patterns of essential and non-essential amino acids, which suggests that the incorporation of a particular amino acid is more dependent on its availability in a readily assimilated form than the organism's auxotrophy for it. For most amino acids the contribution of peptide-bound forms to the formation of biomass was initially between 30 and 60 % with the remainder originating from free amino acids. During the later stages of fermentation we observed a decrease in the utilization of peptide-bound amino acids, thus indicating that the more readily assimilated peptides are gradually exhausted from the medium during growth.

Recombinant protein expression in Lactococcus lactis using the P170 expression system

The use of the Gram-positive bacterium Lactococcus lactis in recombinant protein production has several advantages, including the organism's long history of safe use in food production and the fact that it does not produce endotoxins. Furthermore the current non-dairy L. lactis production strains contain few proteases and can secrete stable recombinant protein to the growth medium. The P170 expression system used for recombinant protein production in L. lactis utilizes an inducible promoter, P170, which is up-regulated as lactate accumulates in the growth medium. We have optimised the components of the expression system, including improved promoter strength, signal peptides and isolation of production strains with increased productivity. Recombinant proteins are produced in a growth medium with no animal-derived components as a simple batch fermentation requiring minimal process control. The accumulation of lactate in the growth medium does, however, inhibit growth and limits the yield from batch and fed-batch processes. We therefore combined the P170 expression system with the REED™ technology, which allows control of lactate concentration by electro-dialysis during fermentation. Using this combination, production of the Staphylococcus aureus nuclease reached 2.5 g L(-1).

The HtrA protease of Streptococcus pneumoniae controls density-dependent stimulation of the bacteriocin blp locus via disruption of pheromone secretion

All fully sequenced strains of Streptococcus pneumoniae (pneumococcus) contain a version of the blp locus which is responsible for the regulation and secretion of a variable repertoire of pneumococcal bacteriocins called pneumocins and their associated immunity proteins. Pneumocins mediate intra- and interspecies competition in vitro and have been shown to provide a competitive advantage in vivo. Pneumocin production is stimulated by extracellular accumulation of the peptide pheromone, BlpC. Both BlpC and the functional pneumocins are secreted out of the cell via the Blp transporter, BlpAB. The conserved surface-expressed serine protease, HtrA, has been shown to limit activation of the locus and secretion of functional pneumocins. In this work, we demonstrate that htrA mutants stimulate the blp locus at lower cell density and to a greater extent than strains expressing wild-type HtrA. This effect is not due to direct proteolytic degradation of secreted pheromone by the protease, but instead is a result of HtrA-mediated disruption of peptide processing and secretion. Because pneumocins are secreted through the same transporter as the pheromone, this finding explains why pheromone supplementation cannot completely restore pneumocin inhibition to strains expressing high levels of HtrA despite restoration of blp transcriptional activity. HtrA restricts pneumocin production to high cell density by limiting the rate of accumulation of BlpC in the environment. Importantly, HtrA does not interfere with the ability of a strain to sense environmental pheromones, which is necessary for the induction of protective immunity in the face of pneumocin-secreting competitors.

Effects of synthetic cohesin-containing scaffold protein architecture on binding dockerin-enzyme fusions on the surface of Lactococcus lactis

BACKGROUND

The microbial synthesis of fuels, commodity chemicals, and bioactive compounds necessitates the assemblage of multiple enzyme activities to carry out sequential chemical reactions, often via substrate channeling by means of multi-domain or multi-enzyme complexes. Engineering the controlled incorporation of enzymes in recombinant protein complexes is therefore of interest. The cellulosome of Clostridium thermocellum is an extracellular enzyme complex that efficiently hydrolyzes crystalline cellulose. Enzymes interact with protein scaffolds via type 1 dockerin/cohesin interactions, while scaffolds in turn bind surface anchor proteins by means of type 2 dockerin/cohesin interactions, which demonstrate a different binding specificity than their type 1 counterparts. Recombinant chimeric scaffold proteins containing cohesins of different specificity allow binding of multiple enzymes to specific sites within an engineered complex.

RESULTS

We report the successful display of engineered chimeric scaffold proteins containing both type 1 and type 2 cohesins on the surface of Lactococcus lactis cells. The chimeric scaffold proteins were able to form complexes with the Escherichia coli β-glucuronidase fused to either type 1 or type 2 dockerin, and differences in binding efficiencies were correlated with scaffold architecture. We used E. coli β-galactosidase, also fused to type 1 or type 2 dockerins, to demonstrate the targeted incorporation of two enzymes into the complexes. The simultaneous binding of enzyme pairs each containing a different dockerin resulted in bi-enzymatic complexes tethered to the cell surface. The sequential binding of the two enzymes yielded insights into parameters affecting assembly of the complex such as protein size and position within the scaffold.

CONCLUSIONS

The spatial organization of enzymes into complexes is an important strategy for increasing the efficiency of biochemical pathways. In this study, chimeric protein scaffolds consisting of type 1 and type 2 cohesins anchored on the surface of L. lactis allowed for the controlled positioning of dockerin-fused reporter enzymes onto the scaffolds. By binding single enzymes or enzyme pairs to the scaffolds, our data also suggest that the size and relative positions of enzymes can affect the catalytic profiles of the resulting complexes. These insights will be of great value as we engineer more advanced scaffold-guided protein complexes to optimize biochemical pathways.

Kefir-isolated Lactococcus lactis subsp. lactis inhibits the cytotoxic effect of Clostridium difficile in vitro

Kefir is a dairy product obtained by fermentation of milk with a complex microbial population and several health-promoting properties have been attributed to its consumption. In this work, we tested the ability of different kefir-isolated bacterial and yeast strains (Lactobacillus kefir, Lb. plantarum, Lactococcus lactis subps. lactis, Saccharomyces cerevisiae and Kluyveromyces marxianus) or a mixture of them (MM) to antagonise the cytopathic effect of toxins from Clostridium difficile (TcdA and TcdB). Cell detachment assays and F-actin network staining using Vero cell line were performed. Although incubation with microbial cells did not reduce the damage induced by C. difficile spent culture supernatant (SCS), Lc. lactis CIDCA 8221 and MM supernatants were able to inhibit the cytotoxicity of SCS to Vero cells. Fraction of Lc. lactis CIDCA 8221 supernatant containing components higher than 10 kDa were responsible for the inhibitory activity and heating of this fraction for 15 min at 100 °C completely abrogated this ability. By dot-blot assay with anti-TcdA or anti-TcdB antibodies, concentration of both toxins seems to be reduced in SCS treated with Lc. lactis CIDCA 8221 supernatant. However, protective effect was not affected by treatment with proteases or proteases-inhibitors tested. In conclusion, we demonstrated that kefir-isolated Lc. lactis CIDCA 8221 secreted heat-sensitive products able to protect eukaryotic cells from cytopathic effect of C. difficile toxins in vitro. Our findings provide new insights into the probiotic action of microorganisms isolated from kefir against virulence factors from intestinal pathogens.

A novel two-component system involved in secretion stress response in Streptomyces lividans

Background

Misfolded proteins accumulating outside the bacterial cytoplasmic membrane can interfere with the secretory machinery, hence the existence of quality factors to eliminate these misfolded proteins is of capital importance in bacteria that are efficient producers of secretory proteins. These bacteria normally use a specific two-component system to respond to the stress produced by the accumulation of the misfolded proteins, by activating the expression of HtrA-like proteases to specifically eliminate the incorrectly folded proteins.

Methodology/Principal Findings

Overproduction of alpha-amylase in S. lividans causing secretion stress permitted the identification of a two-component system (SCO4156-SCO4155) that regulates three HtrA-like proteases which appear to be involved in secretion stress response. Mutants in each of the genes forming part of the two-genes operon that encodes the sensor and regulator protein components accumulated misfolded proteins outside the cell, strongly suggesting the involvement of this two-component system in the S. lividans secretion stress response.

Conclusions/Significance

To our knowledge this is the first time that a specific secretion stress response two-component system is found to control the expression of three HtrA-like protease genes in S. lividans, a bacterium that has been repeatedly used as a host for the synthesis of homologous and heterologous secretory proteins of industrial application.

Engineering signal peptides for enhanced protein secretion from Lactococcus lactis

Lactococcus lactis is an attractive vehicle for biotechnological production of proteins and clinical delivery of therapeutics. In many such applications using this host, it is desirable to maximize secretion of recombinant proteins into the extracellular space, which is typically achieved by using the native signal peptide from a major secreted lactococcal protein, Usp45. In order to further increase protein secretion from L. lactis, inherent limitations of the Usp45 signal peptide (Usp45sp) must be elucidated. Here, we performed extensive mutagenesis on Usp45sp to probe the effects of both the mRNA sequence (silent mutations) and the peptide sequence (amino acid substitutions) on secretion. We screened signal peptides based on their resulting secretion levels of Staphylococcus aureus nuclease and further evaluated them for secretion of Bacillus subtilis α-amylase. Silent mutations alone gave an increase of up to 16% in the secretion of α-amylase through a mechanism consistent with relaxed mRNA folding around the ribosome binding site and enhanced translation. Targeted amino acid mutagenesis in Usp45sp, combined with additional silent mutations from the best clone in the initial screen, yielded an increase of up to 51% in maximum secretion of α-amylase while maintaining secretion at lower induction levels. The best sequence from our screen preserves the tripartite structure of the native signal peptide but increases the positive charge of the n-region. Our study presents the first example of an engineered L. lactis signal peptide with a higher secretion yield than Usp45sp and, more generally, provides strategies for further enhancing protein secretion in bacterial hosts.

Mechanism of action of the arylomycin antibiotics and effects of signal peptidase I inhibition

Clinically approved antibiotics inhibit only a small number of conserved pathways that are essential for bacterial viability, and the physiological effects of inhibiting these pathways have been studied in great detail. Likewise, characterizing the effects of candidate antibiotics that function via novel mechanisms of action is critical for their development, which is of increasing importance due to the ever-growing problem of resistance. The arylomycins are a novel class of natural-product antibiotics that act via the inhibition of type I signal peptidase (SPase), which is an essential enzyme that functions as part of the general secretory pathway and is not the target of any clinically deployed antibiotic. Correspondingly, little is known about the effects of SPase inhibition or how bacteria may respond to mitigate the associated secretion stress. Using genetically sensitized Escherichia coli and Staphylococcus aureus as model organisms, we examine the activity of arylomycin as a function of its concentration, bacterial cell density, target expression levels, and bacterial growth phase. The results reveal that the activity of the arylomycins results from an insufficient flux of proteins through the secretion pathway and the resulting mislocalization of proteins. Interestingly, this has profoundly different effects on E. coli and S. aureus. Finally, we examine the activity of arylomycin in combination with distinct classes of antibiotics and demonstrate that SPase inhibition results in synergistic sensitivity when combined with an aminoglycoside.

Type I signal peptidase and protein secretion in Staphylococcus aureus

Staphylococcus aureus is an important human pathogen whose virulence relies on the secretion of many different proteins. In general, the secretion of most proteins in S. aureus, as well as other bacteria, is dependent on the type I signal peptidase (SPase)-mediated cleavage of the N-terminal signal peptide that targets a protein to the general secretory pathway. The arylomycins are a class of natural product antibiotics that inhibit SPase, suggesting that they may be useful chemical biology tools for characterizing the secretome. While wild-type S. aureus (NCTC 8325) is naturally resistant to the arylomycins, sensitivity is conferred via a point mutation in its SPase. Here, we use a synthetic arylomycin along with a sensitized strain of S. aureus and multidimensional protein identification technology (MudPIT) mass spectrometry to identify 46 proteins whose extracellular accumulation requires SPase activity. Forty-four possess identifiable Sec-type signal peptides and thus are likely canonically secreted proteins, while four also appear to possess cell wall retention signals. We also identified the soluble C-terminal domains of two transmembrane proteins, lipoteichoic acid synthase, LtaS, and O-acyteltransferase, OatA, both of which appear to have noncanonical, internal SPase cleavage sites. Lastly, we identified three proteins, HtrA, PrsA, and SAOUHSC_01761, whose secretion is induced by arylomycin treatment. In addition to elucidating fundamental aspects of the physiology and pathology of S. aureus, the data suggest that an arylomycin-based therapeutic would reduce virulence while simultaneously eradicating an infection.

PpiA, a surface PPIase of the cyclophilin family in Lactococcus lactis

Background

Protein folding in the envelope is a crucial limiting step of protein export and secretion. In order to better understand this process in Lactococcus lactis, a lactic acid bacterium, genes encoding putative exported folding factors like Peptidyl Prolyl Isomerases (PPIases) were searched for in lactococcal genomes.

Results

In L. lactis, a new putative membrane PPIase of the cyclophilin subfamily, PpiA, was identified and characterized. ppiA gene was found to be constitutively expressed under normal and stress (heat shock, H₂O₂) conditions. Under normal conditions, PpiA protein was synthesized and released from intact cells by an exogenously added protease, showing that it was exposed at the cell surface. No obvious phenotype could be associated to a ppiA mutant strain under several laboratory conditions including stress conditions, except a very low sensitivity to H₂O₂. Induction of a ppiA copy provided in trans had no effect i) on the thermosensitivity of an mutant strain deficient for the lactococcal surface protease HtrA and ii) on the secretion and stability on four exported proteins (a highly degraded hybrid protein and three heterologous secreted proteins) in an otherwise wild-type strain background. However, a recombinant soluble form of PpiA that had been produced and secreted in L. lactis and purified from a culture supernatant displayed both PPIase and chaperone activities.

Conclusions

Although L. lactis PpiA, a protein produced and exposed at the cell surface under normal conditions, displayed a very moderate role in vivo, it was found, as a recombinant soluble form, to be endowed with folding activities in vitro.

Response of Lactobacillus casei BL23 to phenolic compounds

AIMS

To determine the inhibitory effect of phenolic compounds on Lactobacillus casei BL23, the role of two component signal transduction systems (TCS) and the response of Lact. casei BL23 to p-coumaric acid.

METHODS AND RESULTS

Growth of Lact. casei BL23 and 17 derivative strains defective in each TCS harboured by this strain in the presence of p-coumaric acid, ferulic acid, caffeic acid or methyl gallate was monitored. Furthermore, changes in the protein content of Lact. casei BL23 when exposed to p-coumaric acid were evaluated by 2D-SDS-PAGE. Eleven proteins differentially expressed in the presence of p-coumaric acid were detected. Six of them could be identified: ClpP and HtrA, involved in protein turnover and folding, acetyl-CoA carboxylase, involved in lipid metabolism, and an arginyl-tRNA synthetase were more abundant, whereas PurL and PurN, involved in purine biosynthesis, were less abundant.

CONCLUSIONS

No significant differences were observed between the parental strain and the TCS-defective mutants. p-Coumaric acid elicited a response against membrane and cytoplasmic damages.

SIGNIFICANCE AND IMPACT OF THE STUDY

The inhibitory effect of phenolic compounds on Lact. casei BL23 has been determined. For the first time, cytoplasmic proteins presumably involved in the response of Lact. casei BL23 against p-coumaric acid have been identified.

Lactococci and lactobacilli as mucosal delivery vectors for therapeutic proteins and DNA vaccines

Food-grade Lactic Acid Bacteria (LAB) have been safely consumed for centuries by humans in fermented foods. Thus, they are good candidates to develop novel oral vectors, constituting attractive alternatives to attenuated pathogens, for mucosal delivery strategies. Herein, this review summarizes our research, up until now, on the use of LAB as mucosal delivery vectors for therapeutic proteins and DNA vaccines. Most of our work has been based on the model LAB Lactococcus lactis, for which we have developed efficient genetic tools, including expression signals and host strains, for the heterologous expression of therapeutic proteins such as antigens, cytokines and enzymes. Resulting recombinant lactococci strains have been tested successfully for their prophylactic and therapeutic effects in different animal models: i) against human papillomavirus type 16 (HPV-16)-induced tumors in mice, ii) to partially prevent a bovine β-lactoglobulin (BLG)-allergic reaction in mice and iii) to regulate body weight and food consumption in obese mice. Strikingly, all of these tools have been successfully transposed to the Lactobacillus genus, in recent years, within our laboratory. Notably, anti-oxidative Lactobacillus casei strains were constructed and tested in two chemically-induced colitis models. In parallel, we also developed a strategy based on the use of L. lactis to deliver DNA at the mucosal level, and were able to show that L. lactis is able to modulate the host response through DNA delivery. Today, we consider that all of our consistent data, together with those obtained by other groups, demonstrate and reinforce the interest of using LAB, particularly lactococci and lactobacilli strains, to develop novel therapeutic protein mucosal delivery vectors which should be tested now in human clinical trials.

HtrA is a major virulence determinant of Bacillus anthracis

We demonstrate that disruption of the htrA (high temperature requirement A) gene in either the virulent Bacillus anthracis Vollum (pXO1(+) , pXO2(+) ), or in the ΔVollum (pXO1(-), pXO2(-), nontoxinogenic and noncapsular) strains, affect significantly the ability of the resulting mutants to withstand heat, oxidative, ethanol and osmotic stress. The ΔhtrA mutants manifest altered secretion of several proteins, as well as complete silencing of the abundant extracellular starvation-associated neutral protease A (NprA). VollumΔhtrA bacteria exhibit delayed proliferation in a macrophage infection assay, and despite their ability to synthesize the major B. anthracis toxins LT (lethal toxin) and ET (oedema toxin) as well as the capsule, show a decrease of over six orders of magnitude in virulence (lethal dose 50% = 3 × 10(8) spores, in the guinea pig model of anthrax), as compared with the parental wild-type strain. This unprecedented extent of loss of virulence in B. anthracis, as a consequence of deletion of a single gene, as well as all other phenotypic defects associated with htrA mutation, are restored in their corresponding trans-complemented strains. It is suggested that the loss of virulence is due to increased susceptibility of the ΔhtrA bacteria to stress insults encountered in the host. On a practical note, it is demonstrated that the attenuated Vollum ΔhtrA is highly efficacious in protecting guinea pigs against a lethal anthrax challenge.

Lactococcus lactis as a live vector: heterologous protein production and DNA delivery systems

Lactic acid bacteria (LAB), widely used in the food industry, are present in the intestine of most animals, including humans. The potential use of these bacteria as mucosal delivery vehicles for vaccinal, medical or technological use has been extensively investigated. Lactococcus lactis, a LAB species, is a potential candidate for the production of biologically useful proteins and for plasmid DNA delivery to eukaryotic cells. Several delivery systems have been developed to target heterologous proteins to a specific cell location (i.e., cytoplasm, cell wall or extracellular medium) and more recently to efficiently transfer DNA to eukaryotic cells. A promising application of L. lactis is its use for the development of live mucosal vaccines. Here, we have reviewed the expression of heterologous protein and the various delivery systems developed for L. lactis, as well as its use as an oral vaccine carrier.

A flagellin-producing Lactococcus strain: interactions with mucin and enteropathogens

Bacillus cereus CH is a probiotic strain used in human nutrition whose adhesion to mucin is dependent on its surface-associated flagellin. Flagellins from the surface of several probiotic Bacillus strains were efficiently extracted with 5 M LiCl and identified by peptide fingerprinting. Based on the proteomic analysis, cloning of the gene coding for the flagellin of B. cereus CH was performed in the lactococcal vector pNZ8110 under the control of a nisin-inducible promoter. The resulting strain, Lactococcus lactis CH, produced a surface-associated flagellin after 6 h of induction with nisin. The recombinant Lactococcus strain adhered strongly to mucin-coated polystyrene plates, whilst inhibiting competitively the adhesion of the pathogens Escherichia coli LMG2092 and Salmonella enterica ssp. enterica LMG15860 to the same molecule. Strain CH could be used in further experimentation for the characterization of the molecular mechanism of action of this probiotic B. cereus CH flagellin.

Comparative transcriptome analysis of Lactococcus lactis subsp. cremoris strains under conditions simulating Cheddar cheese manufacture

Gene expression in response to technological variations can influence fermentation and flavor generation in Cheddar cheese, and can vary from one lactococcal strain to another, perceived as differences in starter performance. The aim of this study was to determine the influence of cheese cooking temperature at 38 °C and salting on the transcriptional profiles of four closely related strains of L. lactis subsp. cremoris under simulated conditions of Cheddar cheese manufacture. Two responses could be distinguished, a core gene expression, corresponding to the common response of all strains and strain-specific response during the Cheddar simulating process. For the core gene expression after heating of inoculated milk at 38 °C, two groups of differentially expressed genes were identified: i) stress response and ii) carbohydrate and amino acid metabolism. The response to combined stresses of heat, acid and salt resulted in: i) general decrease of functions linked to cell division and metabolism, ii) specific responses related to stress such as the induction of genes coding for chaperones and proteases and iii) expression of prophage lytic systems for certain strains. Strain-specific responses were mainly observed in three of the four tested strains. These responses were the induction of genes related to osmotic stress or the release of CodY repression leading to the activation of oligopeptide transporters as well as the bcaT gene, related to amino acid degradation for the production of flavor. Comparing transcriptomes provides a core expression profile that contributes to understanding gene expression responses to environmental variations. The strain-specific responses identify predictive markers for the transcriptional state of starter strains before they enter the cheese ripening phase.

Serological diagnosis of Chlamydia pneumoniae infection: limitations and perspectives

Chlamydia pneumoniae is an obligate intracellular human pathogen responsible for a wide range of acute and chronic human diseases, including pneumonia and other respiratory diseases. Serological methods for the diagnosis of C. pneumoniae infection vary widely, and several authors have reported significant inter- and intra-laboratory variability in diagnostic methods and criteria. Over the past 10 years, numerous studies have focused on the identification of specific antigens for application in serodiagnosis, including the diagnosis of persistent infections. The use of proteomics may enable the development of serological diagnosis kits that offer reliable sensitivity and specificity and might even differentiate between the various stages of infection with this pathogen.

Immobilization of Lactococcus lactis to cellulosic material by cellulose-binding domain of Cellvibrio japonicus

AIMS

Immobilization of whole cells can be used to accumulate cells in a bioreactor and thus increase the cell density and potentially productivity, also. Cellulose is an excellent matrix for immobilization purposes because it does not require chemical modifications and is commercially available in many different forms at low price. The aim of this study was to construct a Lactococcus lactis strain capable of immobilizing to a cellulosic matrix.

METHODS AND RESULTS

In this study, the Usp45 signal sequence fused with the cellulose-binding domain (CBD) (112 amino acids) of XylA enzyme from Cellvibrio japonicus was fused with PrtP or AcmA anchors derived from L. lactis. A successful surface display of L. lactis cells expressing these fusion proteins under the P45 promoter was achieved and detected by whole-cell ELISA. A rapid filter paper assay was developed to study the cellulose-binding capability of these recombinant strains. As a result, an efficient immobilization to filter paper was demonstrated for the L. lactis cells expressing the CBD-fusion protein. The highest immobilization (92%) was measured for the strain expressing the CBD in fusion with the 344 amino acid PrtP anchor.

CONCLUSIONS

The result from the binding tests indicated that a new phenotype for L. lactis with cellulose-binding capability was achieved with both PrtP (LPXTG type anchor) and AcmA (LysM type anchor) fusions with CBD.

SIGNIFICANCE AND IMPACT OF THE STUDY

We demonstrated that an efficient immobilization of recombinant L. lactis cells to cellulosic matrix is possible. This is a step forward in developing efficient immobilization systems for lactococcal strains for industrial-scale fermentations.

Production and purification of staphylococcal nuclease in Lactococcus lactis using a new expression-secretion system and a pH-regulated mini-reactor

BACKGROUND

Staphylococcal (or micrococcal) nuclease or thermonuclease (SNase or Nuc) is a naturally-secreted nucleic acid degrading enzyme that participates in Staphylococcus aureus spread in the infected host. Purified Nuc protein can be used as an exogenous reagent to clear cellular extracts and improve protein purification. Here, a recombinant form of Nuc was produced and secreted in a Gram-positive host, Lactococcus lactis, and purified from the culture medium.

RESULTS

The gene segment corresponding to the S. aureus nuclease without its signal peptide was cloned in an expression-secretion vector. It was then fused to a lactococcal sequence encoding a signal peptide, and expressed under the control of a lactococcal promoter that is inducible by zinc starvation. An L. lactis subsp cremoris model strain (MG1363) transformed with the resulting plasmid was grown in either of two media (GM17v and CDM) that are free of animal compounds, allowing GMP (Good Manufacturing Practice) production. Induction conditions (concentration of the metal chelator EDTA and timing of addition) in small-scale pH-regulated fermentors were optimized using LacMF (Lactis Multi-Fermentor), a home-made parallel fermentation control system able to monitor 12 reactors simultaneously. Large amounts of recombinant Nuc (rNuc) were produced and secreted in both media, and rNuc was purified from GM17v medium in a single-step procedure.

CONCLUSIONS

In L. lactis, rNuc production and secretion were optimal after induction by 0.5 mM EDTA in small scale (200 mL) GM17v exponential phase cultures (at an OD(600) of 2), leading to a maximal protein yield of 210 mg per L of culture medium. Purified rNuc was highly active, displaying a specific activity of 2000 U/mg.

Expression of two Listeria monocytogenes antigens (P60 and LLO) in Lactococcus lactis and examination for use as live vaccine vectors

Listeria monocytogenes is a food-borne intracellular pathogen that mainly infects pregnant and immunocompromised individuals. The pore-forming haemolysin listeriolysin O (LLO), the main virulence factor of Listeria monocytogenes, allows bacteria to escape from the harsh environment of the phagosome to the cytoplasm of the infected cell. This leads to processing of bacterial antigens predominantly through the cytosolic MHC class I presentation pathway. We previously engineered the food-grade bacterium Lactococcus lactis to express LLO and demonstrated an LLO-specific CD8(+) response upon immunization of mice with the engineered L. lactis vaccine strains. In the present work, we examined the immune response and protective efficacy of an L. lactis strain co-expressing LLO and a truncated form of the listerial P60 antigen (tP60). Oral immunization revealed no significant protection against listeriosis with L. lactis expressing LLO, tP60 or the combined LLO/tP60. In contrast, intraperitoneal vaccination induced an LLO-specific CD8(+) immune response with LLO-expressing L. lactis but no significant improvement in protection was observed following vaccination with the combined LLO/tP60 expressing L. lactis strain. This may be due to the low level of tP60 expression in the LLO/tP60 strain. These results demonstrate the necessity for improved oral vaccination strategies using LLO-expressing L. lactis vaccine vectors.

Sense and nonsense from a systems biology approach to microbial recombinant protein production

The 'Holy Grail' of recombinant protein production remains the availability of generic protocols and hosts for the production of even the most difficult target products. The present review provides first an explanation why the shock imposed on bacteria using a standard induction protocol not only arrests growth, but also decreases the number of colony-forming units by several orders of magnitude. Particular emphasis is placed on findings of numerous genome-wide transcriptomic studies that highlight cellular stress, in which the general stress, heat-shock and stringent responses are the underlying basis for the manifestation of the deterioration of cell physiology. We then review common approaches used to solve bottlenecks in protein folding and post-translational modification that result in recombinant protein deposition in cytoplasmic inclusion bodies. Finally, we suggest a generic approach to process design that minimizes stress on the production host and a strategy for isolating improved hosts.

Utilisation des bactéries lactiques comme vecteurs vaccinaux

Aujourd’hui, nous disposons de données suffisantes qui confortent l’intérêt d’utiliser des bactéries lactiques (BL), notamment des souches des lactocoques et lactobacilles, pour le développement de nouvelles stratégies de vaccination mucosale. Les BL sont des bactéries à Gram positif utilisées depuis des millénaires dans la production d’aliments fermentés. Elles sont donc de bonnes candidates pour le développement de nouvelles stratégies de vectorisation orale et constituent des alternatives attractives aux stratégies vaccinales basées sur des bactéries pathogènes atténuées dont l’utilisation présente des risques sanitaires. Ce chapitre passe en revue la recherche et les progrès les plus récents dans l’utilisation des BL comme vecteurs de délivrance de protéines d’intérêt médical pour développer de nouveaux vaccins.

Streptococcus adherence and colonization

Streptococci readily colonize mucosal tissues in the nasopharynx; the respiratory, gastrointestinal, and genitourinary tracts; and the skin. Each ecological niche presents a series of challenges to successful colonization with which streptococci have to contend. Some species exist in equilibrium with their host, neither stimulating nor submitting to immune defenses mounted against them. Most are either opportunistic or true pathogens responsible for diseases such as pharyngitis, tooth decay, necrotizing fasciitis, infective endocarditis, and meningitis. Part of the success of streptococci as colonizers is attributable to the spectrum of proteins expressed on their surfaces. Adhesins enable interactions with salivary, serum, and extracellular matrix components; host cells; and other microbes. This is the essential first step to colonization, the development of complex communities, and possible invasion of host tissues. The majority of streptococcal adhesins are anchored to the cell wall via a C-terminal LPxTz motif. Other proteins may be surface anchored through N-terminal lipid modifications, while the mechanism of cell wall associations for others remains unclear. Collectively, these surface-bound proteins provide Streptococcus species with a "coat of many colors," enabling multiple intimate contacts and interplays between the bacterial cell and the host. In vitro and in vivo studies have demonstrated direct roles for many streptococcal adhesins as colonization or virulence factors, making them attractive targets for therapeutic and preventive strategies against streptococcal infections. There is, therefore, much focus on applying increasingly advanced molecular techniques to determine the precise structures and functions of these proteins, and their regulatory pathways, so that more targeted approaches can be developed.

Production of a recombinant type 1 antifreeze protein analogue by L. lactis and its applications on frozen meat and frozen dough

In this study, a novel recombinant type I antifreeze protein analogue (rAFP) was produced and secreted by Lactococcus lactis, a food-grade microorganism of major commercial importance. Antifreeze proteins are potent cryogenic protection agents for the cryopreservation of food and pharmaceutical materials. A food-grade expression and fermentation system (BSE- and antibiotic-free) for the production and secretion of high levels of rAFP was developed. Lyophilized, crude rAFP produced by L. lactis was tested in a frozen meat and frozen dough processing model. The frozen meat treated with the antifreeze protein showed less drip loss, less protein loss, and a high score on juiciness by sensory evaluation. Frozen dough treated with the rAFP showed better fermentation capacity than untreated frozen dough. Breads baked from frozen dough treated with rAFP acquired the same consumer acceptance as fresh bread.

Transcriptomic response of Lactococcus lactis in mixed culture with Staphylococcus aureus

The mechanisms of interaction between Lactococcus lactis and the food pathogen Staphylococcus aureus are of crucial importance, as one major role of lactic acid bacteria (LAB) in fermented foods is to inhibit undesirable and pathogenic flora. It was never questioned if the presence of a pathogen can actively modify the gene expression patterns of LAB in a shared environment. In this study, transcriptome and biochemical analyses were combined to assess the dynamic response of L. lactis in a mixed culture with S. aureus. The presence of S. aureus hardly affected the growth of L. lactis but dramatically modified its gene expression profile. The main effect was related to earlier carbon limitation and a concomitantly lower growth rate in the mixed culture due to the consumption of glucose by both species. More specific responses involved diverse cellular functions. Genes associated with amino acid metabolism, ion transport, oxygen response, menaquinone metabolism, and cell surface and phage expression were differentially expressed in the mixed culture. This study led to new insights into possible mechanisms of interaction between L. lactis and S. aureus. Moreover, new and unexpected effects of L. lactis on the virulence of S. aureus were discovered, as described elsewhere (S. Even, C. Charlier, S. Nouaille, N. L. Ben Zakour, M. Cretenet, F. J. Cousin, M. Gautier, M. Cocaign-Bousquet, P. Loubière, and Y. Le Loir, Appl. Environ. Microbiol. 75:4459-4472, 2009).

Highly efficient production of the staphylococcal nuclease reporter in Lactobacillus bulgaricus governed by the promoter of the hlbA gene

Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) genome sequence analysis revealed the presence of two genes that encode histone-like HU proteins (hlbA and hlbB) showing extensive similarity to other bacterial homologues. These genes were found to be extremely conserved among several L. bulgaricus strains. The hlbA gene was shown to be constitutively transcribed from a unique promoter (phlbA) during normal growth, whereas hlbB did not seem to be expressed under usual laboratory conditions. Using a reporter cassette in which the staphylococcal nuclease was fused at its N-terminus to the lactococcal signal peptide Usp45 (SP Usp45), we have demonstrated that phlbA promotes high expression of the reporter in L. bulgaricus, which correlated with an abundant secretion of the mature nuclease in the supernatant fraction. Quantification of the exported enzyme reveals a secretion level approximately threefold higher when the expression of the reporter was under the control of phlbA compared with the lactococcal usp45 promoter. Together, these results indicate that phlbA is suitable for gene expression in L. bulgaricus, that SP Usp45 is functionally recognized and processed by the L. bulgaricus secretion machinery and that the nuclease reporter gene can be used for the identification of exported products in this bacterium.

Random mutagenesis identifies novel genes involved in the secretion of antimicrobial, cell wall-lytic enzymes by Lactococcus lactis

Lactococcus lactis is a gram-positive bacterium that is widely used in the food industry and is therefore desirable as a candidate for the production and secretion of recombinant proteins. Previously, we generated a L. lactis strain that expressed and secreted the antimicrobial cell wall-lytic enzyme lysostaphin. To identify lactococcal gene products that affect the production of lysostaphin, we isolated and characterized mutants generated by random transposon mutagenesis that had altered lysostaphin activity. Out of 35,000 mutants screened, only one with no lysostaphin activity was identified, and it was found to contain an insertion in the lysostaphin expression cassette. Ten mutants with higher lysostaphin activity contained insertions in only four different genes, which encode an uncharacterized putative transmembrane protein (llmg_0609) (three mutants), an enzyme catalyzing the first step in peptidoglycan biosynthesis (murA2) (five mutants), a putative regulator of peptidoglycan modification (trmA) (one mutant), and an uncharacterized enzyme possibly involved in ubiquinone biosynthesis (llmg_2148) (one mutant). These mutants were found to secrete larger amounts of lysostaphin than the control strain (MG1363[lss]), and the greatest increase in secretion was 9.8- to 16.1-fold, for the llmg_0609 mutants. The lysostaphin-oversecreting llmg_0609, murA2, and trmA mutants were also found to secrete larger amounts of another cell wall-lytic enzyme (the Listeria monocytogenes bacteriophage endolysin Ply511) than the control strain, indicating that the phenotype is not limited to lysostaphin.

HtrA is essential for efficient secretion of recombinant proteins by Lactococcus lactis

HtrA is a unique protease on the extracellular surface of Lactococcus lactis. It is known to take part in the proteolysis of many secreted recombinant proteins, and the mutation of htrA can lead to the complete stabilization of recombinant proteins. In this work, we have shown that htrA mutation also leads to significant reduction of the efficiency of recombinant-protein secretion. We also show that the level of HtrA can be lowered by the suppression of the acid tolerance response (ATR) in L. lactis. Instead of using an L. lactis htrA mutant, the reduction of the HtrA level in wild-type recombinant cultures of L. lactis by ATR suppression may serve as a better strategy for the production of secreted recombinant proteins.

Lactococcus lactis-expressing listeriolysin O (LLO) provides protection and specific CD8(+) T cells against Listeria monocytogenes in the murine infection model

Lactococcus lactis has previously been proposed as a vaccine platform for the safe delivery of heterologous antigens. Here we utilized L. lactis as a live vector for expression of listeriolysin O (LLO), a major Listeria monocytogenes antigen and virulence factor. A variety of plasmid constructs were designed to permit either constitutive or nisin-inducible expression of secreted or non-secreted LLO in L. lactis. Recombinant strains were subsequently tested in a murine model for vaccination efficacy against L. monocytogenes infection. CD8(+) T lymphocytes specific for the LLO(91-99) epitope were detected when strains were administered via the intraperitoneal (IP) but not the oral route. Challenge with live L. monocytogenes revealed different levels of protection among the three vaccine strains tested with the nisin-inducible LLO-secreting L. lactis strain providing the greatest protection against secondary infection. This work highlights the usefulness of the GRAS (Generally Regarded As Safe) organism L. lactis as the basis of a live vaccine vector against L. monocytogenes. The work suggests that LLO-expressing L. lactis strains may also have the potential to act as a platform for directing other co-expressed antigens towards the cytosolic MHC class I pathway for enhanced stimulation of the CD8(+) T-cell response.

Characterization of DegQVh, a serine protease and a protective immunogen from a pathogenic Vibrio harveyi strain

Vibrio harveyi is an important marine pathogen that can infect a number of aquaculture species. V. harveyi degQ (degQ(Vh)), the gene encoding a DegQ homologue, was cloned from T4, a pathogenic V. harveyi strain isolated from diseased fish. DegQ(Vh) was closely related to the HtrA family members identified in other Vibrio species and could complement the temperature-sensitive phenotype of an Escherichia coli strain defective in degP. Expression of degQ(Vh) in T4 was modulated by temperature, possibly through the sigma(E)-like factor. Enzymatic analyses demonstrated that the recombinant DegQ(Vh) protein expressed in and purified from E. coli was an active serine protease whose activity required the integrity of the catalytic site and the PDZ domains. The optimal temperature and pH of the recombinant DegQ(Vh) protein were 50 degrees C and pH 8.0. A vaccination study indicated that the purified recombinant DegQ(Vh) was a protective immunogen that could confer protection upon fish against infection by V. harveyi. In order to improve the efficiency of DegQ(Vh) as a vaccine, a genetic construct in the form of the plasmid pAQ1 was built, in which the DNA encoding the processed DegQ(Vh) protein was fused with the DNA encoding the secretion region of AgaV, an extracellular beta-agarase. The E. coli strain harboring pAQ1 could express and secrete the chimeric DegQ(Vh) protein into the culture supernatant. Vaccination of fish with viable E. coli expressing chimeric degQ(Vh) significantly (P < 0.001) enhanced the survival of fish against V. harveyi challenge, which was possibly due to the relatively prolonged exposure of the immune system to the recombinant antigen produced constitutively, albeit at a gradually decreasing level, by the carrier strain.

Reduced lysis upon growth of Lactococcus lactis on galactose is a consequence of decreased binding of the autolysin AcmA

When Lactococcus lactis subsp. lactis IL1403 or L. lactis subsp. cremoris MG1363 is grown in a medium with galactose as the carbon source, the culture lyses to a lesser extent in stationary phase than when the bacteria are grown in a medium containing glucose. Expression of AcmA, the major autolysin of L. lactis, is not influenced by the carbon source. Binding studies with a fusion protein consisting of the MSA2 protein of Plasmodium falciparum and the C-terminal peptidoglycan-binding domain of AcmA revealed that cell walls of cells from both subspecies grown on galactose bind less AcmA than cell walls of cells grown on glucose. Cells grown on glucose or galactose and treated with trichloroacetic acid prior to AcmA binding bind similar amounts of AcmA. Analysis of the composition of the lipoteichoic acids (LTAs) of L. lactis IL1403 cells grown on glucose or galactose showed that the LTA composition is influenced by the carbon source: cells grown on galactose contain LTA with less galactose than cells grown on glucose. In conclusion, growth of L. lactis on galactose changes the LTA composition in the cell wall in such a way that less AcmA is able to bind to the peptidoglycan, resulting in a decrease in autolysis.

LysM, a widely distributed protein motif for binding to (peptido)glycans

Bacteria retain certain proteins at their cell envelopes by attaching them in a non-covalent manner to peptidoglycan, using specific protein domains, such as the prominent LysM (Lysin Motif) domain. More than 4000 (Pfam PF01476) proteins of both prokaryotes and eukaryotes have been found to contain one or more Lysin Motifs. Notably, this collection contains not only truly secreted proteins, but also (outer-)membrane proteins, lipoproteins or proteins bound to the cell wall in a (non-)covalent manner. The motif typically ranges in length from 44 to 65 amino acid residues and binds to various types of peptidoglycan and chitin, most likely recognizing the N-acetylglucosamine moiety. Most bacterial LysM-containing proteins are peptidoglycan hydrolases with various cleavage specificities. Binding of certain LysM proteins to cells of Gram-positive bacteria has been shown to occur at specific sites, as binding elsewhere is hindered by the presence of other cell wall components such as lipoteichoic acids. Interestingly, LysM domains of certain plant kinases enable the plant to recognize its symbiotic bacteria or sense and induce resistance against fungi. This interaction is triggered by chitin-like compounds that are secreted by the symbiotic bacteria or released from fungi, demonstrating an important sensing function of LysMs.

Gingipain-dependent interactions with the host are important for survival of Porphyromonas gingivalis

Porphyromonas gingivalis, a major periodontal pathogen, must acquire nutrients from host derived substrates, overcome oxidative stress and subvert the immune system. These activities can be coordinated via the gingipains which represent the most significant virulence factor produced by this organism. In the context of our contribution to this field, we will review the current understanding of gingipain biogenesis, glycosylation, and regulation, as well as discuss their role in oxidative stress resistance and apoptosis. We can postulate a model, in which gingipains may be part of the mechanism for P. gingivalis virulence.

Requirements for surface expression and function of adhesin P1 from Streptococcus mutans

In this report, we define requirements for the successful translocation and functional maturation of the adhesin P1 of Streptococcus mutans. Conformational epitopes recognized by anti-P1 monoclonal antibodies (MAbs) were further characterized, thus facilitating the use of particular MAbs as tools to monitor the locations of various forms of the protein. We show that correct localization of P1 is dependent on structural features of the molecule itself, including a requisite A region-P region intramolecular interaction that occurs within the cell prior to secretion. P1 also was shown to be affected by several members of the protein-folding-secretion-turnover apparatus. It does not achieve a fully functional form in the absence of the trigger factor PPIase homolog RopA, and its translocation is delayed when DnaK levels are limited. In addition, dnaK message levels are differentially altered in the presence of P1 lacking the alanine-rich compared to the proline-rich repeat domains. Lastly, nonsecreted P1 lacking the P region accumulates within the cell in the absence of htrA, implying an intracellular HtrA protease function in the degradation and turnover of this particular internal-deletion polypeptide. However, the opposite effect is seen for full-length P1, suggesting a sensing mechanism and substrate-dependent alteration in HtrA's function and effect that is consistent with its known ability to switch between chaperone and protease, depending on environmental perturbations.

Role of group A Streptococcus HtrA in the maturation of SpeB protease

The serine protease high-temperature requirement A (HtrA) (DegP) of the human pathogen Streptococcus pyogenes (group A Streptococcus; GAS) is localized to the ExPortal secretory microdomain and is reportedly essential for the maturation of cysteine protease streptococcal pyrogenic exotoxin B (SpeB). Here, we utilize HSC5 (M5 serotype) and the in-frame isogenic mutant HSC5DeltahtrA to determine whether HtrA contributes to the maturation of other GAS virulence determinants. Mutanolysin cell wall extracts and secreted proteins were arrayed by 2-DE and identified by MALDI-TOF PMF analysis. HSC5DeltahtrA had elevated levels of cell wall-associated M protein, whilst the supernatant had higher concentrations of M protein fragments and a reduced amount of mature SpeB protease, compared to wild-type (WT). Western blot analysis and protease assays revealed a delay in the maturation of SpeB in the HSC5DeltahtrA supernatant. HtrA was unable to directly process SpeB zymogen (proSpeB) to the active form in vitro. We therefore conclude that HtrA plays an indirect role in the maturation of cysteine protease SpeB.

Lactococcus lactis, an efficient cell factory for recombinant protein production and secretion

The use of Gram-positive bacteria for heterologous protein production proves to be a useful choice due to easy protein secretion and purification. The lactic acid bacterium Lactococcus lactis emerges as an attractive alternative to the Gram-positive model Bacillus subtilis. Here, we review recent work on the expression and secretion systems available for heterologous protein secretion in L. lactis, including promoters, signal peptides and mutant host strains known to overcome some bottlenecks of the process. Among the tools developed in our laboratory, inactivation of HtrA, the unique housekeeping protease at the cell surface, or complementation of the Sec machinery with B. subtilis SecDF accessory protein each result in the increase in heterologous protein yield. Furthermore, our lactococcal expression/secretion system, using both P(Zn)zitR, an expression cassette tightly controlled by environmental zinc, and a consensus signal peptide, SP(Exp4), allows efficient production and secretion of the staphylococcal nuclease, as evidenced by protein yields (protein amount/biomass) comparable to those obtained using NICE or P170 expression systems under similar laboratory conditions. Finally, the toolbox we are developing should contribute to enlarge the use of L. lactis as a protein cell factory.

Production of biological active murine IFN-gamma by recombinant Lactococcus lactis

IFN-gamma is a cytokine produced primarily by both T lymphocytes and natural killer cells and it is considered to be an attractive therapeutic molecule. In the present study, a DNA sequence encoding the mature murine IFN-gamma (muIFN-gamma) protein was cloned and expressed in the food-grade lactic acid bacterium Lactococcus lactis. The activity of recombinant muIFN-gamma produced by genetically engineered L. lactis was confirmed in an antiviral assay using MoV cells infected with Vesicular Stomatitis Virus. The data provide the first demonstration that a Gram-positive bacterium, L. lactis, is able to produce functional muIFN-gamma. This recombinant strain could lead to the development of a new, well-tolerated vector to deliver active muIFN-gamma at the mucosal level.

System using tandem repeats of the cA peptidoglycan-binding domain from Lactococcus lactis for display of both N- and C-terminal fusions on cell surfaces of lactic acid bacteria

Here, we established a system for displaying heterologous protein to the C terminus of the peptidoglycan-binding domain (cA domain) of AcmA (a major autolysin from Lactococcus lactis). Western blot and flow cytometric analyses revealed that the fusion proteins (cA-AmyA) of the cA domain and alpha-amylase from Streptococcus bovis 148 (AmyA) are efficiently expressed and successfully displayed on the surfaces of L. lactis cells. AmyA was also displayed on the cell surface while retaining its activity. Moreover, with an increase in the number of cA domains, the quantity of cA-AmyA fusion proteins displayed on the cell surface increased. When three repeats of the cA domain were used as an anchor protein, 82% of alpha-amylase activity was detected on the cells. The raw starch-degrading activity of AmyA was significantly higher when AmyA was fused to the C terminus of the cA domain than when it was fused to the N terminus. In addition, cA-AmyA fusion proteins were successfully displayed on the cell surfaces of Lactobacillus plantarum and Lactobacillus casei.

Peptidoglycan N-acetylglucosamine deacetylation decreases autolysis in Lactococcus lactis

The gene xynD (renamed pgdA) of Lactococcus lactis IL1403 was shown to encode a peptidoglycan N-acetylglucosamine deacetylase. Inactivation of pgdA in L. lactis led to fully acetylated peptidoglycan, whereas cloning of pgdA on a multicopy plasmid vector resulted in an increased degree of peptidoglycan deacetylation, as shown by analysis of peptidoglycan constituent muropeptides. An increased amount of N-unsubstituted glucosamine residues in peptidoglycan resulted in a reduction of the rate of autolysis of L. lactis cells. The activity of the L. lactis major autolysin AcmA was tested on L. lactis cells or peptidoglycan with different degrees of de-N-acetylation. Deacetylated peptidoglycan exhibited decreased susceptibility to AcmA hydrolysis. This reduced susceptibility to AcmA did not result from reduced AcmA binding to peptidoglycan with an increasing degree of de-N-acetylation. In conclusion, enzymic N-acetylglucosamine deacetylation protects peptidoglycan from hydrolysis by the major autolysin AcmA in L. lactis cells, and this leads to decreased cellular autolysis.

Antimicrobial Activity of Divercin RV41 Produced and Secreted by Lactococcus lactis

Divercin V41 is a class IIa bacteriocin produced by Carnobacterium divergens V41 with a strong anti-Listeria activity. We have previously produced a recombinant form of divercin V41 (DvnRV41) in Escherichia coli strain Origami, by cloning a synthetic gene that codes for a mature divercin RV41 peptide. In this work we describe the inducible expression and secretion of DvnRV41 in the food-grade lactic acid bacterium, Lactococcus lactis. The production of DvnRV41 by recombinant L. lactis was confirmed and quantified by Western blot and ELISA assays. In addition, anti-Listeria activity of DvnRV41 was determined using an agar diffusion test. Although the levels of DvnRV41 produced by recombinant L. lactis were similar to those produced by the natural host, C. divergens V41, the specific activities were lower. In conclusion, our data show that the bacteriocin DvnRV41 is produced and secreted in an active form by L. lactis and that this approach may have important applications in the preservation of foods.

Adaptation and response of Bifidobacterium animalis subsp. lactis to bile: a proteomic and physiological approach

Bile salts are natural detergents that facilitate the digestion and absorption of the hydrophobic components of the diet. However, their amphiphilic nature makes them very inhibitory for bacteria and strongly influences bacterial survival in the gastrointestinal tract. Adaptation to and tolerance of bile stress is therefore crucial for the persistence of bacteria in the human colonic niche. Bifidobacterium animalis subsp. lactis, a probiotic bacterium with documented health benefits, is applied largely in fermented dairy products. In this study, the effect of bile salts on proteomes of B. animalis subsp. lactis IPLA 4549 and its bile-resistant derivative B. animalis subsp. lactis 4549dOx was analyzed, leading to the identification of proteins which may represent the targets of bile salt response and adaptation in B. animalis subsp. lactis. The comparison of the wild-type and the bile-resistant strain responses allowed us to hypothesize about the resistance mechanisms acquired by the derivative resistant strain and about the bile salt response in B. animalis subsp. lactis. In addition, significant differences in the levels of metabolic end products of the bifid shunt and in the redox status of the cells were also detected, which correlate with some differences observed between the proteomes. These results indicate that adaptation and response to bile in B. animalis subsp. lactis involve several physiological mechanisms that are jointly dedicated to reduce the deleterious impact of bile on the cell's physiology.

HtrA in Porphyromonas gingivalis can regulate growth and gingipain activity under stressful environmental conditions

In several micro-organisms, HtrA, a serine periplasmic protease, is considered an important virulence factor that plays a regulatory role in oxidative and temperature stress. The authors have previously shown that the vimA gene product is an important virulence regulator in Porphyromonas gingivalis. Further, purified recombinant VimA physically interacted with the major gingipains and the HtrA from P. gingivalis. To further evaluate a role for HtrA in the pathogenicity of this organism, a 1.5 kb fragment containing the htrA gene was PCR-amplified from the chromosomal DNA of P. gingivalis W83. This gene was insertionally inactivated using the ermF-ermAM antibiotic-resistance cassette and used to create an htrA-deficient mutant by allelic exchange. In one randomly chosen isogenic mutant designated P. gingivalis FLL203, there was increased sensitivity to hydrogen peroxide. Growth of this mutant at an elevated temperature was more inhibited compared to the wild-type. Further, in contrast to the wild-type, there was a significant decrease in Arg-gingipain activity after heat shock in FLL203. However, the gingipain activity in the mutant returned to normal levels after a further 30 min incubation at room temperature. Collectively, these data suggest that HtrA may play a similar role in oxidative and temperature stress in P. gingivalis as observed in other organisms.

VimA is part of the maturation pathway for the major gingipains of Porphyromonas gingivalis W83

The authors have shown previously that the vimA gene, which is part of the bcp-recA-vimA operon, plays an important role in protease activation in Porphyromonas gingivalis. The gingipain RgpB proenzyme is secreted in the vimA-defective mutant P. gingivalis FLL92. An important question that is raised is whether the vimA gene product could directly interact with the proteases for their activation or regulate a pathway responsible for protease activation. To further study the mechanism(s) of VimA-dependent protease activation, the vimA gene product was further characterized. A 39 kDa protein consistent with the size of the predicted VimA protein was purified. In protein–protein interaction studies, the VimA protein was shown to interact with gingipains RgpA, RgpB and Kgp. Immune sera from mice immunized with P. gingivalis immunoreacted with the purified VimA protein. Taken together, these data suggest an interaction of VimA with the gingipains and further confirm the role of this protein in their regulation or maturation.