Expression of recombinant proteins on the surface of the coagulase-negative bacterium Staphylococcus xylosus.

An expression system to allow targeting of heterologous proteins to the cell surface of Staphylococcus xylosus, a coagulase-negative gram-positive bacterium, is described. The expression of recombinant gene fragments, fused between gene fragments encoding the signal peptide and the cell surface-binding regions of staphylococcal protein A, targets the resulting fusion proteins to the outer bacterial cell surface via the membrane-anchoring region and the highly charged cell wall-spanning region of staphylococcal protein A. The expression system was used to secrete fusion proteins containing sequences from a malaria blood-stage antigen and a streptococcal albumin-binding receptor to the cell surface of S. xylosus. Analysis of the recombinant cells by immunogold staining and immunofluorescence revealed that both the receptor and the malaria peptide were properly processed and exposed on the surface of the host cells. However, only approximately 40 to 50% of the recombinant cells were strongly stained with antiserum reactive with the albumin-binding receptor, while approximately 10 to 15% of the cells were stained with antiserum reactive with the malaria peptide. The incomplete staining of some of the cells suggests steric effects that make the recombinant fusion proteins inaccessible to the reactive antibodies because of variable cell wall structures. However, the results demonstrate for the first time that recombinant techniques can be used to express heterologous receptors and immunogens on the surface of gram-positive cells.     

Characterization of a sucrase gene from Staphylococcus xylosus.

The Staphylococcus xylosus gene scrB, encoding a sucrase, has been isolated from a genomic library of S. xylosus constructed in Escherichia coli. The gene was detected by its ability to confer utilization of the glucose and fructose residues of raffinose in an E. coli strain that is not able to metabolize galactose. It was found to reside within a 1.8-kb DNA fragment, the nucleotide sequence of which was determined. One large open reading frame, which is preceded by a ribosome binding site, is encoded on the fragment. Its deduced amino acid sequence yields a protein with a molecular mass of 57.377 kDa which shows significant homology with bacterial sucrose-6-phosphate hydrolases and sucrases. Overexpression of scrB in E. coli by the bacteriophage T7 polymerase promoter system resulted in the production of a protein with an apparent molecular mass of 58 kDa. Disruption of the scrB gene in the S. xylosus genome rendered S. xylosus unable to utilize sucrose. Thus, the ScrB sucrase is essential for sucrose metabolism in S. xylosus.     

Proteomic analysis of the cell envelope fraction of Escherichia coli

We applied proteomics technologies to analyze a membrane preparation of Escherichia coli, wild type strain and of transformants expressing human cytochrome P450s. The proteins were analyzed by two-dimensional electrophoresis and identified by matrix-assisted laser desorption ionization mass spectrometry. The membrane proteins were solubilized with both mild detergents such as CHAPS and strong detergents, such as sodium and lithium dodecyl sulfate, sodium cholate and sodium deoxycholate. In the E. colimembrane fraction, 394 different gene products were identified. Approximately 28% of them were predicted to be integral membrane proteins, of which 100 proteins have been predicted to carry one transmembrane region, ten proteins to carry two, and two proteins to include three transmembrane domains. The remaining are probably membrane-associated and cytosolic proteins. Cytochrome P450s did not enter the immobilized pH gradient strips but were efficiently analyzed in a two-dimensional, two-detergent system. Use of strong solubilizing agents resulted in the detection of about 20 membrane proteins, which were not detected following extraction with mild detergents and chaotropes. The present database is one of the largest for membrane proteins.     

Proteomic analysis of a fraction enriched in cell envelope proteins of Acinetobacter baumannii

Acinetobacter baumannii is a multiresistant opportunistic nosocomial pathogen. A protein fraction was purified and analyzed by 2-DE. Twenty-nine major protein spots were selected for protein identification using trypsin digestion and MS analysis. As the A. baumannii genome has not yet been described, protein identification was performed by homology with other Acinetobacter species in the NCBi database. We identified ribosomal proteins, chaperones, elongation factors and outer membrane proteins (Omp), such as OmpA and the 33-36-kDa OMP. Proteomic analysis of A. baumannii provides a platform for further studies in antimicrobial resistance.     

Proteomic profiling of cell envelope-associated proteins from Staphylococcus aureus

The emergence of highly virulent community acquired Staphylococcus aureus and continued progression of resistance to multiple antimicrobials, including methicillin and vancomycin, marks the reemergence of S. aureus as a serious health care threat. Investigation of proteins localized to the cell surface could help to elucidate mechanisms of virulence and antibiotic resistance in S. aureus. In this study, proteomic profiling methods were developed to solubilize, display, and evaluate abundance levels of proteins present in the supernatants of the lysostaphin-digested cell envelope from cultured vancomycin-intermediate S. aureus (VISA) cells. Combining approaches of 2-DE or chromatographic separation of proteins with MS analyses resulted in the identification of 144 proteins of particular interest. Of these proteins, 48 contained predicted cell wall localization or export signal motifs, including 14 with distinct covalent peptidoglycan-anchor sites, four of which are uncharacterized to date. One of the two most abundant cell envelope proteins, which showed remarkably high variations in MW and pI in the 2-DE gel display, was the S. aureus surface protein G. The display of numerous secreted proteins that are not covalently cell wall-anchored, suggests that, in the exponential growth phase, secreted proteins can be retained physiologically in the cell envelope and may interact with cell wall-anchored proteins and carbohydrate structures in a manner yet to be determined. The remaining 96 proteins, devoid of recognizable motifs, were repeatedly profiled in the VISA cell envelope fractions. We describe a novel semiquantitative method to determine abundance factors of such proteins in 2-DE gels of cell envelope fractions relative to whole cell lysates and discuss these data in the context of true cell envelope localization versus experimentally caused cell lysis.     

Urease from Staphylococcus saprophyticus: purification,characterization and comparison to Staphylococcus xylosus urease

Urease from Staphylococcus saprophyticus was purified more than 800-fold by liquid chromatography reaching homogeneity, as shown by isoelectric focussing, at a maximum specific activity of 1979 U/mg. The molecular weight of the native enzyme was 420000; it consisted of subunits with molecular weights of 72400 (), 20400 (), and 13900 () in an estimated ()₄ stoichiometry. In native gradient polyacrylamide gel electrophoresis urease exhibited a multiple activity band pattern with molecular weights ranging from 420000 to 100000. In the native enzyme, 4.09 (±0.25) atoms of nickel per molecule were detected. The N-terminal amino acids of the urease subunits were identical to those from Staphylococcus xylosus, and amino acid analysis revealed high similarities in both enzymes; no cysteine was detected after acid hydrolysis of vinylpyridinylated urease. Electron micrographs of negatively stained urease specimens from both staphylococci showed identical size and structure.Abbreviation PAGE polyacrylamide gel electrophoresis     

Cloning and sequencing of a plasmid-mediated erythromycin resistance determinant from Staphylococcus xylosus

A 2.3-kb DNA fragment cloned from plasmid pCH200, the largest (52 kb) of four plasmids detected in Staphylococcus xylosus, was found to confer resistance to 14-membered ring macrolides in Bacillus subtilis and Staphylococcus aureus. DNA-sequence analysis of the fragment revealed the presence of an open-reading frame, the deduced product of which was identical to one of the two ATP-binding domains encoded by the macrolide/streptogramin-B-resistance gene msrA of Staphylococcus epidermidis. The observation that a polypeptide homologous to the C-terminus of MsrA is capable of mediating erythromycin resistance in the absence of the N-terminal region is of significance both to the evolution and functional activity of members of the ATP-binding transport super-gene family.     

Comparative analysis of superantigen genes in Staphylococcus xylosus and Staphylococcus aureus isolates collected from a single mammary quarter of cows with mastitis

The purpose of this study was to analyze and compare genes encoding superantigens (SAgs) in Staphylococcus xylosus and Staphylococcus aureus isolates collected simultaneously from milk of the same cows with clinical mastitis. Genes encoding staphylococcal enterotoxins and enterotoxin-like proteins (sea-selu), toxic shock syndrome toxin 1 (tst-1) and exfoliative toxins (eta and etd) were investigated. It was found that among 30 isolates of S. xylosus, 16 (53.3%) harbored from 1 to 10 SAg genes. In total, in 16 SAg positive S. xylosus, 11 different enterotoxin genes were detected: sec, sed, seg, seh, sei, selm, seln, selo, selp, ser, selu and one etd gene encoding exfoliative toxin D. The most prevalent genes were ser, selu, and selo. Among all the positive isolates of S. xylosus, a total of 14 different SAg gene combinations were detected. One combination was repeated in 3 isolates, whereas the rest were detected only once. However, in the case of S. aureus all the 30 isolates harbored the same combination of SAg genes: seg, sei, selm, seln, selo and on the basis of PFGE analysis all belonged to the same clonal type. Also noteworthy was the observation that SAg genes detected in S. aureus have also been found in S. xylosus. The findings of this study further extend previous observations that SAg genes are present not only in S. aureus but also in coagulase-negative staphylococci, including S. xylosus. Therefore, taking into account that the SAg genes are encoded on mobile genetic elements it is possible that these genes can be transferred between different species of coexisting staphylococci.     

Antimicrobial activity of Staphylococcus xylosus from Italian sausages against Listeria monocytogenes

One hundred and twenty-five isolates of Micrococcaceae from Italian salami were tested for antagonistic activities against Listeria monocytogenes. Four isolates, identified as Staphylococcus xylosus , inhibited the growth of all five strains of L. monocytogenes tested. The antagonistic substances produced by strains 39A and 41A were inactivated by some proteases, whereas those from strains 1E and 27E were inactivated only by esterase and lipase. They are neither bacteriophages, nor lytic enzymes like lysostaphin.     

Proteomic analysis of cell surface proteins from Clostridium difficile

Clostridium difficile is a bacterium that causes disease of the large intestine, particularly after treatment with antibiotics. The bacterium produces two toxins (A and B) that are responsible for the pathology of the disease. In addition, a number of bacterial virulence factors associated with adhesion to the gut have previously been identified, including the cell wall protein Cwp66, the high-molecular weight surface layer protein (HMW-SLP) and the flagella. As the genome sequence predicts many other cell wall associated proteins, we have investigated the diversity of proteins in cell wall extracts, with the aim of identifying further virulence factors. We have used a number of methods to remove the proteins associated with the cell wall of C. difficile. Two of the resulting extracts, obtained using low pH glycine treatment and lysozyme digestion of the cell wall, have been analysed in detail by two-dimensional electrophoresis and mass spectrometry. One hundred and nineteen spots, comprising 49 different proteins, have been identified. The two surface layer proteins (SLPs) are the most abundant proteins, and we have also found components of the flagellum. Interestingly, we have also determined that a number of paralogs of the HMW-SLP are expressed, and these could represent targets for further investigation as virulence factors.     

Proteomic analysis of Brucella abortus cell envelope and identification of immunogenic candidate proteins for vaccine development

Brucella abortus is the etiologic agent of bovine brucellosis and causes a chronic disease in humans known as undulant fever. In livestock the disease is characterized by abortion and sterility. Live, attenuated vaccines such as S19 and RB51 have been used to control the spread of the disease in animals; however, they are considered unsafe for human use and they induce abortion in pregnant cattle. For the development of a safer and equally efficacious vaccine, immunoproteomics was utilized to identify novel candidate proteins from B. abortus cell envelope (CE). A total of 163 proteins were identified using 2-DE with MALDI-TOF MS and LC-MS/MS. Some of the major protein components include outer-membrane protein (OMP) 25, OMP31, Omp2b porin, and 60 kDa chaperonin GroEL. 2-DE Western blot analyses probed with antiserum from bovine and a human patient infected with Brucella identified several new immunogenic proteins such as fumarate reductase flavoprotein subunit, F0F1-type ATP synthase alpha subunit, and cysteine synthase A. The elucidation of the immunome of B. abortus CE identified a number of candidate proteins for developing vaccines against Brucella infection in bovine and humans.     

Cloning and restriction analysis of DNA conferring new quinolone antimicrobial agent resistance from Staphylococcus aureus and other coagulase-negative Staphylococcus species

DNA conferring resistance to new quinolone antimicrobial agents (NQR) in clinical isolates of Staphylococcus aureus and coagulase-negative staphylococci (CNS), S. epidermidis and S. haemolyticus, was analyzed after cloning in Escherichia coli. The NQR phenotypes were expressed in E. coli at lower levels. NQR gene(s)-carring HindIII fragments were very similar to each other among S. aureus or CNS, although the S. aureus fragments differed from the CNS fragments in terms of the NQR phenotypes and restriction endonuclease maps. The data suggest the possibility that the NQR genes have disseminated in evolutionarily distinct routes among S. aureus and CNS.     

Interactions between strains of Staphylococcus xylosus and Kocuria varians isolated from fermented meats

AIMS: To evaluate the interactions of Staphylococcus xylosus on Kocuria varians strains isolated from fermented meat products. Methods and Results: Interactions were assessed in vitro by agar spot test, agar well diffusion assay and spectrophotometric assay. The growth of K. varians (five strains) alone was compared with that in the presence of growing cells of S. xylosus (50 strains) or in the presence of heat-treated or untreated supernatants of S. xylosus. Sixteen strains stimulated the growth of K. varians K4, while four strains inhibited the K4 strain. Heated cell-free supernatants of S. xylosus did not have any effect on K. varians. The proteolytic activity of single strains or their combinations was assessed in vitro and in vivo by sodiumdodecylsulfate-polyacrylamide gel electrophoresis of sarcoplasmic protein extracts. Combinations of stimulatory strains of S. xylosus and K. varians showed a higher proteolytic activity compared with that of S. xylosus or K. varians alone. CONCLUSIONS: The interactions between strains may influence both the growth of the co-cultured strains and proteolysis, technologically relevant characteristics. SIGNIFICANCE AND IMPACT OF THE STUDY: The study of interactions between coagulase-negative cocci may guide the formulation of mixed strain starters for the production of fermented sausages.     

Structure-function analysis of the Rho-ADP-ribosylating exoenzyme C3stau2 from Staphylococcus aureus

Exoenzyme C3stau2 from Staphylococcus aureus is a new member of the family of C3-like ADP-ribosyltransferases that ADP-ribosylates RhoA, -B, and -C. Additionally, it modifies RhoE and Rnd3. Here we report on studies of the structure-function relationship of recombinant C3stau2 by site-directed mutagenesis. Exchange of Glu(180) with leucine caused a complete loss of both ADP-ribosyltransferase and NAD glycohydrolase activity. By contrast, exchange of the glutamine residue two positions upstream (Gln(178)) with lysine blocked ADP-ribosyltransferase activity without major changes in NAD glycohydrolase activity. NAD and substrate binding of this mutant protein was comparable to that of the recombinant wild type. Exchange of amino acid Tyr(175), which is part of the recently described ADP-ribosylating toxin turn-turn (ARTT) motif [Han, S., Arvai, A. S., Clancy, S. B., and Tainer, J. A. (2001) J. Mol.Biol. 305, 95-107], with alanine, lysine, or threonine caused a loss of or a decrease in ADP-ribosyltransferase activity but an increase in NAD glycohydrolase activity. Recombinant C3stau2 Tyr175Ala and Tyr175Lys were not precipitated by matrix-bound Rho, supporting a role of Tyr(175) in protein substrate recognition. Exchange of Arg(48) and/or Arg(85) resulted in a 100-fold reduced transferase activity, while the recombinant C3stau2 double mutant R48K/R85K was totally inactive. The data indicate that amino acid residues Arg(48), Arg(85), Tyr(175), Gln(178), and Glu(180) are essential for ADP-ribosyltransferase activity of recombinant C3stau2 and support the role of the ARTT motif in substrate recognition of RhoA by C3-like ADP-ribosyltransferases.     

Proteomic analysis of cell surface-associated proteins from probiotic Lactobacillus plantarum

In the present study, we used a proteomic approach to identify surface-associated proteins from the probiotic bacterium Lactobacillus plantarum 299v. Proteins were extracted from the cell surface using a mild wash in phosphate buffer and analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis. Gel bands were excised and in-gel digested with trypsin. The resulting peptides were analysed by capillary-LC-ESI-MS/MS. The peptide sequences were used for a database search and allowed identification of a total of 29 proteins, many of which could potentially be involved in the action of probiotics in the gastrointestinal tract. The results provide the basis for future studies on the molecular mechanisms of probiotics.     

Expression of glycocalyx by coagulase-negative Staphylococcus species isolated from bovine milk

Two hundred and six strains of coagulase-negative Staphylococcus species were assessed for expression of glycocalyx on serum soft agar, india ink and adherence techniques. The organisms were maintained on trypticase soy agar plates at 4 degrees C for 30 d (120 strains) or stored at -80 degrees C in skim milk for 90 d (60 strains). Additionally, 26 milk samples from cows known to have excreted coagulase-negative staphylococci were used to inoculate serum soft agar directly. Nine of 26 direct culture samples and 43 of 180 strains maintained for an extended period had diffuse-type growth on serum soft agar. The proportion that exhibited an unstained halo by india ink was similar regardless of storage time. Slime production determined by in vitro adherence revealed a higher proportion of positive strains than had been predicted by serum soft agar or india ink techniques. More strains of Staphylococcus chromogenes, Staph. epidermidis, Staph. hominis, Staph. simulans and Staph. warneri expressed glycocalyx than other coagulase-negative Staphylococcus species. These results suggest that most coagulase-negative staphylococci produce slime rather than a capsule. However, evidence for classical encapsulation was demonstrated in several strains by india ink. The finding that Staphylococcus species other than Staph. aureus isolated from bovine milk are capable of glycocalyx production may be of importance in investigations on the relationship between staphylococci and host defence mechanisms.