Arrangement of peptidoglycan in the cell wall of Staphylococcus spp

Bacterium-like particles derived from probiotics: progress, challenges and prospects

Bacterium-like particles (BLPs) are hollow peptidoglycan particles obtained from food-grade Lactococcus lactis inactivated by hot acid. With the advantage of easy preparation, high safety, great stability, high loading capacity, and high mucosal delivery efficiency, BLPs can load and display proteins on the surface with the help of protein anchor (PA), making BLPs a proper delivery system. Owning to these features, BLPs are widely used in the development of adjuvants, vaccine carriers, virus/antigens purification, and enzyme immobilization. This review has attempted to gather a full understanding of the technical composition, characteristics, applications. The mechanism by which BLPs induces superior adaptive immune responses is also discussed. Besides, this review tracked the latest developments in the field of BLPs, including Lactobacillus-derived BLPs and novel anchors. Finally, the main limitations and proposed breakthrough points to further enhance the immunogenicity of BLPs vaccines were discussed, providing directions for future research. We hope that further developments in the field of antigen delivery of subunit vaccines or others will benefit from BLPs.

β-Lactams against the Fortress of the Gram-Positive Staphylococcus aureus Bacterium

The biological diversity of the unicellular bacteria-whether assessed by shape, food, metabolism, or ecological niche-surely rivals (if not exceeds) that of the multicellular eukaryotes. The relationship between bacteria whose ecological niche is the eukaryote, and the eukaryote, is often symbiosis or stasis. Some bacteria, however, seek advantage in this relationship. One of the most successful-to the disadvantage of the eukaryote-is the small (less than 1 μm diameter) and nearly spherical Staphylococcus aureus bacterium. For decades, successful clinical control of its infection has been accomplished using β-lactam antibiotics such as the penicillins and the cephalosporins. Over these same decades S. aureus has perfected resistance mechanisms against these antibiotics, which are then countered by new generations of β-lactam structure. This review addresses the current breadth of biochemical and microbiological efforts to preserve the future of the β-lactam antibiotics through a better understanding of how S. aureus protects the enzyme targets of the β-lactams, the penicillin-binding proteins. The penicillin-binding proteins are essential enzyme catalysts for the biosynthesis of the cell wall, and understanding how this cell wall is integrated into the protective cell envelope of the bacterium may identify new antibacterials and new adjuvants that preserve the efficacy of the β-lactams.

Peptidoglycan layer and disruption processes in Bacillus subtilis cells visualized using quick-freeze, deep-etch electron microscopy

Peptidoglycan, which is the main component of the bacterial cell wall, is a heterogeneous polymer of glycan strands cross-linked with short peptides and is synthesized in cooperation with the cell division cycle. Although it plays a critical role in bacterial survival, its architecture is not well understood. Herein, we visualized the architecture of the peptidoglycan surface in Bacillus subtilis at the nanometer resolution, using quick-freeze, deep-etch electron microscopy (EM). Filamentous structures were observed on the entire surface of the cell, where filaments about 11 nm wide formed concentric circles on cell poles, filaments about 13 nm wide formed a circumferential mesh-like structure on the cylindrical part and a 'piecrust' structure was observed at the boundary. When growing cells were treated with lysozyme, the entire cell mass migrated to one side and came out from the cell envelope. Fluorescence labeling showed that lysozyme preferentially bound to a cell pole and cell division site, where the peptidoglycan synthesis was not complete. Ruffling of surface structures was observed during EM. When cells were treated with penicillin, the cell mass came out from a cleft around the cell division site. Outward curvature of the protoplast at the cleft seen using EM suggested that turgor pressure was applied as the peptidoglycan was not damaged at other positions. When muropeptides were depleted, surface filaments were lost while the rod shape of the cell was maintained. These changes can be explained on the basis of the working points of the chemical structure of peptidoglycan.

Cell shape dynamics during the staphylococcal cell cycle

Staphylococcus aureus is an aggressive pathogen and a model organism to study cell division in sequential orthogonal planes in spherical bacteria. However, the small size of staphylococcal cells has impaired analysis of changes in morphology during the cell cycle. Here we use super-resolution microscopy and determine that S. aureus cells are not spherical throughout the cell cycle, but elongate during specific time windows, through peptidoglycan synthesis and remodelling. Both peptidoglycan hydrolysis and turgor pressure are required during division for reshaping the flat division septum into a curved surface. In this process, the septum generates less than one hemisphere of each daughter cell, a trait we show is common to other cocci. Therefore, cell surface scars of previous divisions do not divide the cells in quadrants, generating asymmetry in the daughter cells. Our results introduce a need to reassess the models for division plane selection in cocci.

Staphylococci are spherical bacteria that divide in sequential orthogonal planes. Here, the authors use super-resolution microscopy to show that staphylococcal cells elongate before dividing, and that the division septum generates less than one hemisphere of each daughter cell, generating asymmetry.

Different walls for rods and balls: the diversity of peptidoglycan

Peptidoglycan performs the essential role of resisting turgor in the cell walls of most bacteria. It determines cell shape, and its biosynthesis is the target for many important antibiotics. The fundamental chemical building blocks of peptidoglycan are conserved: repeating disaccharides cross-linked by peptides. However, these blocks come in many varieties and can be assembled in different ways. So beyond the fundamental similarity, prodigious chemical, organizational and architectural diversity is revealed. Here, we track the evolution of our current understanding of peptidoglycan and underpinning technical and methodological developments. The origin and function of chemical diversity is discussed with respect to some well-studied example species. We then explore how this chemistry is manifested in elegant and complex peptidoglycan organization and how this is interpreted in different and sometimes controversial architectural models. We contend that emerging technology brings about the possibility of achieving a complete understanding of peptidoglycan chemistry, through architecture, to the way in which diverse species and populations of cells meet the challenges of maintaining viability and growth within their environmental niches, by exploiting the bioengineering versatility of peptidoglycan.

Peptidoglycan architecture can specify division planes in Staphylococcus aureus

Division in Staphylococci occurs equatorially and on specific sequentially orthogonal planes in three dimensions, resulting, after incomplete cell separation, in the 'bunch of grapes' cluster organization that defines the genus. The shape of Staphylococci is principally maintained by peptidoglycan. In this study, we use Atomic Force Microscopy (AFM) and fluorescence microscopy with vancomycin labelling to examine purified peptidoglycan architecture and its dynamics in Staphylococcus aureus and correlate these with the cell cycle. At the presumptive septum, cells were found to form a large belt of peptidoglycan in the division plane before the centripetal formation of the septal disc; this often had a 'piecrust' texture. After division, the structures remain as orthogonal ribs, encoding the location of past division planes in the cell wall. We propose that this epigenetic information is used to enable S. aureus to divide in sequentially orthogonal planes, explaining how a spherical organism can maintain division plane localization with fidelity over many generations.

Imaging the nanoscale organization of peptidoglycan in living Lactococcus lactis cells

Peptidoglycans provide bacterial cell walls with mechanical strength. The spatial organization of peptidoglycan has previously been difficult to study. Here, atomic force microscopy, together with cells carrying mutations in cell-wall polysaccharides, has allowed an in-depth study of these molecules.

The spatial organization of peptidoglycan, the major constituent of bacterial cell-walls, is an important, yet still unsolved issue in microbiology. In this paper, we show that the combined use of atomic force microscopy and cell wall mutants is a powerful platform for probing the nanoscale architecture of cell wall peptidoglycan in living Gram-positive bacteria. Using topographic imaging, we found that Lactococcus lactis wild-type cells display a smooth, featureless surface morphology, whereas mutant strains lacking cell wall exopolysaccharides feature 25-nm-wide periodic bands running parallel to the short axis of the cell. In addition, we used single-molecule recognition imaging to show that parallel bands are made of peptidoglycan. Our data, obtained for the first time on living ovococci, argue for an architectural feature of the cell wall in the plane perpendicular to the long axis of the cell. The non-invasive live cell experiments presented here open new avenues for understanding the architecture and assembly of peptidoglycan in Gram-positive bacteria.

cwrA, a gene that specifically responds to cell wall damage in Staphylococcus aureus

Transcriptional profiling data accumulated in recent years for the clinically relevant pathogen Staphylococcus aureus have established a cell wall stress stimulon, which comprises a coordinately regulated set of genes that are upregulated in response to blockage of cell wall biogenesis. In particular, the expression of cwrA (SA2343, N315 notation), which encodes a putative 63 amino acid polypeptide of unknown biological function, increases over 100-fold in response to cell wall inhibition. Herein, we seek to understand the biological role that this gene plays in S. aureus. cwrA was found to be robustly induced by all cell wall-targeting antibiotics tested - vancomycin, oxacillin, penicillin G, phosphomycin, imipenem, hymeglusin and bacitracin - but not by antibiotics with other mechanisms of action, including ciprofloxacin, erythromycin, chloramphenicol, triclosan, rifampicin, novobiocin and carbonyl cyanide 3-chlorophenylhydrazone. Although a DeltacwrA S. aureus strain had no appreciable shift in MICs for cell wall-targeting antibiotics, the knockout was shown to have reduced cell wall integrity in a variety of other assays. Additionally, the gene was shown to be important for virulence in a mouse sepsis model of infection.

Conformation of the phosphate D-alanine zwitterion in bacterial teichoic acid from nuclear magnetic resonance spectroscopy

The conformation of d-alanine (d-Ala) groups of bacterial teichoic acid is a central, yet untested, paradigm of microbiology. The d-Ala binds via the C-terminus, thereby allowing the amine to exist as a free cationic NH(3)(+) group with the ability to form a contact ion pair with the nearby anionic phosphate group. This conformation hinders metal chelation by the phosphate because the zwitterion pair is charge neutral. To the contrary, the repulsion of cationic antimicrobial peptides (CAMPs) is attributed to the presence of the d-Ala cation; thus the ion pair does not form in this model. Solid-state nuclear magnetic resonance (NMR) spectroscopy has been used to measure the distance between amine and phosphate groups within cell wall fragments of Bacillus subtilis. The bacteria were grown on media containing (15)N d-Ala and beta-chloroalanine racemase inhibitor. The rotational-echo double-resonance (REDOR) pulse sequence was used to measure the internuclear dipolar coupling, and the results demonstrate (1) the metal-free amine-to-phosphate distance is 4.4 A and (2) the amine-to-phosphate distance increases to 5.4 A in the presence of Mg(2+) ions. As a result, the zwitterion exists in a nitrogen-oxygen ion pair configuration providing teichoic acid with a positive charge to repel CAMPs. Additionally, the amine of d-Ala does not prevent magnesium chelation in contradiction to the prevailing view of teichoic acids in metal binding. Thus, the NMR-based description of teichoic acid structure resolves the contradictory models, advances the basic understanding of cell wall biochemistry, and provides possible insight into the creation of new antibiotic therapies.

Direct observation of Staphylococcus aureus cell wall digestion by lysostaphin

The advent of Staphylococcus aureus strains that are resistant to virtually all antibiotics has increased the need for new antistaphylococcal agents. An example of such a potential therapeutic is lysostaphin, an enzyme that specifically cleaves the S. aureus peptidoglycan, thereby lysing the bacteria. Here we tracked over time the structural and physical dynamics of single S. aureus cells exposed to lysostaphin, using atomic force microscopy. Topographic images of native cells revealed a smooth surface morphology decorated with concentric rings attributed to newly formed peptidoglycan. Time-lapse images collected following addition of lysostaphin revealed major structural changes in the form of cell swelling, splitting of the septum, and creation of nanoscale perforations. Notably, treatment of the cells with lysostaphin was also found to decrease the bacterial spring constant and the cell wall stiffness, demonstrating that structural changes were correlated with major differences in cell wall nanomechanical properties. We interpret these modifications as resulting from the digestion of peptidoglycan by lysostaphin, eventually leading to the formation of osmotically fragile cells. This study provides new insight into the lytic activity of lysostaphin and offers promising prospects for the study of new antistaphylococcal agents.

Cryo-electron microscopy of cell division in Staphylococcus aureus reveals a mid-zone between nascent cross walls

Cryo-electron microscopy of frozen-hydrated thin sections permits the observation of the real distribution of mass in biological specimens allowing the native structure of bacteria to be seen, including the natural orientation of their surface layers. Here, we use this approach to study the fine ultrastructure of the division site, or septum, of Staphylococcus aureus D(2)C. Frozen-hydrated sections revealed a differentiated cell wall at the septum, showing two high-density regions sandwiched between three low-density zones. The two zones adjacent to the membrane appeared as an extension of the periplasmic space seen in this organism's cell envelope and showed no distinguishing structures within them. Immediately next to these were higher-density zones that corresponded to nascent cross walls of the septum. Unexpectedly, a rather broad low-density zone was seen separating cross walls in the septum. This mid-zone of low density appeared inflated and without visible structures in isolated cell walls, which showed only the high-density zones of the septum. Here, we suggest that frozen-hydrated thin sections have captured a highly fragile septal region, the mid-zone, which results from the dynamic action of autolysis and actively separates daughter cells during division. The two zones next to the membranes are periplasmic spaces. Immediately next to these are the growing cross walls composed of peptidoglycan, teichoic acid and protein.

Native cell wall organization shown by cryo-electron microscopy confirms the existence of a periplasmic space in Staphylococcus aureus

The current perception of the ultrastructure of gram-positive cell envelopes relies mainly on electron microscopy of thin sections and on sample preparation. Freezing of cells into a matrix of amorphous ice (i.e., vitrification) results in optimal specimen preservation and allows the observation of cell envelope boundary layers in their (frozen) hydrated state. In this report, cryo-transmission electron microscopy of frozen-hydrated sections of Staphylococcus aureus D2C was used to examine cell envelope organization. A bipartite wall was positioned above the plasma membrane and consisted of a 16-nm low-density inner wall zone (IWZ), followed by a 19-nm high-density outer wall zone (OWZ). Observation of plasmolyzed cells, which were used to artificially separate the membrane from the wall, showed membrane vesicles within the space associated with the IWZ in native cells and a large gap between the membrane and OWZ, suggesting that the IWZ was devoid of a cross-linked polymeric cell wall network. Isolated wall fragments possessed only one zone of high density, with a constant level of density throughout their thickness, as was previously seen with the OWZs of intact cells. These results strongly indicate that the IWZ represents a periplasmic space, composed mostly of soluble low-density constituents confined between the plasma membrane and OWZ, and that the OWZ represents the peptidoglycan-teichoic acid cell wall network with its associated proteins. Cell wall differentiation was also seen at the septum of dividing cells. Here, two high-density zones were sandwiched between three low-density zones. It appeared that the septum consisted of an extension of the IWZ and OWZ from the outside peripheral wall, plus a low-density middle zone that separated adjacent septal cross walls, which could contribute to cell separation during division.

Cryo-electron microscopy reveals native polymeric cell wall structure in Bacillus subtilis 168 and the existence of a periplasmic space

Ultrarapid freezing of bacteria (i.e. vitrification) results in optimal preservation of native structure. In this study, cryo-transmission electron microscopy of frozen-hydrated sections was used to gain insight into the organization of the Bacillus subtilis 168 cell envelope. A bipartite structure was seen above the plasma membrane consisting of a low-density 22 nm region above which a higher-density 33 nm region or outer wall zone (OWZ) resided. The interface between these two regions appeared to possess the most mass. In intact and in teichoic acid-extracted wall fragments, only a single region was seen but the mass distribution varied from being dense on the inside to less dense on the outside (i.e. similar to the OWZ). In plasmolysed cells, the inner wall zone (IWZ)'s thickness expanded in size but the OWZ's thickness remained constant. As the IWZ expanded it became filled with plasma membrane vesicles indicating that the IWZ had little substance and was empty of the wall's polymeric network of peptidoglycan and teichoic acid. Together these results strongly suggest that the inner zone actually represents a periplasmic space confined between the plasma membrane and the wall matrix and that the OWZ is the peptidoglycan-teichoic acid polymeric network of the wall.

Atomic force microscopy of cell growth and division in Staphylococcus aureus

The growth and division of Staphylococcus aureus was monitored by atomic force microscopy (AFM) and thin-section transmission electron microscopy (TEM). A good correlation of the structural events of division was found using the two microscopies, and AFM was able to provide new additional information. AFM was performed under water, ensuring that all structures were in the hydrated condition. Sequential images on the same structure revealed progressive changes to surfaces, suggesting the cells were growing while images were being taken. Using AFM small depressions were seen around the septal annulus at the onset of division that could be attributed to so-called murosomes (Giesbrecht et al., Arch. Microbiol. 141:315-324, 1985). The new cell wall formed from the cross wall (i.e., completed septum) after cell separation and possessed concentric surface rings and a central depression; these structures could be correlated to a midline of reactive material in the developing septum that was seen by TEM. The older wall, that which was not derived from a newly formed cross wall, was partitioned into two different surface zones, smooth and gel-like zones, with different adhesive properties that could be attributed to cell wall turnover. The new and old wall topographies are equated to possible peptidoglycan arrangements, but no conclusion can be made regarding the planar or scaffolding models.

Purification and partial characterization of a murein hydrolase, millericin B, produced by Streptococcus milleri NMSCC 061

Streptococcus milleri NMSCC 061 was screened for antimicrobial substances and shown to produce a bacteriolytic cell wall hydrolase, termed millericin B. The enzyme was purified to homogeneity by a four-step purification procedure that consisted of ammonium sulfate precipitation followed by gel filtration, ultrafiltration, and ion-exchange chromatography. The yield following ion-exchange chromatography was 6.4%, with a greater-than-2,000-fold increase in specific activity. The molecular weight of the enzyme was 28,924 as determined by electrospray mass spectrometry. The amino acid sequences of both the N terminus of the enzyme (NH(2) SENDFSLAMVSN) and an internal fragment which was generated by cyanogen bromide cleavage (NH(2) SIQTNAPWGL) were determined by automated Edman degradation. Millericin B displayed a broad spectrum of activity against gram-positive bacteria but was not active against Bacillus subtilis W23 or Escherichia coli ATCC 486 or against the producer strain itself. N-Dinitrophenyl derivatization and hydrazine hydrolysis of free amino and free carboxyl groups liberated from peptidoglycan digested with millericin B followed by thin-layer chromatography showed millericin B to be an endopeptidase with multiple activities. It cleaves the stem peptide at the N terminus of glutamic acid as well as the N terminus of the last residue in the interpeptide cross-link of susceptible strains.

Localization of penicillin-binding proteins to the splitting system of Staphylococcus aureus septa by using a mercury-penicillin V derivative

Precise localization of penicillin-binding protein (PBP)-antibiotic complexes in a methicillin-sensitive Staphylococcus aureus strain (BB255), its isogenic heterogeneous methicillin-resistant transductant (BB270), and a homogeneous methicillin-resistant strain (Col) was investigated by high-resolution electron microscopy. A mercury-penicillin V (Hg-pen V) derivative was used as a heavy metal-labeled, electron-dense probe for accurately localizing PBPs in situ in single bacterial cells during growth. The most striking feature of thin sections was the presence of an abnormally large (17 to 24 nm in width) splitting system within the thick cross walls or septa of Hg-pen V-treated bacteria of all strains. Untreated control cells possessed a thin, condensed splitting system, 7 to 9 nm in width. A thick splitting system was also distinguishable in unstained thin sections, thereby confirming that the electron contrast of this structure was not attributed to binding of bulky heavy metal stains usually used for electron microscopy. Biochemical analyses demonstrated that Hg-pen V bound to isolated plasma membranes as well as sodium dodecyl sulfate-treated cell walls and that two or more PBPs in each strain bound to this antibiotic. In contrast, the splitting system in penicillin V-treated bacteria was rarely visible after 30 min in the presence of antibiotic. These findings suggest that while most PBPs were associated with the plasma membrane, a proportion of PBPs were located within the fabric of the cell wall, in particular, in the splitting system. Inhibition of one or more high-M(r) PBPs by beta-lactam antibiotics modified the splitting system and cross-wall structure, therefore supporting a role for these PBPs in the synthesis and architectural design of these structures in S. aureus.

The lysostaphin endopeptidase resistance gene (epr) specifies modification of peptidoglycan cross bridges in Staphylococcus simulans and Staphylococcus aureus

Staphylococcus simulans biovar staphylolyticus produces an extracellular glycylglycine endopeptidase (lysostaphin) that lyses other staphylococci by hydrolyzing the cross bridges in their cell wall peptidoglycans. The genes for endopeptidase (end) and endopeptidase resistance (epr) reside on plasmid pACK1. An 8.4-kb fragment containing end was cloned into shuttle vector pL150 and was then introduced into Staphylococcus aureus RN4220. The recombinant S. aureus cells produced endopeptidase and were resistant to lysis by the enzyme, which indicated that the cloned fragment also contained epr. Treatments to remove accessory wall polymers (proteins, teichoic acids, and lipoteichoic acids) did not change the endopeptidase sensitivity of walls from strains of S. simulans biovar staphylolyticus or of S. aureus with and without epr. Immunological analyses of various wall fractions showed that there were epitopes associated with endopeptidase resistance and that these epitopes were found only on the peptidoglycans of epr+ strains of both species. Treatment of purified peptidoglycans with endopeptidase confirmed that resistance or susceptibility of both species was a property of the peptidoglycan itself. A comparison of the chemical compositions of these peptidoglycans revealed that cross bridges in the epr+ cells contained more serine and fewer glycine residues than those of cells without epr. The presence of the 8.4-kb fragment from pACK1 also increased the susceptibility of both species to methicillin.

Fan-shaped ejections of regularly arranged murosomes involved in penicillin-induced death of staphylococci

Electron microscopic research into the murosomes of staphylococci has shown that the number of murosomes involved in penicillin-induced death varies depending on the experimental conditions employed. With 0.1 micrograms of penicillin G per ml, only 1 of a total of about 20 murosomes, the "killing murosome," completely perforated the pressure-stabilized peripheral cell wall during a three-step process. This strictly localized event was mainly attributed to a mechanical effect being comparable to the process of aneurysm formation. Wall perforation was also considered to mark the very moment of penicillin-induced death ("nonlytic killing event"), while bacteriolysis started only postmortem. By varying the osmolarity of the growth medium, the number of murosomes involved in penicillin-induced killing increased considerably, which resulted in the ejection of a fan-shaped row of murosomes at the second division plane. These data are compatible with the finding that, in untreated or chloramphenicol-treated staphylococci, the activation of the murosomes resulted in (i) the formation of regularly arranged "blebs" on the cell surface, containing traces of disintegrated wall material, and (ii) the subsequent liberation of the murosomes lying underneath, leaving behind their former sites in the peripheral wall as a row of regularly arranged "pores" in every division plane. The number, distribution, and positioning of these blebs corresponded with those of the pores and the original murosomes. The significance of wall autolysins liberated from the first division plane for penicillin-induced wall perforation at the second division plane is discussed.

Structure of the Staphylococcus aureus cell wall determined by the freeze-substitution method

The fine structure of the Staphylococcus aureus cell wall was determined by electron microscopy with the new technique of rapid freezing and substitution fixation. The surface of the cell wall was covered with a fuzzy coat which consisted of fine fibers or an electron-dense mass. Morphological examination of the cell wall, which was treated sequentially with sodium dodecyl sulfate, trypsin, and trichloroacetic acid, revealed that this coat was partially removed by trypsin digestion and was completely removed by trichloroacetic acid extraction but was not affected by sodium dodecyl sulfate treatment, suggesting that the fuzzy coat consists mostly of a complex of teichoic acids and proteins. This was confirmed by the application of the concanavalin A-ferritin technique for teichoic acid and antiferritin immunoglobulin G technique for protein A.

Effects of chitin and its soluble derivatives on survival of Vibrio cholerae O1 at low temperature

Chitin concentrations greater than 0.04% (wt/wt) protected cholera vibrios against killing at low temperature. This protective effect was detected with both the soluble form of chitin, glycol chitin, and the insoluble particulate form of chitin. Some amino acids or peptides also showed the same protective effect.

A model for the three-dimensional structure of peptidoglycan in staphylococci

Although the monomeric units of peptidoglycan in Staphylococcus aureus and other staphylococci are well known, the complete structure of the peptidoglycan has not been elucidated. The peptidoglycan monomeric unit may be divided into three parts: (1) glycan chain piece, consisting of N-acetylglucosaminyl-N-acetylmuramic acid; (2) connecting peptide extending from L-alanine to the alpha-amino group of L-lysine; (3) peptide chain piece, consisting of D-alanine, the remainder of L-lysine not included in the connecting peptide, and pentaglycine (S. aureus) or mixed glycine and serine residues (other staphylococci) attached to the epsilon amino group of lysine. The deformation of cross wall into hemisphere in the course of cell division, the distensibility of peptidoglycan, and the appearance of circular (? spiral) lines in the cross wall and on the surface of the newly-formed hemisphere are clues to the structure of peptidoglycan. In the proposed model, cross wall is formed as a linear spiral with 20 turns extending in a plane from periphery to center of the cell. During cell division, the cross wall is bisected. The cross wall spiral becomes a spiral forming the peripheral wall of a new hemisphere. The width of the spiral on the cell surface is maintained by rigid glycan chains and by covalent bonds linking turns of the spiral. The length of the spiral is about 30 times the diameter of the cell. Flexible polypeptide sheets consisting of parallel polypeptide chains run along the length of the spiral. Individual polypeptides contain an average of ten peptide chain pieces. The glycan chain is a helix with two disaccharide residues per turn; consequently consecutive connecting peptides project in opposite directions and are perpendicular both to the glycan chain and to the peptide chain. In cross wall, hydrogen bonding between polypeptide chains enables the polypeptide sheet to transmit changes in tension. The deformation of cross wall into peripheral wall requires doubling of the external surface area of the peptidoglycan. A change in the angle of the glycan chain with respect to the peptide chain results in an increase of the distance between peptide chains, causing the doubling of surface area. Implications of the model include explanations for the initiation of cell division and for the existence of osmotically growth-dependent staphylococci.

Cell surface characteristics of coagulase-negative staphylococci and their adherence to fluorinated poly(ethylenepropylene)

The ability of 21 nonencapsulated and 15 encapsulated coagulase-negative staphylococci (CNS) to adhere to xylene in xylene-water emulsions and to fluorinated poly(ethylenepropylene) (FEP) films revealed remarkable differences. Nonencapsulated CNS strains adhered well to FEP, whereas their adherence to xylene ranged widely. Encapsulated strains with low adherence to xylene showed slight adherence to FEP. Encapsulated strains which adhered well to xylene ranged widely in their adherence to FEP. It was concluded that results obtained from the xylene adherence test were not predictive of the adherence of CNS to the hydrophobic FEP surface. The number of nonwashed, slime-producing CNS strains adhering to FEP was similar to that of washed bacteria of the same strains. Bacterial adherence to FEP was decreased when FEP films were exposed to a solution containing extracellular products (EP) obtained from a slime-producing CNS strain. Bacterial adherence to xylene also decreased when the bacterial suspensions contained EP. Apparently, initial adherence of CNS to FEP and xylene is hampered by EP. Nonencapsulated and encapsulated CNS pretreated with proteolytic enzymes failed to adhere to xylene and FEP, indicating that intact surface proteins or constituents associated with surface proteins mediated their adherence to xylene and FEP. Freeze-etch replicas of a CNS strain adhering to FEP showed a smooth, flattened area on the bacterial surface at the contact site of the bacteria with the FEP, indicating that an external layer was present at the bacterial surface.

Cross wall synthesis and the arrangement of the wall polymers in the cell wall of Staphylococcus spp

The growing process and the fine structure of the cross wall of Staphylococcus were investigated by electron microscopy. Examination of the tangentially sectioned cross wall revealed that it was initially synthesized as a thin cell wall layer by an invaginated cytoplasmic membrane. The wall thickness soon increased by additional synthesis of the wall from the cytoplasmic membrane located at the side region of the cross wall. Scanning electron microscopic observation of sodium dodecyl sulfate-treated and mechanically separated cross walls revealed that the outer surface of the cross wall exhibits regular circular structures and the inner surface showed has an irregular surface. This indicates that cell wall materials were arranged in a regular circular manner in the initially synthesized thin layer. It is conceivable that in Staphylococcus spp. two cell wall synthesizing systems are present: wall-elongation synthesis in which wall materials are arranged in a regular circular manner and wall-thickening synthesis in which wall materials are arranged in an irregular manner.

Bacterial growth and division: genes, structures, forces, and clocks

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