Chemical composition of the cell walls of Bacillus stearothermophilus

High-throughput, Highly Sensitive Analyses of Bacterial Morphogenesis Using Ultra Performance Liquid Chromatography

The bacterial cell wall is a network of glycan strands cross-linked by short peptides (peptidoglycan); it is responsible for the mechanical integrity of the cell and shape determination. Liquid chromatography can be used to measure the abundance of the muropeptide subunits composing the cell wall. Characteristics such as the degree of cross-linking and average glycan strand length are known to vary across species. However, a systematic comparison among strains of a given species has yet to be undertaken, making it difficult to assess the origins of variability in peptidoglycan composition. We present a protocol for muropeptide analysis using ultra performance liquid chromatography (UPLC) and demonstrate that UPLC achieves resolution comparable with that of HPLC while requiring orders of magnitude less injection volume and a fraction of the elution time. We also developed a software platform to automate the identification and quantification of chromatographic peaks, which we demonstrate has improved accuracy relative to other software. This combined experimental and computational methodology revealed that peptidoglycan composition was approximately maintained across strains from three Gram-negative species despite taxonomical and morphological differences. Peptidoglycan composition and density were maintained after we systematically altered cell size in Escherichia coli using the antibiotic A22, indicating that cell shape is largely decoupled from the biochemistry of peptidoglycan synthesis. High-throughput, sensitive UPLC combined with our automated software for chromatographic analysis will accelerate the discovery of peptidoglycan composition and the molecular mechanisms of cell wall structure determination.

Isolation and preparation of bacterial cell walls for compositional analysis by ultra performance liquid chromatography

The bacterial cell wall is critical for the determination of cell shape during growth and division, and maintains the mechanical integrity of cells in the face of turgor pressures several atmospheres in magnitude. Across the diverse shapes and sizes of the bacterial kingdom, the cell wall is composed of peptidoglycan, a macromolecular network of sugar strands crosslinked by short peptides. Peptidoglycan's central importance to bacterial physiology underlies its use as an antibiotic target and has motivated genetic, structural, and cell biological studies of how it is robustly assembled during growth and division. Nonetheless, extensive investigations are still required to fully characterize the key enzymatic activities in peptidoglycan synthesis and the chemical composition of bacterial cell walls. High Performance Liquid Chromatography (HPLC) is a powerful analytical method for quantifying differences in the chemical composition of the walls of bacteria grown under a variety of environmental and genetic conditions, but its throughput is often limited. Here, we present a straightforward procedure for the isolation and preparation of bacterial cell walls for biological analyses of peptidoglycan via HPLC and Ultra Performance Liquid Chromatography (UPLC), an extension of HPLC that utilizes pumps to deliver ultra-high pressures of up to 15,000 psi, compared with 6,000 psi for HPLC. In combination with the preparation of bacterial cell walls presented here, the low-volume sample injectors, detectors with high sampling rates, smaller sample volumes, and shorter run times of UPLC will enable high resolution and throughput for novel discoveries of peptidoglycan composition and fundamental bacterial cell biology in most biological laboratories with access to an ultracentrifuge and UPLC.

Peptidoglycan at its peaks: how chromatographic analyses can reveal bacterial cell wall structure and assembly

The peptidoglycan (PG) cell wall is a unique macromolecule responsible for both shape determination and cellular integrity under osmotic stress in virtually all bacteria. A quantitative understanding of the relationships between PG architecture, morphogenesis, immune system activation and pathogenesis can provide molecular-scale insights into the function of proteins involved in cell wall synthesis and cell growth. High-performance liquid chromatography (HPLC) has played an important role in our understanding of the structural and chemical complexity of the cell wall by providing an analytical method to quantify differences in chemical composition. Here, we present a primer on the basic chemical features of wall structure that can be revealed through HPLC, along with a description of the applications of HPLC PG analyses for interpreting the effects of genetic and chemical perturbations to a variety of bacterial species in different environments. We describe the physical consequences of different PG compositions on cell shape, and review complementary experimental and computational methodologies for PG analysis. Finally, we present a partial list of future targets of development for HPLC and related techniques.

Effect of restrictive temperature on cell wall synthesis in a temperature-sensitive mutant of Bacillus stearothermophilus

A temperature-sensitive mutant of Bacillus stearothermophilus, TS-13, was unable to grow above 58 degrees C, compared to 72 degrees C for the wild type. Actively growing TS-13 cells lysed within 2 h when exposed to a restrictive temperature of 65 degrees C. Peptidoglycan synthesis stopped within 10 to 15 min postshift before a shut down of other macromolecular syntheses. Composition of preexisting peptidoglycan was not altered, nor was new peptidoglycan of aberrant composition formed. No significant difference in autolysin activity was observed between the mutant and the wild type at 65 degrees C. Protoplasts of TS-13 cells were able to synthesize cell wall material at 52 degress C, but not at 65 degrees C. This wall material remained closely associated with the cell membrane at the outer surface of the protoplasts, forming small, globular, membrane-bound structures which could be visualized by electron microscopy. These structures reacted with fluorescent antibody prepared against purified cell walls. Production of this membrane-associated wall material could be blocked by bacitracin, which inhibited cell wall synthesis at the level of transport through the membrane. The data were in agreement with previous studies showing that at the restrictive temperature this mutant is unable to alter its membrane fatty acid and phospholipid composition with temperature such that it is not able to maintain a membrane lipid composition which permits normal membrane function at the restrictive temperature.

Characterization of a bacteriophage-induced, host-specific lytic enzyme from lysates of Bacillus stearothermophilus infected with bacteriophage TP-8

Phage TP-8 lysates of Bacillus stearothermophilus 4S or 4S(8) contain lytic activity exhibiting two pH optima, one at pH 6.5 and the other at pH 7.5. Using a variety of fractionation procedures, the two lytic activities could not be separated. At pH 7.5 the lytic enzyme is an endopeptidase which hydrolyzes the l-alanyl-d-glutamyl linkage in the peptide subunits of the cell wall peptidoglycan and at pH 6.5 it exhibits N-acetylmuramidase activity. Endopeptidase activity is inhibited by NaCl and neither lytic activity was significantly affected by divalent cations or ethylenediaminetetraacetic acid. Crude lysates contain 2.5 to 3.0 times more endopeptidase activity than N-acetylmuramidase activity. The ratio of the two lytic activities (endopeptidase/N-acetylmuramidase) changes to 1.3 to 1.7 during the course of purification, to 1.0 after isoelectric focusing, and 3.9 and 6.00 after exposure for 2 h at 60 and 65 C, respectively. We conclude that the two lytic activities may be associated with a single protein or a lytic enzyme complex composed of two enzymes. Lytic activity at pH 7.5 is more effective in solubilizing cells or cell walls than the lytic activity at pH 6.5. LiCl extracts of 4S and 4S(8) cells contain lytic activity exhibiting endopeptidase activity at pH 7.5 and N-acetylmuramidase activity at pH 6.5. Lytic activity in these LiCl extracts also has a number of other properties in common with those in lysates of phage TP-8. We proposed that the lytic enzyme(s) are not coded for by the phage genome but are part of the host autolytic system.

Effect of temperature on the growth and cell wall chemistry of a facultative thermophilic Bacillus

The morphology and cell wall composition of Bacillus coagulans, a facultative thermophile, were examined as a function of growth temperature. The morphology of the organism varied when it was grown at different temperatures; at 37 C the organism grew as individual cells which increased in length with increasing growth temperature. At 55 C it grew in long chains of cells. Cell wall prepared from cells grown at 37 C contained 44% teichoic acid by weight, whereas cells grown at 55 C contained 29% teichoic acid. Teichoic acid from these cells was a polymer of glycerol phosphate containing galactose and ester alanine. The ratio of ester alanine to phosphate was significantly higher in cell walls and teichoic acid from 37 C-grown cells compared with those from 55 C-grown cells. Other differences observed were that cells grown at 55 C contained a lower level of autolytic ability, produced cell walls which bound more Mg(2+), and contained less peptide cross-bridging in its peptidoglycan layer than cells grown at 37 C.

Phenotypes of pleiotropic-negative sporulation mutants of Bacillus subtilis

The phenotypic properties of representatives of the five genetic classes of pleiotropic-negative sporulation mutants have been investigated. Protease production, alkaline and neutral proteases, was curtailed in spoA mutants, but the remainder of mutant classes produced both proteases, albeit at reduced levels. The spoA and spoB mutants plaqued phi2 and phi15 at high efficiency, but the efficiency of plating of these phages on spoE, spoF, and spoH mutants was drastically reduced. Antibiotic was produced by the spoH mutants and to a degree by some spoF mutants, but the other classes did not produce detectable activity. The spoA mutants were less responsive to catabolite repression of histidase synthesis by glucose than was the wild type. Severe catabolite repression could be induced in spoA mutants by amino acid limitation, suggesting that the relaxation of catabolite repression observed is not due to a defect in the mechanism of catabolite repression. Although others have shown a perturbation in cytochrome regulation in spoA and spoB mutants, the primary dehydrogenases, succinate dehydrogenase and reduced nicotinamide adenine dinucleotide dehydrogenase, leading to these cytochromes are unimpaired in all mutant classes. A comparison of the structural components of cell walls and membranes of spoA and the wild type is made. The pleiotropic phenotypes of these mutants are discussed.

Peptidoglycan types of bacterial cell walls and their taxonomic implications

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Structure of the cell wall of Bacillus stearothermophiluys: mode of action of a thermophilic bacteriophage lytic enzyme

The mode of action of a bacteriophage lytic enzyme on cell walls of Bacillus stearothermophilus (NCA 1503-4R) has been investigated. The enzyme is an endopeptidase which catalyzes the hydrolysis of the l-alanyl-d-glutamyl linkage in peptide subunits of the cell wall peptidoglycan. Preliminary studies on the soluble components in lytic cell wall digests indicate that the glycan moiety is composed of alternating glucosamine and muramic acid; one half of the muramic acid residues contain the tripeptide, l-alanyl-d-glutamyldiaminopimelic acid, and the remaining residues contain the tetrapeptide, l-alanyl-d-glutamyldiaminopimeyl-d-alanine. Almost one half of the peptide subunits are involved in cross-linkages of chemotype I. A structure for the cell wall peptidoglycan is proposed in the light of these findings.

Isolation of spheroplast membranes and stability of spheroplasts of Bacillus stearothermophilus

Spheroplasts were prepared by lysozyme digestion of the cell wall and ruptured by suspension in 0.15 m NaCl, followed by centrifugation at 30,900 x g for 35 min, and by a final suspension in 0.05 m NaCl for 12 to 16 hr at 5 C. The membrane ghosts were washed four times in tris(hydroxylmethyl)aminomethane (Tris) magnesium buffer and once in distilled water. The intact membranes resembled empty sacs with narrow slits in which the cytoplasm was extruded. A 92% recovery of cell membrane was obtained with all membrane preparations. The spheroplasts do not require a stabilizing medium to keep them from rupturing, and they are stable for 2 to 3 hr when exposed to a temperature of 65 C. The membrane content of the cell increases with age of culture (mid-log, 16.5%; late-log, 17.0%; and stationary, 17.6%) and temperature of growth (55 C, 16.5%; and 65 C, 17.8%), and it is unaffected by composition of the growth medium. The ratio of the protein to lipid content of the membrane increases with the complexity of the medium, age of culture (mid-log, 3.65; late-log, 3.91; and stationary, 4.15), and temperature of growth (55 C, 3.65; and 65 C, 5.22). The ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) content of the membranes was 9.0 to 13.7% and 0.3 to 0.8%, respectively. Reducing sugar (determined as glucose) amounts to 0.9 to 1.0% of the membrane weight and did not significantly vary for the different membrane preparations. Medium composition, age of culture, and temperature of growth have no significant effect on the amount of each amino acid in the membrane. Aspartic acid, glutamic acid, alanine, leucine, and lysine are present in the greatest amount and represent 12.9 to 14.1%, 10.4 to 11.3%, 9.6 to 10.3%, 7.7 to 8.8%, and 7.6 to 8.5% of the membrane peptide, respectively. Prior to the rupture of the spheroplasts, 25.0, 15.7, and 50.0% of the protein, RNA, and DNA, respectively, is lost. In potassium phosphate-magnesium buffer without sucrose, 90% of the protein and RNA and 95% of the DNA is lost from the spheroplasts. In the presence of sucrose, the leakage of RNA and DNA is similar to that observed for spheroplasts suspended in Tris magnesium buffer; however, the leakage of protein is 2.4 times greater.

Purification and properties of a thermophilic bacteriophage lytic enzyme

A phage lytic enzyme was isolated from lysates of Bacillus stearothermophilus (NCA 1503-4R). The enzyme was purified 1,998-fold with a 27% recovery of enzyme activity. By use of polyacrylamide gel electrophoresis and sucrose gradient centrifugation the enzyme was judged free from protein contaminants. The lytic enzyme was active over a pH range of 6.0 to 7.0, with a maximum at 6.3, and it was stable between pH 7.0 and 8.0 and at 5.0 and unstable between pH 5.5 and 6.5. The temperature coefficient (Q(10)) was 2.27 between 35 and 45 C, 2.01 between 45 and 55 C, and 2.00 between 50 and 60 C. Lytic enzyme in 0.1 m sodium phosphate was not inactivated after a 1-hr exposure to temperatures below 65.5 C, whereas a 1% inactivation was observed at 70.6 C. A 2-hr exposure at 60.1, 65.5, and 70.6 C resulted in an inactivation of 1.2, 9.6, and 12.0%, respectively. A sodium phosphate concentration of at least 0.1 m was necessary for the prolonged exposure of lytic enzyme at 55 C (pH 6.3), whereas 0.005 m was required for maximal lytic activity. Lytic activity was stimulated 169, 165, and 160% by 10(-4)m Mg(++), Ca(++), and Mn(++), respectively. Lytic activity was inhibited 75% by 10(-4)m ethylenediaminetetraacetic acid (EDTA). The EDTA inhibition could be reversed by the addition of excess Mg(++), Ca(++), or Mn(++). Lytic activity was not affected by NaCl, KCl, or NH(4)Cl. Lytic activity was inhibited 100, 91, 25, 61, and 56% by 10(-4)m Hg(++), Cu(++), Zn(++), p-chloromercuribenzoate, and p-hydroxymercuribenzoate, respectively. Cysteine or 2-mercaptoethanol did not stimulate lytic activity, nor were these sulfhydryl compounds required for maintenance of enzyme activity during handling or storage. Cell walls were rapidly solubilized when incubated with lytic enzyme. Lytic action was complete after 1.5 min, with a 70% reduction in optical density (OD). Cell walls without lytic enzyme showed no reduction in OD during this period. The solubilization of N-terminal amino groups paralleled the reduction in OD and reached a level of 0.3 mumole/mg of cell wall after 4 min of incubation. Cell walls with and without lytic enzyme treatment showed a 3- and a 1.3-fold increase, respectively, in N-terminal amino groups after 3 hr of incubation. There was no release of reducing power in either the untreated cell wall suspensions or those treated with lytic enzyme. Electron micrographs of treated and untreated cell walls showed that the enzyme partially degrades the cell wall with the release of small wall fragments.