Function of teichoic acids and effect of novobiocin on control of Mg2+ at the bacterial membrane

Cell differentiation defines acute and chronic infection cell types in Staphylococcus aureus

A central question to biology is how pathogenic bacteria initiate acute or chronic infections. Here we describe a genetic program for cell-fate decision in the opportunistic human pathogen Staphylococcus aureus, which generates the phenotypic bifurcation of the cells into two genetically identical but different cell types during the course of an infection. Whereas one cell type promotes the formation of biofilms that contribute to chronic infections, the second type is planktonic and produces the toxins that contribute to acute bacteremia. We identified a bimodal switch in the agr quorum sensing system that antagonistically regulates the differentiation of these two physiologically distinct cell types. We found that extracellular signals affect the behavior of the agr bimodal switch and modify the size of the specialized subpopulations in specific colonization niches. For instance, magnesium-enriched colonization niches causes magnesium binding to S. aureusteichoic acids and increases bacterial cell wall rigidity. This signal triggers a genetic program that ultimately downregulates the agr bimodal switch. Colonization niches with different magnesium concentrations influence the bimodal system activity, which defines a distinct ratio between these subpopulations; this in turn leads to distinct infection outcomes in vitro and in an in vivo murine infection model. Cell differentiation generates physiological heterogeneity in clonal bacterial infections and helps to determine the distinct infection types.

While in hospital, patients can be unwittingly exposed to bacteria that can cause disease. These hospital-associated bacteria can lead to potentially life-threatening infections that may also complicate the treatment of the patients’ existing medical conditions. Staphylococcus aureus is one such bacterium, and it can cause several types of infection including pneumonia, blood infections and long-term infections of prosthetic devices.

It is thought that S. aureus is able to cause so many different types of infection because it is capable of colonizing distinct tissues and organs in various parts of the body. Understanding the biological processes that drive the different infections is crucial to improving how these infections are treated.

S. aureus lives either as an independent, free-swimming cell or as part of a community known as a biofilm. These different lifestyles dictate the type of infection the bacterium can cause, with free-swimming cells producing toxins that contribute to intense, usually short-lived, infections and biofilms promoting longer-term infections that are difficult to eradicate. However, it is not clear how a population of S. aureus cells chooses to adopt a particular lifestyle and whether there are any environmental signals that influence this decision.

Here, Garcia-Betancur et al. found that S. aureus populations contain small groups of cells that have already specialized into a particular lifestyle. These groups of cells collectively influence the choice made by other cells in the population. While both lifestyles will be represented in the population, environmental factors influence the numbers of cells that initially adopt each type of lifestyle, which ultimately affects the choice made by the rest of the population. For example, if the bacteria colonize a tissue or organ that contains high levels of magnesium ions, the population is more likely to form biofilms.

In the future, the findings of Garcia-Betancur et al. may help us to predict how an infection may develop in a particular patient, which may help to diagnose the infection more quickly and allow it to be treated more effectively.

Effects of temperature and sodium chloride concentration on the phospholipid and fatty acid compositions of a halotolerant Planococcus sp

The phospholipid headgroup composition and fatty acid composition of a gram-positive halotolerant Planococcus sp. (strain A4a) were examined as a function of growth temperature (5 to 35 degrees C) and NaCl content (0 to 1.5 M) of the growth medium. When the growth temperature was decreased, the relative amount of mono-unsaturated branched-chain fatty acids increased. When Planococcus sp. strain A4a was grown in media containing high NaCl concentrations, the relative amount of the major fatty acid, Ca15:0, increased. The relative amount of anionic phospholipid also increased when the NaCl concentration of the growth medium was increased. The increase in anionic phospholipid content resulted from a decrease in the relative mole percent content of phosphatidylethanolamine and an increase in the relative mole percent content of cardiolipin.

Chemical basis for selectivity of metal ions by the Bacillus subtilis cell wall

The use of equilibrium dialysis techniques established that isolated cell walls of Bacillus subtilis possess selective affinities for several cations. The binding of these cations to the cell wall was influenced by the presence of various functional groups in the peptidoglycan matrix. Selective chemical modification of the free carboxyl and amino groups showed that when amino groups were replaced by neutral, bulky, or negatively charged groups, the sites available for cation complexing generally increased. Introduction of positive charges into the wall resulted in a marked decrease in the numbers of metal binding sites and usually a decrease in the apparent association constants. Both teichoic acid and peptidoglycan contribute to the sites available for interaction with metals. Hill plots of equilibrium dialysis data suggest that metal binding to cell walls involves negative cooperativity. Competition between various metals for binding sites suggested that the cations complex with identical sites on the cell walls. When the hydrogen ion concentration was increased, the affinity of the walls for metals decreased, but the numbers of metal binding sites remained constant, suggesting that cations and protons also compete for the same sites.

Effects of streptomycin and novobiocin on Staphylococcus aureus gene expression

Streptomycin and novobiocin induced production of protein A and inhibited production of alpha- and beta-hemolysins in mutants of Staphylococcus aureus strains RN450 and RN1 resistant to these antibiotics. Streptomycin, but not novobiocin, also inhibited propagation of bacteriophages of serological group B, whereas phages of group A were unaffected. Streptomycin had to be present at adsorption of the phage, and 10 mM CACL2 reversed the inhibitory effect. Lysogenization and competence induction occurred in the presence of streptomycin, suggesting that some early phage genes were expressed.

Membrane lipoteichoic acid of Streptococcus pyogenes and its stabilized L-form and the effect of two antibiotics upon its cellular content

Membrane lipoteichoic acid continues to be synthesized by an osmotically fragile, stabilized L-form of Streptococcus pyogenes. Chromatographic and electrophoretic comparisons indicate that the lipid componenent of lipoteichoic acid in this L-form and its parental streptococcus is glycerophosphoryldiglucosyl diglyceride and not phosphatidylkojibiosyl diglyceride. Based upon dry weight determinations, the yield of lipoteichoic acid from the L-form is 0.19%, as compared with 0.97% from the streptococcus. When grown with bacitracin the L-form contains the same amount of teichoic acid as when grown without this antibiotic; however, its lipoteichoic acid content is reduced by 85%. Similarly, the L-form grown with novobiocin for 10 h contains only 17% of the teichoic acid found in control cells.

Magnesium and anion requirements of rodB mutants of Bacillus subtilis

rodB mutants of Bacillus subtilis have been found to require several hundred-fold more Mg2+ in a minimal growth medium than the wild type to achieve rapid growth. In the presence of all concentrations of Cl-, the organisms grow as deformed cocci, but with 10 mM Mg2+ and Br-, I-, or NO3- present they grow as rods. The morphology is then directly under the control of the concentration of both Mg2+ and anion. Originally, it was found that L-glutamic acid in the medium brought about the change from deformed spheres to rods. This amino acid will similarly function at a much lower concentration when the higher concentrations of Mg2+ and Cl- are also present. At a constant concentration of L-glutamate, the morphology can be controlled by varying the Mg2+ concentration. In the presence of Mg2+ and I-, the morphological change is temperature sensitive. At 30 C rods are formed and at 42 C deformed cocci are formed. The requirement of a rodB mutant for a high concentration of magnesium and the round morphology have been shown to be most probably due to a single mutation.

Cell wall composition of novobiocin-resistant pleiotropic mutant staphylococci

Physically purified cell walls were prepared from selected pleiotropic novobiocin-resistant staphylococcal strains. The quantitative amino acid, amino sugar, and phosphorus contents of these walls are reported. This pleiotype was culturally diagnosed by its inability to support the growth of typing phages, inability to release latent bacteriophage, failure to elaborate coagulase, altered sugar catabolic pattern, and resistance to novobiocin. The strains were divided into two groups on the basis of wall composition. The walls of both groups of strains appeared to possess at least two phosphorus-containing polymers. On group of strains contained elevated levels of phosphorus in the cell walls. The second group contained the novel amino sugar galactosamine in the cell walls. This amino sugar is probably associated with one of the phosphorus-containing wall polymers of this group. On the basis of the data presented, it is suggested that the pleiotropy of these strains is the result of genetic change in the control of the biosynthesis of teichoic acids.

Effect of inhibition of deoxyribonucleic acid and protein synthesis on the direction of cell wall growth in Streptococcus faecalis

Selective inhibition of protein synthesis in Streptococcus faecalis (ATCC 9790) was accompanied by a rapid and severe inhibition of cell division and a reduction of enlargement of cellular surface area. Continued synthesis of cell wall polymers resulted in rapid thickening of the wall to an extent not seen in exponential-phase populations. Thus, the normal direction of wall growth was changed from a preferential feeding out of new wall surface to that of thickening existing cell surfaces. However, the overall manner in which the wall thickened, from nascent septa toward polar regions, was the same in both exponential-phase and inhibited populations. In contrast, selective inhibition of deoxyribonucleic acid (DNA) synthesis using mitomycin C was accompanied by an increase in cellular surface area and by division of about 80% of the cells in random populations. Little or no wall thickening was observed until the synthesis of macromolecules other than DNA was impaired and further cell division ceased. Concomitant inhibition of both DNA and protein synthesis inhibited cell division but permitted an increase in average cell volume. In such doubly inhibited cells, walls thickened less than in cells inhibited for protein synthesis only. On the basis of the results obtained, a model for cell surface enlargement and cell division is presented. The model proposes that: (i) each wall enlargement site is influenced by an individual chromosome replication cycle; (ii) during chromosome replication peripheral surface enlargement would be favored over thickening (or septation); (iii) a signal associated with chromosome termination would favor thickening (and septation) at the expense of surface enlargement; and (iv) a factor or signal related to protein synthesis would be required for one or more of the near terminal stages of cell division or cell separation, or both.

Immunological properties of teichoic acids

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Teichoic acid of a stabilized L-form of Streptococcus pyogenes

A stabilized L-form of Streptococcus pyogenes continues to synthesize glycerol teichoic acid. This polymer was obtained from S. pyogenes and its L-form, treated in identical fashion, and compared. Highly purified glycerol teichoic acid from only the L-form was found to be devoid of d-alanine and to have a shorter chain length. Otherwise, the glycerol teichoic acid from these two organisms was found to be a 1,3-phosphodiester-linked glycerophosphate polymer substituted with d-glucose. Evidence is presented that most, if not all, of the glycerol teichoic acid in this streptococcus lies between the wall and membrane. A possible need for the continued synthesis of a minute amount of glycerol teichoic acid by this L-form for survival is discussed in terms of the known function of teichoic acids in bacteria.

The function of teichoic acids in cation control in bacterial membranes

1. The effects of teichoic acids on the Mg(2+)-requirement of some membrane-bound enzymes in cell preparations from Bacillus licheniformis A.T.C.C. 9945 were examined. 2. The biosynthesis of the wall polymers poly(glycerol phosphate glucose) and poly(glycerol phosphate) by membrane-bound enzymes is strongly dependent on Mg(2+), showing maximum activity at 10-15mm-Mg(2+). 3. When the membrane is in close contact with the cell wall and membrane teichoic acid, the enzyme systems are insensitive to added Mg(2+). The membrane appears to interact preferentially with the constant concentration of Mg(2+) that is bound to the phosphate groups of teichoic acid in the wall and on the membrane. When the wall is removed by the action of lysozyme the enzymes again become dependent on an external supply of Mg(2+). 4. A membrane preparation that retained its membrane teichoic acid was still dependent on Mg(2+) in solution, but the dependence was damped so that the enzymes exhibited near-maximal activity over a much greater range of concentrations of added Mg(2+); this preparation contained Mg(2+) bound to the membrane teichoic acid. The behaviour of this preparation could be reproduced by binding membrane teichoic acid to membranes in the presence of Mg(2+). Addition of membrane teichoic acid to reaction mixtures also had a damping effect on the Mg(2+) requirement of the enzymes, since the added polymer interacted rapidly with the membrane. 5. Other phosphate polymers behaved in a qualitatively similar way to membrane teichoic acid on addition to reaction mixtures. 6. It is concluded that in whole cells the ordered array of anionic wall and membrane teichoic acids provides a constant reservoir of bound bivalent cations with which the membrane preferentially interacts. The membrane teichoic acid is the component of the system which mediates the interaction of bound cations with the membrane. The anionic polymers in the wall scavenge cations from the medium and maintain a constant environment for the membrane teichoic acid. Thus a function of wall and membrane teichoic acids is to maintain the correct ionic environment for cation-dependent membrane systems.

Autolysis of microbial cells: salt activation of autolytic enzymes in a mutant of Staphylococcus aureus

The effect of various salts on the autolysis of cell wall of a ribitol teichoic acid-deficient mutant of Staphylococcus aureus H (strain 52A5 carrying tar-1) was compared with the parent strain. In the presence of high concentrations of certain salts such as 1.0 m NaCl, the mutant undergoes autolysis with the release of osmotically sensitive spheroplasts. The parent strain is not affected by these conditions. The stimulation of lysis is related to an activation of N-acylmuramyl-l-alanine amidase.

The lipid-teichoic acid complex in the cytoplasmic membrane of Streptococcus faecalis N.C.I.B. 8191

1. A lipid-teichoic acid complex was isolated from Streptococcus faecalis N.C.I.B. 8191. The covalent nature of the linkage between teichoic acid and lipid was established. 2. The complex exhibits macromolecular properties in solution, and ultracentrifugation studies show that these are due to micelle formation. 3. From chemical studies it is concluded that the teichoic acid is a poly(glycerol phosphate) in which some of the glycerol hydroxyl groups possess kojibiosyl [2-O-alpha-d-glucopyranosyl-(1-->2)-alpha-d- glucopyranosyl] substituents, together with d-alanine ester residues. 4. The lipid is 1-kojibiosyl diglyceride, already known as a membrane component of this organism, with probably a phosphatidyl substituent. The phosphatidyl kojibiosyl diglyceride is attached to the teichoic acid through a phosphodiester linkage, and the chain of the teichoic acid contains 28-35 units. 5. Although the complex represents the whole of the membrane teichoic acid in this organism, only about 12% of the membrane glycolipid is associated with teichoic acid. 6. Two phosphatidyl glycolipids, closely resembling that bearing the teichoic acid, were isolated from the lipids of the organism and were partly characterized.

Biosynthesis of the wall teichoic acid in Bacillus licheniformis

1. The biosynthesis of the wall teichoic acid, poly(glycerol phosphate glucose), has been studied with a particulate membrane preparation from Bacillus licheniformis A.T.C.C. 9945. The precursor CDP-glycerol supplies glycerol phosphate residues, whereas UDP-glucose supplies only glucose to the repeating structure of the polymer. 2. Synthesis proceeds through polyprenol phosphate derivatives, and chemical studies and pulse-labelling techniques show that the first intermediate is the phosphodiester, glucose polyprenol monophosphate. CDP-glycerol donates a glycerol phosphate residue to this to give a second intermediate, (glycerol phosphate glucose phosphate) polyprenol. 3. The glucose residue in the lipid intermediates has the beta configuration, and chain extension in the synthesis of polymer occurs by transglycosylation with inversion of anomeric configuration at two stages.