The interaction of magnesium ions with teichoic acid

Lactobacillus casei extracellular vesicles stimulate EGFR pathway likely due to the presence of proteins P40 and P75 bound to their surface

In the complex interplay of beneficial bacteria with the host, there are few examples of bacterial metabolites and effector molecules that have been consistently identified. Protective effects on the intestinal epithelium have been ascribed to P40 and P75, two well characterized cell wall muramidases, present in the culture supernatant of strains belonging to the taxon Lactobacillus casei/paracasei/rhamnosus. This work reports that Lactobacillus casei BL23 extracellular vesicles (BL23 EVs) have a small size (17–20 nm or 24–32 nm, depending on the method used) and contain lipoteichoic acid (LTA). Interestingly, all detected P40 and most of P75 were associated to EVs and possibly located at their external surface, as shown by proteinase K digestion. Biosensor assays showed that both proteins bind LTA and vesicles, suggesting that they could bind to ligands like LTA present on BL23 EVs. Native BL23 EVs have a moderate proinflammatory effect and they were able to induce phosphorylation of the epidermal growth factor receptor (EGFR), showing an effect similar to purified P40 and P75 and leading to the conclusion that the activity described in the supernatant (postbiotic) of these bacteria would be mainly due to P40 and P75 bound to EVs.

Microbial Community Drivers in Anaerobic Granulation at High Salinity

In the recent years anaerobic sludge granulation at elevated salinities in upflow anaerobic sludge blanket (UASB) reactors has been investigated in few engineering based studies, never addressing the microbial community structural role in driving aggregation and keeping granules stability. In this study, the combination of different techniques was applied in order to follow the microbial community members and their structural dynamics in granules formed at low (5 g/L Na⁺) and high (20 g/L Na⁺) salinity conditions. Experiments were carried out in four UASB reactors fed with synthetic wastewater, using two experimental set-ups. By applying 16S rRNA gene analysis, the comparison of granules grown at low and high salinity showed that acetotrophic Methanosaeta harundinacea was the dominant methanogen at both salinities, while the dominant bacteria changed. At 5 g/L Na⁺, cocci chains of Streptoccoccus were developing, while at 20 g/L Na⁺ members of the family Defluviitaleaceae formed long filaments. By means of Fluorescence in Situ Hybridization (FISH) and Scanning Electron Microscopy (SEM), it was shown that aggregation of Methanosaeta in compact clusters and the formation of filaments of Streptoccoccus and Defluviitaleaceae during the digestion time were the main drivers for the granulation at low and high salinity. Interestingly, when the complex protein substrate (tryptone) in the synthetic wastewater was substituted with single amino acids (proline, leucine and glutamic acid), granules at high salinity (20 g/L Na⁺) were not formed. This corresponded to a decrease of Methanosaeta relative abundance and a lack of compact clustering, together with disappearance of Defluviitaleaceae and consequent absence of bacterial filaments within the dispersed biomass. In these conditions, a biofilm was growing on the glass wall of the reactor instead, highlighting that a complex protein substrate such as tryptone can contribute to granules formation at elevated salinity.

Structure and mechanism of TagA, a novel membrane-associated glycosyltransferase that produces wall teichoic acids in pathogenic bacteria

Staphylococcus aureus and other bacterial pathogens affix wall teichoic acids (WTAs) to their surface. These highly abundant anionic glycopolymers have critical functions in bacterial physiology and their susceptibility to β-lactam antibiotics. The membrane-associated TagA glycosyltransferase (GT) catalyzes the first-committed step in WTA biosynthesis and is a founding member of the WecB/TagA/CpsF GT family, more than 6,000 enzymes that synthesize a range of extracellular polysaccharides through a poorly understood mechanism. Crystal structures of TagA from T. italicus in its apo- and UDP-bound states reveal a novel GT fold, and coupled with biochemical and cellular data define the mechanism of catalysis. We propose that enzyme activity is regulated by interactions with the bilayer, which trigger a structural change that facilitates proper active site formation and recognition of the enzyme's lipid-linked substrate. These findings inform upon the molecular basis of WecB/TagA/CpsF activity and could guide the development of new anti-microbial drugs.

EPS Glycoconjugate Profiles Shift as Adaptive Response in Anaerobic Microbial Granulation at High Salinity

Anaerobic granulation at elevated salinities has been discussed in several analytical and engineering based studies. They report either enhanced or decreased efficiencies in relation to different Na⁺ levels. To evaluate this discrepancy, we focused on the microbial and structural dynamics of granules formed in two upflow anaerobic sludge blanket (UASB) reactors treating synthetic wastewater at low (5 g/L Na⁺) and high (20 g/L Na⁺) salinity conditions. Granules were successfully formed in both conditions, but at high salinity, the start-up inoculum quickly formed larger granules having a thicker gel layer in comparison to granules developed at low salinity. Granules retained high concentrations of sodium without any negative effect on biomass activity and structure. 16S rRNA gene analysis and Fluorescence in Situ Hybridization (FISH) identified the acetotrophic Methanosaeta harundinacea as the dominant microorganism at both salinities. Fluorescence lectin bar coding (FLBC) screening highlighted a significant shift in the glycoconjugate pattern between granules grown at 5 and 20 g/L of Na⁺, and the presence of different extracellular domains. The excretion of a Mannose-rich cloud-like glycoconjugate matrix, which seems to form a protective layer for some methanogenic cells clusters, was found to be the main distinctive feature of the microbial community grown at high salinity conditions.

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.

Toxicity of chlortetracycline and its metal complexes to model microorganisms in wastewater sludge

Complexation of antibiotics with metals is a well-known phenomenon. Wastewater treatment plants contain metals and antibiotics, thus it is essential to know the effect of these complexes on toxicity towards microorganisms, typically present in secondary treatment processes. In this study, stability constants and toxicity of chlortetracycline (CTC) and metal (Ca, Mg, Cu and Cr) complexes were investigated. The calculated stability constants of CTC-metal complexes followed the order: Mg-CTC>Ca-CTC>Cu-CTC>Cr-CTC. Gram positive Bacillus thuringiensis (Bt) and Gram negative Enterobacter aerogenes (Ea) bacteria were used as model microorganisms to evaluate the toxicity of CTC and its metal complexes. CTC-metal complexes were more toxic than the CTC itself for Bt whereas for Ea, CTC and its metal complexes showed similar toxicity. In contrast, CTC spiked wastewater sludge (WWS) did not show any toxic effect compared to synthetic sewage. This study provides evidence that CTC and its metal complexes are toxic to bacteria when they are biologically available. As for WWS, CTC was adsorbed to solid part and was not biologically available to show measurable toxic effects.

Changes in Sodium, Calcium, and Magnesium Ion Concentrations That Inhibit Geobacillus Biofilms Have No Effect on Anoxybacillus flavithermus Biofilms

This study investigated the effects of varied sodium, calcium, and magnesium concentrations in specialty milk formulations on biofilm formation by Geobacillus spp. and Anoxybacillus flavithermus. The numbers of attached viable cells (log CFU per square centimeter) after 6 to 18 h of biofilm formation by three dairy-derived strains of Geobacillus and three dairy-derived strains of A. flavithermus were compared in two commercial milk formulations. Milk formulation B had relatively high sodium and low calcium and magnesium concentrations compared with those of milk formulation A, but the two formulations had comparable fat, protein, and lactose concentrations. Biofilm formation by the three Geobacillus isolates was up to 4 log CFU cm(-2) lower in milk formulation B than in milk formulation A after 6 to 18 h, and the difference was often significant (P ≤ 0.05). However, no significant differences (P ≤ 0.05) were found when biofilm formations by the three A. flavithermus isolates were compared in milk formulations A and B. Supplementation of milk formulation A with 100 mM NaCl significantly decreased (P ≤ 0.05) Geobacillus biofilm formation after 6 to 10 h. Furthermore, supplementation of milk formulation B with 2 mM CaCl2 or 2 mM MgCl2 significantly increased (P ≤ 0.05) Geobacillus biofilm formation after 10 to 18 h. It was concluded that relatively high free Na(+) and low free Ca(2+) and Mg(2+) concentrations in milk formulations are collectively required to inhibit biofilm formation by Geobacillus spp., whereas biofilm formation by A. flavithermus is not impacted by typical cation concentration differences of milk formulations.

Equilibrium binding behavior of magnesium to wall teichoic acid

Peptidoglycan and teichoic acids are the major cell wall components of Gram-positive bacteria that obtain and sequester metal ions required for biochemical processes. The delivery of metals to the cytoplasmic membrane is aided by anionic binding sites within the peptidoglycan and along the phosphodiester polymer of teichoic acid. The interaction with metals is a delicate balance between the need for attraction and ion diffusion to the membrane. Likewise, metal chelation from the extracellular fluid must initially have strong binding energetics that weaken within the cell wall to enable ion release. We employed atomic absorption and equilibrium dialysis to measure the metal binding capacity and metal binding affinity of wall teichoic acid and Mg2+. Data show that Mg2+ binds to WTA with a 1:2Mg2+ to phosphate ratio with a binding capacity of 1.27 μmol/mg. The affinity of Mg2+ to WTA was also found to be 41×10(3) M(-1) at low metal concentrations and 1.3×10(3) M(-1) at higher Mg2+ concentrations due to weakening electrostatic effects. These values are lower than the values describing Mg2+ interactions with peptidoglycan. However, the binding capacity of WTA is 4 times larger than peptidoglycan. External WTA initially binds metals with positive cooperativity, but metal binding switches to negative cooperativity, whereas interior WTA binds metals with only negative cooperativity. The relevance of this work is to describe changes in metal binding behavior depending on environment. When metals are sparse, chelation is strong to ensure survival yet the binding weakens when essential minerals are abundant.

Standardized assay medium to measure Lactococcus lactis enzyme activities while mimicking intracellular conditions

Knowledge of how the activity of enzymes is affected under in vivo conditions is essential for analyzing their regulation and constructing models that yield an integrated understanding of cell behavior. Current kinetic parameters for Lactococcus lactis are scattered through different studies and performed under different assay conditions. Furthermore, assay conditions often diverge from conditions prevailing in the intracellular environment. To establish uniform assay conditions that resemble intracellular conditions, we analyzed the intracellular composition of anaerobic glucose-limited chemostat cultures of L. lactis subsp. cremoris MG 1363. Based on this, we designed a new assay medium for enzyme activity measurements of growing cells of L. lactis, mimicking as closely as practically possible its intracellular environment. Procedures were optimized to be carried out in 96-well plates, and the reproducibility and dynamic range were checked for all enzyme activity measurements. The effects of freezing and the carryover of ammonium sulfate from the addition of coupling enzymes were also established. Activities of all 10 glycolytic and 4 fermentative enzymes were measured. Remarkably, most in vivo-like activities were lower than previously published data. Yet, the ratios of V(max) over measured in vivo fluxes were above 1. With this work, we have developed and extensively validated standard protocols for enzyme activity measurements for L. lactis.

In vitro analysis of the Staphylococcus aureus lipoteichoic acid synthase enzyme using fluorescently labeled lipids

Lipoteichoic acid (LTA) is an important cell wall component of Gram-positive bacteria. The key enzyme responsible for polyglycerolphosphate lipoteichoic acid synthesis in the Gram-positive pathogen Staphylococcus aureus is the membrane-embedded lipoteichoic acid synthase enzyme, LtaS. It is presumed that LtaS hydrolyzes the glycerolphosphate head group of the membrane lipid phosphatidylglycerol (PG) and catalyzes the formation of the polyglycerolphosphate LTA backbone chain. Here we describe an in vitro assay for this new class of enzyme using PG with a fluorescently labeled fatty acid chain (NBD-PG) as the substrate and the recombinant soluble C-terminal enzymatic domain of LtaS (eLtaS). Thin-layer chromatography and mass spectrometry analysis of the lipid reaction products revealed that eLtaS is sufficient to cleave the glycerolphosphate head group from NBD-PG, resulting in the formation of NBD-diacylglycerol. An excess of soluble glycerolphosphate could not compete with the hydrolysis of the fluorescently labeled PG lipid substrate, in contrast to the addition of unlabeled PG. This indicates that the enzyme recognizes and binds other parts of the lipid substrate, besides the glycerolphosphate head group. Furthermore, eLtaS activity was Mn(2+) ion dependent; Mg(2+) and Ca(2+) supported only weak enzyme activity. Addition of Zn(2+) or EDTA inhibited enzyme activity even in the presence of Mn(2+). The pH optimum of the enzyme was 6.5, characteristic for an enzyme that functions extracellularly. Lastly, we show that the in vitro assay can be used to study the enzyme activities of other members of the lipoteichoic acid synthase enzyme family.

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.

Rapid removal of lead and cadmium from water by specific lactic acid bacteria

Cadmium and lead are highly toxic metals. People are exposed to them primarily through food and water. Available conventional methods (precipitation, flocculation, ion exchange, and membrane filtration) for removal of these metals from water at low concentrations are claimed to be expensive and inefficient. Different microbes have been proposed to be an efficient and economical alternative in heavy metal removal from water. In this work, specific lactic acid bacteria (LAB) were assessed for their ability to remove cadmium and lead from water. Significant removal was observed, and it was found to be metal and bacterial strain specific. Removal was a fast, metabolism-independent surface process. It was also strongly influenced by pH, indicating that ion exchange mechanisms could be involved. The most effective metal removers were Bifidobacterium longum 46, Lactobacillus fermentum ME3 and Bifidobacterium lactis Bb12. The highest maximum cadmium and lead removal capacities of 54.7 mg metal/g and 175.7 mg/g dry biomass, respectively, were obtained with B. longum 46.

Wall teichoic acid polymers are dispensable for cell viability in Bacillus subtilis

An extensive literature has established that the synthesis of wall teichoic acid in Bacillus subtilis is essential for cell viability. Paradoxically, we have recently shown that wall teichoic acid biogenesis is dispensable in Staphylococcus aureus (M. A. D'Elia, M. P. Pereira, Y. S. Chung, W. Zhao, A. Chau, T. J. Kenney, M. C. Sulavik, T. A. Black, and E. D. Brown, J. Bacteriol. 188:4183-4189, 2006). A complex pattern of teichoic acid gene dispensability was seen in S. aureus where the first gene (tarO) was dispensable and later acting genes showed an indispensable phenotype. Here we show, for the first time, that wall teichoic acid synthesis is also dispensable in B. subtilis and that a similar gene dispensability pattern is seen where later acting enzymes display an essential phenotype, while the gene tagO, whose product catalyzes the first step in the pathway, could be deleted to yield viable mutants devoid of teichoic acid in the cell wall.

Cation-induced transcriptional regulation of the dlt operon of Staphylococcus aureus

Lipoteichoic and wall teichoic acids (TA) are highly anionic cell envelope-associated polymers containing repeating polyglycerol/ribitol phosphate moieties. Substitution of TA with D-alanine is important for modulation of many cell envelope-dependent processes, such as activity of autolytic enzymes, binding of divalent cations, and susceptibility to innate host defenses. D-Alanylation of TA is diminished when bacteria are grown in medium containing increased NaCl concentrations, but the effects of increased salt concentration on expression of the dlt operon encoding proteins mediating D-alanylation of TA are unknown. We demonstrate that Staphylococcus aureus transcriptionally represses dlt expression in response to high concentrations of Na(+) and moderate concentrations of Mg(2+) and Ca(2+) but not sucrose. Changes in dlt mRNA are induced within 15 min and sustained for several generations of growth. Mg(2+)-induced dlt repression depends on the ArlSR two-component system. Northern blotting, reverse transcription-PCR, and SMART-RACE analyses suggest that the dlt transcript begins 250 bp upstream of the dltA start codon and includes an open reading frame immediately upstream of dltA. Chloramphenicol transacetylase transcriptional fusions indicate that a region encompassing the 171 to 325 bp upstream of dltA is required for expression and Mg(2+)-induced repression of the dlt operon in S. aureus.

Selective accumulation of light or heavy rare earth elements using gram-positive bacteria

The accumulation of samarium from a solution only containing samarium by Arthrobacter nicotianae was examined. The amount of accumulated samarium was strongly affected by the concentration of samarium and pH of the solution. The accumulation of samarium by the strain was very rapid and reached equilibrium within 3h. The accumulation of samarium-europium or europium-gadolinium from the solution containing the two metals using various actinomycetes and gram-positive bacteria was also examined. Most of the tested strains could accumulate similar amounts of samarium and europium; however, most of the tested strains could accumulate a greater amount of europium than gadolinium. Especially, the amounts of accumulated europium using gram-positive bacteria were higher than those using actinomycetes. The selective accumulations of light or heavy rare earth elements (REEs) using A. nicotianae and Streptomyces albus were also examined. The amounts of accumulated samarium and europium were higher than those of the other light REEs using both microorganisms. S. albus can accumulate greater lutetium than other REEs from a solution containing yttrium and eight heavy REEs. On the other hand, A. nicotianae can accumulate higher amounts of terbium and ytterbium than that of the other heavy REEs from the same solution. A. nicotianae can also accumulated higher amounts of Sm than other REEs from a solution containing six light REEs.

The cell wall of lactic acid bacteria: surface constituents and macromolecular conformations

A variety of strains of the genus Lactobacillus was investigated with respect to the structure, softness, and interactions of their outer surface layers in order to construct structure-property relations of the Gram-positive bacterial cell wall. The role of the conformational properties of the constituents of the outer cell-wall layers and their spatial distribution on the cell wall is emphasized. Atomic force microscopy was used to resolve the surface structure, interactions, and softness of the bacterial cell wall at nanometer-length scales and upwards. The pH-dependence of the electrophoretic mobility and a novel interfacial adhesion assay were used to analyze the average physicochemical properties of the bacterial strains. The bacterial surface is smooth when a compact layer of globular proteins constitutes the outer surface, e.g., the S-layer of L. crispatus DSM20584. In contrast, for two other S-layer containing strains (L. helveticus ATCC12046 and L. helveticus ATCC15009), the S-layer is covered by polymeric surface constituents which adopt a much more extended conformation and which confer a certain roughness to the surface. Consequently, the S-layer is important for the overall surface properties of L. crispatus, but not for the surface properties of L. helveticus. Both surface proteins (L. crispatus DSM20584) and (lipo)teichoic acids (L. johnsonii ATCC332) confer hydrophobic properties to the bacterial surface whereas polysaccharides (L. johnsonii DSM20533 and L. johnsonii ATCC 33200) render the bacterial surface hydrophilic. Using the interfacial adhesion assay, it was demonstrated that hydrophobic groups within the cell wall adsorb limited quantities of hydrophobic compounds. The present work demonstrates that the impressive variation in surface properties displayed by even a limited number of genetically-related bacterial strains can be understood in terms of established colloidal concepts, provided that sufficiently detailed structural, chemical, and conformational information on the surface constituents is available.

A continuum of anionic charge: structures and functions of D-alanyl-teichoic acids in gram-positive bacteria

Teichoic acids (TAs) are major wall and membrane components of most gram-positive bacteria. With few exceptions, they are polymers of glycerol-phosphate or ribitol-phosphate to which are attached glycosyl and D-alanyl ester residues. Wall TA is attached to peptidoglycan via a linkage unit, whereas lipoteichoic acid is attached to glycolipid intercalated in the membrane. Together with peptidoglycan, these polymers make up a polyanionic matrix that functions in (i) cation homeostasis; (ii) trafficking of ions, nutrients, proteins, and antibiotics; (iii) regulation of autolysins; and (iv) presentation of envelope proteins. The esterification of TAs with D-alanyl esters provides a means of modulating the net anionic charge, determining the cationic binding capacity, and displaying cations in the wall. This review addresses the structures and functions of D-alanyl-TAs, the D-alanylation system encoded by the dlt operon, and the roles of TAs in cell growth. The importance of dlt in the physiology of many organisms is illustrated by the variety of mutant phenotypes. In addition, advances in our understanding of D-alanyl ester function in virulence and host-mediated responses have been made possible through targeted mutagenesis of dlt. Studies of the mechanism of D-alanylation have identified two potential targets of antibacterial action and provided possible screening reactions for designing novel agents targeted to D-alanyl-TA synthesis.

The effects of magnesium, calcium and EDTA on slime production by Staphylococcus epidermidis strains

Effect of magnesium, calcium and EDTA on slime production by 15 slime-positive and 13 slime-negative Staphylococcus epidermidis strains isolated from various clinical specimens was determined. The slime production on tryptic soy broth was significantly enhanced after addition of 128 mumol/L Mg2+. Similarly, the addition of Ca2+ caused a significant increase in slime production of all tested strains when concentration of Ca2+ exceeded 64 mumol/L. In contrast, in the presence of EDTA the slime production by all strains was significantly reduced. Hence Ca2+ and Mg2+ increase slime production of S. epidermidis. This finding is important in the context of the pathogenesis of biomedical implant infections caused by S. epidermidis.

Isolation and characterization of teichoic acid-lake substance as an adhesin of Staphylococcus aureus to HeLa cells

A cell wall component that bound to HeLa cells (HeLa cell-binding CWC) was isolated from a clinical isolate of Staphylococcus aureus. The HeLa cell-binding CWC was resistant to heat (100 C, 1 hr) and proteases, did not stain with Coomassie Brilliant Blue R-250 on SDS-PAGE but stained as a broad band with antiserum against the strain on Western blots. These data suggest that the HeLa cell-binding CWC is not a protein, and may be teichoic acid. Purified teichoic acid bound to HeLa cells, whereas fractions without teichoic acid did not. In Western blots, HeLa cell-binding CWC appeared as a broad band of less than 35 kDa, similar to that of purified teichoic acid. These data suggest that the HeLa cell-binding CWC obtained in this study is teichoic acid. Teichoic acid inhibited S. aureus adherence to HeLa cells and bound to the cells time and dose dependently, in a saturable and reversible manner, and therefore appears to be an adhesin of S. aureus to HeLa cells.

Competitive binding of calcium and magnesium to streptococcal lipoteichoic acid

Equilibrium dialysis was used to investigate the binding capacity and affinity of lipoteichoic acid (LTA) from the Gram-positive bacterium Streptococcus sanguis for calcium and magnesium by a competitive method. LTA was shown to bind approx. 1 mol of either calcium or magnesium per mole phosphate. Calcium and magnesium dissociation constants were found to be 8.39 +/- 0.31 mmol/l and 15.01 +/- 2.01 mmol/l respectively, indicating that S. sanguis LTA will preferentially bind calcium. LTA may act as a calcium buffer by reducing the free calcium concentration to which the cell is exposed. The capacity to produce large quantities of LTA could thus be as important as aciduricity in selection of species at caries-prone sites.

Iron-binding affinity of bacterial vaccine polysaccharides which contain phosphodiester linkages as part of the polymer chain and of other polyphosphates, including DNA

The interaction of iron (II) with bacterial polysaccharides, possessing phosphodiester bonds as part of their polymer chain, has been studied by equilibrium binding dialysis using atomic absorption spectrophotometry. Ferrous ions were found to bind with a stoichiometry of one per two phosphates and with a binding constant of about 2.5 x 10(3) M-1. Similar results, but with larger (ca 1 x 10(4) M-1) binding constants were observed with DNA. This interaction helps explain the depolymerization of polyphosphates which has been observed in the presence of iron salts, and highlights the need to avoid iron contamination of vaccines (and other substances) which contain phosphodiester bonds. The interaction may also be a means of iron sequestration in bacteria which possess these cell-surface polyphosphates.

The effects of magnesium, calcium, EDTA, and pH on the in vitro adhesion of Staphylococcus epidermidis to plastic

The effects of increasing concentrations of magnesium (Mg2+), calcium (Ca2+) or EDTA, and pH on the adhesion of five slime-positive strains of Staphylococcus epidermidis (Se+) to plastic were examined using an in vitro microwell assay. The addition of Mg2+ (as either MgSO4 or MgCl2) to the bacterial suspension in concentrations as low as 16 microM significantly enhanced the adhesion of all test strains to plastic (P < 0.001). Similarly, the addition of Ca2+ (as CaCl2) in concentrations exceeding 128 microM produced a significant increase in the adhesion of all test strains, but not to the extent observed with Mg2+. In contrast, the adhesion of all test strains to plastic was significantly reduced in the presence of EDTA at concentrations greater than 8 mM. However, EDTA in concentrations as low as 0.25 mM caused a significant decrease in the adhesion of two strains of Se+. The effect of pH was variable, but at a pH of 5.0 and 6.0, the adhesion of all test strains was significantly reduced compared to control values at a pH of 7.0. Two strains showed a significant increase in adhesion at a pH of 8.0. We also compared the effects of these variables on the adherence of a slime-negative phase variant derived from a slime-positive parent strain. With the exception of pH, the adhesion of both strains in response to increasing divalent cations or EDTA was similar. These data indicate that, in addition to hydrophobic interactions, ligand-specific binding, and slime production, pH and divalent cations, especially Mg2+, are important determinants of the adhesion of S. epidermidis to plastic surfaces in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and characterization of lipoteichoic acid, a cell envelope component involved in preventing phage adsorption, from Lactococcus lactis subsp. cremoris SK110

The cell envelope of the phage-resistant Lactococcus lactis subsp. cremoris SK110 differed from its phage-sensitive variant by the presence of a galactosyl-containing component. This component was present in material obtained from SK110 by a mild alkali treatment. In a similar fraction extracted from SK112, no galactosyl-containing components were detected. With respect to gel permeation chromatography and electrophoretic mobility, identical characteristics of the alkali-extracted material and purified lipoteichoic acid (LTA) were measured. Chemical analysis of the latter component showed the absence of galactose in LTA isolated from SK112, whereas it was present in LTA obtained from SK110. In this paper, we propose that galactosyl-containing LTA is involved in preventing phage adsorption to L. lactis subsp. cremoris SK110.

Cell Surface Characteristics of Bacteriophage-Resistant Lactococcus lactis subsp. cremoris SK110 and Its Bacteriophage-Sensitive Variant SK112

Several cell surface characteristics of bacteriophage-resistant Lactococcus lactis subsp. cremoris SK110 were compared with those of its phage-sensitive derivative SK112. After centrifugation, SK110 cells resisted suspension more strongly than SK112 cells. SK112 was more negatively charged and had a more hydrophobic cell surface than SK110. Furthermore, SK112 was agglutinated in the presence of concanavalin A, whereas SK110 was not. The opposite was observed upon incubation of cells of either strain with a lectin from Ricinus communis. A mild alkali treatment decreased the differences in the cell surface characteristics of the two strains remarkably.

Structure of macroamphiphiles from several Bifidobacterium strains

Lipoteichoic acid-like substances, macroamphiphiles, were isolated from cell homogenates of Bifidobacterium bifidum YIT 4007 and YIT 4013, Bifidobacterium breve YIT 4010 and YIT 4014, and Bifidobacterium longum YIT 4021 by phenol extraction followed by nuclease digestion, gel chromatography, ion-exchange chromatography, and hydrophobic interaction chromatography. The macroamphiphile preparations from these five strains contained D-glucose, D-galactose, glycerol, phosphorus, L-alanine, and fatty acids in molar ratios of 1.00, 1.57 to 1.95, 1.02 to 1.99, 0.97 to 1.72, 0.15 to 0.46, and 0.16 to 0.43. Data from structural analyses including methylation, 1H nuclear magnetic resonance measurement, alkaline hydrolysis, mild acid hydrolysis, and hydrogen fluoride treatment led to the most likely common structure for the macroamphiphiles of the examined strains, (formula; see text) where Gro-P is glycerophosphate, m is the number of repeating units of galactofuranan, and n is the number of repeating units of glucan. Whereas the polymers from the respective strains differed in the numbers of repeating units of the galactofuranan and glucan moieties and in the number of fatty acid residues, the proposed structure is essentially the same as that reported previously for the macroamphiphile of B. bifidum subsp. pennsylvanicum DSM 20239 by W. Fischer (Eur. J. Biochem. 165:639-646, 1987).

Studies on the conformation of and metal ion binding by teichoic acid of Staphylococcus aureus

Teichoic acid (TA) isolated from the gram-positive bacteria S. aureus binds cationic dyes like pinacyanol (PCYN), 1,9-dimethyl methylene blue, acridine orange, etc., depicting blue-shifted metachromasia, and they bind the cationic dye carbocyanine depicting the red-shifted J band. TAs do not show any uv absorption band, and exhibition of tailing CD in the short uv region hints at its chiral conformation. Chiral conformation of TA has been confirmed from the induction of strong biphasic CD in the TA-carbocyanine system. Relative affinities for Ca2+, Mg2+, and Na+ have been probed from the disruption of metachromasia of the TA-dye system by these ions. Results show Ca2+ and Mg2+ to be almost equally effective in destroying the metachromasia of the TA-PCYN system, thus not supporting the hypothesis of special affinity for Mg2+ ion.

Surface properties of Streptococcus salivarius HB and nonfibrillar mutants: measurement of zeta potential and elemental composition with X-ray photoelectron spectroscopy

To characterize the functional cell surface, the zeta potentials and elemental surface composition of Streptococcus salivarius HB and a range of mutants with known molecular surface structures were determined. Zeta potentials of fully hydrated cells were measured as a function of pH in dilute potassium phosphate solutions, yielding isoelectric points of the strains. Elemental composition (O, C, N, and P) of the outer 2 to 5 nm of the freeze-dried cell surfaces were measured by X-ray photoelectron spectroscopy. An increasing loss of proteinaceous fibrillar surface antigens of the mutants was found to be accompanied by a progressive decrease in the N/C ratio from 0.104 in the parent strain HB to 0.053 in mutant HBC12. Simultaneously, the value of the isoelectric point shifted from 3.0 to 1.3. In a previous study (A.H. Weerkamp, H.C. van der Mei, and J. W. Slot, Infect. Immun. 55:438-455, 1987) on the cell surfaces of the same strains, it was shown that removal of fibrils led to increased exposure of (lipo)teichoic acid at the surface, which explains the low isoelectric point caused by the low pKa of the phosphate groups.

The functions of autolysins in the growth and division of Bacillus subtilis

Some bacteria, such as streptococci, exhibit growth from discrete and well-defined zones. In Streptococcus faecalis, growth zones can be observed in the electron microscope, and the position of the zone can be used as a marker for cell cycle events. Growth of the cell surface of Bacillus subtilis appears to be by a much different mechanism from that of streptococci. Cell elongation takes place by the insertion at many sites in the cell cylinder of peptidoglycan components. The insertion occurs on the inner face of the wall, and upon cross linking, the new wall material becomes stress bearing and older wall is pushed to the surface. When old wall reaches the surface, it becomes susceptible to excision by autolysins, resulting in wall turnover; cell elongation, due to the stretching of the cross-linked peptidoglycan, therefore, accompanies turnover and does not require a specialized growth zone.

Characteristics of the binding of aminoglycoside antibiotics to teichoic acids. A potential model system for interaction of aminoglycosides with polyanions

The binding of the aminoglycoside antibiotic dihydrostreptomycin to defined cell-wall teichoic acids and to lipoteichoic acid isolated from various gram-positive eubacteria was followed by equilibrium dialysis. Dihydrostreptomycin was used at a wide range of concentration under different conditions of ionic strength, concentration of teichoic acid, presence of cationic molecules like Mg2+, spermidine, other aminoglycoside antibiotics (gentamicin, neomycin, paromomycin). Interaction of dihydrostreptomycin with teichoic acid was found to be a cooperative binding process. The binding characteristics seem to be dependent on structural features of teichoic acid and are influenced by cationic molecules. Mg2+, spermidine and other aminoglycosides antibiotics inhibit the binding of dihydrostreptomycin to teichoic acid competitively. The binding of aminoglycosides to teichoic acids is considered as a model system for the interaction of aminoglycoside antibiotics with cellular polyanions. Conclusions of physiological significance are drawn.

Binding of metallic ions to the outer membrane of Escherichia coli

The binding of metal ions by the outer membrane of Escherichia coli K-12 strain AB264 was investigated by using outer membrane obtained after Triton X-100 extraction of purified cell envelopes. Binding studies, conducted under saturating conditions, indicated a selective trapping of certain metallic ions. Low-dose electron microscopy of metal-loaded samples revealed an aggregative deposition of lead on one surface of the membrane which suggests that at least one distinctive binding site is asymmetrically arranged in these outer membrane vesicles.