The Lipoteichoic Acids and Lipoglycans of Gram-positive Bacteria: A Chemotaxonomic Perspective

Lipoteichoic acids influence cell shape and bacterial division of Streptococcus suis serotype 2, but play a limited role in the pathogenesis of the infection

Streptococcus suis serotype 2 is a major swine pathogen and a zoonotic agent, causing meningitis in both swine and humans, responsible for substantial economic losses to the swine industry worldwide. The pathogenesis of infection and the role of bacterial cell wall components in virulence have not been fully elucidated. Lipoproteins, peptidoglycan, as well as lipoteichoic acids (LTA) have all been proposed to contribute to virulence. In the present study, the role of the LTA in the pathogenesis of the infection was evaluated through the characterisation of a mutant of the S. suis serotype 2 strain P1/7 lacking the LtaS enzyme, which mediates the polymerization of the LTA poly-glycerolphosphate chain. The ltaS mutant was confirmed to completely lack LTA and displayed significant morphological defects. Although the bacterial growth of this mutant was not affected, further results showed that LTA is involved in maintaining S. suis bacterial fitness. However, its role in the pathogenesis of the infection appears limited. Indeed, LTA presence reduces self-agglutination, biofilm formation and even dendritic cell activation, which are important aspects of the pathogenesis of the infection caused by S. suis. In addition, it does not seem to play a critical role in virulence using a systemic mouse model of infection.

Lipoarabinomannan mediates localized cell wall integrity during division in mycobacteria

The growth and division of mycobacteria, which include clinically relevant pathogens, deviate from that of canonical bacterial models. Despite their Gram-positive ancestry, mycobacteria synthesize and elongate a diderm envelope asymmetrically from the poles, with the old pole elongating more robustly than the new pole. The phosphatidylinositol-anchored lipoglycans lipomannan (LM) and lipoarabinomannan (LAM) are cell envelope components critical for host-pathogen interactions, but their physiological functions in mycobacteria remained elusive. In this work, using biosynthetic mutants of these lipoglycans, we examine their roles in maintaining cell envelope integrity in Mycobacterium smegmatis and Mycobacterium tuberculosis. We find that mutants defective in producing mature LAM fail to maintain rod cell shape specifically at the new pole and para-septal regions whereas a mutant that produces a larger LAM becomes multi-septated. Therefore, LAM plays critical and distinct roles at subcellular locations associated with division in mycobacteria, including maintenance of local cell wall integrity and septal placement.

Lipoarabinomannan regulates septation in Mycobacterium smegmatis

The growth and division of mycobacteria, which include several clinically relevant pathogens, deviate significantly from that of canonical bacterial models. Despite their Gram-positive ancestry, mycobacteria synthesize and elongate a diderm envelope asymmetrically from the poles, with the old pole elongating more robustly than the new pole. In addition to being structurally distinct, the molecular components of the mycobacterial envelope are also evolutionarily unique, including the phosphatidylinositol-anchored lipoglycans lipomannan (LM) and lipoarabinomannan (LAM). LM and LAM modulate host immunity during infection, but their role outside of intracellular survival remains poorly understood, despite their widespread conservation among non-pathogenic and opportunistically pathogenic mycobacteria. Previously, Mycobacterium smegmatis and Mycobacterium tuberculosis mutants producing structurally altered LM and LAM were shown to grow slowly under certain conditions and to be more sensitive to antibiotics, suggesting that mycobacterial lipoglycans may support cellular integrity or growth. To test this, we constructed multiple biosynthetic lipoglycan mutants of M. smegmatis and determined the effect of each mutation on cell wall biosynthesis, envelope integrity, and division. We found that mutants deficient in LAM, but not LM, fail to maintain cell wall integrity in a medium-dependent manner, with envelope deformations specifically associated with septa and new poles. Conversely, a mutant producing abnormally large LAM formed multiseptated cells in way distinct from that observed in a septal hydrolase mutant. These results show that LAM plays critical and distinct roles at subcellular locations associated with division in mycobacteria, including maintenance of local cell envelope integrity and septal placement.

Bifidobacteria cell wall-derived exo-polysaccharides, lipoteichoic acids, peptidoglycans, polar lipids and proteins - their chemical structure and biological attributes

A variety of health benefits has been documented to be associated with the consumption of probiotic bacteria, namely bifidobacteria and lactobacilli. Thanks to the scientific advances in recent years we are beginning to understand the molecular mechanisms by which bacteria in general and probiotic bacteria in particular act as host physiology and immune system modulators. More recently, the focus has shifted from live bacteria towards bacteria-derived defined molecules, so called postbiotics. These molecules may represent safer alternative compared to the live bacteria while retaining the desired effects on the host. The excellent source of effector macromolecules is the bacterial envelope. It contains compounds that are pivotal in the adhesion phenomenon, provide direct bacteria-to-host signaling capacity and the associated physiological impact and immunomodulatory properties of bacteria. Here we comprehensively review the structure and biological role of Bifidobacterium surface and cell wall molecules: exopolysaccharides, cell wall polysaccharides, lipoteichoic acids, polar lipids, peptidoglycans and proteins. We discuss their involvement in direct signaling to the host cells and their described immunomodulatory effects.

Immunohistochemical Detection of Propionibacterium acnes in the Retinal Granulomas in Patients with Ocular Sarcoidosis

The etiology of sarcoidosis is still obscure; however, Mycobacteria and Propionibacterium acnes are considered the most implicated etiological agent for sarcoidosis. To investigate whether P. acnes is an etiological agent for sarcoid uveitis, we analyzed the frequency of P. acnes detected within the biopsied retinas from patients with ocular sarcoidosis by immunohistochemistry with a P. acnes-specific monoclonal antibody (PAB antibody). Eleven patients (12 eyes) with sarcoid uveitis were enrolled in this study. Eight patients with rhegmatogenous retinal detachment, two patients with non-sarcoid uveitis, and two patients with vitreoretinal lymphoma were enrolled as controls. In the sarcoidosis group, granulomas were mainly observed in the inner retinal layer filled with CD4+ cells and CD68+ cells, indicating the Th1 immune response. P. acnes, identified as round bodies that reacted with the PAB antibody, were present in 10/12 samples (83%) from 9/11 patients (82%) with sarcoidosis. These round bodies were scattered within the retinal granulomas mainly in the inner retinal layer. In the control group, no round bodies were detected. Our results suggested that P. acnes could be associated with sarcoid uveitis. We hypothesize that sarcoid granulomas may be formed by a Th1 immune response to P. acnes hematogenously transmitted to the retina.

Smart polyhydroxyalkanoate nanobeads by protein based functionalization

The development of innovative medicines and personalized biomedical approaches calls for new generation easily tunable biomaterials that can be manufactured applying straightforward and low-priced technologies. Production of functionalized bacterial polyhydroxyalkanoate (PHA) nanobeads by harnessing their natural carbon-storage granule production system is a thrilling recent development. This branch of nanobiotechnology employs proteins intrinsically binding the PHA granules as tags to immobilize recombinant proteins of interest and design functional nanocarriers for wide range of applications. Additionally, the implementation of new methodological platforms regarding production of endotoxin free PHA nanobeads using Gram-positive bacteria opened new avenues for biomedical applications. This prompts serious considerations of possible exploitation of bacterial cell factories as alternatives to traditional chemical synthesis and sources of novel bioproducts that could dramatically expand possible applications of biopolymers.

From the Clinical Editor

In the 21st century, we are coming into the age of personalized medicine. There is a growing use of biomaterials in the clinical setting. In this review article, the authors describe the use of natural polyhydroxyalkanoate (PHA) nanoparticulates, which are formed within bacterial cells and can be easily functionalized. The potential uses would include high-affinity bioseparation, enzyme immobilization, protein delivery, diagnostics etc. The challenges of this approach remain the possible toxicity from endotoxin and the high cost of production.

Gram-positive bacterial lipoglycans based on a glycosylated diacylglycerol lipid anchor are microbe-associated molecular patterns recognized by TLR2

Innate immune recognition is the first line of host defense against invading microorganisms. It is a based on the detection, by pattern recognition receptors (PRRs), of invariant molecular signatures that are unique to microorganisms. TLR2 is a PRR that plays a major role in the detection of Gram-positive bacteria by recognizing cell envelope lipid-linked polymers, also called macroamphiphiles, such as lipoproteins, lipoteichoic acids and mycobacterial lipoglycans. These microbe-associated molecular patterns (MAMPs) display a structure based on a lipid anchor, being either an acylated cysteine, a glycosylated diacylglycerol or a mannosyl-phosphatidylinositol respectively, and having in common a diacylglyceryl moiety. A fourth class of macroamphiphile, namely lipoglycans, whose lipid anchor is made, as for lipoteichoic acids, of a glycosylated diacylglycerol unit rather than a mannosyl-phosphatidylinositol, is found in Gram-positive bacteria and produced by certain Actinobacteria, including Micrococcus luteus, Stomatococcus mucilaginosus and Corynebacterium glutamicum. We report here that these alternative lipoglycans are also recognized by TLR2 and that they stimulate TLR2-dependant cytokine production, including IL-8, TNF-α and IL-6, and cell surface co-stimulatory molecule CD40 expression by a human macrophage cell line. However, they differ by their co-receptor requirement and the magnitude of the innate immune response they elicit. M. luteus and S. mucilaginosus lipoglycans require TLR1 for recognition by TLR2 and induce stronger responses than C. glutamicum lipoglycan, sensing of which by TLR2 is dependent on TLR6. These results expand the repertoire of MAMPs recognized by TLR2 to lipoglycans based on a glycosylated diacylglycerol lipid anchor and reinforce the paradigm that macroamphiphiles based on such an anchor, including lipoteichoic acids and alternative lipoglycans, induce TLR2-dependant innate immune responses.

Lipoteichoic acid in Streptomyces hygroscopicus: structural model and immunomodulatory activities

Gram positive bacteria produce cell envelope macroamphiphile glycopolymers, i.e. lipoteichoic acids or lipoglycans, whose functions and biosynthesis are not yet fully understood. We report for the first time a detailed structure of lipoteichoic acid isolated from a Streptomyces species, i.e. Streptomyces hygroscopicus subsp. hygroscopicus NRRL 2387T. Chemical, MS and NMR analyses revealed a polyglycerolphosphate backbone substituted with α-glucosaminyl and α-N-acetyl-glucosaminyl residues but devoid of any amino-acid substituent. This structure is very close, if not identical, to that of the wall teichoic acid of this organism. These data not only contribute to the growing recognition that lipoteichoic acid is a cell envelope component of Gram positive Actinobacteria but also strongly support the recently proposed hypothesis of an overlap between the pathways of lipoteichoic acid and wall teichoic acid synthesis in these bacteria. S. hygroscopicus lipoteichoic acid induced signalling by human innate immune receptor TLR2, confirming its role as a microbe-associated molecular pattern. Its activity was partially dependant on TLR1, TLR6 and CD14. Moreover, it stimulated TNF-α and IL-6 production by a human macrophage cell line to an extent similar to that of Staphylococcus aureus lipoteichoic acid. These results provide new clues on lipoteichoic acid structure/function relationships, most particularly on the role of the polyglycerolphosphate backbone substituents.

The determinants of the actinorhizal symbiosis

The actinorhizal symbiosis is a major contributor to the global nitrogen budget, playing a dominant role in ecological successions following disturbances. The mechanisms involved are still poorly known but there emerges the vision that on the plant side, the kinases that transmit the symbiotic signal are conserved with those involved in the transmission of the Rhizobium Nod signal in legumes. However, on the microbial side, complementation with Frankia DNA of Rhizobium nod mutants failed to permit identification of symbiotic genes. Furthermore, analysis of three Frankia genomes failed to permit identification of canonical nod genes and revealed symbiosis-associated genes such as nif, hup, suf and shc to be spread around the genomes. The present review explores some recently published approaches aimed at identifying bacterial symbiotic determinants.

Lipoteichoic acid biosynthesis: two steps forwards, one step sideways?

Lipoteichoic acids (LTAs) are membrane-anchored molecules in the cell envelopes of Gram-positive bacteria. Until recently, they were considered to be restricted to the Firmicutes, which include important pathogens such as Staphylococcus aureus and Streptococcus pneumoniae. Polyanionic LTAs have fundamentally important roles in divalent cation retention within the Gram-positive cell envelope and thereby influence bacterial cell division. Thus, LTA biosynthesis provides an attractive target for the development of novel antimicrobial interventions. Recent studies, notably two investigations of S. aureus and another of Bacillus subtilis, have greatly improved our understanding of the genetic basis of LTA biosynthesis. In addition, reports have revealed that at least some members of the Actinobacteria (another phylum of Gram-positive bacteria) produce LTAs, rather than the lipoglycans previously assumed to be typical of this taxon. The availability of whole bacterial genome sequences has enabled us to perform comparative analyses to shed light on the distribution of putative LTA biosynthetic genes among bacteria. Here, we discuss the results of these genomic analyses, together with the current literature, and propose that LTA biosynthesis in Actinobacteria might be fundamentally different to that in most Firmicutes.

Polyhydroxyalkanoates in Gram-positive bacteria: insights from the genera Bacillus and Streptomyces

Gram-positive bacteria, notably Bacillus and Streptomyces, have been used extensively in industry. However, these microorganisms have not yet been exploited for the production of the biodegradable polymers, polyhydroxyalkanoates (PHAs). Although PHAs have many potential applications, the cost of production means that medical applications are currently the main area of use. Gram-negative bacteria, currently the only commercial source of PHAs, have lipopolysaccharides (LPS) which co-purify with the PHAs and cause immunogenic reactions. On the other hand, Gram- positive bacteria lack LPS, a positive feature which justifies intensive investigation into their production of PHAs. This review summarizes currently available knowledge on PHA production by Gram- positive bacteria especially Bacillus and Streptomyces. We hope that this will form the basis of further research into developing either or both as a source of PHAs for medical applications.

Identification of a lipoarabinomannan-like lipoglycan in the actinomycete Gordonia bronchialis

The cell envelopes of actinomycetes contain lipidated macroamphiphiles, of which the most extensively characterised are the lipoarabinomannans of mycobacteria and related bacteria. We have investigated the mycolic acid-containing actinomycete Gordonia bronchialis and identified the presence of a lipoarabinomannan-like lipoglycan. The extraction and purification procedures recovered a second amphiphilic fraction with properties suggesting a phosphatidylinositol mannoside, consistent with studies of other Gordonia species.

Cell wall teichoic acids: structural diversity, species specificity in the genusNocardiopsis, and chemotaxonomic perspective

Data on the structures of cell wall teichoic acids, the anionic carbohydrate-containing polymers, found in many Gram-positive bacteria have been summarized and the polymers of the actinomycete genus Nocardiopsis have been considered from the taxonomic standpoint. The structures of these polymers or their combinations have been demonstrated to be indicative of each of seven Nocardiopsis species and two subspecies, verified by the DNA-DNA relatedness data, and to correlate well with the grouping of the organisms based on 16S rDNA sequences. As each of the intrageneric taxa discussed is definable by the composition of teichoic acids, the polymers are considered to be valuable taxonomic markers for the Nocardiopsis species and subspecies. The (13)C NMR spectra of the polymers, data on the products of their chemical degradation, and distinguishing constituents of whole cell walls derived from teichoic acids are discussed, which are useful for identification of certain polymers and members of the genus Nocardiopsis at the species and subspecies level in microbiological practice.

Identification of a lipoarabinomannan-like lipoglycan in Gordonia rubropertincta

Lipoarabinomannans are well characterised lipoglycans present in the cell envelopes of mycobacteria and closely related bacteria. To define further the distribution of these lipoglycans we have investigated the mycolic acid-containing bacterium Gordonia rubropertincta and, by analysis of carbohydrate composition and antigenic cross-reactivity, demonstrated the presence of a lipoarabinomannan-like lipoglycan. A fraction that appeared to contain higher phosphatidylinositolmannosides was also isolated.

Macroamphiphilic cell envelope components of Rhodococcus equi and closely related bacteria

Recent progress towards an understanding of the architecture of the mycobacterial cell envelope (P.J. Brennan and H. Nikaido, Annual Review of Biochemistry 64 (1995) 29-63) provides a model with features more generally applicable to cell envelope organisation in other mycolic acid-containing bacteria. Using this archetype, a model for the organisation of the rhodococcal cell envelope is presented here, with particular reference to cell envelope composition in Rhodococcus equi. The likelihood that mycolic acids bound to the cell wall arabinogalactan contribute to the formation of a distinct outer lipid layer is emphasised. Furthermore, the model incorporates recent work which has characterised rhodococcal macroamphiphiles (lipoglycans and lipoproteins), including the VapA virulence-associated lipoproteins of R. equi.

Small-angle X-ray scattering analysis of pneumococcal lipoteichoic acid phase structure

X-Ray-scattering analysis was performed on micelles of lipoteichoic acid from Streptococcus pneumoniae. This lipoteichoic acid differs from poly(glycerophosphate) and poly(glycosylglycerophosphate) lipoteichoic acids by a unique positively charged diacylglyceroglycolipid anchor and a complex structure of the hydrophilic chain which is composed of zwitterionic tetrasaccharide ribitol phosphate repeats each carrying two zwitterionic phosphocholine substituents. The size distribution of the lipoteichoic acid micelles was sufficiently homogenous to determine their size and some related molecular parameters by small-angle scattering analysis. Nearly independent on the ionic strength of the aqueous dispersion, an average micelle contained about 150 lipoteichoic acid molecules arranged in a spherical assembly with a diameter of about 23 nm, whereby the hydrophilic region occupied an outer shell of about 8.5 nm thickness. Taken this as the average chain length of LTA in the micelle and 7.2 repeats per chain, each repeat contributed about 1.2 nm to the thickness of the hydrophilic shell as compared to 2.4 nm for a fully extended chain conformation and 1.1 nm estimated for a more helical arrangement [Klein, R. A., Hartmann, R., Egge, H., Behr, T. & Fischer, W. (1994) Carbohydr. Res. 256, 189-222]. A comparison with the micelle of poly(glycerophosphate) lipoteichoic acid of Staphylococcus aureus suggests that the supramolecular structure is largely independent of the structure of the hydrophilic chain and solely dictated by the small cross-sectional area of the diacylglycerol moiety common to all lipoteichoic acids and lipoglycans of gram-positive bacteria.

Bacteria, molds, and toxins in water-damaged building materials

Microbial toxins and eukaryotic cell toxicity from indoor building materials heavily colonized by fungi and bacteria were analyzed. The dominant colonizers at water-damaged sites of the building were Stachybotrys chartarum (10(3) to 10(5) visible conidia cm-2), Penicillium and Aspergillus species (10(4) CFU mg-1), gram-negative bacteria (10(4) CFU mg-1), and mycobacteria (10(3) CFU mg-1). The mycobacterial isolates were most similar to M. komossense, with 98% similarity of the complete 16S rDNA sequence. Limulus assay of water extracts prepared from a water-damaged gypsum liner revealed high contents of gram-negative endotoxin (17 ng mg-1 of E. coli lipopolysaccharide equivalents) and beta-D-glucan (210 ng mg-1 of curdlan equivalents). High-performance liquid chromatography analysis of the methanol extracts showed that the water-damaged gypsum liner also contained satratoxin (17 ng mg-1). This methanol-extracted substance was 200 times more toxic to rabbit skin and fetus feline lung cells than extract of gypsum liner sampled from a non-water-damaged site. The same extract contained toxin(s) that paralyzed the motility of boar spermatozoa at extremely low concentrations; the 50% effective concentration was 0.3 microgram of dry solids per ml. This toxicity was not explainable by the amount of bacterial endotoxin, beta-D-glucan, or satratoxin present in the same extract. The novel in vitro toxicity test that utilized boar spermatozoa as described in this article is convenient to perform and reproducible and was a useful tool for detecting toxins of microbial origin toward eukaryotic cells not detectable in building materials by the other methods.

Micrococcus luteus cells and cell walls induce anaphylactoid reactions accompanied by early death and serum cytokines in mice primed with muramyl dipeptide

Micrococcus luteus strains at a dose of 500 microg of whole cells caused anaphylactoid reactions leading to death in some instances within 1 h in C3H/HeN mice primed with muramyl dipeptide (MDP, 100 microg). Tumor necrosis factor (TNF) and interleukin-6 (IL-6) were induced in the serum of half and of all the surviving mice, respectively. Cell wall specimens of M. luteus so far examined also caused anaphylactoid reactions accompanied by early death and one strain induced high levels of TNF and IL-6. Cytoplasmic membranes also induced IL-6. Essentially similar results were obtained with representative M. luteus cells and a cell wall specimen in MDP-primed C3H/HeJ mice. These results indicate that M. luteus has virulence activities that are associated with the induction of septic shock and systemic inflammatory diseases.

A chemotaxonomic study of the lipoglycans of Rhodococcus rhodnii N445 (NCIMB 11279)

Rhodococcus rhodnii N445 was investigated for the presence of macroamphiphilic lipoglycan. Purification of a hot phenol-water extract by hydrophobic interaction chromatography allowed the resolution of three lipoglycan fractions. The two main preparations contained lipoglycans with carbohydrate compositions consistent with the presence of lipoarabinomannan and lipomannan, whilst the minor fraction appeared to contain a mixture of these two lipoglycans. The fatty acid composition of the lipoglycans resembled that of the whole cells except that the relative proportion of unsaturated fatty acids was decreased. Although lipoarabinomannan and structurally-related lipomannan lipoglycans from representatives of the genus Mycobacterium have been extensively studied, this is the first report of the lipoglycan composition of a representative of the genus Rhodococcus as presently defined. These findings provide further chemotaxonomic evidence that lipoarabinomannan-type lipoglycans are widely distributed throughout the mycolic acid-containing actinomycetes.

Identification of a lipoarabinomannan-like lipoglycan in Corynebacterium matruchotii

The oral organism Corynebacterium matruchotii was investigated for the presence of lipoteichoic acid, as this common polyanionic macroamphiphilic component of Gram-positive bacteria has been implicated in phenomena related to calcium binding. Phenol-water extraction followed by a small-scale, hydrophobic-interaction chromatography step yielded carbohydrate-containing preparations that were distinguished from lipoteichoic acid by their low phosphorus content. Subsequently, large-scale phenol-water extracts from each of three strains of C. matruchotii were purified by hydrophobic-interaction chromatography and shown to contain a heterogeneous lipoglycan fraction. The major fatty acids present were the same as for the whole-cell fatty acid profiles but differed in their relative amounts. Qualitative analysis of the lipoglycan fractions revealed similarities of carbohydrate composition with a previously characterized lipoglycan fraction from C. diphtheriae and with the lipoarabinomannan/lipomannans found in the genus Mycobacterium. The carbohydrate composition and the low phosphorus content indicated that lipoteichoic acid was absent from C. matruchotii. The calcium-binding properties of C. matruchotii therefore cannot be attributed to lipoteichoic acid.