Polysaccharide covalently linked to the peptidoglycan of the cyanobacterium Synechocystis sp. strain PCC6714

Cell-cell communication through septal junctions in filamentous cyanobacteria

Septal junctions are cell-cell connections that mediate intercellular communication in filamentous cyanobacteria. The septal peptidoglycan is perforated by dozens of 20 nm-wide nanopores, through which these proteinaceous structures traverse, physically connecting adjacent cells. On each cytoplasmic side, every septal junction contains a flexible cap structure that closes the connection in a reversible manner upon stress. This gating mechanism reminds of the gap junctions from metazoans and represents a primordial control system for cell-cell communication. In this review, we summarize the knowledge about formation of the nanopore array as the framework for incorporation of cell-cell connecting septal junctions. Furthermore, the architecture of septal junctions, proteins involved in septal junction constitution and regulation of intercellular communication will be addressed.

Bacteriophage φEf11 ORF28 Endolysin, a Multifunctional Lytic Enzyme with Properties Distinct from All Other Identified Enterococcus faecalis Phage Endolysins

ϕEf11 is a temperate Siphoviridae bacteriophage that infects strains of Enterococcus faecalis The ϕEf11 genome, encompassing 65 open reading frames (ORFs), is contained within 42,822 bp of DNA. Within this genome, a module of six lysis-related genes was identified. Based upon sequence homology, one of these six genes, ORF28, was predicted to code for an N-acetylmuramoyl-l-alanine amidase endolysin of 46.133 kDa, composed of 421 amino acids. The PCR-amplified ORF28 was cloned and expressed, and the resulting gene product was affinity purified to homogeneity. The purified protein was obtained from a fusion protein that exhibited a molecular mass of 72.5 kDa, consistent with a 46.1-kDa protein combined with a fused 26.5-kDa glutathione S-transferase tag. It produced rapid, profound lysis in E. faecalis populations and was active against 73 of 103 (71%) E. faecalis strains tested. In addition, it caused substantial destruction of E. faecalis biofilms. The lysin was quite stable, retaining its activity for three years in refrigerated storage, was stable over a wide range of pHs, and was unaffected by the presence of a reducing agent; however, it was inhibited by increasing concentrations of Ca²⁺ Liquid chromatography-mass spectrometry analysis of E. faecalis cell wall digestion products produced by the ORF28 endolysin indicated that the lysin acted as an N-acetylmuramidase, an endo-β-N-acetylglucosaminidase, and an endopeptidase, rather than an N-acetylmuramoyl-l-alanine amidase. The ϕEf11 ORF28 lysin shared 10% to 37% amino acid identity with the lytic enzymes of all other characterized E. faecalis bacteriophages.IMPORTANCE The emergence of multidrug-resistant pathogenic microorganisms has brought increasing attention to the urgent need for the development of alternative antimicrobial strategies. One such alternative to conventional antibiotics employs lytic enzymes (endolysins) that are produced by bacteriophages in the course of lytic infection. During lytic infection by a bacteriophage, these enzymes hydrolyze the cell wall peptidoglycan, resulting in the lysis of the host cell. However, external endolysin application can result in lysis from without. In this study, we have cloned, expressed, purified, and characterized an endolysin produced by a bacteriophage infecting strains of Enterococcus faecalis The lysin is broadly active against most of the tested E. faecalis strains and exhibits multifunctional enzymatic specificities that differ from all other characterized endolysins produced by E. faecalis bacteriophages.

Singlet oxygen imaging using fluorescent probe Singlet Oxygen Sensor Green in photosynthetic organisms

Formation of singlet oxygen (¹O₂) was reported to accompany light stress in plants, contributing to cell signaling or oxidative damage. So far, Singlet Oxygen Sensor Green (SOSG) has been the only commercialized fluorescent probe for ¹O₂ imaging though it suffers from several limitations (unequal penetration and photosensitization) that need to be carefully considered to avoid misinterpretation of the analysed data. Herein, we present results of a comprehensive study focused on the appropriateness of SOSG for ¹O₂ imaging in three model photosynthetic organisms, unicellular cyanobacteria Synechocystis sp. PCC 6803, unicellular green alga Chlamydomonas reinhardtii and higher plant Arabidopsis thaliana. Penetration of SOSG differs in both unicellular organisms; while it is rather convenient for Chlamydomonas it is restricted by the presence of mucoid sheath of Synechocystis, which penetrability might be improved by mild heating. In Arabidopsis, SOSG penetration is limited due to tissue complexity which can be increased by pressure infiltration using a shut syringe. Photosensitization of SOSG and SOSG endoperoxide formed by its interaction with ¹O₂ might be prevented by illumination of samples by a red light. When measured under controlled conditions given above, SOSG might serve as specific probe for detection of intracellular ¹O₂ formation in photosynthetic organisms.

MWCNTs-like protection layer formation on bacterial cellulose bundles as a potential material for suspended resonator

Suspended carbon naotubes (CNTs) resonator is a sensitive detector for chemical and biological applications. Small sizes of CNTs can enhance sensitivity, but increase complexity for fabrication. In order to overcome the challenges, a novel technique has been developed to produce a long, sensitive and high tensile strength carbon nanotubes (CNT) coated bacterial cellulose (BC) bundle. This study demonstrates the use of ultrasonication to perform carboxyl functionalized multi-walled carbon nanotubes (MWCNTs-COOH) self-assembling on the surface of BC bundles (BC/MWCNTs) via hydrogen bonds. Ultrasonication can disrupt dense cellulose network and produce the long BC/MWCNTs bundles ranging from 30 to 100 μm. Raman spectroscopy shows a drop at peak of hydroxyl (-OH, 3700 m(-1)) and carbonyl (C=O, 1600 cm(-1)). This indicates the formation of the continuous MWCNTs-like protection layer on BC surface. Electrical properties of the BC/MWCNTs bundles showed linearity from -6 V to +6 V. Composites with BC treated by higher ultrasonic powers, 100 W, show higher conductivity comparing to 80 W. Sensitivity from 10(-7) to 10(-9) A of long BC/MWCNTs composite bundles is reported in this paper. This technique may be competitive to the current state of carbon nanotubes resonator.

The Peptidoglycan-Binding Protein SjcF1 Influences Septal Junction Function and Channel Formation in the Filamentous Cyanobacterium Anabaena

Filamentous, heterocyst-forming cyanobacteria exchange nutrients and regulators between cells for diazotrophic growth. Two alternative modes of exchange have been discussed involving transport either through the periplasm or through septal junctions linking adjacent cells. Septal junctions and channels in the septal peptidoglycan are likely filled with septal junction complexes. While possible proteinaceous factors involved in septal junction formation, SepJ (FraG), FraC, and FraD, have been identified, little is known about peptidoglycan channel formation and septal junction complex anchoring to the peptidoglycan. We describe a factor, SjcF1, involved in regulation of septal junction channel formation in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120. SjcF1 interacts with the peptidoglycan layer through two peptidoglycan-binding domains and is localized throughout the cell periphery but at higher levels in the intercellular septa. A strain with an insertion in sjcF1 was not affected in peptidoglycan synthesis but showed an altered morphology of the septal peptidoglycan channels, which were significantly wider in the mutant than in the wild type. The mutant was impaired in intercellular exchange of a fluorescent probe to a similar extent as a sepJ deletion mutant. SjcF1 additionally bears an SH3 domain for protein-protein interactions. SH3 binding domains were identified in SepJ and FraC, and evidence for interaction of SjcF1 with both SepJ and FraC was obtained. SjcF1 represents a novel protein involved in structuring the peptidoglycan layer, which links peptidoglycan channel formation to septal junction complex function in multicellular cyanobacteria. Nonetheless, based on its subcellular distribution, this might not be the only function of SjcF1.

Cell-cell communication is central not only for eukaryotic but also for multicellular prokaryotic systems. Principles of intercellular communication are well established for eukaryotes, but the mechanisms and components involved in bacteria are just emerging. Filamentous heterocyst-forming cyanobacteria behave as multicellular organisms and represent an excellent model to study prokaryotic cell-cell communication. A path for intercellular metabolite exchange appears to involve transfer through molecular structures termed septal junctions. They are reminiscent of metazoan gap junctions that directly link adjacent cells. In cyanobacteria, such structures need to traverse the peptidoglycan layers in the intercellular septa of the filament. Here we describe a factor involved in the formation of channels across the septal peptidoglycan layers, thus contributing to the multicellular behavior of these organisms.

Production and early preservation of lipid biomarkers in iron hot springs

The bicarbonate-buffered anoxic vent waters at Chocolate Pots hot springs in Yellowstone National Park are 51-54°C, pH 5.5-6.0, and are very high in dissolved Fe(II) at 5.8-5.9 mg/L. The aqueous Fe(II) is oxidized by a combination of biotic and abiotic mechanisms and precipitated as primary siliceous nanophase iron oxyhydroxides (ferrihydrite). Four distinct prokaryotic photosynthetic microbial mat types grow on top of these iron deposits. Lipids were used to characterize the community composition of the microbial mats, link source organisms to geologically significant biomarkers, and investigate how iron mineralization degrades the lipid signature of the community. The phospholipid and glycolipid fatty acid profiles of the highest-temperature mats indicate that they are dominated by cyanobacteria and green nonsulfur filamentous anoxygenic phototrophs (FAPs). Diagnostic lipid biomarkers of the cyanobacteria include midchain branched mono- and dimethylalkanes and, most notably, 2-methylbacteriohopanepolyol. Diagnostic lipid biomarkers of the FAPs (Chloroflexus and Roseiflexus spp.) include wax esters and a long-chain tri-unsaturated alkene. Surprisingly, the lipid biomarkers resisted the earliest stages of microbial degradation and diagenesis to survive in the iron oxides beneath the mats. Understanding the potential of particular sedimentary environments to capture and preserve fossil biosignatures is of vital importance in the selection of the best landing sites for future astrobiological missions to Mars. This study explores the nature of organic degradation processes in moderately thermal Fe(II)-rich groundwater springs--environmental conditions that have been previously identified as highly relevant for Mars exploration.

The exo-proteome and exo-metabolome of Nostoc punctiforme (Cyanobacteria) in the presence and absence of nitrate

The ability of nitrogen-fixing filamentous Cyanobacteria to adapt to multiple environments comes in part from assessing and responding to external stimuli, an event that is initiated in the extracellular milieu. While it is known that these organisms produce numerous extracellular substances, little work has been done to characterize both the metabolites and proteins present under standard laboratory growth conditions. We have assessed the extracellular milieu of Nostoc punctiforme when grown in liquid culture in the presence and absence of a nitrogen source (nitrate). The extracellular proteins identified were enriched in integrin β-propellor domains and calcium-binding sites with sequences unique to N. punctiforme, supporting a role for extracellular proteins in modulating species-specific recognition and behavior processes. Extracellular proteases are present and active under both conditions, with the cells grown with nitrate having a higher activity when normalized to chlorophyll levels. The released metabolites are enriched in peptidoglycan-derived tetrasaccharides, with higher levels in nitrate-free media.

The N-acetylmuramic acid 6-phosphate etherase gene promotes growth and cell differentiation of cyanobacteria under light-limiting conditions

Inactivation of sll0861 in Synechocystis sp. strain PCC 6803 or the homologous gene alr2432 in Anabaena sp. strain PCC 7120 had no effect on the growth of these organisms at a light intensity of 30 micromol photons m(-2) s(-1) but reduced their growth at a light intensity of 5 or 10 micromol photons m(-2) s(-1). In Anabaena, inactivation of the gene also significantly reduced the rate of heterocyst differentiation under low-light conditions. The predicted products of sll0861 and alr2432 and homologs of these genes showed similarity to N-acetylmuramic acid 6-phosphate etherase (MurQ), an enzyme involved in peptidoglycan recycling, in Escherichia coli. E. coli murQ and the cyanobacterial homologs could functionally substitute for each other. We hypothesize that murQ in cyanobacteria promotes low-light adaptation through reutilization of peptidoglycan degradation products.

Species-specific cell wall binding affinity of the S-layer proteins of mosquitocidal bacterium Bacillus sphaericus C3-41

The binding affinities and specificities of six truncated S-layer homology domain (SLH) polypeptides of mosquitocidal Bacillus sphaericus strain C3-41 with the purified cell wall sacculi have been assayed. The results indicated that the SLH polypeptide comprised of amino acids 31 to 210 was responsible for anchoring the S-layer subunits to the rigid cell wall layer via a distinct type of secondary cell wall polymer and that a motif of the recombinant SLH polypeptide comprising amino acids 152 to 210 (rSLH(152-210)) was essential for the stable binding of the S-layer with the bacterial cell walls. The quantitative assays revealed that the K(D) (equilibrium dissociation constant) values of rSLH(152-210) and rSLH(31-210) with purified cell wall sacculi were 1.11 x 10(-6) M and 1.40 x 10(-6) M, respectively. The qualitative assays demonstrated that the SLH domain of strain C3-41 could bind only to the cell walls or the cells treated with 5 M guanidinium hydrochloride of both toxic and nontoxic B. sphaericus strains but not to those from other bacteria, indicating the species-specific binding of the SLH polypeptide of B. sphaericus with bacterial cell walls.

Suppression of the lethality of high light to a quadruple HLI mutant by the inactivation of the regulatory protein PfsR in Synechocystis PCC 6803

A regulatory gene, designated pfsR (photosynthesis, Fe homeostasis and stress-response regulator), was discovered by a genetic screen in Synechocystis PCC 6803. Deletion of the gene from a high light-sensitive strain lacking four hli genes (4Xhli) restored viability to the parental strain under high light conditions. The quintuple mutant pfsR-/4Xhli retained photosystem-II and oxygen evolution capacity at levels similar to the wild-type levels under high light conditions. The transcripts of the two bfr genes (encoding bacterioferritin) were found to be constitutively up-regulated, whereas the transcripts of ho1 gene (encoding a heme oxygenase) were greatly down-regulated in high light upon deletion of pfsR. Under intermediate high intensity light, the pfsR deletion strains accumulated carotenoids and chlorophyll a to a significantly higher level than their corresponding parental strains. An exacerbated, transient increase in oxygen evolution during the early hours of high light acclimation and a somewhat increased steady-state level of photosystem-II-mediated oxygen evolution observed in the 4Xhli strain were brought back to the wild-type levels upon deletion of pfsR from the strain. The pfsR deletion mutants were found to be less sensitive to iron limitation under low light conditions and to suffer less lipid peroxidation following exposure to high light. Therefore, inactivation of PfsR resulted in tighter control of iron availability, which in turn reduced oxidative stress during photosynthesis in high light. These studies have revealed a critical role of PfsR in regulation of iron homeostasis and stress response.

Myxoxanthophyll is required for normal cell wall structure and thylakoid organization in the cyanobacterium Synechocystis sp. strain PCC 6803

Myxoxanthophyll is a carotenoid glycoside in cyanobacteria that is of unknown biological significance. The sugar moiety of myxoxanthophyll in Synechocystis sp. strain PCC 6803 was identified as dimethyl fucose. The open reading frame sll1213 encoding a fucose synthetase orthologue was deleted to probe the role of fucose and to determine the biological significance of myxoxanthophyll in Synechocystis sp. strain PCC 6803. Upon deletion of sll1213, a pleiotropic phenotype was obtained: when propagated at 0.5 micromol photons m(-2) s(-1), photomixotrophic growth of cells lacking sll1213 was poor. When grown at 40 micromol photons m(-2) s(-1), growth was comparable to that of the wild type, but cells showed a severe reduction in or loss of the glycocalyx (S-layer). As a consequence, cells aggregated in liquid as well as on plates. At both light intensities, new carotenoid glycosides accumulated, but myxoxanthophyll was absent. New carotenoid glycosides may be a consequence of less-specific glycosylation reactions that gained prominence upon the disappearance of the native sugar moiety (fucose) of myxoxanthophyll. In the mutant, the N-storage compound cyanophycin accumulated, and the organization of thylakoid membranes was altered. Altered cell wall structure and thylakoid membrane organization and increased cyanophycin accumulation were also observed for deltaslr0940K, a strain lacking zeta-carotene desaturase and thereby all carotenoids but retaining fucose. Therefore, lack of myxoxanthophyll and not simply of fucose results in most of the phenotypic effects described here. It is concluded that myxoxanthophyll contributes significantly to the vigor of cyanobacteria, as it stabilizes thylakoid membranes and is critical for S-layer formation.

Characterization and implications of the cell surface reactivity of Calothrix sp. strain KC97

The cell surface reactivity of the cyanobacterium Calothrix sp. strain KC97, an isolate from the Krisuvik hot spring, Iceland, was investigated in terms of its proton binding behavior and charge characteristics by using acid-base titrations, electrophoretic mobility analysis, and transmission electron microscopy. Analysis of titration data with the linear programming optimization method showed that intact filaments were dominated by surface proton binding sites inferred to be carboxyl groups (acid dissociation constants [pK(a)] between 5.0 and 6.2) and amine groups (mean pK(a) of 8.9). Sheath material isolated by using lysozyme and sodium dodecyl sulfate generated pK(a) spectra similarly dominated by carboxyls (pK(a) of 4.6 to 6.1) and amines (pK(a) of 8.1 to 9.2). In both intact filaments and isolated sheath material, the lower ligand concentrations at mid-pK(a) values were ascribed to phosphoryl groups. Whole filaments and isolated sheath material displayed total reactive-site densities of 80.3 x 10(-5) and 12.3 x 10(-5) mol/g (dry mass) of cyanobacteria, respectively, implying that much of the surface reactivity of this microorganism is located on the cell wall and not the sheath. This is corroborated by electrophoretic mobility measurements that showed that the sheath has a net neutral charge at mid-pHs. In contrast, unsheathed cells exhibited a stronger negative-charge characteristic. Additionally, transmission electron microscopy analysis of ultrathin sections stained with heavy metals further demonstrated that most of the reactive binding sites are located upon the cell wall. Thus, the cell surface reactivity of Calothrix sp. strain KC97 can be described as a dual layer composed of a highly reactive cell wall enclosed within a poorly reactive sheath.

The S-layer homology domain as a means for anchoring heterologous proteins on the cell surface of Bacillus anthracis

Bacillus anthracis synthesizes two S-layer proteins, each containing three S-layer homology (SLH) motifs towards their amino-terminus. In vitro experiments suggested that the three motifs of each protein were organized as a structural domain sufficient to bind purified cell walls. Chimeric genes encoding the SLH domains fused to the levansucrase of Bacillus subtilis were constructed and integrated on the chromosome. Cell fractionation and electron microscopy studies showed that both heterologous polypeptides were targeted to the cell surface. In addition, surface-exposed levansucrase retained its enzymatic and antigenic properties. Preliminary results concerning applications of this work are presented.

Production and cell surface anchoring of functional fusions between the SLH motifs of the Bacillus anthracis S-layer proteins and the Bacillus subtilis levansucrase

Many surface proteins of Gram-positive bacteria contain motifs, about 50 amino acids long, called S-layer homology (SLH) motifs. Bacillus anthracis, the causal agent of anthrax, synthesizes two S-layer proteins, each with three SLH motifs towards the amino-terminus. We used biochemical and genetic approaches to investigate the involvement of these motifs in cell surface anchoring. Proteinase K digestion produced polypeptides lacking these motifs, and stable three-motif polypeptides were produced in Escherichia coli that were able to bind the B. anthracis cell walls in vitro, demonstrating that the three SLH motifs were organized into a cell surface anchoring domain. We also determined the function of these SLH domains by constructing chimeric genes encoding the SLH domains fused to the normally secreted levansucrase of Bacillus subtilis. Cell fractionation and electron microscopy studies showed that each three-motif domain was sufficient for the efficient anchoring of levansucrase onto the cell surface. Proteins consisting of truncated SLH domains fused to levansucrase were unstable and associated poorly with the cell surface. Surface-exposed levansucrase retained its enzymatic and antigenic properties.

The S-layer proteins of two Bacillus stearothermophilus wild-type strains are bound via their N-terminal region to a secondary cell wall polymer of identical chemical composition

Two Bacillus stearothermophilus wild-type strains were investigated regarding a common recognition and binding mechanism between the S-layer protein and the underlying cell envelope layer. The S-layer protein from B. stearothermophilus PV72/p6 has a molecular weight of 130,000 and assembles into a hexagonally ordered lattice. The S-layer from B. stearothermophilus ATCC 12980 shows oblique lattice symmetry and is composed of subunits with a molecular weight of 122,000. Immunoblotting, peptide mapping, N-terminal sequencing of the whole S-layer protein from B. stearothermophilus ATCC 12980 and of proteolytic cleavage fragments, and comparison with the S-layer protein from B. stearothermophilus PV72/p6 revealed that the two S-layer proteins have identical N-terminal regions but no other extended structurally homologous domains. In contrast to the heterogeneity observed for the S-layer proteins, the secondary cell wall polymer isolated from peptidoglycan-containing sacculi of the different strains showed identical chemical compositions and comparable molecular weights. The S-layer proteins could bind and recrystallize into the appropriate lattice type on native peptidoglycan-containing sacculi from both organisms but not on those extracted with hydrofluoric acid, leading to peptidoglycan of the A1gamma chemotype. Affinity studies showed that only proteolytic cleavage fragments possessing the complete N terminus of the mature S-layer proteins recognized native peptidoglycan-containing sacculi as binding sites or could associate with the isolated secondary cell wall polymer, while proteolytic cleavage fragments missing the N-terminal region remained unbound. From the results obtained in this study, it can be concluded that S-layer proteins from B. stearothermophilus wild-type strains possess an identical N-terminal region which is responsible for anchoring the S-layer subunits to a secondary cell wall polymer of identical chemical composition.

Evidence that the N-terminal part of the S-layer protein from Bacillus stearothermophilus PV72/p2 recognizes a secondary cell wall polymer

The S-layer of Bacillus stearothermophilus PV72/p2 shows oblique lattice symmetry and is composed of identical protein subunits with a molecular weight of 97,000. The isolated S-layer subunits could bind and recrystallize into the oblique lattice on native peptidoglycan-containing sacculi which consist of peptidoglycan of the A1gamma chemotype and a secondary cell wall polymer with an estimated molecular weight of 24,000. The secondary cell wall polymer could be completely extracted from peptidoglycan-containing sacculi with 48% HF, indicating the presence of phosphodiester linkages between the polymer chains and the peptidoglycan backbone. The cell wall polymer was composed mainly of GlcNAc and ManNAc in a molar ratio of 4:1, constituted about 20% of the peptidoglycan-containing sacculus dry weight, and was also detected in the fraction of the S-layer self-assembly products. Extraction experiments and recrystallization of the whole S-layer protein and proteolytic cleavage fragments confirmed that the secondary cell wall polymer is responsible for anchoring the S-layer subunits by the N-terminal part to the peptidoglycan-containing sacculi. In addition to this binding function, the cell wall polymer was found to influence the in vitro self-assembly of the guanidinium hydrochloride-extracted S-layer protein. Chemical modification studies further showed that the secondary cell wall polymer does not contribute significant free amino or carboxylate groups to the peptidoglycan-containing sacculi.

Forty-five years of developmental biology of photosynthetic bacteria

Developmental biology and cell differentiation of photosynthetic prokaryotes are less noticed fields than the showpieces of eukaryotes, e.g. Drosophila melanogaster. The large metabolic versatility of the facultative purple bacteria and their great capability to adapt to different ecological conditions, however, aroused the inquisitiveness to investigate the process of cell differentiation and to use these bacteria as model system to study structure, function and biosynthesis of the photosynthetic apparatus. The great progress in research in this field paved the way to study principal mechanisms of cellular organization and differentiation in these bacteria. In this article, the history of the research on membrane structure and development of anoxygenic photosynthetic prokaryotes during the last 45 years is described. A personal account of how I entered the field through research on the phototaxis of cyanobacteria is given. Intracytoplasmic membranes (ICM) were detected by electron microscopy in cyanobacteria and in purple non-sulfur bacteria. The formation of ICM by invagination of the cytoplasmic membrane in purple bacteria was observed for the first time. Investigations on the effect of changes in oxygen tension and light intensity on the formation of pigments and intracytoplasmic membranes followed. The isolation, purification, and analysis of light-harvesting complexes and of pigment-binding proteins was the next step of our research. Lipopolysaccharides and peptidoglycans were detected and analyzed in the outer membrane of photosynthetic bacteria. Functional membrane differentiation includes variations in the rates of photophosphorylation and electron transport. Molecular genetic approaches have initiated the investigation of transcriptional regulation and the analysis of correlation between pigment and protein synthesis. Molecular analysis of assembly of light-harvesting complexes and membrane differentiation are the present aspects of our research. Cell differentiation has been considered under evolutionary view.

Primary structure of cyanelle peptidoglycan of Cyanophora paradoxa: a prokaryotic cell wall as part of an organelle envelope

The peptidoglycan layer surrounding the photosynthetic organelles (cyanelles) of the protist Cyanophora paradoxa is thought to be a relic of their cyanobacterial ancestors. The separation of muropeptides by gel filtration and reverse-phase high-performance liquid chromatography revealed four different muropeptide monomers. A number of muropeptides were identical in retention behavior to muropeptides of Escherichia coli, while others had remarkably long retention times with respect to their sizes, as indicated by gel filtration. Molecular mass determination by plasma desorption and matrix-assisted laser desorption ionization mass spectrometry showed that these unusual muropeptides had molecular masses greater by 112 Da or a multiple thereof than those of ones common to both species. Fast atom bombardment-tandem mass spectrometry of these reduced muropeptide monomers allowed the localization of the modification to D-glutamic acid. High-resolution fast atom bombardment-mass spectrometry and amino acid analysis revealed N-acetylputrescine to be the substituent (E. Pittenauer, E. R. Schmid, G. Allmaier, B. Pfanzagl, W. Löffelhardt, C. Quintela, M. A. de Pedro, and W. Stanek, Biol. Mass Spectrom. 22:524-536, 1993). In addition to the 4 monomers already known, 8 dimers, 11 trimers, and 6 tetramers were characterized. An average glycan chain length of 51 disaccharide units was determined by the transfer of [U-14C]galactose to the terminal N-acetylglucosamine residues of cyanelle peptidoglycan. The muropeptide pattern is discussed with respect to peptidoglycan biosynthesis and processing.

The hglK gene is required for localization of heterocyst-specific glycolipids in the cyanobacterium Anabaena sp. strain PCC 7120

Mutant strain 543 of the cyanobacterium Anabaena sp. strain PCC 7120 was originally isolated as a Fox- mutant following chemical mutagenesis. Ultrastructural analysis shows that in nitrogen-replete media the vegetative cells of the mutant are more cylindrical and have thicker septa than those of the wild type, while in nitrogen-free media the mutant heterocysts lack the normal glycolipid layer external to the cell wall. Although this layer is absent, strain 543 heterocysts nevertheless contain heterocyst-specific glycolipids, as determined by thin-layer chromatography. The mutation in strain 543 is in a gene we have named hglK, encoding a protein of 727 amino acids. The wild-type HglK protein appears to contain four membrane-spanning regions followed by 36 repeats of a degenerate pentapeptide sequence, AXLXX. The mutation in strain 543 introduces a termination codon immediately upstream of the pentapeptide repeat region. A mutant constructed by insertion of an antibiotic resistance cassette near the beginning of the hglK gene has the same phenotype as strain 543. We propose that hglK encodes a protein necessary for the localization of heterocyst glycolipids and that this function requires the pentapeptide repeats of the HglK protein.

Structural characterization of the cyanelle peptidoglycan of Cyanophora paradoxa by 252Cf plasma desorption mass spectrometry and fast atom bombardment/tandem mass spectrometry

A strategy for the structural characterization of the four major NaBH4-reduced peptidoglycan monomers derived from muramidase-digested peptidoglycan from the cyanelles of the flagellate Cyanophora paradoxa Korschikoff is described. Initial molecular weight determination of these glycopeptides was performed by positive and negative ion plasma desorption mass spectrometry. Due to the presence of two pairs of disaccharide tripeptide and disaccharide tetrapeptide monomers differing in mass by 112 units, respectively, an as yet unknown peptidoglycan modification either at the carbohydrate or at the peptide moiety was assumed. beta-Elimination of the disaccharide unit from the unreduced peptidoglycan monomers yielded the corresponding (modified) N1-lactyltripeptides and -tetrapeptides, respectively. These peptides, N-terminally blocked with lactic acid, unambiguously showed the modification to be located on the peptide moiety. By positive ion fast atom bombardment/hybrid tandem mass spectrometry of the reduced peptidoglycan monomers as well as of the corresponding deglycosylated monomers (= N1-lactylpeptides) the modification was determined to be linked to the glutamic acid moiety. Based on combined data from plasma desorption mass spectrometry, tandem mass spectrometry, accurate mass measurement and amino acid analysis of the acid hydrolysate after derivatization with o-phthaldialdehyde by high-performance liquid chromatography we could establish the structure of the modification as N-acetylputrescine. Finally, the confirmation of the linkage of the glutamic acid to diaminopimelic acid via the gamma-COOH was based on the presence of a-type peptide backbone fragment ions in the positive ion plasma desorption mass spectra of the modified N1-lactylpeptides.

Teichuronic acid reducing terminal N-acetylglucosamine residue linked by phosphodiester to peptidoglycan of Micrococcus luteus

Teichuronic acid-peptidoglycan complex isolated from Micrococcus luteus cells by lysozyme digestion in osmotically stabilized medium was treated with mild acid to cleave the linkage joining teichuronic acid to peptidoglycan. This labile linkage was shown to be the phosphodiester which joins N-acetylglucosamine, the residue located at the reducing end of the teichuronic acid, through its anomeric hydroxyl group to a 6-phosphomuramic acid, a residue of the glycan strand of peptidoglycan. 31P nuclear magnetic resonance spectroscopy of the lysozyme digest of cell walls demonstrated the presence of a phosphodiester which was converted to a phosphomonoester by the conditions which released teichuronic acid from cell walls. Reduction of acid-liberated reducing end groups by NaB3H4 followed by complete acid hydrolysis yielded [3H] glucosaminitol from the true reducing end residue of teichuronic acid and [3H]glucitol from the sites of fragmentation of teichuronic acid. The amount of N-acetylglucosamine detected was approximately stoichiometric with the amount of phosphate in the complex. Partial fragmentation of teichuronic acid provides an explanation of the previous erroneous identification of the reducing end residue.

Peptidoglycan-polysaccharide complex in the cell wall of the filamentous prochlorophyte Prochlorothrix hollandica

A peptidoglycan-polysaccharide complex composed of N-acetylglucosamine, N-acetylmuramic acid, muramic acid 6-phosphate, L-alanine, D-alanine, D-glutamic acid, meso-diaminopimelic acid, N-acetylmannosamine, mannose, galactose, glucose, and phosphate was isolated from cell walls of the filamentous prochlorophyte Prochlorothrix hollandica; this complex was similar in chemical composition and structure to that found in cyanobacteria. Peptide patterns of partial acid hydrolysates of the isolated peptidoglycan revealed an A1 gamma structure with direct cross-linkage (m-diaminopimelic acid-D-alanine) of the peptide side chains. The degree of cross-linkage (63%) was found to be in the range of values obtained for gram-positive bacteria and cyanobacteria.