Role of disulfide bonds in maintaining the structural integrity of the sheath of Leptothrix discophora SP-6

Identification of lthB, a Gene Encoding a Putative Glycosyltransferase Family 8 Protein Required for Leptothrix Sheath Formation

The bacterium Leptothrix cholodnii generates cell chains encased in sheaths that are composed of woven nanofibrils. The nanofibrils are mainly composed of glycoconjugate repeats, and several glycosyltransferases (GTs) are required for its biosynthesis. However, only one GT (LthA) has been identified to date. In this study, we screened spontaneous variants of L. cholodnii SP6 to find those that form smooth colonies, which is one of the characteristics of sheathless variants. Genomic DNA sequencing of an isolated variant revealed an insertion in the locus Lcho_0972, which encodes a putative GT family 8 protein. We thus designated this protein LthB and characterized it using deletion mutants and antibodies. LthB localized adjacent to the cell envelope. ΔlthB cell chains were nanofibril free and thus sheathless, indicating that LthB is involved in nanofibril biosynthesis. Unlike the ΔlthA mutant and the wild-type strain, which often generate planktonic cells, most ΔlthB organisms presented as long cell chains under static conditions, resulting in deficient pellicle formation, which requires motile planktonic cells. These results imply that sheaths are not required for elongation of cell chains. Finally, calcium depletion, which induces cell chain breakage due to sheath loss, abrogated the expression of LthA, but not LthB, suggesting that these GTs cooperatively participate in glycoconjugate biosynthesis under different signaling controls. IMPORTANCE In recent years, the regulation of cell chain elongation of filamentous bacteria via extracellular signals has attracted attention as a potential strategy to prevent clogging of water distribution systems and filamentous bulking of activated sludge in industrial settings. However, a fundamental understanding of the ecology of filamentous bacteria remains elusive. Since sheath formation is associated with cell chain elongation in most of these bacteria, the molecular mechanisms underlying nanofibril sheath formation, including the intracellular signaling cascade in response to extracellular stimuli, must be elucidated. Here, we isolated a sheathless variant of L. cholodnii SP6 and thus identified a novel glycosyltransferase, LthB. Although mutants with deletions of lthA, encoding another GT, and lthB were both defective for nanofibril formation, they exhibited different phenotypes of cell chain elongation and pellicle formation. Moreover, LthA expression, but not LthB expression, was influenced by extracellular calcium, which is known to affect nanofibril formation, indicating the functional diversities of LthA and LthB. Such molecular insights are critical for a better understanding of ecology of filamentous bacteria, which, in turn, can be used to improve strategies to control filamentous bacteria in industrial facilities.

Porous Pellicle Formation of a Filamentous Bacterium, Leptothrix

The bacterium Leptothrix cholodnii generates filaments encased in a sheath comprised of woven nanofibrils. In static liquid culture, L. cholodnii moves toward the air-liquid interface, where it forms porous pellicles. Observations of aggregation at the interface reveal that clusters consisting of only a few bacteria primarily grow by netting free cells. These growing clusters hierarchically enlarge through the random docking of other small clusters. We find that the bacteria swim using their polar flagellum toward the interface, where their sheath assists them in intertwining with others and thereby promotes the formation of small clusters. In contrast, sheathless hydrophobic mutant cells get stuck to the interface. We find that the nanofibril sheath is vital for robust pellicle formation as it lowers cell surface hydrophobicity by 60%, thereby reducing their adsorption and enabling cells to move toward and stick together at the air-liquid interface. IMPORTANCE Efficient and sustainable management of water resources is becoming a fundamental issue for supporting growing populations and for developing economic activity. Fundamental to this management is the treatment of wastewater. Microorganisms are the active component of activated sludge that is employed in the biodegradation process of many wastewater treatment facilities. However, uncontrolled growth of filamentous bacteria such as Sphaerotilus often results in filamentous bulking, lowering the efficiency of water treatment systems. To prevent this undesirable condition, strategies based on a fundamental understanding of the ecology of filamentous bacteria are required. Although the filamentous bacterium Leptothrix cholodnii, which is closely related to Sphaerotilus, is a minor inhabitant of activated sludge, its complete genome sequence is known, making gene manipulation relatively easy. Moreover, L. cholodnii generates porous pellicles under static conditions, which may be a characteristic of filamentous bulking. We show that both swimming motility and nanofibril-mediated air-liquid interface attachment are required for porous pellicle formation. These insights are critical for a better understanding of the characteristics of filamentous bulking and might improve strategies to control activated sludge.

Shrimp thrombospondin (TSP): presence of O-β1,4 N-acetylglucosamine polymers and its function in TSP chain association in egg extracellular matrix

We characterized the existence of O-β(1,4)-GlcNAc polymers (β1,4GNP) that were anchored on the O-linked glycosylation sites of shrimp thrombospondin (pmTSP-II). There were five putative β1,4GNP linkages on the epithelial growth factor-like domain of pmTSP-II. Antibody against O-β-GlcNAc (CTD110.6) was used to prove the existence of linear and complex β1,4GNP. The antibody well reacted with linear chito-triose, -tetraose and -pentaose conjugated with phosphatidylethanolamine lipid. The immunoreactivity could also be detected with a complex β1,4GNP within pmTSP-II (at MW > 250 kDa). Upon denaturing the protein with SDS-PAGE buffer, the size of pmTSP-II was shifted to be 250 kDa, approximately 2.5 folds larger than the deduced molecular mass of pmTSP-II (110 kDa), suggesting additional association of pmTSP-II apart from its known disulfide bridging. This was confirmed by chitinase digestion on pmTSP-II protein leading to the subsequent smaller protein bands at 110–170 kDa in time- and concentration-dependent manners. These bands well reacted with CTD110.6 antibody and disappeared after extensive chitinase hydrolysis. Together, we believe that β1,4GNP on pmTSP-II serve the function in an inter-chain association to provide structural architecture of egg extracellular matrix, a novel function of pmTSP-II in reproductive biology.

Leptothrix cholodnii Response to Nutrient Limitation

Microorganisms are widely utilized for the treatment of wastewater in activated sludge systems. However, the uncontrolled growth of filamentous bacteria leads to bulking and adversely affects wastewater treatment efficiency. To clarify the nutrient requirements for filament formation, we track the growth of a filamentous bacterium, Leptothrix cholodnii SP-6 in different nutrient-limited conditions using a high aspect-ratio microfluidic chamber to follow cell-chain elongation and sheath formation. We find that limitations in Na⁺, K⁺, and Fe²⁺ yield no observable changes in the elongation of cell chains and sheath formation, whereas limitations of C, N, P, or vitamins lead to more pronounced changes in filament morphology; here we observe the appearance of partially empty filaments with wide intercellular gaps. We observe more dramatic differences when SP-6 cells are transferred to media lacking Mg²⁺ and Ca²⁺. Loss of Mg²⁺ results in cell autolysis, while removal of Ca²⁺ results in the catastrophic disintegration of the filaments. By simultaneously limiting both carbon and Ca²⁺ sources, we are able to stimulate planktonic cell generation. These findings paint a detailed picture of the ecophysiology of Leptothrix, which may lead to improved control over the unchecked growth of deleterious filamentous bacteria in water purification systems.

Environmental applications of microbial extracellular polymeric substance (EPS): A review

During the last decade, water demand and wastewater generation has increased due to urbanization around the globe which had led to an increase in the utilization of chemicals/synthetic polymers for treating the wastewaters. These synthetic polymers used during the coagulation/flocculation process are non-renewable, non-biodegradable, and have a potential neurotoxic and carcinogenic effect. From the literature it is clear that extracellular polymer substance (EPS) is a potential bioflocculant, moreover it is renewable, biodegradable, eco-friendly, non-toxic as well as economically valued product. The various identification techniques and extraction methods of EPS are elaborated. Further application of EPS as absorbent in removing the dye from the industrial effluent is presented. Moreover EPS as a potential adsorbent for heavy metal removal from the various effluent is discussed. In addition, EPS is also utilized for soil remediation and soil erosion control. Mainly, EPS as bioflocculant in treating raw water, wastewater treatment, leachate and sludge management are summarized in this review.

Structural determination of the sheath-forming polysaccharide of Sphaerotilus montanus using thiopeptidoglycan lyase which recognizes the 1,4 linkage between α-d-GalN and β-d-GlcA

Sphaerotilus natans is a filamentous sheath-forming bacterium commonly found in activated sludge. Its sheath is assembled from a thiolic glycoconjugate called thiopeptidoglycan. S. montanus ATCC-BAA-2725 is a sheath-forming member of stream biofilms, and its sheath is morphologically similar to that of S. natans. However, it exhibits heat susceptibility, which distinguishes it from the S. natans sheath. In this study, chemical composition and solid-state NMR analyses suggest that the S. montanus sheath is free of cysteine, indicating that disulfide linkage is not mandatory for sheath formation. The S. montanus sheath was successfully solubilized by N-acetylation, allowing solution-state NMR analysis to determine the sugar sequence. The sheath was susceptible to thiopeptidoglycan lyase prepared from the thiopeptidoglycan-assimilating bacterium, Paenibacillus koleovorans. The reducing ends of the enzymatic digests were labeled with 4-aminobenzoic acid ethyl ester, followed by HPLC. Two derivatives were detected, and their structures were determined. We found that the sheath has no peptides and is assembled as follows: [→4)-β-d-GlcA-(1→4)-β-d-Glc-(1→3)-β-d-GalNAc-(1→4)-α-d-GalNAc-(1→4)-α-d-GalN-(1→]_n (β-d-Glc and α-d-GalNAc are stoichiometrically and substoichiometrically 3-O-acetylated, respectively). Thiopeptidoglycan lyase was thus confirmed to cleave the 1,4 linkage between α-d-GalN and β-d-GlcA, regardless of the peptide moiety. Furthermore, vital fluorescent staining of the sheath demonstrated that elongation takes place at the tips, as with the S. natans sheath.

Preparation and Characterization of Additional Metallic Element-Containing Tubular Iron Oxides of Bacterial Origin

Biogenic microtubular iron oxides (BIOXs) derived from Leptothrix spp. are known as promising multifunctional materials for industrial applications such as ceramic pigments and catalyst carriers. Here, we report unprecedented BIOX products with additive depositions of various metallic elements prepared by a newly devised "two-step" method using an artificial culture system of Leptothrix cholodnii strain OUMS1; the method comprises a biotic formation of immature organic sheaths and subsequent abiotic deposition of Fe and intended elements on the sheaths. Chemical composition ratios of the additional elements Al, Zr, and Ti in the respective BIOXs were arbitrarily controllable depending on initial concentrations of metallic salts added to reaction solutions. Raman spectroscopy exemplified an existence of Fe-O-Al linkage in the Al-containing BIOX matrices. Time-course analyses revealed the underlying physiological mechanism for the BIOX formation. These results indicate that our advanced method can contribute greatly to creations of innovative bioderived materials with improved functionalities.

Polyfunctional Nanofibril Appendages Mediate Attachment, Filamentation, and Filament Adaptability in Leptothrix cholodnii

Leptothrix is a species of Fe/Mn-oxidizing bacteria known to form long filaments composed of chains of cells that eventually produce a rigid tube surrounding the filament. Prior to the formation of this brittle microtube, Leptothrix cells secrete hair-like structures from the cell surface, called nanofibrils, which develop into a soft sheath that surrounds the filament. To clarify the role of nanofibrils in filament formation in L. cholodnii SP-6, we analyze the behavior of individual cells and multicellular filaments in high-aspect ratio microfluidic chambers using time-lapse and intermittent in situ fluorescent staining of nanofibrils, complemented with atmospheric scanning electron microscopy. We show that in SP-6 nanofibrils are important for attachment and their distribution on young filaments post-attachment is correlated to the directionality of filament elongation. Elongating filaments demonstrate a surprising ability to adapt to their physical environment by changing direction when they encounter obstacles: they bend or reverse direction depending on the angle of the collision. We show that the forces involved in the collision can be used to predict the behavior of filament. Finally, we show that as filaments grow in length, the older region becomes confined by the sheath, while the newly secreted nanofibrils at the leading edge of the filament form a loose, divergent, structure from which cells periodically escape.

Biosorption of metal elements by exopolymer nanofibrils excreted from Leptothrix cells

Leptothrix species, aquatic Fe-oxidizing bacteria, excrete nano-scaled exopolymer fibrils. Once excreted, the fibrils weave together and coalesce to form extracellular, microtubular, immature sheaths encasing catenulate cells of Leptothrix. The immature sheaths, composed of aggregated nanofibrils with a homogeneous-looking matrix, attract and bind aqueous-phase inorganics, especially Fe, P, and Si, to form seemingly solid, mature sheaths of a hybrid organic-inorganic nature. To verify our assumption that the organic skeleton of the sheaths might sorb a broad range of other metallic and nonmetallic elements, we examined the sorption potential of chemically and enzymatically prepared protein-free organic sheath remnants for 47 available elements. The sheath remnants were found by XRF to sorb each of the 47 elements, although their sorption degree varied among the elements: >35% atomic percentages for Ti, Y, Zr, Ru, Rh, Ag, and Au. Electron microscopy, energy dispersive x-ray spectroscopy, electron and x-ray diffractions, and Fourier transform infrared spectroscopy analyses of sheath remnants that had sorbed Ag, Cu, and Pt revealed that (i) the sheath remnants comprised a 5-10 nm thick aggregation of fibrils, (ii) the test elements were distributed almost homogeneously throughout the fibrillar aggregate, (iii) the nanofibril matrix sorbing the elements was nearly amorphous, and (iv) these elements plausibly were bound to the matrix by ionic binding, especially via OH. The present results show that the constitutive protein-free exopolymer nanofibrils of the sheaths can contribute to creating novel filtering materials for recovering and recycling useful and/or hazardous elements from the environment.

Amino group in Leptothrix sheath skeleton is responsible for direct deposition of Fe(III) minerals onto the sheaths

Leptothrix species produce microtubular organic-inorganic materials that encase the bacterial cells. The skeleton of an immature sheath, consisting of organic exopolymer fibrils of bacterial origin, is formed first, then the sheath becomes encrusted with inorganic material. Functional carboxyl groups of polysaccharides in these fibrils are considered to attract and bind metal cations, including Fe(III) and Fe(III)-mineral phases onto the fibrils, but the detailed mechanism remains elusive. Here we show that NH₂ of the amino-sugar-enriched exopolymer fibrils is involved in interactions with abiotically generated Fe(III) minerals. NH₂-specific staining of L. cholodnii OUMS1 detected a terminal NH₂ on its sheath skeleton. Masking NH₂ with specific reagents abrogated deposition of Fe(III) minerals onto fibrils. Fe(III) minerals were adsorbed on chitosan and NH₂-coated polystyrene beads but not on cellulose and beads coated with an acetamide group. X-ray photoelectron spectroscopy at the N1s edge revealed that the terminal NH₂ of OUMS1 sheaths, chitosan and NH₂-coated beads binds to Fe(III)-mineral phases, indicating interaction between the Fe(III) minerals and terminal NH₂. Thus, the terminal NH₂ in the exopolymer fibrils seems critical for Fe encrustation of Leptothrix sheaths. These insights should inform artificial synthesis of highly reactive NH₂-rich polymers for use as absorbents, catalysts and so on.

Structure of perosamine-containing polysaccharide, a component of the sheath of Thiothrix fructosivorans

A sheath-forming and sulfur-oxidizing bacterium, Thiothrix fructosivorans, was heterotrophically cultured. The sheath, which is an extracellular microtube, was prepared by selectively removing the cells using lysozyme, sodium dodecyl sulfate, and sodium hydroxide. Solid-state (13)C-nuclear magnetic resonance (NMR) spectrum revealed that the sheath is assembled from a glycan possessing acetyl and methyl groups. When the sheath was deacetylated, the original microtube structure was lost and the sheath became soluble under acidic conditions, revealing the importance of acetyl groups in maintaining the sheath structure. Equimolar d-glucose, d-glucosamine, and l-fucose were detected in the acid hydrolysate of the sheath by gas liquid chromatography. In addition to these sugars, β-GlcN-(1→4)-Glc and unidentified sugar were detected by analyzing the hydrolysate using high-performance liquid chromatography analysis. (1)H and (13)C NMR spectroscopy was used to identify a disaccharide composed of 4-deoxy-4-aminorhamnose (perosamine, Rha4N) and fucose. N-Acetyl-perosamine prepared from the disaccharide was polarimetric and exhibited a d-configuration. The previously unidentified disaccharide was found to be α-d-Rhap4N-(1→3)-d-Fuc. According to (1)H and (13)C NMR analyses, the deacetylated sheath-forming polysaccharide was found to h have a main chain of [→4)-β-d-GlcpN-(1→4)-β-d-Glcp-(1→]n, to which disaccharide side chains of α-d-Rhap4N-(1→3)-α-l-Fucp-(1→ were attached at position 3 of Glc.

Structural and spatial associations between Fe, O, and C in the network structure of the Leptothrix ochracea sheath surface

The structural and spatial associations of Fe with O and C in the outer coat fibers of the Leptothrix ochracea sheath were shown to be substantially similar to the stalk fibers of Gallionella ferruginea, i.e., a central C core, probably of bacterial origin, and aquatic Fe interacting with O at the surface of the core.

Identifying residues in antigenic determinants by chemical modification

Chemical modification of the side chains of amino acid residues was one of the first methods developed to investigate epitopes in protein antigens. The principle of the method is that alteration of the structure of a key residue of an epitope by a chemical modification will alter reactivity with antibody by affecting either specificity or avidity or both. Chemical modification has the advantage that it can be applied to discontinuous as well as continuous epitopes and may be of value in identifying cryptic epitopes. We consider here the several recent studies that have applied site-specific chemical modification to the identification of epitopes on antigens, including the use of formaldehyde, glutaraldehyde, and acid anhydrides, to produce allergoids where determinants important to reaction with IgE are modified but the ability to elicit an IgG response is retained. It is noteworthy that modification of amino groups with charge reversal appears to be the most useful approach. The approach to the use of site-specific chemical modification as a tool for the study of protein function is discussed, and emphasis is placed on the necessity to (1) validate the specificity of modification and (2) assess potential conformational change that may occur secondary to modification. Finally, a list of chemical reagents used for protein modification is presented, together with properties and references to use.

Prosthecobacter fluviatilis sp. nov., which lacks the bacterial tubulin btubA and btubB genes

Leptothrix cholodnii is a sheathed bacterium often found in metal-rich and oligotrophic aquatic environments. A bacterial strain that is able to degrade the NaOH-treated sheath of L. cholodnii was isolated. The isolate was a Gram-negative, aerobic and prosthecate bacterium. The optimum growth temperature and pH were 30 degrees C and pH 7.0, respectively. The DNA G+C content was 62.9 mol%. The major respiratory quinone was MK-6. A phylogenetic analysis based on the 16S rRNA gene indicated that the isolate is a member of the genus Prosthecobacter. The nearest relative was the type strain of Prosthecobacter vanneervenii, with a similarity of 97.1 %. However, the isolate does not possess the bacterial tubulin genes, btubA and btubB, unique to known species of the genus Prosthecobacter. It is proposed that the isolate represents a novel species, Prosthecobacter fluviatilis sp. nov. The type strain is HAQ-1(T) (=JCM 14805(T) =KACC 12649(T) =KCTC 22182(T)).

Composition of the sheath produced by the green alga Chlorella sorokiniana

AIMS

To investigate the chemical characterization of the mucilage sheath produced by Chlorella sorokiniana.

METHODS AND RESULTS

Algal mucilage sheath was hydrolysed with NaOH, containing EDTA. The purity of the hydrolysed sheath was determined by an ATP assay. The composition of polysaccharide in the sheath was investigated by high-performance anion-exchange chromatography with pulsed amperometric detection. Sucrose, galacturonic acid, xylitol, inositol, ribose, mannose, arabinose, galactose, rhamnose and fructose were detected in the sheath as sugar components. Magnesium was detected in the sheath as a divalent cation using inductively coupled argon plasma. The sheath matrix also contained protein.

CONCLUSIONS

It appears that the sheath is composed of sugars and metals. Mucilage sheath contains many kinds of saccharides that are produced as photosynthetic metabolites and divalent cations that are contained in the culture medium.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report on chemical characterization of the sheath matrix produced by C. sorokiniana.

Structural analysis of the sheath of a sheathed bacterium, Leptothrix cholodnii

Leptothrix cholodnii is an aerobic sheath-forming bacterium often found in oligotrophic and metal-rich aquatic environments. The sheath of this bacterium was isolated by selectively lysing the cells. Glycine and cysteine were the major amino acids of the sheath. The sheath was readily dissolved in hydrazine, and a polysaccharide substituted with cysteine was recovered from the solution. Galactosamine, glucosamine and galacturonic acid were detected in the hydrazinolysate by gas liquid chromatography analysis. FAB-MS analysis of the hydrazinolysate suggested a sugar sequence of HexN-GalA-HexN-HexN. Methylation linkage analysis revealed the presence of 4-linked GalA, 3-linked HexN and 4-linked HexN. The sulfhydryl groups of the sheath were used for labeling with the fluorogenic reagent, 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F). The labeled sheath (ABD-sheath) was partially hydrolyzed and three fluorescent fragments were purified by HPLC. One of them was identified as ABD-cysteine. The second one was found to be the ABD-cysteine tetramer. Another fragment was indicated to be a pentasaccharide substituted with ABD-cysteine by nuclear magnetic resonance (NMR) analysis. It can be assumed that the polysaccharide and peptide moieties of the sheath are connected by a cysteine residue. NMR analysis of the hydrazinolysate revealed that the polysaccharide moiety of the sheath was constructed from a pentasaccharide repeating unit containing 2-amino-2-deoxygalacturonic acid (GalNA), as shown below. -->4)-alpha-GalNA-(1-->4)-alpha-D-GalN(p)-(1-->4)-alpha-D-GalA(p)-(1-->4)-beta-D-GlcN(p)-(1-->3)-beta-D-GalN(p)-(1-->.

Mitsuaria chitosanitabida gen. nov., sp. nov., an aerobic, chitosanase-producing member of the ‘Betaproteobacteria’

Four strains (3001T, 2, 12 and 13), which were isolated as chitosanase-producing bacteria from soil from Matsue city (Japan), were studied phenotypically, genotypically and phylogenetically. Based on sequence analysis of 16S rRNA genes, DNA G+C content (67·4–69·2 mol%), quinone type (UQ-8), major fatty acid composition (3-OH 10 : 0, 3-OH 14 : 0) and other phylogenetic studies, strains 3001T, 12 and 13 were found to occupy a separate position in the ‘Betaproteobacteria’. Roseateles depolymerans, Rubrivivax gelatinosus and Ideonella dechloratans were their closest neighbours (93–95 % 16S rRNA gene sequence similarity). The 16S rRNA gene sequence and other characteristics suggested that strain 2 belonged to the genus Flavobacterium. DNA–DNA hybridization experiments supported the conclusion that strains 3001T, 12 and 13 were of the same species (72–78 % DNA hybridization) and only distantly related to I. dechloratans and R. gelatinosus. It is proposed that strains 3001T, 12 and 13 represent a novel genus and species for which the name Mitsuaria chitosanitabida gen. nov., sp. nov. is proposed. The type strain of Mitsuaria chitosanitabida is 3001T (=IAM 14711T=ATCC BAA-476T).

Development of an improved procedure for isolation and purification of exopolysaccharides produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483

A method was developed for the isolation and purification of exopolysaccharide (EPS) produced by Lactobacillus delbrueckii subsp. bulgaricus NCFB 2483 that can be adapted for industrial-scale operation. Hydrolyzed milk medium, which was ultrafiltered to remove molecular species larger than 2.5 x 10(5) Da, was found to be a suitable growth medium for the bacteria, which produced approximately 400 mg EPS/l . Optimal isolation of EPS was achieved using centrifugation, filtration and ethanol precipitation methods. Insoluble and soluble EPS fractions were obtained. The soluble fraction was purified using a series of ethanol precipitations to achieve approximately 98% (w/w) purity. This fraction consisted of galactose, glucose, rhamnose and mannose in the ratio of approximately 5:1:0.6:0.5, with traces of glucosamine.

The calculative nature of microbe-mineral interactions

Microorganisms continually redefine themselves at many levels, including the molecule, cell, and community. Although it was initially assumed that this resulted from the genesis of information within DNA alone, it has since been shown that innovation originates at multiple levels. This occurs through calculative units, each unit consisting of two proliferating structures, one nested within the other and each undergoing changes in structural geometry that affect the proliferation rate of the other. For example, the recombination of genetic structures affects the proliferation of community structures, and the recombination of community structures affects the proliferation of genetic structures. The proliferation of a nested series of structures (e.g., genes proliferating within cells, cells proliferating within communities, communities proliferating within ecosystems) results in a logic circuit that calculates the form and function of each structural element in the series. In this situation each element functions as both a habitat and an inhabitant (environment and organism), and it is this dichotomy that determines the balance of nature. Nested geological structures, such as minerals and continents, also proliferate and redefine themselves in much the same way. Microbe-mineral interactions thus link nested biological calculations to an analogous set of nested geological calculations. Examples include the microorganisms involved in the nucleation (proliferation) of ferric hydroxides, carbonates, silicates, and ice crystals.

Structure of the polysaccharide isolated from the sheath of Sphaerotilus natans

A polysaccharide was isolated from the sheath of a sheathed bacterium, Sphaerotilus natans. The sheath polysaccharide (SPS) was composed of D-glucose and D-(N-acetyl)galactosamine in molar ratios of 1:4. Methylation linkage analysis revealed the presence of the residues of 4-linked glucose, 4-linked (N-acetyl)galactosamine, and 3-linked (N-acetyl)galactosamine in molar ratios of 1:3:1. The oligomer of SPS was prepared with an SPS-specific degrading enzyme from a sheath-degrading bacterium, Paenibacillus koleovorans. The oligomer was derivatized and subjected to fast atom bombardment-mass spectrometry to investigate the monosaccharide sequence of SPS. The structure of SPS was confirmed by nuclear magnetic resonance. The resulting data showed that SPS is a straight-chained basic polysaccharide constructed of a pentasaccharide repeating unit.

Purification and properties of an enzyme capable of degrading the sheath of Sphaerotilus natans

Microorganisms which can degrade and grow on the purified sheath of a sheathed bacterium Sphaerotilus natans were collected from soil and river water. Two bacterial strains were isolated from the soil and designated strains TB and TK. Both strains are rod shaped, negatively stained by gram staining, facultatively anaerobic, and formed ellipsoidal endospores. These characteristics suggested that the isolates belong to the genus Paenibacillus, according to Ash et al. (C. Ash, F. G. Priest, and M. D. Collins, Antonie Leeuwenhoek 64:253-260, 1993). Phylogenetic analysis based on the 16S rDNA supported this possibility. Purification of the sheath-degrading enzyme was carried out from the culture broth of strain TB. The molecular weight of the enzyme was calculated to be 78,000 and 50, 000 by sodium dodecyl sulfate-polyacrylamide electrophoresis and gel filtration chromatography, respectively. Enzyme activity was optimized at pH 6.5 to 7.0 and 30 to 40 degrees C. The reaction was accelerated by the addition of Mg(2+), Ca(2+), Fe(3+), and iodoacetamide, whereas it was inhibited by the addition of Cu(2+), Mn(2+), and dithiothreitol. The enzyme acted on the polysaccharide moiety of the sheath, producing an oligosaccharide the size of which was between the sizes of maltopentaose and maltohexaose. As the reaction proceeded, the absorbance at 235 nm of the reaction mixture increased, suggesting the generation of unsaturated sugars. Incorporation of unsaturated sugars was also suggested by the thiobarbituric acid reaction. It is possible that the enzyme is not a hydrolytic enzyme but a kind of polysaccharide eliminase which acts on the basic polysaccharide.

Subunit-specific interactions of cyanide with the N-methyl-D-aspartate receptor

Cyanide can potentiate N-methyl-D-aspartate receptor-mediated physiological responses in neurons. Here we show that this phenomenon may be attributable to a subunit-specific chemical modification of the receptor directly by the toxin. N-Methyl-D-aspartate (30 microM)-induced whole cell responses in mature (22-29 days in vitro) rat cortical neurons were potentiated nearly 2-fold by a 3-5-min treatment with 2 mM potassium cyanide, as did a similar treatment with 4 mM dithiothreitol. A 1-min incubation with the thiol oxidant 5,5'-dithiobis(2-nitrobenzoic acid) (0.5 mM) readily reversed the potentiation induced by either cyanide or dithiothreitol. Cyanide did not increase further currents previously potentiated by dithiothreitol nor was it able to potentiate responses during brief co-application with the agonist. Transient expression studies in Chinese hamster ovary cells with wild-type and mutated recombinant N-methyl-D-aspartate subunits (NR) demonstrated that cyanide selectively potentiated NR1/NR2A receptors, presumably via the chemical reduction of NR2A. In contrast, currents mediated by NR1/NR2B receptors were somewhat diminished by the metabolic inhibitor. Some of the effects of cyanide on NR1/NR2B receptors may be mediated by the formation of a thiocyanate adduct with a cysteine residue located in NR1. Cyanide thus is able to distinguish chemically between two different N-methyl-D-aspartate receptor subtypes and produce diametrically opposing functional effects.

A mutation that affects fibril protein, development, cohesion and gene expression in Myxococcus xanthus

Extracellular matrix fibrils are involved in the cell-cell interactions of the social prokaryote, Myxococcus xanthus. The fibrils are composed of a carbohydrate backbone and a set of five integral fibrillar proteins (IFPs) ranging from 14 to 66 kDa. As part of an attempt to understand the function(s) of the IFPs, a mutant (ifp-1:20) was generated that lacks IFP-1:20, one of the fibril proteins, as shown by Western blot analysis of both whole cells and isolated fibrils. Unlike those of the parent strain, the fibrils of the mutant were removed easily from the cells by shear forces. Development in ifp-1:20 was aberrant--aggregation and early mound formation were delayed by 6-10 h and mature fruiting bodies never formed. Myxospore production was also greatly reduced. Additionally, fibril-mediated cohesion in ifp-1:20 was changed. Cohesion resulted in chains of cells rather than the characteristic clumps of cells seen for the parent strain. Isolated ifp-1:20 fibrils, unlike wild-type fibrils, could not rescue cohesion of non-cohesive, fibril-negative dsp cells, supporting the notion that the fibrils were functionally altered. The mutation also reduced developmental gene expression by three- to fourfold in omega 4521, a transposon insertion mutant expressed early in development. Expression of a later developmental gene fusion was not affected, suggesting that the fibrils may not be required for later developmental gene expression. These data suggest that intact fibrils may function early in development to facilitate close cell proximity for signal exchange.

Unusually Stable Spinae from a Freshwater Chlorobium sp

A green Chlorobium sp. with spinae, strain JSB1, was isolated from an enrichment culture previously obtained from Fayetteville Green Lake, N.Y. (J. S. Brooke, J. B. Thompson, T. J. Beveridge, and S. F. Koval, Arch. Microbiol. 157:319-322, 1992). Cells were gram-negative, nonmotile rods which contained bacteriochlorophyll c and chlorosomes. Spinae were best seen by transmission electron microscopy in thin sections of cells fixed in the presence of tannic acid. High-resolution scanning electron microscopy showed the spinae randomly distributed at the cell surface and at the junctions between cells. Spinae were physically sheared from cells and isolated from the culture supernatant by ultrafiltration. As observed by electron microscopy, spinae demonstrated unusual structural stability when exposed for 1 h at 37 deg C to chemical treatments such as hydrogen bond-breaking agents, detergents, metal-chelating agents, proteases, and organic solvents. They were stable for 1 h at 37 deg C over the pH range 2.3 to 9.9 and in 1 M HCl and 1 M NaOH. The structural integrity of the spinae was also maintained when spinae were subjected to harsher treatments of autoclaving in 2% (wt/vol) sodium dodecyl sulfate and exposure to dithiothreitol at pH 9 for 1 h at 100 deg C. Partially dissociated spinae were obtained after 5 h at 100 deg C in 1 M HCl and 1 M NaOH. In acid, the tubular spinae became amorphous structures, with no helical striations visible. In alkali, the spinae had dissociated into irregular aggregates of disks. Since both high temperature and extremes of pH were required to achieve partial dissociation of the spinae, the strength of the structure presumably comes from covalent bonding.

Ultrastructure and chemical composition of the sheath of Leptothrix discophora SP-6

Light microscopy and transmission electron microscopy of thin sections and metal-shadowed specimens showed that the sheath of Leptothrix discophora SP-6 (ATCC 51168) is a tube-like extracellular polymeric structure consisting of a condensed fabric of 6.5-nm-diameter fibrils underlying a more diffuse outer capsular layer. In thin sections, outer membrane bridges seen to contact the inner sheath layer suggested that the sheath fabric was attached to the outer layer of the gram-negative cell wall. The capsular polymers showed an affinity for cationic colloidal iron and polycationic ferritin, indicating that they carry a negative charge. Cell-free sheaths were isolated by treatment with a mixture of lysozyme, EDTA, and N-lauroylsarcosine (Sarkosyl) or sodium dodecyl sulfate (SDS). Both Sarkosyl- and SDS-isolated sheaths were indistinguishable in microscopic appearance. However, the Mn-oxidizing activity of Sarkosyl-isolated sheaths was more stable than that of SDS-isolated sheaths. The Sarkosyl-isolated sheaths also contained more 2-keto-3-deoxyoctanoic acid and more outer membrane protein than SDS-isolated sheaths. The oven-dried mass of detergent-isolated sheaths represented approximately 9% of the total oven-dried biomass of SP-6 cultures; the oven-dried sheaths contained 38% C, 6.9% N, 6% H, and 2.1% S and approximately 34 to 35% carbohydrate (polysaccharide), 23 to 25% protein, 8% lipid, and 4% inorganic ash. Gas-liquid chromatography showed that the polysaccharide was an approximately 1:1 mixture of uronic acids (glucuronic, galacturonic, and mannuronic acids and at least one other unidentified uronic acid) and an amino sugar (galactosamine). Neutral sugars were not detected. Amino acid analysis showed that sheath proteins were enriched in cysteine (6 mol%). The cysteine residues in the sheath proteins probably provide sulfhydryls for disulfide bonds that play an important role in maintaining the structural integrity of the sheath (D. Emerson and W.C. Ghiorse, J. Bacteriol. 175:7819-7827, 1993).