Sulfide pulsing as the controlling factor of spinae production in Chlorobium limicola strain UdG 6038

Chlorobium limicola UdG 6038, a green sulfur bacterium, was isolated from anoxic sediments. Cells were gram-negative, non-motile, ovoid shaped, and contained chlorobactene and bacteriochlorophyll c as the main photosynthetic pigments. The DNA G+C content was 56.4 mol%. Ultrastructural studies revealed the presence of abundant spinae (45–110 spinae per cell) attached to the cell wall. India-ink-stained cells observed under the optical microscope were surrounded by a large capsule (5–11 μm total diameter). The presence of this capsule was coincident with the presence of a large number of spinae (> 30 spinae per cell). The mucilaginous capsule was attached to the spinae without penetrating it. In batch culture, the synthesis of spinae in strain UdG 6038 was not affected by changes in temperature, pH, salt concentration, or illumination at physiological ranges and hence, the cells remained spined. The control of spinae production was experimentally confirmed using a semicontinuous batch culture refed by sulfide pulsing. The culture remained at a low spination level (> 30 spinae per cell) only when the duration of sulfide starvation between pulses was less than 5 h. After longer sulfide starvation periods, the cells remained spined (more than 38 ± 6.3 spinae per cell). This observation supports the idea that the duration of sulfide limitation in the culture plays a key role in controlling the spination process in strain C. limicola UdG 6038. Chlorobium spinae may play an eco-physiological role in buoyancy capacity and adhesion of sulfur globules to the cells in natural environments where sulfide concentrations are expected to be highly variable. Revision received: 13 November 1995 / Accepted: 19 January 1996     

Regulatory properties of the ADPglucose pyrophosphorylase from Rhodopseudomonas sphaeroides and from Rhodopseudomonas gelatinosa

Highly purified fractions of chlorosomes and cytoplasmic membranes were isolated from Chloroflexus aurantiacus Ok-70-fl and Chlorobium limicola 6230. These fractions were comparatively analyzed for their pigmentation, phospholipid, glycolipid, and cytochrome c content as well as for their specific activities of succinate dehydrogenase and NADH-oxidase. The data showed that there are some differences in pigmentation and phospholipid content between the isolated fractions of Chloroflexus and Chlorobium. Chlorosomes of Chloroflexus contained a specific BChl a-complex with a characteristic absorption maximum at about 790 nm. This BChl a-complex could not be detected in spectra of chlorosomes from Chlorobium. The near infrared region of the spectra of the isolated cytoplasmic membranes of both organisms revealed considerable differences: The BChl a-complexes of Chloroflexus membranes exhibited peaks at 806 and 868 nm whereas the membranes of Chlorobium had a single BChl a-peak at 710 nm. In contrast to the findings with Chlorobium the chlorosomes of Chloroflexus contained at least twice as much phospholipids as did the cytoplasmic membranes. In Chlorobium the phospholipid content of cytoplasmic membranes is three times that of their chlorosomes. The distribution of all other components (carotenoid composition, enzyme activities, cytochrome c content, and glycolipids) was about the same in both strains. From the data it was concluded that differences in the organization of the photosynthetic apparatus are mainly based on differences of the organization of the photosynthetic units in the cytoplasmic membrane and probably the kind of linkage of the light harvesting system in the chlorosomes with the reaction center in the cytoplasmic membranes.Abbreviations BChl c bacteriochlorophyll c - BChl a bacteriochlorophyll a - DSM Deutsche Sammlung von Mikrorganismen     

Circular dichroism of green bacterial chlorosomes

Positive and negative bands in previously measured circular dichroism (CD) spectra of Chlorobium limicola chlorosomes appeared to be sign-reversed relative to those of Chloroflexus aurantiacus chlorosomes in the 740–750 nm spectral region where bacteriochlorophyll (BChl) c absorbs maximally. It was not clear, however, whether this difference was intrinsic to the chlorosomes or was due to differences in the procedures used to prepare them. We therefore repeated the CD measurements using chlorosomes isolated from both Cb. limicola f. thiosulfatophilum and Cf. aurantiacus using the method of Gerola and Olson (1986, Biochim. Biophys. Acta 848: 69–76). Contrary to the earlier results, both types of chlorosomes had very similar CD spectra, suggesting that both have similar arrangements of BChl c molecules. The previously reported difference between the CD spectra of Chlorobium and Chloroflexus chlorosomes is due to the instability of Chlorobium chlorosomes, which can undergo a hypsochromic shift in their near infrared absorption maximum accompanied by an apparent inversion in their near infrared CD spectrum during isolation. Treating isolated chlorosomes with the strong ionic detergent sodium dodecylsulfate, which removes BChl a, does not alter the arrangement of BChl c molecules in either Chloroflexus or Chlorobium chlorosomes, as indicated by the lack of an effect on their CD spectra.Abbreviations BChl bacteriochlorophyll - Cb. Chlorobium - CD circular dichroism - Cf. Chloroflexus - NIR near infrared     

A thermophilic green sulfur bacterium from New Zealand hot springs,Chlorobium tepidum sp. nov.

Thermophilic green sulfur bacteria of the genus Chlorobium were isolated from certain acidic high sulfide New Zealand hot springs. Cells were Gram-negative nonmotile rods of variable length and contained bacteriochlorophyll c and chlorosomes. Cultures of thermophilic chlorobia grew only under anaerobic, phototrophic conditions, either photoautotrophically or photoheterotrophically. The optimum growth temperature for the strains of thermophilic green sulfur bacteria isolated was 47–48°C with generation times of about 2 h being observed. The upper temperature limit for growth was about 52°C. Thiosulfate was a major electron donor for photoautotrophic growth while sulfide alone was only poorly used. N₂ fixation was observed at 48°C and cell suspensions readily reduced acetylene to ethylene. The G+C content of DNA from strains of thermophilic chlorobia was 56.5–58.2 mol% and the organisms positioned phylogenetically within the green sulfur bacterial branch of the domain Bacteria. The new phototrophs are described as a new species of the genus Chlorobium, Chlorobium tepidum.This paper is dedicated to Professor Norbert Pfennig on the occasion of his 65th birthday     

Chlorobium chlorochromatii sp. nov., a symbiotic green sulfur bacterium isolated from the phototrophic consortium “Chlorochromatium aggregatum”

A symbiotic green sulfur bacterium, strain CaD, was isolated from an enrichment culture of the phototrophic consortium “Chlorochromatium aggregatum”. The capability of the epibiont to grow in pure culture indicates that it is not obligately symbiotic. Cells are Gram-negative, nonmotile, rod-shaped and contain chlorosomes. Strain CaD is obligately anaerobic and photolithoautotrophic, using sulfide as electron donor. Acetate and peptone are photoassimilated in the presence of sulfide and hydrogencarbonate. Photosynthetic pigments contain bacteriochlorophylls a and c, and γ-carotene and OH-γ-carotene glucoside laurate as the dominant carotenoids. In cells from pure cultures, chlorosomes are equally distributed along the inner face of the cytoplasmic membrane. In contrast, the distribution of the chlorosomes in symbiotic epibiont cells is uneven, with chlorosomes being entirely absent at the site of attachment to the central bacterium. The symbiotic epibiont cells display a conspicuous additional layered structure at the attachment site. The G + C content of genomic DNA of strain CaD is 46.7 mol%. On the basis of 16S rRNA sequence comparison, the strain is distantly related to Chlorobium species within the green sulfur bacteria phylum (≤94.6% sequence homology). The novel isolate is therefore described as a novel species within the genus Chlorobium, Chlorobium chlorochromatii.     

Variation in phlorotannin content within two species of brown macroalgae (Desmarestia anceps and D. menziesii) from the Western Antarctic Peninsula

Phlorotannins are metabolites found only in the Phaeophyceae (brown algae) and have a variety of metabolic roles, including both primary (e.g. cell wall construction) and secondary (e.g. herbivore defence and UV protection). This study aimed to establish the level of variation of phlorotannins in two species of dominant Antarctic macroalgae (Desmarestia anceps and D. menziesii). Thirteen samples were taken from specific locations throughout the thallus of multiple individuals at two depths at three locations near Anvers Island, Antarctica. Overall average concentrations were 0.117±0.003 g g^–1dwt in D. anceps and 0.052±0.002 g g^–1dwt in D. menziesii. Concentrations varied greatly at the 13 sampling locations in each individual, but not in any consistent manner. Significant variation occurred between locations in both species and between depths in D. anceps.     

Pinocytosis and locomotion in amoebae

Summary Different methods were used to demonstrate the existence of Ca⁺⁺-binding sites (Ca⁺⁺-bs) at the plasma membrane ofAmoeba proteus. In pinocytoting animals the number (indicated by the average distanced in nm) and size (average longitudinal axiss in nm) of Ca⁺⁺-bs at the cytoplasmic surface of the cell membrane were significantly increased (d=162±15;n=41 ands=93±5;n=47) in comparison to controls (d=208 ±21;n=37 ands=59±8;n=45). The ratio of P: Ca obtained by X-ray microanalysis was in the range of 1.5. The differences observed in the two experimental groups of amoebae are explained by conformational changes in the molecular structure and an increased Ca⁺⁺-permeability of the plasma membrane during induced pinocytosis.Microplasmodia of the acellular slime moldPhysarum polycephalum investigated for comparison were found to have no Ca⁺⁺-bs at the interior cell surface.     

Imaging Escherichia coli using functionalized core/shell CdSe/CdS quantum dots

The internalization of a series of water-soluble CdSe/CdS quantum dots (QDs) stabilized by citrate, isocitrate, succinate, and malate by Escherichia coli is established by epifluorescence and confocal fluorescence scanning microscopy, fluorimetry, and UV–vis spectroscopy on whole and lysed bacterial cells. The organic-acid-stabilized QDs span a range in size from 3.8±1.1 to 6.0±2.4 nm with emission wavelengths from 540 to 630 nm. QDs of different sizes (i.e., 3.8–6 nm) can enter the bacterium and be detected on different fluorescence channels with little interference from other QDs as a result of the distinct emission profiles (i.e., 540–630 nm, respectively). Costaining QD-labeled E. coli with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) demonstrates that the QDs and DAPI are colocalized within E. coli, whereas costaining QD-labeled E. coli with membrane dye FM4-64 shows that the FM4-64 is localized in the outer bacterial membrane and that the QDs are inside.Electronic Supplementary Material Supplementary material is available to authorized users in the online version of this article at .     

The occurrence of coryneform bacteria in the leaf cavity of Azolla

Coryneform bacteria were found associated with the nitrogen fixing blue-green alga, Anabaena azollae in the leaf cavity of Azolla caroliniana. Plate counts indicated ca. 7,400±1,900 bacterial cells per mature leaf cavity or approximately 1 bacterial cell for every algal cell. No other type of bacterium was found in these cavities.     

Composition and optical properties of reaction centre core complexes from the green sulfur bacteria Prosthecochloris aestuarii and Chlorobium tepidum

Photosynthetically active reaction centre core (RCC) complexes were isolated from two species of green sulfur bacteria, Prosthecochloris (Ptc.) aestuarii strain 2K and Chlorobium (Chl.) tepidum, using the same isolation procedure. Both complexes contained the main reaction centre protein PscA and the iron–sulfur protein PscB, but were devoid of Fenna–Matthews–Olson (FMO) protein. The Chl. tepidum RCC preparation contained in addition PscC (cytochrome c). In order to allow accurate determination of the pigment content of the RCC complexes, the extinction coefficients of bacteriochlorophyll (BChl) a in several solvents were redetermined with high precision. They varied between 54.8 mM⁻¹ cm⁻¹ for methanol and 97.0 mM⁻¹ cm⁻¹ for diethylether in the Q_Y maximum. Both preparations appeared to contain 16 BChls a of which two are probably the 13²-epimers, 4 chlorophylls (Chls) a 670 and 2 carotenoids per RCC. The latter were of at least two different types. Quinones were virtually absent. The absorption spectra were similar for the two species, but not identical. Eight bands were present at 6 K in the BChl a Q_Y region, with positions varying from 777 to 837 nm. The linear dichroism spectra showed that the orientation of the BChl a Q_Y transitions is roughly parallel to the membrane plane; most nearly parallel were transitions at 800 and 806 nm. For both species, the circular dichroism spectra were dominated by a strong band at 807–809 nm, indicating strong interactions between at least some of the BChls. The absorption, CD and LD spectra of the four Chls a 670 were virtually identical for both RCC complexes, indicating that their binding sites are highly conserved and that they are an essential part of the RCC complexes, possibly as components of the electron transfer chain. Low temperature absorption spectroscopy indicated that typical FMO–RCC complexes of Ptc. aestuarii and Chl. tepidum contain two FMO trimers per reaction centre. This revised version was published online in June 2006 with corrections to the Cover Date.     

Autecology of an intertidal Alaskan harpacticoid copepod Apolethon sp.

The life history and ecology of a harpacticoid copepod, Apolethon sp., were investigated for one year in the intertidal zone of a subarctic bay in southeastern Alaska. Core samples were collected biweekly at the 0 m tidal level from March, 1992 through March, 1993; zonation and vertical distribution were determined from additional samples. Large seasonal variations in density of Apolethon sp. parallelled that of the total harpacticoid community, with highest densities (124.3±12.5 10 cm^–2; mean ± standard error) in March and lowest densities in May and October (7.6±4.5). The sex ratio of Apolethon sp. varied directly with population density, varying from <0.1 to 1.2 (male:female) during the study period. The species was restricted to a relatively narrow vertical band within the intertidal zone, having its greatest density at – 1 m and being rare above + 1 m tidal height. Adult Apolethon sp. bear conspicuous ovoid mucin structures located laterally on the genital double-somite. The mucin structures are unique to the species; several putative functions are discussed.     

Ecological problems of Lake Ladoga: causes and solutions

We studied the outcome of competition between a large (Brachionus calyciflorus) and a small (Anuraeopsis fissa) rotifer species at five algal (Scenedesmus acutus) concentrations (0.5 × 10⁶ to 40.5 × 10⁶ cells ml^–1) and with varying initial densities in mixed populations (100 to 0% of B. calcyciflorus or A. fissa), the combined initial biomass being 0.2 µg ml^–1 in all test jars. Experiments were conducted at 28 ± 1 °C.Regardless of food concentration, B. calcyciflorus showed a greater increase in biomass than A. fissa, peak densities (mean ± standard error) at the lowest food concentration in the controls being 1.34 ± 0.31 µg dry weight ml^–1 and 0.82 ± 0.08 dry weight ml^–1, respectively. At the lower food concentrations, A. fissa displaced B. calyciflorus and vice versa at the higher food concentrations. At the intermediate food concentrations of 4.5 × 10⁶ cells ml^–1, B. calyciflorus outcompeted A. fissa only if its initial population density was three times higher. The rates of population growth in controls varied from 0.792 ± 0.06 d^–1 to 1.492 ± 0.13 d^–1 for B. calyciflorus and 0.445 ± 0.04 to 0.885 ± 0.01 for A. fissa depending on food level. When both species were introduced together, low food levels favoured higher abundance of A. fissa than B. calyciflorus, suggesting, in nature, it is likely that small Anuraeopsis colonize oligotrophic water bodies more successfully than larger Brachionus. The results also suggest that the outcome of competition depends not only on the size of the competing species and food availability but also on their colonizing density.     

Soil type affects nitrogen conservation in foliage of small Pinus sylvestris L. trees

Nutrient conservation in plants and soil fertility may be intricately linked. We studied nitrogen conservation in small Scots pine (Pinus sylvestrisL.) trees growing in stands on organogenic Dystric Histosols and on mineral Podzols. Nitrogen-resorption efficiency (NRE) and proficiency (NRP) of senescent needles, and mean residence time of nitrogen (MRT) were studied in relation to needle surface area, needle longevity, and leaf mass per area (LMA). Trees on Podzols had higher nitrogen concentration in green needles than the trees on Dystric Histosols, but the nitrogen concentration of yellowing needles was similar for trees on both soil types. NRE averaged 65±3.5% (mean±SD) and 56±7.2% for the trees on Podzols and Dystric Histosols, respectively. Neither NRP (0.44±0.05% and 0.35±0.07%, respectively) nor MRT (8.4±2.3 and 6.1±1.2 years) differed significantly between the stands on the two soil types. Mean needle surface area was significantly smaller in trees on Dystric Histosols (76±29 mm²) than on Podzols (131±38 mm²), whereas needle longevity varied between 2 and 4 years independently of the soil type. Trees invested, on average, the same amount of dry matter per unit of needle area on both soil types. Growth of trees, measured as increment of shoot length, was more restricted on Dystric Histosols (55±18 mm yr^–1) than on Podzols (184±44 mm yr^–1). The results of the correlation analysis applied to pooled data were inconsistent with the relations between traits of stress resistance syndrome observed in inter-specific comparisons. The study indicated that Scots pine trees relocated nitrogen from senescent foliage more efficiently on mineral Podzols than on organogenic Dystric Histosols, but the minimum nitrogen concentration of needles appeared to be similar on both soil types.     

Further evidence from sectioned material in support of the existence of a linear terminal complex in cellulose synthesis

Summary Transmembrane linear terminal complexes considered to be involved in the synthesis of cellulose microfibrils have been described in the plasma membrane ofBoergesenia forbesii. Evidence for the existence of these structures has been obtained almost exlusively using the freeze etching technique. In the present study an attempt has been made to complete these studies using conventional fixation, staining, and sectioning procedures. In developing cells ofBoergesenia forbesii, strongly stained structures traversing the plasma membrane and averaging 598.9 nm ± 171.3 nm in length, 28.7 nm ± 4.2 nm in width, and 35.2 nm ± 6.6 nm in depth have been demonstrated. These structures are considered to be linear terminal complexes. At their distal (cell wall) surface, they appear to be closely associated with cellulose microfibrils. At the proximal (cytoplasmic) surface, they are associated with microtubules and polysomes. A model of the possible interrelation of the terminal complexes and microtubules leading to the generation of cell wall microfibrils is proposed.     

Fine-layer depth relationships of lakewater chemistry, planktonic algae and photosynthetic bacteria in meromictic Lake Fidler, Tasmania

SUMMARY.

• 1 Use of a multi-column thin-layer pneumatic sampler and modified analytic procedures has enabled resolutions of chemical and biological strata at 2.5 or 5.0 cm depth intervals. Examination of meromictic Lake Fidler, Tasmania, indicates the presence of a thin, intense stratum of bacteriochlorohyll d in the upper monimolimnion, associated with a discrete stratum of Chlorobium cf. limicola at the microaerobic interface between the oxygenated and sulphide-rich zones.
• 2 Algae included small populations of Chlorophyceae, Chrysophyceae, Bacillariophyceae and Cryptophyceae. Bacteria included microaerophils and obligate anaerobes, pigmented and colourless, in well-defined strata in the upper monimolimnion. A population of the microcrustacean Calamoecia tasmanica tasmanica was present in the mixolimnion. Chaoborus larvae were concentrated within the Chlorobium layer.
• 3 The chemical profile of Lake Fidler was stable, with a chemocline constant in position relative to the lake bottom. The surface water levels rose and fell through a distance of 1m in conjunction with heavy rainfall in the rainforest, and with river level variation, but had no measurable effect on the absolute position of the chemocline. Marked heterogeneity of dissolved substances at depths in the vicinity of bacteria suggested endogenous influence on pH and gelbstoff (‘gilvin’ in Australia).
• 4 Downwelling light attenuation was influenced primarily by gelbstoff (‘gilvin’) in the mixolimnion, with only red light (peak at 700 nm) measurable below 2 m. Light was absorbed mainly by Chlorobium in the monimolimnion, and was unmeasurable deeper than 3 m.
• 5 The absorption spectrum of the bacteriochlorophyll d in vivo, with a maximum absorbance at 721 nm, corresponds with the available downwelling light penetrating the mixolimnion to the Chlorobium layer.

     

Atomic force microscopy investigations of heterogeneities in the adhesion energies measured between pathogenic and non-pathogenic Listeria species and silicon nitride as they correlate to virulence and adherence

Atomic force microscopy (AFM) was used to probe heterogeneities in adhesion energies measured between pathogenic and non-pathogenic species of Listeria and silicon nitride in water at four levels. Adhesion energies were quantified on individual bacterial cells (cell level), bacterial cells that belonged to an individual Listeria strain but varied in their cultures (strain level), bacterial cells that belonged to an individual Listeria species but varied in their strain type (species level) and on bacterial cells that belonged to the Listeria genus but varied in their species type (genus level). To quantify heterogeneities in the adhesion energies, a heterogeneity index (HI) was defined based on quantified standard errors of mean. At the cell level, spatial variations in the adhesion energies were not observed. For the strain, species, and genus levels, the HI increased with increased adhesion energies. At the species level, the HI increased with strain virulence.     

Coexistence of Chlorobium and Chromatium in a sulfide-limited continuous culture

Competition experiments between Chromatium vinosum and Chlorobium limicola in sulfide-limited continuous culture under photolithoautotrophic conditions resulted in the coexistence of both organisms. The ratio between the two bacteria was dilution-rate as well as pH dependent. The observed coexistence can be explained as a hitherto not reported form of dual substrate limitation. The two substrates involved are the electron donors sulfide (growth-limiting substrate in the reservoir vessel) and extracellular elemental sulfur (formed by Chlorobium as a result of sulfide oxidation). It is argued that, although Chlorobium may have the better affinity for both substrates involved, Chromatium can compete successfully on the basis of its intracellular storage of sulfur. Ecological implication of the observed coexistence with respect to natural blooms are discussed.     

Variation in needle-trace diameter in respect of needle morphology in five conifer species

Needle traces have been used for revealing historical changes in needle longevity of Pinus sylvestris L. and Picea abies (L.) H. Karst. In this paper we compared the needle-trace diameter of five conifer species [Abies sibirica Ledeb., Picea abies, Pinus sylvestris, Pseudotsuga menziesii (Mirb.) Franco and Taxus baccata L.] in respect of needle size. In case of P. sylvestris, we studied how needle-trace diameter varied among different growing sites and among different shoots within a site, and related that variation to needle morphology and structure. Pinus sylvestris had the greatest diameter of needle traces (mean±SD =233±30 m) followed by T. baccata (141±19 m) and P. menziesii (121±30 m). The smallest needle-trace diameter was in A. sibirica (85±21 m) and P. abies (80±18 m). Among species, the needle-trace diameter was strongly correlated with needle length (r =0.93, P <0.05). Within P. sylvestris, the needle-trace diameter was significantly affected by location (P <0.001) and varied significantly among shoots within a location (P <0.001). The shoots of P. sylvestris which had greater average diameter of needle traces, tended to have longer (r =0.36, P <0.05), wider (r =0.55, P <0.05) and heavier (r =0.64, P <0.05) needles with greater stomatal density (r =0.55, P <0.05). Although our results do not allow the use of needle-trace diameter to predict properties of needle structure at the present stage, they nevertheless indicate general trends and point to a need for further studies.     

Relatedness measured by oligonucleotide probe DNA fingerprints and an estimate of the mating system of Sea Lavender (Limonium carolinianum)

Using DNA fingerprint markers within species and populations of wild plants requires information on the relationship between fingerprint similarity and relatedness. We identified a hypervariable marker based on oliog(GATA)₄-hybridization of DpnII-cut genomic DNA from Sea Lavender (Limonium carolinianum). Banding patterns were somatically stable and highly variable among unrelated individuals. Band molecular-weight sizing errors (as a percent of band molecular weight) were estimated at 0.44%±0.003 within gels and 0.76%±0.964 between gels. Band sizing errors defined a 99% confidence bin of ±0.95% (1.90% total) of molecular weight. Band-sharing estimates were based on this bin size and on variance estimates that compensate for non-independent comparisons. Band-sharing among nine unrelated individuals () was 0.198±0.O11. Experimental pollinations designed to produce selfed, fulland half-sib progeny groups led to five selfed progeny groups and no outcrossed progeny (mean band-sharing, ovS=0.468±0.074). A linear regression between band-sharing (S) and relatedness (r) assuming 17% inbreeding was r=0.006+0.914*S (R²=0.973) and established the maximum amount of inbreeding. ovS(0.392±0.022) estimated from wild pollinated seeds from four maternal families was intermediate to unrelated individuals and experimental selfed progeny, giving evidence for mixed mating in wild plants. More extensive plant pedigrees with known levels of inbreeding will be needed to measure variation in the relationship between S and r among populations and families.     

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.