THE IMPACT OF STORM-FLOW ON RIVER BIOFILM ARCHITECTURE1

The impact of storm-flow on river biofilm architecture was investigated using transmission (TEM) and scanning (SEM) electron microscopy. TEM resin substrata were colonized under light-grown (LG) or dark-grown (DG) conditions for 33 weeks in the Clywedog River, North Wales, prior to exposure to ambient-flow (approx. 60 cm·s^?1) or storm-flow (approx. 235 cm·s^?1+ river sediment) in a laboratory flume. Line transect methodology was used to quantify information from TEM ultrathin sections of LG material. In the LG ambient-flow biofilm, bacteria were more abundant directly adjacent to the substratum and were noticeably denser directly under the adnate diatom Cocconeis. Higher in the biofilm, the bacteria were loosely dispersed in the matrix between other cells. Cyanobacteria occurred most frequently as single cells but were also found in large “palisade” formations adjacent to the substratum. Significant horizontal and vertical nearest-neighbor associations were noted for both bacteria and cyanobacteria. Cells of Cocconeis were common adjacent to the substratum, providing shelter to, and often elevated upon, an “organic pad” of bacteria, cyanobacteria, and densely staining exopolysaccharide. Cyanobacteria and Cocconeis were resistant to removal by storm-flow, but Cocconeis frustules were sometimes damaged. Bacteria in the LG storm-flow samples were less common adjacent to the substratum and were sometimes more dispersed higher in the biofilm than in ambient-flow samples. We suggest that storm-flow hydrodynamic forces may redistribute bacteria adjacent to the substratum into higher areas of the biofilm. In addition, bacteria and the exopolysaccharide matrix were sometimes removed down to the substratum by storm-flow, unless beneath Cocconeis. The DG biofilm consisted almost entirely of bacteria. Storm-flow only removed surface growth from DG biofilms, and SEM revealed peritrich stalk abrasion and “blow-down.” Pre-disturbance biofilm architecture appears to influence the form of destruction. We suggest that the “microcosms” of Cocconeis and their underlying cells not only serve as an inoculum to recolonize the surface when conditions permit but enhance immigration by interrupting flow patterns across the surface.     

Cellular changes associated with rest and quiescence in winter-dormant vascular cambium of<Emphasis Type="Italic"> Pinus contorta</Emphasis>

In winter, dormant cambial cells contain many small vacuoles interspersed throughout the cytoplasm. This differs dramatically from actively growing cambial cells whose structure is dominated by large central vacuoles. Structure reported in studies using conventional chemical fixation and transmission electron microscopy (TEM) conflicts with that described earlier for live cambial cells using light microscopy. In this study, cryofixation (high-pressure freezing/freeze substitution) was used to preserve dormant Pinus contorta fusiform cambial cells, revealing structure more consistent with that in early micrographs of live cambial cells. At the ultrastructural level, the plasmalemma was consistently smooth and tightly associated with the cell wall, contrary to the highly in-folded plasmalemma seen in chemically fixed cambial cells. In addition, both TEM and live-cell confocal microscopy demonstrated that, in some places, dormant cells were partitioned into more numerous, smaller vacuoles than were observed after chemical fixation. Populations of different vacuoles were apparent based on size, shape and membrane staining. Larger vacuoles had prominent tonoplasts and were often present as axially elongated, interconnecting networks with associated microfilament bundles. Endoplasmic reticulum fragmented during rest into numerous vesicular structures similar to small vacuoles, then with the transition to quiescence reformed into the smooth cisternal form.     

Probing the consequences of antenna modification in cyanobacteria

Photosynthetic organisms rely on antenna systems to harvest and deliver energy from light to reaction centers. In fluctuating photic environments, regulation of light harvesting is critical for a photosynthetic organism’s survival. Here, we describe the use of a suite of phycobilisome mutants to probe the consequences of antenna truncation in the cyanobacterium Synechocystis sp. PCC 6803. Studies using transmission electron microscopy (TEM), hyperspectral confocal fluorescence microscopy (HCFM), small-angle neutron scattering (SANS), and an optimized photobioreactor system have unraveled the adaptive strategies that cells employ to compensate for antenna reduction. As the phycobilisome antenna size decreased, changes in thylakoid morphology were more severe and physical segregation of the two photosystems increased. Repeating distances between thylakoid membranes measured by SANS were correlated with TEM data, and corresponded to the degree of phycobilisome truncation. Thylakoid membranes were found to have a high degree of structural flexibility, and changes in the membrane system upon illumination were rapid and reversible. Phycobilisome truncation in Synechocystis 6803 reduced the growth rate and lowered biomass accumulation. Together, these results lend a dynamic perspective to the intracellular membrane organization in cyanobacteria cells and suggest an adaptive mechanism that allows cells to adjust to altered light absorption capabilities, while highlighting the cell-wide implications of antenna truncation.     

Silver enhancement of lectin-gold and enzyme-gold cytochemical labelling of eggs of the nematode Onchocerca gibsoni

Summary Wheat germ agglutinin—gold and chitinase—gold complexes were used to demonstrate the presence of chitin on the surfaces of eggs of the animal parasitic nematodeOnchocerca gibsoni. The gold complexes were enhanced by silver intensification and examined by light microscopy (LM), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Distinctive labelling of the egg surfaces was obtained with both probes in all three microscope modes. The results indicate that the small colloidal gold markers (3–10 nm) commonly used for high resolution TEM studies may be silver enhanced and also used for sensitive LM and SEM studies.     

Phycobiliprotein fluorescence of Nostoc punctiforme changes during the life cycle and chromatic adaptation: characterization by spectral confocal laser scanning microscopy and spectral unmixing

Many cyanobacteria are highly adaptable to light quality, and many species undergo a complex life cycle. In this study we show that adaptive changes in the photosynthetic apparatus of cyanobacteria are not only caused by environmental, but also by developmental factors. Spectral confocal laser scanning microscopy (CLSM) was used to analyse in vivo the fluorescence spectra of the photosynthetic pigments chlorophyll a (Chl a), allophycocyanin (APC), phycocyanin (PC) and phycoerythrin (PE) of two Nostoc punctiforme strains. Changes in pigment fluorescence emission occurred in different developmental stages. Strain 1:1-26 showed an emission maximum at 674 nm in motile hormogonia stages, whereas vegetative stages showed maxima at 658 and 575 nm. These changes were not caused by chromatic adaptation. In contrast, the second strain (1:1-26lg) showed distinct fluorescence spectra, pigment localization and clear chromatic adaptation in red light. When these properties are known, both strains can be easily distinguished by the spectral CLSM method, which also allows the localization of the pigments within single cells. To calculate the contribution of individual phycobiliproteins to the observed changes, fluorescence spectra were analysed by spectral unmixing. This allowed the mathematical estimation of fluorescence shares for the individual phycobiliproteins in different developmental stages and both before and after chromatic adaptation. It is concluded that care should be taken when characterizing cyanobacteria by differences in pigment fluorescence, because these differences are influenced not only by chromatic adaptation, but also developmental stages. Spectral CLSM offers a powerful method to study the phycobiliprotein composition in vivo.     

Efficacy of a dual fluorescence method in detecting the viability of overwintering cyanobacteria

Chill in the light is the major environmental stress that cyanobacteria encounter in winter. Cyanobacterial cells may acquire chill‐light tolerance upon exposure to low temperature in autumn and early winter. We sought to establish the efficacy of the dual fluorescence method in detecting the viability of overwintering cyanobacteria and to provide further evidence for the chill‐light tolerance of preconditioned cyanobacteria. Synechocystis sp. PCC 6803 and Microcystis aeruginosa PCC 7806 were exposed to chill (5°C)‐light stress with or without pretreatment at 15°C and stained with SYTO 9 and propidium iodide. Live and dead cells were observed under a fluorescence microscope, and the percentage of viable cells was quantified on a microplate reader. The dual fluorescence method showed consistent results with tests of the ability to reinitiate growth. Cell viability was quantitatively correlated with ratio of SYTO 9/propidium iodide fluorescence. Previously, Microcystis colonies in Lake Taihu had been found to accumulate RNA‐binding protein 1 in autumn and winter. Use of this method directly showed the viability of such Microcystis colonies throughout the winter.

Significance and Impact of the Study

This study established the efficacy of the dual fluorescence method in evaluating the viability of cyanobacteria under chill‐light stress. The results provided the direct evidence for acquired chill‐light tolerance and the viability of overwintering Microcystis colonies. Such information can be useful in prediction of cyanobacterial blooms.     

Splenic angioleiomyoma in an owl monkey (Aotus nancymae)

Background An adult male owl monkey (Aotus nancymae) underwent a splenectomy. When the spleen was removed, a small, nodular mass slightly bulging over the splenic surface was noted. Methods The mass was examined by light and transmission electron microscopy and by immunohistochemistry. Results On light microscopy, the mass was well‐circumscribed, non‐encapsulated, and composed of haphazardly arranged smooth muscle bundles admixed with numerous small capillary‐like structures containing blood. Immunohistochemical (IHC) staining revealed the tumor was strongly positive for smooth muscle actin yielding vascular smooth muscle bundles, and for Factor VIII, staining endothelial cells within the smooth muscle bundles. Transmission electron microscopy (TEM) showed a large portion of the cells to be atypical appearing smooth muscle and a few cells had structures resembling Weibel–Palade bodies indicating endothelial cells. Conclusions Based on cell morphology, by light and TEM, and IHC a final diagnosis of splenic angioleiomyoma was made. This is, to our knowledge, the first report of an angioleiomyoma in a non‐human primate.     

Distribution of virus-like Particles in an Oligotrophic Marine Environment (Alboran Sea,Western Mediterranean)

Viruses are abundant in a variety of aquatic environments, often exceeding bacterial abundance by one order of magnitude. In the present study, the spatial distribution of viruses in offshore waters of the Alboran Sea (Western Mediterranean) have been studied to determine the relationships between viruses and host communities in this oligotrophic marine environment. Viral abundance was determined using two methods: (i) epifluorescence light microscopy using the dsDNA binding fluorochrome DAPI, and (ii) direct counts by transmission electron microscopy (TEM). The results obtained were significantly different; the highest viral counts were obtained by mean of TEM analyses. In all the samples tested the number of viruses was exceeded by the bacterial concentrations, with a ratio between viral and bacterial titers varying between 1.4 and 20. VLP (virus-like particle) counts were not significantly correlated (p > 0.001) with chlorophyll a concentration or the abundance of cyanobacteria. However, there was a positive and significant correlation with bacterial abundance (p < 0.001). The analysis of size and morphology of viral particles by TEM and the correlation obtained between the numbers of VLP and bacteria suggest that the majority of the viral particles in the Alboran Sea are bacteriophages. None of the indirect evidence suggested that eukaryotic algae or cyanobacteria were important host organisms in these waters.     

Light and Electron Microscopy of the Compatible Interaction Between Arabidopsis and the Downy Mildew Pathogen Peronospora parasitica

In this study, we focused on compatible interactions between Peronospora parasitica isolate Emoy‐2 and wild‐type (Oy‐0) and mutant (Ws‐eds1) Arabidopsis thaliana accessions by using light and transmission electron microscopy (TEM). Light microscopy of compatible interactions revealed that conidia germinated and penetrated through the anticlinal cell walls of two epidermal cells. Rapid spreading of the hyphal growth with formation of numerous haustoria within the mesophyll cells was subsequently followed by profuse sporulation in the absence of host cell necrosis on both wild‐type and mutant accessions. TEM observations revealed that coenocytic intercellular hyphae ramified and spread intercellularly throughout the host tissue forming several haustoria in host mesophyll cells. Intracellular haustoria were lobed with the diameter of 6–7 μm. Each haustorium was connected to intercellular hyphae in the absence of apparent haustorial neck. The cytoplasm of the haustorium included the organelles characteristic of the pathogen. Callose‐like deposits were frequently observed at sites of penetration around the proximal region of the haustorial neck. Apart from a few callose ensheatments, no obvious response was observed in host cells following formation of haustoria. Most of mesophyll cells contained normal haustoria and the host cytoplasm displayed a high degree of structural integrity. Absence of host cell wall alteration and cell death in penetrated host cell of both accessions suggest that the pathogen exerts considerable control over basic cellular processes and in this respect, response to this biotroph oomycete differs considerably from responses to other pathogens such as necrotrophs.     

Entrapment and lysis of the cyanobacterium Phormidium luridum by aqueous colonies of Myxococcus xanthus PCO2

A Myxococcus xanthus isolate from a farm drainage ditch, designated strain PCO2, is capable of rapidly inducing lysis of both agar and liquid-grown cultures of the cyanobacterium, Phormidium luridum, var. olivacea. Microscopic studies of the predator-prey interaction demonstrate that lysis of the cyanobacterium occurs within clumps and spherules formed by the cells of M. xanthus PCO2. In the earliest stage, one sees the formation of irregular microclumps of bacteria and cyanobacterial filaments. As these clumps mature, colonies 1 to 6 mm in diameter develops. The center of these densely green colonies contains cyanohacteria in various stages of degradation, while the periphery is almost exclusively a tightly woven mass of myxobacterial cells. Electron microscopy shows that long extrusions from the outer membrane of the M. xanthus PCO2 cells are involved in the formation both of initial clumps and of mature colonial spherules. These extrusions appear to efficiently entangle the cyanobacterial filaments in the culture environment. Predator-to-prey ratios of 1/10, 1/100 and 1/1,000 have resulted in cyanobacterial lysis. Because the entrapment and lysis of P. luridum filaments by M. xanthus PCO2 appears to be independent of any other heterotrophic nutritional requirement, as well as of environmental agitation, this system has potential as a biological control technique for undesirable aquatic cyanobacteria.Abbreviations TEM transmission electron microscopy - SEM scanning electron microscopy - AB algae broth - ABT algae broth plus 0.2% tryptone     

Effects of bacillamide and newly synthesized derivatives on the growth of cyanobacteria and microalgae cultures

The antialgal activity of newly synthesized bacillamides against several cyanobacteria and microalgae isolates was screened using a rapid 96-well microplate bioassay. Cultures were exposed to serial dilutions of each bacillamide derivative (0–160 μg mL⁻¹) in the microplate wells and daily optical measurements were used to estimate growth over a 216 h period. Inhibition values (%) were calculated from the estimated growth curves and inhibitory concentrations (IC₅₀-216 h) were obtained from the sigmoidal inhibition curves fitted by regression analysis. The effects of bacillamides on cell morphology and ultrastructure were also analysed by light and transmission electron microscopy. In general, the toxic cyanobacteria Microcystis aeruginosa, Aphanizomenon gracile, Anabaena circinalis and Anabaenopsis circularis were much more sensitive to bacillamides then the chlorophytes Ankistrodesmus falcatus and Scenedesmus obliquus. However, clear signs of morphological and ultrastructural changes induced by bacillamide were observed on both cyanobacteria and chlorophytes. Other cyanobacteria, namely the nostocalean Nodularia spumigena and the oscillatorialeans Leptolyngbya sp. and Planktothrix rubescens, exhibit higher tolerances to bacillamides, similar to that shown by different eukaryotic microalgae. Diatoms, on the other hand, proved to be quite as sensitive to most bacillamides as the most affected cyanobacteria. The properties of 5-iodo-Bacillamide (algicide or algistatic) were further investigated. This compound acted as an algistactic agent against eukaryotic algae and, depending on its concentration, acted as either an algicide or algistactic agent against most of the cyanobacteria tested. Although bacillamides cannot be considered as broad spectrum cyanobacterial algicides, different bacillamides might be of use in selectively controlling the growth of particular species of cyanobacteria.     

RESTING CYST FORMATION OF EUTREPTIELLA GYMNASTICA (EUGLENOPHYCEAE) IN THE NORTHERN COASTAL BALTIC SEA1

Resting cyst formation of Eutreptiella gymnastica Throndsen was observed during a mesocosm experiment, where nutrient enrichment had induced almost a unialgal bloom. Cells and resting cysts of E. gymnastica were examined in scanning (SEM) and transmission electron microscopy (TEM) and light microscopy. Mature cysts were spherical, with a smooth thick mucilaginous cover that appeared layered when observed with the TEM. Intermediate forms were spherical and lacking flagella and a mucilaginous cover; the euglenoid pellicular striation and canal opening were easily visible. The volume of these intermediate spherical cells and mature cysts was estimated to have increased threefold compared to flagellated cells and contained many paramylon grains. When the cells were grazed by zooplankton, the paramylon grains passed the gut intact and were packed into fecal pellets. Intact undigested paramylon grains were observed in SEM after the breaking up of the pellets.     

Effects of Daphnia exudates and sodium octyl sulphates on filament morphology and cell wall thickness of Aphanizomenon gracile (Nostocales), Cylindrospermopsis raciborskii (Nostocales) and Planktothrix agardhii (Oscillatoriales)

Grazing is recognized as one of the selective factors shaping the morphology and physiology of cyanobacteria. A recent study has shown that the filamentous cyanobacterium Aphanizomenon gracile strain SAG 31.79 thickened in the presence of Daphnia (Cladocera) and its exudates. The aims of our study were: (1) to determine whether this type of response to Daphnia cues is common for other strains of A. gracile, and other species of filamentous cyanobacteria, (2) to test whether the response is due to nutrients recycled by Daphnia, or kairomone induced, and (3) whether it is related to toxin production. Prior to the experiment, cyanobacterial strains were inspected using chromatographic methods for the presence of two toxins, cylindrospermopsin (CYN) and three homologues of microcystin (MC-RR, MC-YR, MC-LR). HPLC analyses showed that all strains were free of cylindrospermopsin, whereas microcystins were detected only in one strain (Planktothrix agardhii). We then tested whether Daphnia exudates can cause thickening of cyanobacterial filaments, which would suggest the morphological changes in cyanobacterial filaments are caused by recycled nutrients. Cyanobacteria were also exposed to sodium octyl sulphate (a commercially available Daphnia kairomone). Transmission electron microscopy (TEM) was used to check whether Daphnia exudates and sodium octyl sulphate trigger thickening of cyanobacterial cell walls, which would be a defence mechanism against grazing. The TEM analysis revealed no significant effect of either Daphnia exudates or kairomone (sodium octyl sulphate) on the cell wall thickness of cyanobacteria. However, our study showed that Daphnia exudates triggered filament thickening in nostocalean cyanobacteria, while filaments of the oscillatorialean strain P. agardhii did not show this response. It was also demonstrated that sodium octyl sulphate alone can also cause filament thickening, which suggests that this might be a specific defence response to the presence of grazers.     

Seasonal shifts in community composition and proteome expression in a sulphur-cycling cyanobacterial mat

Seasonal changes in light and physicochemical conditions have strong impacts on cyanobacteria, but how they affect community structure, metabolism, and biogeochemistry of cyanobacterial mats remains unclear. Light may be particularly influential for cyanobacterial mats exposed to sulphide by altering the balance of oxygenic photosynthesis and sulphide-driven anoxygenic photosynthesis. We studied temporal shifts in irradiance, water chemistry, and community structure and function of microbial mats in the Middle Island Sinkhole (MIS), where anoxic and sulphate-rich groundwater provides habitat for cyanobacteria that conduct both oxygenic and anoxygenic photosynthesis. Seasonal changes in light and groundwater chemistry were accompanied by shifts in bacterial community composition, with a succession of dominant cyanobacteria from Phormidium to Planktothrix, and an increase in diatoms, sulphur-oxidizing bacteria, and sulphate-reducing bacteria from summer to autumn. Differential abundance of cyanobacterial light-harvesting proteins likely reflects a physiological response of cyanobacteria to light level. Beggiatoa sulphur oxidation proteins were more abundant in autumn. Correlated abundances of taxa through time suggest interactions between sulphur oxidizers and sulphate reducers, sulphate reducers and heterotrophs, and cyanobacteria and heterotrophs. These results support the conclusion that seasonal change, including light availability, has a strong influence on community composition and biogeochemical cycling of sulphur and O₂ in cyanobacterial mats.     

Does pigment composition reflect phytoplankton community structure in differing temperature and light conditions in a deep alpine lake? An approach using HPLC and delayed fluorescence techniques1

In vivo delayed fluorescence (DF) and HPLC/CHEMTAX pigment analyses were used to investigate seasonal and depth distributions of phytoplankton in a deep alpine mesotrophic lake, Mondsee (Austria). Using chl a equivalents, we determined significant relationships with both approaches. Community structure derived from pigment ratios of homogenous samples was compared with microscopic estimations using biovolume conversion factors. An advantage of the HPLC/CHEMTAX method was that it gave good discrimination among phytoplankton groups when based on a pigment ratio matrix derived from multiple regression analysis. When a single algal group was dominant, such as epilimnetic diatoms or hypolimnetic cyanobacteria in the deep chl maxima, HPLC/CHEMTAX results were significantly correlated with microscopic estimations (diatoms: r = 0.93; cyanobacteria: r = 0.94). Changes in the composition of photosynthetically active pigments were investigated with DF and benefited from excitation spectra that considered all light‐harvesting pigments, which made it possible to assess the enhancement of accessory photosynthetically active pigments relative to active chl a (chl a_DF672). Changes in similarity index, based on normalized DF spectra, confirmed compositional shifts observed by microscopy. At chosen wavelengths of DF spectra, 534 and 586 nm, we generally observed a significantly inverse relationship between normalized DF intensities and temperature and light along both seasonal and depth gradients. The relative increase in photosynthetically active pigments other than chl a_DF672 under low light and temperature was caused by an increasing dominance of diatoms and/or phycobilin‐rich cyanobacteria and Cryptophyta. DF spectra provided a more accurate picture of community pigments acclimated to light and temperature conditions than the β‐carotene:chl a ratio derived from HPLC.     

Pollen morphology of some species belonging to Codonoprasum and Allium sections of Allium (Liliaceae-Alliaceae) genus

Pollen morphology of 14 Allium L. species grown in Turkey, that belong to the sections Codonoprasum and Allium, were investigated under LM (light microscopy) and by SEM (scanning electron microscopy). However, the pollens of 5 species were investigated under TEM (transmission electron microscopy). Detailed pollen morphological characteristics are given for Allium in the family on the basis of the results presented here together with data from the literature. The genera Allium homogeneous in both aperture type and exine ornamentation. It is suggested that some palynological characters, such as aperture type and the presence of an operculum, could be of taxonomic value at the section level.     

Screening of different algae for green synthesis of gold nanoparticles

The cyanobacteria Phormidium valderianum, P. tenue and Microcoleus chthonoplastes and the green algae Rhizoclonium fontinale, Ulva intestinalis, Chara zeylanica and Pithophora oedogoniana were exposed to hydrogen tetrachloroaurate solution and were screened for their suitability for producing nano‐gold. All three cyanobacteria genera and two of the green algae (Rhizoclonium fontinale and Ulva intestinalis) produced gold nanoparticles intracellularly, confirmed by purple colouration of the thallus within 72?h of treatment at 20°C. Extracted nanoparticle solutions were examined by UV‐vis spectroscopy, transmission electron microscopy (TEM) and X‐ray diffractometry (XRD). XRD confirmed the reduction of Au (III) to Au (0). UV‐vis spectroscopy and TEM studies indicated the production of nanoparticles having different shapes and sizes. Phormidium valderianum synthesized mostly spherical nanoparticles, along with hexagonal and triangular nanoparticles, at basic and neutral pHs (pH 9 and pH 7, respectively). Medicinally important gold nanorods were synthesized (together with gold nanospheres) only by P. valderianum at acidic pH (pH 5); this was initially determined by two surface plasmon bands in UV‐vis spectroscopy and later confirmed by TEM. Spherical to somewhat irregular particles were produced by P. tenue and Ulva intestinalis (TEM studies). The UV‐vis spectroscopy of the supernatant of other algal extracts indicated the formation of mostly spherical particles. Production of gold nanoparticles by algae is more ecofriendly than purely chemical synthesis. However, the choice of algae is important: Chara zeylanica and Pithophora oedogoniana were found to be unable to produce nanoparticles.     

Visualization of proteins in intact cells with a clonable tag for electron microscopy

Identification of proteins in 3D maps of cells is a main challenge in structural cell biology. For light microscopy (LM) clonable reagents such as green fluorescent protein represented a real revolution and equivalent reagents for transmission electron microscopy (TEM) have been pursued for a long time. To test the viability of the metal-binding protein metallothionein (MT) as a tag for TEM in cells we have studied three MT-fusion proteins in Escherichia coli: AmiC, a component of the division ring, RecA, a DNA-binding protein, and a truncated cytoplasmic form of maltose-binding protein (MBP). Proteins fused to MT were expressed in E. coli. live cells treated with gold salts were processed by fast-freezing and freeze-substitution. Small electron-dense particles were detected in sections of bacteria expressing the MT-fusion proteins and immunogold labelling confirmed that these particles were associated to the fusion proteins. The distribution of the particles correlated with the functional locations of these proteins: MBP–MT3 concentrated in the cytoplasm, AmiC-MT1 in the bacterial division ring and RecA-MT1 in the nucleoid. The electron-dense tag was easily visualized by electron tomography and in frozen-hydrated cells.     

Consecutive light microscopy, scanning-transmission electron microscopy and transmission electron microscopy of traumatic human brain oedema and ischaemic brain damage

Cortical biopsies of 11 patients with traumatic brain oedema were consecutively studied by light microscopy (LM) using thick plastic sections, scanning-transmission electron microscopy ((S)TEM) using semithin plastic sections and transmission electron microscopy (TEM) using ultrathin sections. Samples were glutaraldehyde-osmium fixed and embedded in Araldite or Epon. Thick sections were stained with toluidine-blue for light microscopy. Semithin sections were examined unstained and uncoated for (S)TEM. Ultrathin sections were stained with uranyl and lead. Perivascular haemorrhages and perivascular extravasation of proteinaceous oedema fluid were observed in both moderate and severe oedema. Ischaemic pyramidal and non-pyramidal nerve cells appeared shrunken, electron dense and with enlargement of intracytoplasmic membrane compartment. Notably swollen astrocytes were observed in all samples examined. Glycogen-rich and glycogen-depleted astrocytes were identified in anoxic-ischaemic regions. Dark and hydropic satellite, interfascicular and perivascular oligodendrocytes were also found. The status spongiosus of severely oedematous brain parenchyma observed by LM and (S)TEM was correlated with the enlarged extracellular space and disrupted neuropil observed by TEM. The (S)TEM is recommended as a suitable technique for studying pathological processes in the central nervous system and as an informative adjunct to LM and TEM.