Compact water-window transmission X-ray microscopy

We demonstrate sub-100 nm resolution water-window soft X-ray full-field transmission microscopy with a compact system. The microscope operates at lambda = 3.37 nm and is based on a 100 Hz table-top regenerative debris-free droplet-target laser-plasma X-ray source in combination with normal-incidence multilayer condenser optics for sample illumination. High-spatial-resolution imaging is performed with a 7.3% efficiency nickel zone plate and a 1024 x 1024 pixel CCD detector. Images of dry test samples are recorded with exposure times of a few minutes and show features smaller than 60 nm.

Parasitic diatoms inside antarctic sponges

Antarctic sponges may host large populations of planktonic and benthic diatoms. After settling on the sponge, these diatoms enter its body through pinacocytes (1) and form, there, large mono- or pauci-specific assemblages. Yet the total amount of carbohydrates in the invaded sponge tissue is inversely correlated with that of chlorophyll-a. We suggest, therefore, that endobiont diatoms utilize the products of the metabolism of their host as an energy source. This is the first evidence indicating that an endobiotic autotrophic organism may parasitize its animal host. Moreover, this unusual symbiotic behavior could be a successful strategy that allows the diatom to survive in darkness.

Vertical migration behaviour of diatom assemblages of Wadden Sea sediments (Dangast, Germany): a study using cryo-scanning electron microscopy

The vertical migration behaviour of diatom assemblages inhabiting Wadden Sea sediments near Dangast (Germany) was investigated using cryo-scanning electron microscopy. The diatom assemblages were dominated by small Navicula species. Intertidal sediments which were located at different distances from the high tide level or stayed submerged even throughout low tides were chosen. Samples were prepared and cryofixed in the field. Sampling was restricted to three sets: (i) before the onset of vertical migration, (ii) 3 to 5 h after the onset of vertical migration, and (iii) before the area became flooded again or just prior to dusk. The diatom assemblages inhabiting the different types of sediments did not always show the same response. When the tidal cycle exposed the sediment surfaces during the night cell densities increased in the early morning hours with the onset of light. Later on, although the photon flux density was still increasing, cell densities stayed constant or decreased before the water flooded the areas around noon. In experiments in which the water drained off around noon and the areas became exposed throughout the entire afternoon, cell densities increased even up to dusk when the photon flux density had dropped to values below 20 microM photons m-2 s-1. In an experiment in which the last sampling occurred at 10.15 pm, when the photon flux density had already declined below 10 microM photons m-2 s-1, cell densities had decreased to lower values. This was ca. 1 h before the area was flooded again. Finally, cryo-scanning electron microscopy revealed frequently occurring micro-patches of diatom assemblages which could be differentiated into typical areas of lower and higher cell densities further complicating the pattern of light or water cover induced movements.

Oxygen-evolving diatom thylakoid membranes

Two protocols were developed that yielded purified oxygen-evolving thylakoid membranes from the diatom Cylindrotheca fusiformis. One protocol employed sonication, while the second involved French press lysis of protoplasts formed by brief culture of cells in a cation-depleted medium. Regardless of the method of cell breakage, some damage to electron transport components occurred. For preservation of both light-dependent electron transport activity and in vivo fluorescence properties, 2 M sorbitol proved to be more effective than 1 M sorbitol, regardless of the method used for cell lysis. Thylakoids purified in 2 M sorbitol using the protoplast/French press method showed the best preservation of in vivo fluorescence emission signals and Photosystem II activity with ferricyanide was completely inhibited by DCMU. Thylakoids purified in 2 M sorbitol using sonication had higher rates of Photosystem II activity with ferricyanide, but this activity was less sensitive to DCMU. Whole-chain electron transport activity was low in all preparations. This is the first report of O2 evolution and of long-wavelength fluorescence in purified thylakoids of any chromophytic alga.

Scanning and transmission electron microscopical evidence of the capacity of diatoms to penetrate the alveolo-capillary barrier in drowning

The diagnostic value of diatom analysis for drowning is considered to be one of the most controversial arguments in forensic medicine. However, the theoretical assumption of the method, i.e. the capacity of diatoms to penetrate the alveolo-capillary barrier during drowning, has never been addressed. Using scanning (SEM) and transmission electron microscopy (TEM), we have investigated the interaction of a natural population of diatoms and an unialgal culture of Phaeodactylum tricornutum (PT) with the alveolo-capillary barrier in an experimental model of drowning. The SEM analysis allowed the identification of several diatom species along the whole airways and their close interaction with the alveolar wall, but was poorly informative about the effective penetration of diatoms into pulmonary vessels. The TEM analysis was more informative and allowed a precise identification of the PT cells in alveolar spaces and to detect their phagocytosis by alveolar macrophages. PT penetrated into the pulmonary vessels through the thinnest portions of the alveolo-capillary barrier and through the interstitial spaces and were identified in pulmonary capillaries and venules. The morphological demonstration of the capacity of diatoms to penetrate the alveolo-capillary barrier is a step forward in assessing the potentiality, reliability and limitations of diatom analysis on a new basis as a tool for the diagnosis of drowning.

Substratum adhesion and gliding in a diatom are mediated by extracellular proteoglycans

Diatoms are unicellular microalgae encased in a siliceous cell wall, or frustule. Pennate diatoms, which possess bilateral symmetry, attach to the substratum at a slit in the frustule called the raphe. These diatoms not only adhere, but glide across surfaces whilst maintaining their attachment, secreting a sticky mucilage that forms a trail behind the gliding cells. We have raised monoclonal antibodies to the major cell surface proteoglycans of the marine raphid diatom Stauroneis decipiens Hustedt. The antibody StF.H4 binds to the cell surface, in the raphe and to adhesive trails and inhibits the ability of living diatoms to adhere to the substratum and to glide. Moreover, StF.H4 binds to a periodate-insensitive epitope on four frustule-associated proteoglycans (relative molecular masses 87, 112, and > 200 kDa). Another monoclonal antibody, StF.D5, binds to a carbohydrate epitope on the same set of proteoglycans, although the antibody binds only to the outer surface of the frustule and does not inhibit cell motility and adhesion.

["Depilation" by micro-algae?]

Itching, reddening and depilation of body hairs was reported by swimmers in the Attersee-lake in Austria. Initially, an environmental crime was suspected. However, further investigations showed that a biological cause was probably responsible for these symptoms. The accrustations found on body hairs turned out in the scanning electron microscope to be dried mucus containing numerous diatoms. The prevailing micro-algae were identified as Cyclotella comensis. Thus, although the phenomenon had a natural, harmless cause, it may happen again given the appropriate environmental conditions.

Toxic action of copper on the membrane system of a marine diatom measured by flow cytometry

Flow cytometric measurements were used to investigate the toxic action of copper on some Phaeodactylum tricornutum membrane systems. Throughout the time of metal exposure, the percentage of viable cells decreased as copper concentration increased. The forward scatter signal increased as a result of copper exposure. After 72 h of metal exposure, cultures with 0.5 and 1 mg l-1 of copper showed an important increase in the peroxidase activity in comparison with control cells. Cells cultured with copper presented alterations in the membrane potential, increasing as copper concentration increased, after 96 h of metal exposure. Results obtained in this work showed that copper induced a degenerative process in P. tricornutum cells, closely related with alternations or disorders in membrane systems.

Alveus, gen. nov. (Bacillariaceae, Bacillariophyta), a heavily silicified diatom found in warm water oceans

Scanning electron microscope images of complete and damaged frustules of Nitzschia marina Grun. revealed an unusual chambered structure of the valve. This structure is not present in any existing nitzschioid genus and warrants an independent generic status for this taxon, which is therefore separated into Alveus gen. nov. Generic and emended specific definitions are provided and presented in the context of their relationship to other genera within the family Bacillariaceae. Deep relief of the inner surface of Alveus valves is similar to that of genera Fragilariopsis, Denticulopsis, Neodenticula, and Crucidenticula. It differs from all these diatoms in the alveolar striation. This heavily silicified diatom was found in samples from the US Joint Global Oceanographic Flux Studies cruise TT007 stations 2 and 4, (9 degrees and 5 degrees N respectively, 140 degrees W) in the equatorial Pacific. Presently, this uncommon species is restricted to warm waters. It is very common in the surface sediments of the equatorial Pacific and Indian Ocean and in the tropical and subtropical Atlantic. The sedimentary record of Alveus marinus goes back to the Middle Late Miocene (approximately 8 Ma years).

A hybrid scanning force and light microscope for surface imaging and three-dimensional optical sectioning in differential interference contrast

The design of a scanned-cantilever-type force microscope is presented which is fully integrated into an inverted high-resolution video-enhanced light microscope. This set-up allows us to acquire thin optical sections in differential interference contrast (DIC) or polarization while the force microscope is in place. Such a hybrid microscope provides a unique platform to study how cell surface properties determine, or are affected by, the three-dimensional dynamic organization inside the living cell. The hybrid microscope presented in this paper has proven reliable and versatile for biological applications. It is the only instrument that can image a specimen by force microscopy and high-power DIC without having either to translate the specimen or to remove the force microscope. Adaptation of the design features could greatly enhance the suitability of other force microscopes for biological work.

The effects of diazepam on mitosis and the microtubule cytoskeleton. I. Observations on the diatoms Hantzschia amphioxys and Surirella robusta

The effects of diazepam (DZP) on mitosis and the microtubule (MT) cytoskeleton in the live diatoms Hantzschia amphioxys and Surirella robusta were followed using time-lapse video microscopy. Similarly treated cells were fixed and later examined for immunoflouresence staining of MTs or for transmission electron microscopy. DZP treatment (250 microM) had no effect on interphase cells but affected mitosis, resulting in the majority of prometaphase and metaphase chromosomes releasing from one or both spindle poles and collecting irregularly along the central spindle. Chromosomes remaining attached to one pole continued to display slight prometaphase oscillations; however, this activity was never observed in metaphase spindles. Following removal of DZP, some chromosomes still bipolarly attached, immediately released elastically from one pole. Within the first 2 minutes of recovery, all chromosomes recommenced spindle attachment, exhibiting normal prometaphase oscillations and proceeded through mitosis. DZP treatment during anaphase had no detectable effect on chromosome motion or cell cleavage. These results suggest that DZP acts as an anti-MT agent, selectively affecting polar MTs at prophase, prometaphase and metaphase, and thereby weakening kinetochore connection to the poles. From these and other results (unpublished), its mode of action is different to that of most anti-MT agents.

Image sharpness and contrast transfer in coherent confocal microscopy

Confocal microscopes provide clear, thin optical sections with little disturbance from regions of the specimen that are not in focus. In addition, they appear to provide somewhat greater lateral and axial image resolution than with non-confocal microscope optics. To address the question of resolution and contrast transfer of light microscopes, a new test slide that enables the direct measurement of the contrast transfer characteristics (CTC) of microscope optics at the highest numerical aperature has been developed. With this new test slide, the performance of a confocal scanning laser microscope operating in the confocal reflection mode and the non-confocal transmission mode was examined. The CTC curves show that the confocal instrument maintains exceptionally high contrast (up to twice that with non-confocal optics) as the dimension of the object approaches the diffraction limit of resolution; at these dimensions, image detail is lost with non-confocal microscopes owing to a progressive loss of image contrast. Furthermore, we have calculated theoretical CTC curves by modelling the confocal and non-confocal imaging modes using discrete Fourier analysis. The close agreement between the theoretical and experimental CTC curves supports the earlier prediction that the coherent confocal and the incoherent non-confocal imaging mode have the same limit of resolution (defined here as the inverse of the spatial frequency at which the contrast transfer converges to zero). The apparently greater image resolution of the coherent confocal optics is a consequence of the improved contrast transfer at spacings which are close to the resolution limit.

Novel method for stereo imaging in light microscopy at high magnifications

A new method for realizing direct stereoscopic (3D) views of thick microscopic sections employs multiple oblique illuminating beams and a single objective lens. Excellent 3D images are obtained in the higher magnification range, where conventional stereo microscopes no longer function. Using conventional microscope optics, significant increases in depth of focus and sharpness are demonstrated.

Observation of biological materials by X-ray photoelectron-conversion contact microscopy

Dried biological specimens, such as fossil diatoms, collagen, nerve tissue and spicule of Trepang, were observed by X-ray photoelectron-conversion contact microscopy. A spatial resolution of 0.2 microns was attained. The fossil diatom image shows a clear difference below and above the carbon K-absorption edge (4.46 nm).