Possible role of ubiquitin in silica biomineralization in diatoms: identification of a homologue with high silica affinity

In diatom silicon biomineralization peptides are believed to play a role in silica precipitation and the consequent structure direction of the cell wall. Characterization of such peptides should reveal the nature of this organic-inorganic interaction, knowledge that may eventually well be used to expand the existing range of artificial silicas ("biomimicking"). Biochemical studies on Navicula pelliculosa revealed a set of proteins, which have a high affinity for a solid silica matrix; some were only eluted from the matrix when SDS-denaturation was applied. One of the proteins with an affinity for silica, about 8.5 kDa, is shown to be a homologue of ubiquitin on the basis of its N-terminal amino acid sequence; ubiquitin itself is a highly conserved 8.6 kDa protein that is involved in protein degradation. This finding is in line with a model of silica biomineralization in diatoms that implies the removal of templating polypeptides when pores in the growing cell wall develop. Western blotting with specific anti-ubiquitin antibodies confirmed cross-reactivity. Immunocytochemical localization of ubiquitin indicates that it is present along the diatom cell wall and inside pores during different stages of valve formation.

Bioinspired synthesis of new silica structures

Silicon and oxygen are the two most abundant elements in the Earth's crust but despite the vast scientific literature on crystalline and amorphous silica, new chemistries, structures and applications continue to be discovered for compounds formed from these elements--thus we present here for the first time the formation of new amorphous silica structures that were uniquely synthesized by a bioinspired synthetic system.

Ice binding, recrystallization inhibition, and cryoprotective properties of ice-active substances associated with Antarctic sea ice diatoms

Extracellular macromolecules associated with Antarctic sea ice diatoms were previously shown to have ice-binding activities. The function of these ice-active substances (IASs) has not been identified. Here we show that two of the IASs have a strong ability to inhibit the recrystallization of ice, possibly signifying a cryoprotectant function. To test this possibility, two species of marine diatom (one Antarctic and one temperate) were subjected to a single freeze-thaw cycle (approximately 20h at -4 or -5 degrees C) in the presence or absence of IAS. Viability, based on a double staining technique, was 15-29% higher in the presence of IAS. Etching of single crystal ice hemispheres grown from dilute IAS solutions indicated that the IASs bind to specific faces of ice and are incorporated into the ice lattice. Together, these results suggest that the IASs acts as a cryoprotectant, probably through some ice-binding mechanism.

Microbial spheres: a novel cyanobacterial-diatom symbiosis

Cyanobacteria, algae and bacteria are widespread inhabitants of North Sea microbial mats. Our studies of these populations showed uncommon modes of living and extraordinary structures, which have not been described before. The structures are spherical objects covering a community of cyanobacteria, diatoms and bacteria. The cultivation of these communities in the laboratory and intensive observations of their exceptional movement has led to some spectacular findings. The sphere formations go through different phases with variation in the dominance of different microorganisms. The role of the bacteria is the most important in the first phase, and can be increased by the addition of signal substances. Spheres surrounded by envelopes of unknown composition and permeability appear, with numerous bacteria and sporadic diatoms inside. Then the cyanobacteria penetrate the spheres and arrange themselves at the surface. The communities proliferate over some weeks and are finally released. Laboratory expositions of the microbial communities to different parameters pinpoint the limits of sphere formation. The metabolic products of the sphere communities are concentrated in the spheres and lead to a different kind of compound compared with the surrounding environment. In this way, the microbial communities strongly influence the structure of the sediments. Uncommon circular structures, which develop into spheres between 0.08 and 3 mm in size were found in subcultures of non-axenic filamentous cyanobacteria enrichments from North Sea microbial mats. These filamentous cyanobacteria ( Phormidium sp.) together with associated benthic diatoms of the genus Navicula and associated heterotrophic bacteria were held as reproducible synergistic cultures. Phormidium sp. filaments tightly intertwined with each other, formed the surface of the spheres, trapping diatoms inside. The formation of "spheres" was the result of radial and synchronous movements of the cyanobacteria. In old cultures, the direction of the cyanobacterial movement has turned in the opposite direction, away from the sphere. The integrity of large "spheres" was influenced by chemotactic phenomena and maintained by some type of trichome-trichome interaction. This suggests the presence of metabolic secondary products, which attract cyanobacteria and influence their movement in a form of chemotactic response.

Valve morphology of the benthic diatom Fallacia marnieri (Manguin) Witkowski (Sellaphoraceae--Bacillariophyta)

The genus Fallacia Stickle & Mann includes naviculoid birraphid diatoms with H-like plastids, valves with uniseriate striae and covered by porous conopea, rounded areolae occluded by hymens, and depressed hyaline lyriform area characterizing the valvar surface. The species Fallacia marnieri was found in samples collected in King George Island, Antarctic Peninsula, on which an electron microscopy study and literature revision were carried out. From this investigation, we found that since Fallacia marnieri has the diagnostic structures of the genus, its recent inclusion in Fallacia is justified. The species was found on rocks of an intertidal region, and seems to be endemic in cold regions, as indicated in the literature.

Algicidal activity and gliding motility of Saprospira sp. SS98-5

A marine bacterium, Saprospira sp. SS98-5, which was isolated from Kagoshima Bay, Japan, was able to kill and lyse the cells of the diatom Chaetoceros ceratosporum. The multicellular filamentous cells of this bacterium captured the diatom cells, formed cell aggregates, and lysed them in an enriched sea water (ESS) liquid medium. Strain SS98-5 also formed plaques on double layer agar plates incorporating diatom cells. The diatom cell walls were partially degraded at the contact sites with the bacteria, the bacteria invaded from there into the diatom cells, and then the diatom cells were completely lysed. The strain possessed gliding motility and grew as spreading colonies on ESS agar plates containing lower concentrations of polypeptone (below 0.1%) while forming nonspreading colonies on ESS agar plates containing 0.5% polypeptone. Electron micrographs of ultrathin sections demonstrated that microtubule-like structures were observable only in gliding motile cells. Both the gliding motility and the microtubule-like structures were diminished by the addition of podophyllotoxin, an inhibitor of microtubule assembly, suggesting that the microtubule-like structures observed in these bacterial cells are related to their gliding motility.

[A new approach to biodiversity: morphological plasticity of a fresh-water diatom]

Population responses of a planktonic freshwater diatom, Asterionella formosa Hassal, to the hydrodynamic anthropic disturbances were studied at the landscape scale, along a series of nine reservoirs, for a period of 18 months. The analysis of biotic descriptors as cell abundance, cell length and architecture has shown a strong morphological plasticity of this diatom. The morphological variability of A. formosa in response to hydrodynamic conditions favours the colonization of lacustrine freshwater ecosystem for this species. The determination of architectural indices allowed us to distinguish a modification of biodiversity along a disturbance gradient for population level.

In vivo characterization of diatom multipartite plastid targeting signals

Plastids of diatoms and related algae are delineated by four membranes: the outermost membrane (CER) is continuous with the endoplasmic reticulum while the inner two membranes are homologous to plastid envelope membranes of vascular plants and green algae. Proteins are transported into these plastids by pre-sequences that have two recognizable domains. To characterize targeting of polypeptides within diatom cells, we generated constructs encoding green fluorecent protein (GFP) fused to leader sequences. A fusion of GFP to the pre-sequence of BiP [an endoplasmic reticulum (ER)-localized chaperone] resulted in accumulation of GFP within the ER; a construct encoding the pre-sequence of a plastid protein fused to GFP was directed into the plastids. Additional constructs demonstrated that the N-terminal region of the bipartite plastid targeting pre-sequence was necessary for transport of polypeptides to the lumen of the ER, while the C-terminal region was shown to enable the proteins to traverse the plastid double envelope membrane. Our data strongly support the hypothesis of a multi-step plastid targeting process in chromophytic algae and raises questions about the continuity of the ER and CER and the function of the latter in polypeptide trafficking.

A study of the evolution of the particle boundary layer in a reservoir, using laser particle sizing

The dynamics of the particle boundary layer in the Boadella reservoir was studied using an in situ laser optical particle-sizing instrument. This layer was found at the bottom of the reservoir from summer until the end of the year, when the reservoir was fully mixed. Most of the particles in this layer are remnants of the summer algae bloom and are trapped in the boundary layer due to the thermal stratification. The phytoplankton bloom is mainly composed of diatoms, with diameter d approximately 5 microm and green algae with diameter d approximately 15 microm. Inorganic particles and decomposed organic particles with d < 3 microm are also encountered in the boundary layer. On the other hand, particles with diameter between 30 and 100 microm are mostly found in the epilimnion of the reservoir. These are a mixture of aggregates of inorganic particles, colonies of phytoplankton, zooplankton, detritus, etc. Different mixing events occurring during autumn resuspended the small particles in the boundary layer, while the greater particles settled down. The extent of the resuspension has been parameterized with a non-dimensional number that balances the stress across the interface and the strength of the stratification.

From sanddabs to blue whales: the pervasiveness of domoic acid

Domoic acid (DA) is a potent food web transferred algal toxin that has caused dramatic mortality events involving sea birds and sea lions. Although no confirmed DA toxicity events have been reported in whales, here we present data demonstrating that humpback and blue whales are exposed to the toxin and consume DA contaminated prey. Whale fecal samples were found to contain DA at levels ranging from 10 to 207microg DA g(-1) feces via HPLC-UV methods. SEM analysis of whale feces containing DA, collected from krill-feeding whales, revealed the presence of diatom frustules identified as Pseudo-nitzschia australis, a known DA producer. Humpback whales were observed feeding on anchovies and sardines that contained DA at levels ranging from 75 to 444microg DA g(-1) viscera. DA contamination of whale feces and fish occurred only during blooms of toxic Pseudo-nitzschia. Additionally, several novel fish species collected during a toxic diatom bloom were tested for DA. Fish as diverse as benthic sanddabs and pelagic albacore were found to contain the neurotoxin, suggesting that DA permeates benthic as well as pelagic communities.

A phase separation model for the nanopatterning of diatom biosilica

Diatoms are encased in an intricately patterned wall that consists of amorphous silica. Species-specific fabrication of this ornate biomineral enables taxonomists to identify thousands of diatom species. The molecular mechanisms that control this nanofabrication and generate the diversity of patterns is not well understood. A simple model is described, in which repeated phase separation events during wall biogenesis are assumed to produce self-similar silica patterns in smaller and smaller scales. On the basis of this single assumption, the apparently complex patterns found in the valves of the diatom genus Coscinodiscus can be predicted. Microscopic analysis of valves in statu nascendi from three different Coscinodiscus species supports the conclusions derived from the model.

Characterization of the adhesive mucilages secreted by live diatom cells using atomic force microscopy

Atomic Force Microscopy (AFM) resolved the topography and mechanical properties of two distinct adhesive mucilages secreted by the marine, fouling diatom Craspedostauros australis. Tapping mode images of live cells revealed a soft and cohesive outer mucilage layer that encased most of the diatom's siliceous wall, and force curves revealed an adhesive force of 3.58 nN. High loading force, contact mode imaging resulted in cantilever 'cleaned' cell walls, which enabled the first direct observation of the active secretion of soft mucilage via pore openings. A second adhesive mucilage consisted of strands secreted at the raphe, a distinct slit in the silica wall involved in cell-substratum attachment and motility. Force measurements revealed a raphe adhesive strand(s) resistant to breaking forces up to 60 nN, and these strands could only be detached from the AFM cantilever probe using the manual stepper motor.

Marine biofouling: a sticky problem

Organisms that colonise underwater surfaces, such as barnacle larvae and spores of algae, use a diverse array of biological 'glues' to provide both temporary and more permanent adhesion. The practical consequence of colonisation by these organisms is biofouling - something that has plagued mariners for years - causing increased drag and, in extreme cases, corrosion. Might there be a biological solution to this biological problem?

Revealing the molecular secrets of marine diatoms

Diatoms are unicellular photosynthetic eukaryotes that contribute close to one quarter of global primary productivity. In spite of their ecological success in the world's oceans, very little information is available at the molecular level about their biology. Their most well-known characteristic is the ability to generate a highly ornamented silica cell wall, which made them very popular study organisms for microscopists in the last century. Recent advances, such as the development of a range of molecular tools, are now allowing the dissection of diatom biology, e.g., for understanding the molecular and cellular basis of bioinorganic pattern formation of their cell walls and for elucidating key aspects of diatom ecophysiology. Making diatoms accessible to genomics technologies will potentiate greatly these efforts and may lead to the use of diatoms to construct submicrometer-scale silica structures for the nanotechnology industry.

Association of periphytic diatom species of artificial substrate in lotic environments in the Arroio Sampaio Basin, RS, Brazil: relationships with abiotic variables

Associations of diatom species were identified, in the Arroio Sampaio Basin, Rio Grande do Sul, Brazil, based on monthly samplings over a year along Arroio Sampaio and its main tributaries, using polyamide thread as an artificial substrate. The species groupings showed four different environments: medium-lower course of Arroio Sampaio; and lower course of Arroio Teresinha; upper course of Arroio Sampaio; and lower course of Arroio Duvidosa. Among the physical and chemical variables measured, water pollution, particularly organic contamination and eutrophication, measured from BOD, and total phosphate concentration, respectively, appeared to be one of the most important environmental factors determining the composition and structure of species associations in the area studied.

A novel fluorescent silica tracer for biological silicification studies

BACKGROUND

Biological silica production has drawn intense attention and several molecules involved in biosilicification have been identified. Cellular mechanisms, however, remain unknown mainly due to the lack of probes required for obtaining information on live specimens.

RESULTS

The fluorescence spectra of the compound 2-(4-pyridyl)-5-((4-(2-dimethylaminoethylaminocarbamoyl)methoxy)phenyl)oxazole (PDMPO) are affected by the presence of >3.2 mM silicic acid. Increase in intensity and shift in the fluorescence coincide with the polymerization of Si. The unique PDMPO-silica fluorescence is explored here to visualize Si deposition in living diatoms. The fluorophore is selectively incorporated and co-deposited with Si into the newly synthesized frustules (the outer silica shells) showing an intense green fluorescence.

CONCLUSIONS

We suggest that a fluorescence shift is due to an interaction between PDMPO and polymeric silicic acid. PDMPO is an excellent probe for imaging newly deposited silica in living cells and has also a potential for a wide range of applications in various Si-related disciplines, including biology of living organisms as diatoms, sponges, and higher plants, clinical research (e.g. lung fibrosis and cancer, bone development, artificial bone implantation), and chemistry and physics of materials research.

A simple method for SEM examination of sectioned diatom frustules

We describe an innovative yet straightforward method to obtain high quality thin sections of diatom exoskeletons for observation by scanning electron microscopy (SEM). The use of this new technique allows for clear observations of some ultrastructural valve features, including the raphe, which are generally difficult to observe and describe accurately using transmission electron microscopy analysis of thin sections or SEM of randomly fractured diatom valves. In addition, because this method involves the complete removal of the organic content of the diatom cells, resulting in clean and mostly undisturbed skeletal thin cross-sections, even the intact valvar structures of weak girdle bands can be studied.

Molecular insights into the novel aspects of diatom biology

Diatoms are unicellular photosynthetic eukaryotes that are thought to contribute as much as 25% of global primary productivity. In spite of their ecological importance in the worlds oceans, very little information is available at the molecular level about the novel aspects of their biology. Recent advances, such as the development of gene transfer protocols, are now allowing the genetic dissection of diatom biology. Notable examples are advances in understanding the genetic basis for the silica-based bioinorganic pattern formation of their cell walls and for elucidating key aspects of diatom ecophysiology. The potentiation of current research will allow an evaluation of the use of diatoms to construct submicrometre-scale silicon structures for the nanotechnology industry and will reveal the molecular secrets underlying their ecological success.

Haslea salstonica sp. nov. and Haslea pseudostrearia sp. nov. (Bacillariophyta), two new epibenthic diatoms from the Kingsbridge estuary, United Kingdom

Two new diatom species, Haslea salstonica and Haslea pseudostrearia are described in light and electron microscopy and compared with two well-known members of Haslea. Scanning electron microscope observations confirm that the new species belong to the genus Haslea. This study extends previous observations on the genus, particularly with respect to the development of a pseudostauros. The characteristic features of the genus are discussed briefly.

Micromechanical and structural properties of a pennate diatom investigated by atomic force microscopy

The mechanisms behind natural nanofabrication of highly structured silicas are increasingly being investigated. We have explored the use of a standard Nanoscope III Multimode atomic force microscope (AFM) to study the silica shell of diatoms. The delicate structures of the shell surface of the diatom Navicula pelliculosa (Bréb.) Hilse were imaged and the shell's micromechanical properties were measured semi-quantitatively with a resolution down to approximately 10 nm. The technique to measure elasticity and hardness with the AFM was demonstrated to be useable even on these hard glass-like surfaces. Different experimental configurations and evaluation methods were tested. They gave a consistent result of the shell micromechanical properties. The first results showed that the diatom shell's overall hardness and elasticity was similar to that of known silicas. However, regions with different mechanical properties were distinguished. The elastic modulus varied from 7 to 20 GPa, from 20 to 100 GPa and from 30 to hundreds of GPa depending on the location. In general, the hardness measurements showed similar spatial differences. The hardness values ranged from 1 to 12 GPa but one specific part of the shell was even harder. Hence, certain localized regions of the shell were significantly harder or more elastic. These regions coincide with known characteristic features and mechanisms appearing at the different stages of the shell's growth. These results show that this method serves as a complementary tool in the study of silica biomineralization, and can detect eventual crystalline phases.

Geometrical constraints on the development of a diatom

In a plane hexagonal array of pores such as occurs in Thalassiosira oestrupii and other related species of marine diatom, the presence of a single, exceptional pore near the center of the array can cause the distortion in the pattern in such a way that the pores tend to diminish in diameter D with increasing distance R from the center. By a simple mathematical argument it is shown that for large values of R/D the pore diameter D varies as R(-1/6). This decrease in pore diameter with distance may have some developmental consequences. The law is generalized to other types of pattern. The second type of constraint, related to the presence of outer boundaries, is also discussed.

Changes in the photosynthetic apparatus of diatoms in response to low and high light intensities

The centric diatom Cyclotella cryptica and two strains of the pennate diatom Phaeodactylum tricornutum were grown under low and high light intensities (300 lux and 3,000 lux) over 4-6 weeks. Growth was monitored by repetitive cell count. The culture media were replaced weekly to avoid morphological and biochemical alterations caused by nutrient depletion. The ultrastructure of the cells was examined by transmission electron microscopy. Alterations in the light-harvesting antenna systems were investigated by Western immunoblotting. Both diatoms reduced the plastid area, i.e. decreased the amount of thylakoid lamellae, under high light intensity. The thylakoids still ran in groups of three with parallel orientation within the chloroplasts. The girdle band lamellae were not affected. The amounts of storage compounds and vacuoles increased. SDS-PAGE of total cell protein followed by Western immunoblotting with antisera directed against subunits of the light-harvesting antenna systems of C. cryptica (cc-antiserum) and the cryptophyte Cryptomonas maculata (cmac-antiserum) revealed that both diatoms reduced the amount of antenna polypeptides under increased light intensity. The cc-antiserum immunodecorated two bands with relative molecular masses (Mr) of 18,000 and 22,000 in C. cryptica. Both decreased under high light conditions to 67.2 +/- 6.1%. Five to seven bands in the Mr range of 14,000-27,000 were recognized in P. tricornutum. They decreased to 83 +/- 5.3%. Furthermore, the immunolabeling pattern for both strains differed under the two light regimes. The cmac-antiserum immunodecorated two polypeptides with Mr of 24,000 and 23,000 in C. cryptica, while both strains of P. tricornutum had five polypeptides in the Mr range of 14,000-24,000 that showed some differences in staining intensities between the two strains and in response to the light intensity applied.

DSK1, a kinesin-related protein involved in anaphase spindle elongation, is a component of a mitotic spindle matrix

DSK1 is a kinesin-related protein that is involved in anaphase spindle elongation in the diatom Cylindrotheca fuisiformis [Wein et al., 1996: J. Cell Biol. 113:595-604]. DSK1 staining appeared to be concentrated in the gap that forms as the two half-spindles separate, suggesting that DSK1 may be part of a non-microtubule spindle matrix. We set out to investigate this possibility using three-dimensional high-resolution fluorescence microscopy, and biochemical methods of tubulin extraction. Three-dimensional fluorescence microscopy reveals that DSK1 remains in the midzone after the bulk of the microtubules from the two half-spindles have left the region. Biochemical studies show that CaCl2 extraction of tubulin from a mitotic spindle preparation does not extract similar proportions of DSK1 protein. Immunofluorescence confirms that this CaCl2 extraction leaves behind spindle-like bars that are recognized by anti-DSK1, but not by anti-tubulin antibodies. We conclude that DSK1 is part of, or attached to, a non-microtubule scaffold in the diatom central spindle. This discovery has implications for both the structural organization of the mitotic spindle and the mechanism of spindle elongation.