PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Diatoms”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1997

Extracellular Matrix Assembly in Diatoms (Bacillariophyceae) (I. A Model of Adhesives Based on Chemical Characterization and Localization of Polysaccharides from the Marine Diatom Achnanthes longipes and Other Diatoms).

Extracellular adhesives from the diatoms Achnanthes longipes, Amphora coffeaeformis, Cymbella cistula, and Cymbella mexicana were characterized by monosaccharide and methylation analysis, lectin-fluorescein isothiocyanate localization, and cytochemical staining. Polysaccharide was the major component of adhesives formed during cell motility, synthesis of a basal pad, and/or production of a highly organized shaft. Hot water-insoluble/hot 0.5 M NaHCO3-soluble anionic polysaccharides from A. longipes and A. coffeaeformis adhesives were primarily composed of galactosyl (64-70%) and fucosyl (32-42%) residues. In A. longipes polymers, 2,3-, t-, 3-, and 4-linked/substituted galactosyl, t-, 3-, 4-, and 2-linked fucosyl, and t- and 2-linked glucuronic acid residues predominated. Adhesive polysaccharides from C. cistula were EDTA-soluble, sulfated, consisted of 83% galactosyl (4-, 4,6-, and 3,4-linked/substituted) and 13% xylosyl (t-, 4f/5p-, and 3p-linked/substituted) residues, and contained no uronosyl residues. Ulex europaeus agglutinin uniformly localized [alpha](1,2)-L-fucose units in C. cistula and Achnanthes adhesives formed during motility and in the pads of A. longipes. D-Galactose residues were localized throughout the shafts of C. cistula and capsules of A. coffeaeformis. D-Mannose and/or D-glucose, D-galactose, and [alpha](t)-L-fucose residues were uniformly localized in the outer layers of A. longipes shafts by Cancavalia ensiformis, Abrus precatorius, and Lotus tetragonolobus agglutinin, respectively. A model for diatom cell adhesive structure was developed from chemical characterization, localization, and microscopic observation of extracellular adhesive components formed during the diatom cell-attachment process.

Journal Article↗
PubMed2006

Prevalence of diatom frustules in non-vegetarian foodstuffs and its implications in interpreting identification of diatom frustules in drowning cases.

Detection of diatom frustules in bone marrow (diatom test) is used for diagnosing ante-mortem drowning where the usual signs of drowning are not present in dead bodies recovered from water. However, controversies over the reliability of diatom test results are continuing. There have been indications on the possibilities of diatoms entering into systemic circulation from atmospheric air, food and drink. While diatoms have been demonstrated in the gut content of edible marine forms such as shrimps and clams, the present study, for the first time, provides empirical evidence on the prevalence as well as abundance of diatom frustules in the samples of cooked non-vegetarian foodstuffs that impend human consumption in Kelantan, Malaysia. It is found that 50 g each of cleaned and cooked prawns and of clams impending human consumption contain about 8360 and 29,054 diatom frustules, respectively. A person accustomed to prawn and clam food would be ingesting an estimated 2 million diatoms in a single year. Considering the suggestion that detection of five diatom frustules in 10 g of bone marrow would suffice for concluding drowning as mode of death, and the fact that there is yet no proof that diatom frustules do not enter into the human systemic circulation through the digestive tract, the estimated number of diatom frustules routinely ingested acquires significance since entry of a few of such ingested frustules into the systemic circulation can lead to false positive test results. The findings of this research raise two important issues: first, population based routine food related diatom ingestion requires to be estimated, and, second, studies have to be initiated to categorically prove or disprove the possibility of entry of diatom frustules into the systemic circulation via the digestive tract.

Animals↗
PubMed1997

The diagnostic value of the diatom test for drowning, II. Validity: analysis of diatoms in bone marrow and drowning medium.

In part two of this series, we investigated the characteristics of diatom frustules recovered from bone marrow and samples of putative drowning medium in case of freshwater drownings. A total of 52 cases of freshwater drowning with diatoms in the femoral bone marrow in which a sample of the putative drowning medium was also collected were available for analysis. The same types of diatoms were found in the bone marrow and putative drowning medium in 47 cases (90%) indicating that the water samples were representative of the site of drowning in at least 90% of freshwater drownings. In the remaining 5 cases (10%), the diatoms in the water samples did not match those in the bone marrow indicating that the site of body and water sample recovery were likely geographically remote from the site of drowning. In cases with matching diatoms in the bone marrow and drowning medium, the diatoms were consistently the smallest and most abundant types represented in the water samples. In addition, there were highly stereotyped physical characteristics of typical "drowning-associated" diatoms with small pennate diatoms representing the most common type of frustule found in the bone marrow. In an additional 34 cases of putative drowning in water that lacked detectable diatoms, 29 cases (85%) lacked diatoms in the bone marrow. Analysis of the diatom content of samples of putative drowning medium by month revealed that winter months had the highest frequency of samples devoid of diatoms. These data indicate that the true positive rate of the diatom test for drowning is at least 90% and that small pennate frustules are most commonly associated with drowning, particular in non winter months.

Bone Marrow↗
PubMed1996

Evolution of the diatoms (Bacillariophyta). II. Nuclear-encoded small-subunit rRNA sequence comparisons confirm a paraphyletic origin for the centric diatoms.

A phylogeny of the diatoms was inferred from comparisons of nuclear-encoded small subunit ribosomal RNA coding regions using maximum likelihood, weighted maximum parsimony, and neighbor-joining distance methods with Jukes and Cantor, Kimura, Gamma, van de Peer, and LogDet evolutionary models. Analyses of 30 taxa in 11 orders recovered two clades (Clades I and II). Neither of these clades correspond to the three classes of diatoms presently recognized or to the traditionally recognized radially symmetrical centric diatoms or bilaterally symmetrical pennate diatoms. All analyses show that the centric diatoms are a paraphyletic lineage. Tests of alternative phylogenies that address existing hypotheses regarding diatom systematics with the maximum likelihood and maximum parsimony methods support the two clades. Clade I is defined by centric diatom orders with specialized tubes, termed labiate processes, located peripherally in the cell wall. Clade II contains (1) bi(multi)polar centric diatoms with centrally located labiate processes, (2) centric diatoms with other central tubes termed strutted processes, and (3) pennate diatoms. Morphological evidence from fossil assemblages and cytological architecture support the results of the molecular analyses, whereas morphological features of extant diatoms are too derived to resolve the deeper branches in the tree.

Animals↗
PubMed2005

Diatomics: toward diatom functional genomics.

For diatom biologists one of the most interesting research areas over the next years will be in linking mathematical models for pattern formation with information derived from molecular genetic, biochemical, and physiological studies. A major goal of this research is to exploit diatom proficiency in biogenic silica formation to develop strategies for bio-inspired nanofabrication of silicon based materials. Development of high-throughput methods for the functional analysis of diatom genes is a key step toward this goal. In this article we review the different techniques available to investigate gene and protein function in diatoms. Furthermore, to make diatom research as effective as possible the research community must address the question of which diatom species should be developed as a model. Choice of a diatom model organism should be made on the basis of several criteria, such as the ease of genetic manipulation, ecological relevance, or biomineralization capability. Phaeodactylum tricornutum is one of the principal three species that are candidates for such a model. For this species we have accomplished the first large-scale analysis of 12000 expressed sequence tags (ESTs) and have organized it in a queryable database, Phaeodactylum tricornutum database (PtDB). A summary of the functional analysis of this EST collection is presented, and genes of particular interest are highlighted.

Chromosome Mapping↗
PubMed1994

Application of a simple enzymatic digestion method for diatom detection in the diagnosis of drowning in putrified corpses by diatom analysis.

The reliability and applicability of quantitative and qualitative diatom analysis by an enzymatic digestion method in the diagnosis of drowning of putrified bodies has been evaluated. The authors report the analysis of water and organ samples of 12 immersion cases using light microscopy. This study included control organ samples from the bodies of persons who died from causes other than drowning. Organ samples were treated by both chemical and enzymatic methods, the first one using concentrated nitric acid and the second proteinase K. Diatoms were present in most organ samples of the immersed corpses; no diatoms could be found in the control samples. Our experience was that the enzymatic method seemed to be more convenient in terms of rapidity, safety and environmental protection than chemical digestion. The number of diatoms recovered with both methods was similar. Qualitative and quantitative analysis of both water and organ samples of immersion cases supported the diagnosis of death by drowning in 41.6% of the putrified cases studied. The authors suggest that diatom analysis using enzymatic digestion of organs can be used as a criterion for positive diagnosis of drowning in cases involving putrified bodies.

Brain↗
PubMed2002

Inhibition of embryonic development and fertilization in broadcast spawning marine invertebrates by water soluble diatom extracts and the diatom toxin 2-trans,4-trans decadienal.

Water soluble diatom extracts and the diatom aldehyde 2-trans,4-trans decadienal were assayed on the gametes and embryos of the broadcast spawning polychaetes Arenicola marina and Nereis virens and the echinoderms Asterias rubens and Psammechinus miliaris. Both crude cellular extracts and purified aldehyde were found to inhibit fertilization, embryogenesis and hatching success in a dose dependent manner. Intact diatom cells had no discernable effect on fertilization or development. Extracts of Skeletonema costatum were generally more effective than Nitzschia commutata in inhibiting development and fertilization. There was considerable interspecific variation in terms of toxin sensitivity. The polychaetes were more sensitive to the effects than the echinoderms. Within the polychaetes A. marina was the more tolerant in terms of developmental competence but N. virens had a higher fertilization rate. Echinoid embryos were more tolerant than asteroid embryos. This is the first study to present data on the inhibition of fertilization success by diatom extracts and aldehydes. Our observations are discussed in relation to temporal patterns in spawning and possible adaptive mechanisms to avoid diatom toxicity.

Adaptation, Physiological↗
PubMed1997

Use of Percoll gradient centrifugation for the isolation of diatoms from Wadden Sea sediments; diatom yields, species recoveries and population diversity.

The technique of Percoll gradient centrifugation was applied to samples from Wadden Sea sediments of the shoreside near Dangast (German Bight). Experiments were also performed with Wadden Sea sediment inoculated with diatoms and with axenic and mixed diatom cultures. For axenic and mixed cultures, total recoveries ranged from 6 to 70% of the diatoms loaded onto the gradients, whereas the yields were less than 5% in most of the experiments with Wadden Sea sediments. The extraction of diatoms from mixed cultures and from sediment samples was not quantitative, neither in terms of biodiversity nor of total individuals extracted, because the rates of recovery varied for the different species. Diatom cells extracted by Percoll gradient centrifugation were devoid of sand grains and debris. The obtained material was suitable to be used in biochemical experiments, in cultural studies and for electron microscopy. The overall cell morphology and subcellular organelle organization was excellent and appeared to be unaffected by the purification procedure. The results and advantages and disadvantages of the technique are discussed.

Cell Size↗
PubMed2005

Diatom auxospore scales and early stages in diatom frustule morphogenesis: their potential for use in nanotechnology.

Incomplete, forming diatom cell wall components have potential uses in nanotechnology that differ from those of mature frustules. Diminutive, discoid auxospore scales, produced after sexual reproduction, could also be evaluated for their value. The structure of developing diatom valves and girdle bands is generally simple, since features such as cribra and other ornamentation have yet to be added. They are also more lightly silicified. Bullulae and honeycomb structures give strength to the final framework of some species using a minimal amount of silica. The morphogenesis of girdle bands is shown to be unidirectional in a marine centric species, forming open-ended cylinders, another potential shape for the arsenal of structures useful to nanotechnologists.

Biomimetics↗
PubMed1997

Extracellular Matrix Assembly in Diatoms (Bacillariophyceae) (II. 2,6-Dichlorobenzonitrile Inhibition of Motility and Stalk Production in the Marine Diatom Achnanthes longipes).

The cellulose synthesis inhibitor 2,6-dichlorobenzonitrile (DCB) and the DCB analogs 2-chloro-6-fluorobenzonitrile, 3-amino-2,6-dichlorobenzonitrile, and 5-dimethylamino-naphthalene-1-sulfonyl-(3-cyano-2, 4-dichloro)aniline (DCBF) inhibited extracellular adhesive production in the marine diatom Achnanthes longipes, resulting in a loss of motility and a lack of permanent adhesion. The effect was fully reversible upon removal of the inhibitor, and cell growth was not affected at concentrations of inhibitors adequate to effectively interrupt the adhesion sequence. Video microscopy revealed that the adhesion sequence was mediated by the export and assembly of polymers, and consisted of initial attachment followed by cell motility and eventual production of permanent adhesive structures in the form of stalks that elevated the diatom above the substratum. A. longipes adhesive polymers are primarily composed of noncellulosic polysaccharides (B.A. Wustman, M.R. Gretz, and K.D. Hoagland [1997] Plant Physiol 113: 1059-1069). These results, together with the discovery of DCB inhibition of extracellular matrix assembly in noncellulosic red algal unicells (S.M. Arad, O. Dubinsky, and B. Simon [1994] Phycologia 33: 158-162), indicate that DCB inhibits synthesis of noncellulosic extracellular polysaccharides. A fluorescent probe, DCBF, was synthesized and shown to inhibit adhesive polymer production in the same manner as DCB. DCBF specifically labeled an 18-kD polypeptide isolated from a membrane fraction. Inhibition of adhesion by DCB and its analogs provides evidence of a direct relationship between polysaccharide synthesis and motility and permanent adhesion.

Journal Article↗
PubMed2005

Vibrational excitation of diatomic molecular ions in strong field ionization of diatomic molecules.

A model based on the strong-field and Born-Oppenheimer approximations qualitatively describes the distribution over vibrational states formed in a diatomic molecular ion following ionization of the neutral molecule by intense laser pulses. Good agreement is found with a recent experiment [X. Urbain et al., Phys. Rev. Lett. 92, 163004 (2004)]. In particular, the observed deviation from a Franck-Condon-like distribution is reproduced. Additionally, we demonstrate control of the vibrational distribution by a variation of the peak intensity or a change of frequency of the laser pulse.

Journal Article↗
PubMed2005

Vibrational energy relaxation rates via the linearized semiclassical approximation: applications to neat diatomic liquids and atomic-diatomic liquid mixtures.

We report the results obtained from the application of our previously proposed linearized semiclassical method for computing vibrational energy relaxation (VER) rates (J. Phys. Chem. A 2003, 107, 9059, 9070) to neat liquid oxygen, neat liquid nitrogen, and liquid mixtures of oxygen and argon. Our calculations are based on a semiclassical approximation for the quantum-mechanical force-force correlation function, which puts it in terms of the Wigner transforms of the force and the product of the Boltzmann operator and the force. The calculation of the multidimensional Wigner integrals is made feasible by the introduction of a local harmonic approximation. A systematic analysis has been performed of the temperature and mole-fraction dependences of the VER rate constant, as well as the relative contributions of centrifugal and potential forces, and of different types of quantum effects. The results were found to be in very good quantitative agreement with experiment, and they suggest that this semiclassical approximation can capture the quantum enhancement, by many orders of magnitude, of the experimentally observed VER rate constants over the corresponding classical predictions.

Algorithms↗