Use Of Diatoms Research Articles

Prospects of Manipulating Diatom Silica Nanostructure

A key to the development of nanotechnology will be the ability to make complex nanoscaled three-dimensional structures at low cost and in large numbers. The wide variety of structures in the silicified cell walls of diatoms offers a promising natural source of such materials. Diatom silica can be converted into other materials, with maintenance of detailed morphology. To facilitate the use of diatoms in nanotechnology, specific manipulation of the structure in vivo will be desirable. This article explores the possibilities of manipulating diatom silica structure, by nongenetic and genetic means. Nongenetic influences that affect silica structure include changes in environmental conditions and life cycle stages and the presence or absence of particular compounds. The genetically based natural variation in structure in different diatom species indicates that genetic manipulation is possible. To achieve this, however, several goals must be met. The first is to identify cell wall synthesis (CWS) genes involved in structure formation. The recently completed genome sequence of Thalassiosira pseudonana opens the door for genomic and proteomic approaches to accomplish this. An important method to determine the function of CWS genes will be to modify gene sequences or expression and monitor the effect on structure. Performing gene modifications is straightforward, and modified genes can be introduced into diatoms, but the current inability to replace native diatom genes with modified copies could be a problem. However, there are feasible approaches yet to be applied to achieve this goal. It is very likely that continued development and application of molecular genetic techniques will enable us to specifically modify diatom silicified structures and provide a detailed understanding of the underlying mechanism of their formation.

Comparison of Diatoms, Exfoliated Graphite, Single-Wall Nanotubes, Multiwall Nanotubes, and Silica for the Synthesis of the Nanomagnet Mn<SUB>12</SUB>

We have completed a preliminary series of experiments that compare the silicate shells of the marine organism diatoms to Single-Wall NanoTubes (SWNT), Multi-Wall NanoTubes (MWNT), Exfoliated Graphite (EG), and silica as templates for producing nanostructures of the manganese acetate cluster Mn12 (Mn12[CH3(COO)16(H2O)4O12].(2)CH3COOH.4H2O). Mn12 exhibits magnetic properties because of the molecular arrangement within the cluster and exhibits no exchange couplings between the individual clusters. Data from scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and laser diffraction are discussed in terms of research that can expand the use of diatoms and other materials as templates for nanostructures.

ENVIRONMENTAL QUALITY EVALUATION OF ALPINE SPRINGS IN NW ITALY USING BENTHIC DIATOMS

This study was undertaken to obtain a picture of the environmental quality of 6 springs in the Ligurian Alps, situated within the Natural Reserve of the Upper Pesio and Tanaro Valleys in the Piemonte Region of NW Italy. Benthic diatom communities were sampled in Spring, Summer and Autumn of 2001. Based on 98 identified taxa, diatom indices were calculated and statistical analyses were undertaken to integrate the information derived from the known ecological preferences of the diatoms. During the summer, activities, such as sheep and cattle pastures, water abstraction and recreation intensify. The EPI-D (Eutrophication Pollution Index—Diatoms) for all samples was calculated on the basis of the diatom communities. With few exceptions, the index was always within the first quality class. An index based on the proportion of motile diatom species (belonging to the genera Navicula, Nitzschia and Surirella) was adopted in this work. It indicated a slight degree of impact, in part caused by human activities, in two springs. The causes were ascribed to a combination of pasture and recreational activities. The Classification (TWINSPAN) and Ordination (CA) of diatom species distinguished 2 different pH preferences groups, while analyses by means of circle of correlations separated environmental variables and sample groups. The use of diatoms proved to be appropriate for the evaluation of springs and high altitude mountain brooks of the type considered in the present study. This important application could be used in the management of aquatic environments in alpine regions, including protected areas, where other standardized methods (including those based on macroinvertebrates) are difficult or impossible to use.

Assessing the short‐term response of stream diatoms to acidity using inter‐basin transplantations and chemical diffusing substrates

Summary1. Acid‐base status has major effects on diatoms, but there is little information on their short‐term response to changing acidity. This is despite the use of diatoms as bioindicators in streams where acid episodes are important during rainstorms (hours to days) or snowmelt (days to weeks). In the Llyn Brianne experimental catchments (Wales, UK), we attempted to mimic the effects of short‐term acidification by (i) reciprocally transplanting diatoms between two streams of contrasting acidity and (ii) using acid‐diffusing substrates.2. Diatom diversity decreased rapidly on substrata transplanted from the circumneutral into the acidic stream, and increased in the reciprocal transplantation. Changes in dominant taxa occurred within three days in the acidic stream because of the rapid growth of Eunotia exigua, and by nine days in the circumneutral stream because of the proliferation of Achnanthidium minutissimum. Transplants were near indistinguishable from ambient assemblages by day 12.3. There were no effects of enclosures on assemblage composition, but diatoms responded more rapidly to altered chemistry in enclosures with coarse mesh (26 × 50 mm) than finer mesh (320 μm).4. Chemical diffusing substrates comprised terracotta tiles attached to dosing reservoirs that created locally acid (using H2SO4) or metal‐rich conditions (using MnSO4) in the circumneutral stream over 26 days. Diatom responses were compared with reference substrates dosed with deionised or circumneutral stream water, and we also assessed whether effects were moderated by macroinvertebrate grazers.5. Surface pH was lower by 1–2 pH units on acid‐dosed substrates than on reference tiles or in surrounding streamwater. Grazed assemblages on acid‐dosed substrates differed significantly from ungrazed reference assemblages, acquiring significantly greater relative abundance of Eunotia spp. However, the magnitude of response was less than in the between‐stream transplantations either because (i) metal exposure and base cation concentrations differed between the transplants and dosing substrates or (ii) diatom response to reduced pH on the diffusing substrates was restricted by the scarcity of acidobiontic diatoms in the circumneutral stream. Similar filter, founder or dominance effects might also affect diatom responses to real acid episodes.6. These data show that diatom assemblages can respond rapidly and directly to changes in acid‐base status, but short‐term acidification might affect diatoms more rapidly than subsequent recovery. Because the experimental methods used were imperfect representations of episodic effects, diatom response to real acid events requires further field evaluation.

Heterotrophic production of eicosapentaenoic acid by microalgae

Eicosapentaenoic acid (EPA) is an ω-3 polyunsaturated fatty acid that plays an important role in the regulation of biological functions and prevention and treatment of a number of human diseases such as heart and inflammatory diseases. As fish oil fails to meet the increasing demand for purified EPA, alternative sources are being sought. Microalgae contain large quantities of high-quality EPA and they are considered a potential source of this important fatty acid. Some microalgae can be grown heterotrophically on cheap organic substrate without light. This mode of cultivation can be well controlled and provides the possibility to maximize EPA production on a large scale. Numerous strategies have been investigated for commercial production of EPA by microalgae. These include screening of high EPA-yielding microalgal strains, improvement of strains by genetic manipulation, optimization of culture conditions, and development of efficient cultivation systems. This paper reviews recent advances in heterotrophic production of EPA by microalgae with an emphasis on the use of diatoms as producing organisms.

Diatoms and sockeye salmon ( Oncorhynchus nerka ) population dynamics: Reconstructions of salmon-derived nutrients over the past 2,200 years in two lakes from Kodiak Island, Alaska

The return of hundreds to millions of adult sockeye salmon (Oncorhynchus nerka), which have returned from the ocean to their natal nursery lake environment to spawn, can result in significant nutrient loading. By analyzing sedimentary diatom assemblages from nursery lakes, we demonstrated that a salmon-derived nutrient signal could be traced over time and be used to infer past sockeye salmon population dynamics. We conducted a ∼2,200 year paleolimnological study of two Alaskan sockeye salmon nursery lakes, Karluk and Frazer lakes. The two lakes are very similar, except that sockeye salmon were only introduced into Frazer Lake in 1951 (first spawners returned in 1956). In both lakes we found a strong correspondence between diatom assemblages and the number of adult salmon spawners recorded in the historical data (∼40 and 70 years for Frazer and Karluk lakes, respectively). Given this robust relationship, we then used our analyses of diatoms from Karluk Lake over the past ∼2,200 years to gain insight into salmon-derived nutrient loading changes (which are directly related to the number of sockeye salmon spawners). The diatom record from Karluk Lake recorded dramatic species changes on both decadal and century timescales, and was strongly correlated with an independent indicator of sockeye salmon abundances, δ15N. Together, these data suggest pronounced variability in sockeye salmon abundances at Karluk Lake over the past ∼2,200 years. The direct impacts of regional environmental variability were not likely responsible for the patterns apparent in Karluk Lake, as the diatom and δ15N profiles from Frazer Lake were relatively stable prior to the introduction of sockeye salmon. Application of total phosphorus transfer functions to the Karluk and Frazer lakes' diatom records revealed that sockeye salmon carcasses substantially increased the trophic status in these lakes, which has important implications for the health of juvenile salmon that rear in nursery lakes. Overall, this paper illustrates the potential use of diatoms in reconstructing past sockeye salmon population dynamics, which in turn can lead to a greater understanding of the mechanisms influencing abundances of sockeye salmon.

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.

Benthic diatoms in USA rivers: distributions along spatial and environmental gradients

AimTo study large‐scale patterns of benthic diatom assemblages in rivers, to assess the relative importance of environmental and geographical factors affecting their composition, and to evaluate the implications of these patterns for the use of diatoms as indicators of water quality, particularly nutrient enrichment.LocationThe United States Geological Survey (USGS) National Water Quality Assessment (NAWQA) Programme data set covers the conterminous United States.MethodsWe employed gradient analysis to understand the floristic structure of the data set and to discover major ecological gradients underlying variation in species composition at different spatial scales (entire US, Omernik Level 1 and Level 2 ecoregions). We used variance partitioning to separate the effect of environmental and spatial characteristics.ResultsAt the national scale, three major ecological gradients were evident. The first was a complex `downstream' gradient from fast‐flowing, mostly oligotrophic, highland rivers to predominantly eutrophic rivers of high‐ and low‐elevation plains. The second was a gradient integrating water mineral content and pH, which separated the soft and often more acidic waters of the humid eastern part of US from the alkaline waters of arid western regions. The third obvious gradient was related to latitudinal and altitudinal variation of temperature. Up to one‐third of the total explainable variation in species data was attributed solely to geographical factors not correlated with measured environmental characteristics. We present several examples of species with complex patterns of spatial distribution.Main conclusionsAlthough environment consistently plays the most important role in structuring diatom assemblages in rivers, spatial factors also explain some variation in diatom distribution, especially at the continental scale. Most of the species that are confined to limited geographical areas are not yet described and await future taxonomic work. We show that selection of species which could serve as indicators of nutrient enrichment in US rivers is not a straightforward procedure. The existence of complex environmental gradients, and still poorly understood spatial patterns of species distribution, precludes attempts to develop uniform diatom‐based metrics that would be applicable everywhere in the US. We advocate the development and calibration of metrics based on data sets collected from more limited geographical areas, and that include sites having relatively narrow ranges of environmental characteristics other than that which the metrics are designed to indicate.

Use of Diatoms and Macroinvertebrates as Bioindicators of Water Quality in Southern Ontario Rivers

The effectiveness of diatoms and macroinvertebrates as indicators of environmental conditions in lotic systems was compared in a regional assessment. Benthic samples were collected during summer 2000 from 35 Provincial Water Quality Monitoring river stations in the Grand, Credit, Maitland and Upper Thames watersheds in southern Ontario. Patterns of diatom and macroinvertebrate taxon distributions in relation to environmental variables were determined using canonical correspondence analysis (CCA). Total nitrate, phosphate, conductivity and alkalinity were significant in explaining diatom data, while alkalinity, total nitrate, ammonium and total Kjeldahl nitrogen were significant in explaining invertebrate data. The eigenvalues of the first two CCA axes were significant (p < 0.05) for both diatoms and invertebrates, while the invertebrate analysis explained more taxonomic variation (19% vs. 12%). Regression and calibration models were developed for total nitrate. The correlation between taxon-inferred and observed values was higher for diatoms than invertebrates in the analysis (0.70 vs. 0.59), however, cross-validation with bootstrapping indicated that apparent coefficients may be inflated. Biotic indices were also calculated. The composite invertebrate metric scores gave a slightly closer representation of water quality conditions than the diatom trophic index, but, biotic indices were not as effective as CCA in describing sites. Overall, the invertebrate and diatom communities were similar in their abilities to predict water quality.

Role of benthic diatoms in the implementation of the Urban Wastewater Treatment Directive in the River Wear, North-East England

The use of diatoms to monitor rivers in the UK was stimulated largely bythe requirements of the European Union's “Urban Wastewater TreatmentDirective”. The Trophic Diatom Index (TDI) was developed to assist theinterpretation of benthic diatom assemblages from UK rivers. This paperdescribes how data collected from one river, the River Wear in N-E England,sampled over a five-year period, was used to provide information about thepotential benefits of nutrient removal on major sewage treatment works.Althoughthe TDI indicated a clear increase in eutrophication with distance downstream,interpretation was confused by considerable within-site variability.Multivariate techniques such as TWINSPAN, when used alongside diatom indices,provide a more rigorous interpretation of longitudinal changes. The potentialfor using statistical power analysis to design sensitive monitoring programsusing benthic diatoms is also described.

Use of diatoms for freshwater quality evaluation in Portugal.

Use of diatoms for freshwater quality evaluation in Portugal.

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.

Diatom fluxes in surface sediments of the Goban Spur continental margin, NE Atlantic Ocean

Abstract. Continental slopes are presumed key areas for deposition of organic carbon exported from the shelf. Analysis of across-slope differences in diatom and silicoflagellate fluxes recorded in bottom sediments of the Goban Spur margin, a typical North Atlantic slope environment, was carried out to test if they can provide information on the magnitude of advection of material from the shelf into deeper waters. Total diatom and silicoflagellate accumulation rates showed strong across-slope differences. Minimum values are recorded at the shelf break where maximum surface productivity conditions occur while the deeper sampling stations record fluxes as high as 183×106 valves cm–2 ka–1. While high diatom fluxes show a clear correspondence with the activity of a permanent bottom nepheloid layer operating in the region, they do not correlate with productivity patterns observed in the water column. Diatom assemblages are mainly composed of Chaetoceros resting spores and Thalassionema nitzschioides (Grunow) Grunow ex Hustedt, typical indicators of spring bloom conditions in the area. The absence of clear across-slope trends in the diatom assemblages is interpreted as the effect of random mixing driven by the strong hydrodynamic regime provoked by the activity of the bottom nepheloid layer. The dominance of Chaetoceros resting spores across the slope is related to important exportation of shelf-derived production. However, due to the broad ecological tolerances of the main taxa composing the diatom assemblages, they do not allow precise estimations on the magnitude of the primary vertical flux vs. the secondary lateral flux in this slope environment. Use of the tychoplanktonic and benthic diatoms, which are restricted to the neritic realm, allows only the estimation of the minimum amount of shelf-derived diatoms reaching the slope sediments (at least 13% of the total diatom assemblage for the upper slope area of the Goban Spur). This study shows that major limitations exist for the use of diatoms preserved in surface sediments of this area as tracers of shelf-derived production transported to the continental slope.

The reconstruction of late Quaternary Antarctic sea-ice distribution—the use of diatoms as a proxy for sea-ice

The study of annual diatom transfer from the Southern Ocean surface to the sea floor using time-series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea-ice extent. The application and robustness of the proposed proxy are demonstrated by the study of Late Pleistocene sediment cores recovered from different environmental regimes in the Southern Ocean. Relative amounts of the sea-ice indicator diatoms Fragilariopsis cylindrus and Fragilariopsis curta of >3% in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea-ice. Summer sea-ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export, in the presence (>3% of diatom assemblage) of the deep-temperature diatom Fragilariopsis obliquecostata. The spatial and temporal distribution pattern of the sea-ice proxy indicates significant sea-ice variations during Marine Isotope Stages 1 and 5 in the present Antarctic Zone of the Southern Ocean. During glacial maxima, the Antarctic winter sea-ice was extended into the present Polar Front Zone, while the Antarctic summer sea-ice was most probably expanded into the area of the present winter sea-ice edge. During the short climatic optima at the onset of interglacial periods, the winter sea-ice extent was distinctly reduced.

Biology and Larval Feeding Habits of Coexisting Hydroptilidae (Trichoptera) from a Small Woodland Stream in Northeastern Ohio

Hydroptila consimilis Mosely, Ochrotrichia spinosa (Ross), and O. wojcickyi Blickle exhibited a close association with the appearance of the filamentous chlorophyte Cladophora (April to June) in a small woodland stream in northeastern Ohio. Laboratory rearings showed that these microcaddisflies displayed similar life cycles and exhibited hypermetamorphosis. H. consimilis mandibles are specialized for piercing individual cells within filaments of Cladophora to facilitate removal of cellular contents, whereas Ochrotrichia spp. have robustly cusped mandibles suited for piercing Cladophora and scraping diatoms from benthic substrates. Proportional similarity analysis of videotaped behavior illustrated that the feeding habits of third-instar Ochrotrichia exhibited a low similarity (0.44) to the other instars tested (Ochrotrichia fifth and Hydroptila first, third, and fifth) because of their frequent consumption of diatoms (17% of feeding efforts); all other instars tested were highly similar to each other (0.72–0.86). This division of trophic resources (i.e., differential use of diatoms versus Cladophora) minimized niche overlap between the two genera. All instars of H. consimilis and Ochrotrichia spp. fed heavily on the apical (therefore the smallest) cells of Cladophora filaments, and the time required to consume cells decreased significantly as larvae matured (P < 0.05). Larval Hydroptilidae are well adapted morphologically and behaviorally to consume Cladophora, and these algal filaments appear to represent a heterogeneous food source just as terrestrial host plants are for the array of phytophagous insects that use them.

Mycobacterial DNA not detected in liver sections from patients with primary biliary cirrhosis

Background/Aims: Recent studies in primary biliary cirrhosis have reported the detection of serum antibodies against Mycobacterium gordonae and of myco-bacterial DNA in liver sections. The aim of this study was to investigate whether mycobacterial DNA is present in liver biopsy material in primary biliary cirrhosis. Methods: Archival liver biopsy specimens from 11 patients with primary biliary cirrhosis (10 female, mean age 52 years) and 11 patients with autoimmune hepatitis (10 female, mean age 53 years) were identified. Positive control tissue comprised five archival lymph node specimens from patients with tuberculous lymph-adenopathy, three of which had stained positive on ZN staining, and also a liver biopsy specimen from a patient with tuberculous hepatitis (ZN positive). Fixed sections were deparaffinised and DNA was extracted by mechanical disruption with glass beads. DNA was purified by use of diatoms and lysis in guanidinium thiocyanate in a technique previously validated for archival DNA. Primers were directed to amplify a partial 16S ribosomal RNA gene yielding the species-specific character for mycobacteria, and also to amplify the constitutively-expressed human gene GAPDH. Results: The polymerase chain reaction was shown to be capable of detecting 1 fg of M. gordonae DNA in ‘spiked’ samples, equivalent to 1–5 bacterial cells. No mycobacterial DNA was detected in liver biopsy samples from either the primary biliary cirrhosis or autoimmune hepatitis groups. Of the tuberculous control sections, mycobacterial DNA was detected in four of five lymph nodes and the liver biopsy specimen. GAPDH amplification was detected in all tested samples from liver disease and tuberculous control samples. Conclusion: These data do not support a role for mycobacteria in the aetiology of primary biliary cirrhosis.

Using Diatoms as Indicators of Ecological Conditions in Lotic Systems: A Regional Assessment

Benthic diatoms and water chemistry were sampled from 49 stream sites in the Mid- Atlantic Highlands region of the United States to evaluate the use of diatoms as indicators of envi- ronmental conditions in streams across varying geographic and ecoregional areas. Diatom samples were collected from depositional and erosional habitats in a randomly selected reach in each stream site. Patterns of diatom species distributions in relation to environmental variables were determined using canonical correspondence analysis. Diatom species in both habitats were highly correlated with a pH gradient. A second gradient was correlated with variables that were commonly associated with agricultural runoff such as turbidity and total phosphorus. The relationship between diatoms and major environmental variables was quantified with regres- sion and calibration models. The correlation between diatom-inferred and observed pH was high (r2 = 0.90). Cross-validation with jackknifing showed that pH models were reasonably robust (r2 = 0.69 for depositional habitats, r2 = 0.67 for erosional habitats). The regression and calibration models for the depositional habitats had only slightly higher predictive powers than those of erosional habitats. The relationship between diatoms and important environmental variables was robust and quanti- fiable, and the sensitivity of diatom assemblages to environmental conditions did not differ between erosional and depositional habitats. Therefore we concluded that diatoms can be used as quantitative indicators of environmental conditions in lotic systems.

The use of diatoms to assess past and present water quality

Abstract Diatoms possess a number of attributes which contribute to their suitability as biological indicators. They are highly sensitive to water chemistry changes, abundant in aquatic environments, largely cosmopolitan in distribution, less habitat dependent than macroinverte‐brates and have a well‐studied taxonomy and ecology. Furthermore, the preservation of diatom valves in lake sediments means that they can provide otherwise unavailable baseline data which can be used to assess and contextualize human impacts on aquatic ecosystems. The value of diatoms as bioindicators in contemporary and palaeolimnological studies has been well established overseas. Despite this, they have been under‐utilized in Australia. This paper outlines some of the applications and potential for the use of diatoms as biological indicators in Australia.

The use of diatoms in monitoring the development of created wetlands at a sandmining site in Western Australia

The use of diatoms in monitoring the development of created wetlands at a sandmining site in Western Australia

Integrated Multidisciplinary Biostratigraphic and Paleoecologic Study of Southern California Neogene Coastal Sections: ABSTRACT

This integrated biostratigraphic and paleoecologic study of several Neogene sections of coastal southern California is based on the use of diatoms, calcareous nannofossils, palynology, and benthic foraminifera. The study included the Naples Bluff, Topanga Canyon, and Newport Bay sections, and DSDP Site 468.