The Multifaceted Inhibitory Effects of an Alkylquinolone on the Diatom Phaeodactylum tricornutum

The mechanisms underlying interactions between diatoms and bacteria are crucial to understand diatom behaviour and proliferation, and can result in far-reaching ecological consequences. Recently, 2-alkyl-4-quinolones have been isolated from marine bacteria, both of which (the bacterium and isolated chemical) inhibited growth of microalgae, suggesting these compounds could mediate diatom–bacteria interactions. The effects of several quinolones on three diatom species have been investigated. The growth of all three was inhibited, with half-maximal inhibitory concentrations reaching the sub-micromolar range. By using multiple techniques, dual inhibition mechanisms were uncovered for 2-heptyl-4-quinolone (HHQ) in Phaeodactylum tricornutum. Firstly, photosynthetic electron transport was obstructed, primarily through inhibition of the cytochrome b₆f complex. Secondly, respiration was inhibited, leading to repression of ATP supply to plastids from mitochondria through organelle energy coupling. These data clearly show how HHQ could modulate diatom proliferation in marine environments.     

Marine diatom Navicula jeffreyi from biochemical composition and physico-chemical surface properties to understanding the first step of benthic biofilm formation

To understand the first step of marine benthic microbial mat formation and biofouling phenomena, caused by diatoms in the marine environment, the surface properties of the epipelic diatom Navicula jeffreyi were studied and the composition of its bound Extracellular Polymeric Substances (EPS) was determined. These parameters are determining factors for the initial adhesion step of diatoms to other constituents that start marine fouling. Surface energy of a diatom cell layer was determined using the sessile drop technique and highlights that diatoms show a moderate hydrophobic character (contact angle with water >68°), no Lewis acid character (γ⁺?<1?mJ/m²), and a low Lewis basic character (γ^??=?16.1?mJ/m²). An extraction procedure using a cationic resin subtracted only the bound EPS. Biochemical assays showed that there were 2.5 times more proteins than sugars. The propensity of Navicula jeffreyi diatom to adhere to five different solid surfaces, showing a gradient in their hydrophobic and hydrophilic character, was measured. The attachment densities were high on hydrophobic surfaces such as polytetrafluoroethylene and very low on substrata with surface free energy over 40–50?mJ/m². Using a thermodynamic approach, the free energy of adhesion of the diatom to the five substrata was determined, and led to a very strong correlation with attachment densities for polytetrafluoroethylene, polyamide, polyethylene, and stainless steel.     

Atomic force microscopy (AFM) characterisation of the porous silica nanostructure of two centric diatoms

The porous silica nanostructure of two marine, centric diatoms, Coscinodiscus sp. and Thalassiosira eccentrica was investigated by atomic force microscopy (AFM). Important morphological features of the silica frustules of diatoms are described, including: the organisation of porous silica layers, their topography, pore size, shape and density. The outer layer of Coscinodiscus sp., commonly called the cribellum, consists of a characteristic hexagonal array of pores with pore sizes of around 45 nm. This thin membrane covers a second structural layer where two different silica surfaces are identified. The outer part, known as the cribrum consists of hexagonally packed pores of about 200 nm diameter. The inner part, known as the foramen layer, consists of larger and radially distributed holes with a diameter of around 1,150 nm. The second diatom species investigated, T. eccentrica produces a frustule with one silica structural layer featuring two different porous surfaces. The outer surface has large (800 nm diameter) holes (foramen) while the inner surface contains a porous wall with pores comparable in size to the Coscinodiscus sp. cribellum. The inner and outer surfaces of the frustule wall of both diatoms are hence in reverse order. However, the size of the small pores is similar for both species. High-resolution AFM also revealed the granular nanostructure of the diatom biosilica with grain sizes from 20 to 70 nm diameters.     

Manganese-Doped Zinc Orthosilicate-Bearing Phosphor Microparticles with Controlled Three-Dimensional Shapes Derived from Diatom Frustules

Mn-doped zinc orthosilicate (Zn₂SiO₄)-bearing phosphor microparticles were synthesized with controlled three-dimensional (3-D) morphologies inherited from the microshells (frustules) of diatoms (unicellular algae). Silica-based diatom frustules were first coated with manganese and zinc oxide nanoparticles by exposure to an acetate precursor solution and then firing at 700°C. Subsequent reaction of the nanoparticles with the underlying silica at 1050°C yielded compact, continuous, and conformal Mn-doped Zn₂SiO₄ coatings on the frustule surfaces. The converted 3-D microparticles exhibited bright green emission upon stimulation with 275-nm light. Photoluminescent microparticles with a wide variety of well-controlled 3-D morphologies can be mass produced with this simple, low-cost bioclastic process.     

Annual variation of fresh water quality in the Gachang Dam reservoir

This paper investigated the relationship between the annual variation of the algae population and the physicochemical properties of the water reservoired in the Gachang Dam in the hopes of serving as a guideline in the production of a clean water supply to regions of the city of Taegu. Summer thermal stratification was formed in the freshwater reservoired in the Gachang Dam and thus dissolved oxygen (DO) decreased according to the depth of the water. The pH of epilimnion was much higher than that of hypolimnion in summer because of the difference in the photosynthesis rate of algae. In July, at the beginning of the rainy season, the amount of total nitrogen (T-N) in the freshwater reached a maximum of 1.92 mg/L without an increase in the amount of total phosphorus (T-P). In August, the concentration of T-P in the freshwater increased steeply and reached 0.12 mg/L.Aulacoseira spp. (diatoms) were predominantly distributed in the freshwater throughout the year andSynedra andAsterionella (diatoms) predominantly populated in the spring. However,Anabaena andMicrocystis (blue-green algae), which caused malodor and a bad taste, flourished predominantly in epilimnion in August when the temperature of the water at the surface region increased to the maximum and the concentration of T-P was sufficiently high.     

Study on the correlation of lab assay and field test for fouling-release coatings

In this paper, two organisms, diatom and Ulva spore, were employed to evaluate the antifouling performance of five fouling-release (FR) coatings in laboratory, and field test was also assessed. The correlation of lab assay and field test was studied using Spearman's rank correlation test. The results show that the Spearman's coefficient (r_s) between lab assay and field static test is 0.975 (p = 0.005) for diatom and 0.949 (p = 0.014) for Ulva spore respectively, which are significant at the 95% probability level. This indicates that the lab static assays using diatom and Ulva spore have good agreement with field static test. For dynamic performance evaluation, the r_s between diatoms adhesion assay and field dynamic test is 0.894 (p = 0.041) while the r_s for Ulva spore is 0.289 (p = 0.638), indicating the lab dynamic assay with diatom is accordance with the field dynamic test. Therefore, diatom was used to evaluate the performance of coating materials which exhibits the satisfactory correlation and consistency between lab assessment and field test, confirming that diatom is an adapted evaluation organism to evaluate FR coatings.     

Morphological Factors Involved in Adhesion of Acid-Cleaned Diatom Silica

Purpose

Diatoms, unicellular microalgae with silica cell walls, have strong adhesive properties, which are dominated by chemical interactions between secreted organic material and the substrate. Possible technological applications of diatoms are likely to involve the adhesion of silica particles, or derivatives, which have been cleaned of organic material. Because the morphologies of diatom cell walls are far more complex than defined model structures, the relationship between morphology and adhesion for such materials is unknown.

Methods

In this paper we develop a new approach to monitor the adhesion of acid-cleaned diatom silica using parallel-plate flow chambers. We have evaluated factors such as settling time, extent of dryness, and substrate properties, and compared diatom species with silica features differing in size, shape, and percentage of surface contact area.

Results

Results indicated better adhesion of particles with higher surface contact area below a threshold of overall size, and a contribution by the number of possible contact surfaces to initial adhesion. We identified two stages in adhesion response to increasing shear stress. In the first stage, at low shear stress, species-dependent morphology played a major role in determining the strength of adhesion. After loosely adhered particles were removed at low shear, a second stage of persistent adhesion emerged at higher shear stresses. In the second stage, variations in morphology had a much smaller effect on adhesion.

Conclusions

These results identify conditions and fundamental morphological features for adhesion that can be utilized in future technological applications of silica particles with complex shapes.     

Removal of freshwater diatoms (Synedra acus and Stephanodiscus sp.) by preozonation and addition of polyamine coagulant-aid

Pilot studies were conducted for the removal of two freshwater diatoms (Synedra acus andStephanodiscus sp.). Poly aluminum chloride (PAC), one of the coagulants commonly used in conventional potable water treatment, was found to be not effective in removing diatoms, especially forSynedra. In this work, preozonation and polyamine coagulant-aid in the presence of PAC were compared with each other and combined to investigate their performances on removing diatoms. It was found that the preozonation and polyamine coagulant-aid increased the removal rate significantly for both diatoms, better performance than PAC alone. When polyamine coagulant-aid and preozonation were combined with PAC, approximately 90% ofSynedra and 100% ofStephanodiscus were eliminated. It can be concluded that the combination of preozonation and polyamine coagulant-aid in the presence of PAC could be a promising solution for removing resistant diatoms in water treatment.     

Boronic Acid Moieties Stabilize Adhesion of Microalgal Biofilms on Glassy Substrates: A Chemical Tool for Environmental Applications

Photosynthetic organisms such as diatoms microalgae provide innovative routes to eco-friendly technologies for environmental pollution bioremediation. Living diatoms are capable to incorporate in vivo a wide variety of chemical species dispersed in seawater, thus being promising candidates for eco-friendly removal of toxic contaminants. However, their exploitation requires immobilization methods that allow to confine microalgae during water treatment. Here we demonstrate that a biofilm of Phaeodactylum tricornutum diatom cells grown on the surface of a glassy substrate bearing boronic acid protruding moieties is stably anchored to the substrate resisting mechanical stress and it is suitable for removal of up to 80 % metal ions (As, Cr, Cu, Zn, Sn, Pb, Sb) in a model polluted water sample. Control experiments also suggest that stabilization of the biofilm adhesion occurs by interaction of boronic acid surface groups of the substrate with the hydroxyl groups of diatoms extracellular polysaccharides.     

Survey of the Chemical Defence Potential of Diatoms: Screening of Fifty Species for α,β,γ,δ-unsaturated aldehydes

In recent years a negative influence of diatom-derived ,,,-unsaturated aldehydes (PUA) on the reproductive success of copepods and invertebrates has been suggested. Since adverse chemical properties of diatoms would question the traditional view of the marine food web, this defense mechanism has been investigated in detail, but the PUA-release by test organisms has only been determined in a few cases. The observed effects were nevertheless frequently discussed from a general point of view often leading to contradictory conclusions. We have examined the PUA-production of 50 diatom species (71 isolates) in order to provide a basis for the interpretation of laboratory and field results on the influence of diatom food on the reproductive success of their consumers. PUA-production is species and strain dependent. Thirty-six percent of the investigated species (38% of the cultivated isolates) release ,,,-unsaturated aldehydes upon cell disruption in concentrations from 0.01 to 9.8 fmol per cell. Thalassiosira rotula and Thalassiosira pacifica, major spring-bloom forming diatoms isolated from Roscoff (Bretagne, English Channel, France) and Puget Sound (Washington, USA) were among the PUA-producing strains.     

Artificial ceramic diatoms with multiscale photonic architectures via nanoimprint lithography for CO2 photoreduction

The elaborated photonic architectures and unique light manipulation ability of diatoms provide inspirations for the design of efficient artificial photosynthetic systems. However, the biomimetic synthesis of artificial diatoms with accurate control over nanoscale geometry for scalable production has been a great challenge. Herein, diatom Coscinodiscus sp. is served as a model for the biomimetic production of artificial ceramic diatoms with multiscale photonic architectures for CO₂ photoreduction. Optical finite-difference time-domain simulations are conducted to investigate the optical mechanisms on enhanced light harvesting and to establish a modified structural model. Electron Beam Lithography and Nanoimprint Lithography are applied to fabricate artificial TiO₂ diatoms with elaborated periodic photonic structures and high surface areas (169.4 m² g⁻¹). Artificial photosynthesis via CO₂ reduction enhances CO and CH₄ evolution on the artificial diatoms by up to 2.75- and 2.3-fold, respectively, compared with the corresponding powder sample. Furthermore, gas diffusion behaviors, closely related to the gas-phase reaction, are investigated by theoretical simulation to reveal the hierarchical structural effects on catalytic efficiency. This work provides a new pathway to design and biomimetic synthesis of artificial structures for enhanced performances.     

Controls on the Recycling and Preservation of Biogenic Silica from Biomineralization to Burial

The recycling of biogenic silica (bSiO₂) produced by diatoms is a vital process sustaining a significant fraction of primary production in the oceans. The efficiency with which bSiO₂ dissolves controls the availability of nutrient silicon in the water column, and modulates the export of organic carbon to the deep sea. Environmental conditions during biomineralization (temperature, nutrient availability, light, etc.) affect the silicification and weathering resistance of diatom frustules, while ecosystem processes, including grazing and aggregation, are determining factors for the recycling of bSiO₂ in the water column. Bacterial colonization of dead diatoms leads to the decomposition of the protective organic layers allowing for the dissolution of bSiO₂ to begin. The dissolution rate of diatom frustules is a function of the physicochemical properties of both the silica (e.g., specific surface area, degree of hydration and condensation, impurities) and the aqueous medium (e.g., temperature, pH, pressure, electrolyte composition). In sediments, the dissolution of bSiO₂ is controlled by the presence of lithogenic minerals, aging processes and the build up of dSi in the pore waters. In particular, interactions between lithogenic silicate minerals and bSiO₂ may initiate rapid diagenetic alterations that favor the preservation of bSiO₂.     

The Vegetation Silica Pool in a Developing Tidal Freshwater Marsh

Tidal marshes play an important role in the estuarine Si cycle. Dissolved silicon (DSi) is taken up by marsh diatom communities and by tidal marsh vegetation. Delivery of DSi back to the estuary after biogenic silica dissolution potentially increases the resilience of the estuary against harmful effects of DSi depletion events. Tidal freshwater marsh vegetation, often dominated by reed (Phragmites australis) has previously been hypothesized to contribute to the Si buffering function of tidal marshes, by dissolution of reed biogenic Si (BSi) into the soil pore water and consequent seepage of DSi to the estuary. In this study the Si pool in the vegetation of a restored tidal freshwater marsh was quantified using species-based cover-biomass relationships and Si analyses. The Si pool in the aboveground biomass increased from 1.2 to 6.5 t km^?2 during the first 6 years of colonization by tidal freshwater marsh species. Our results indicate that young tidal freshwater marshes have a high potential to build up a large vegetation Si pool quickly, mostly due to colonization by species that have both high Si concentrations and high biomass production (e. g. P. australis). This Si pool in vegetation could act both as a long-term sink for Si along estuaries (should Si remain buried in the sediments) or as a short-term source for DSi (should Si be dissolved to DSi).     

Tailoring the Surface of Aluminum-Enriched Diatom Biosilica

Aluminosilicates are widely used as sorbent materials, ion exchangers, and catalysts. While they are often synthesized by hydrothermal methods, microorganisms may open “green” synthesis ways. Diatoms can incorporate aluminum into their micro- and nanostructured silica-based cell walls. Thus, diatoms create intricately structured aluminosilicate materials. The present study investigates not only possible morphological changes during the in vivo Al-enrichment of the diatom species Thalassiosira pseudonana, but also the increase of the specific surface area of Al-enriched biosilica in vitro by etching with alkaline solutions.     

Silicification and Biosilicification. Part 4. Effect of Template Size on the Formation of Silica

Silicification at neutral pH and under ambient conditions is of growing interest due to its close relationship with biosilicification. In diatoms biosilicification has been reported to occur at (or close to) neutral pH and it has been shown that protein molecules act as catalysts/templates/scaffolds for this elegant materials chemistry. In this investigation various catalysts/templates have been studied for their role in silicification in vitro. We have used functionalized C₆₀ fullerene, R5 (an important polypeptide from the amino acid sequence of a silaffin protein), poly-l-lysine (PLL) and two poly(allylamine hydrochloride) (PAH) samples having different molecular weights. An aqueous silica precursor was used and ordered silica structures were produced in each of the systems studied. The sizes of the silica structures appear to correlate with the size, in solution, of the templating/scaffolding agents. Biological systems exhibit hierarchical structures with remarkable control of morphologies over different length scales. The use of templating/scaffolding agents having different sizes and shapes is one possible paradigm for the production of such structures in vivo.     

Biological processing of nanostructured silica in diatoms

The most outstanding example of biological processing of silicon occurs in the unicellular algae known as diatoms. The diatom cell wall contains nanostructured silica with features exceeding current manufacturing capabilities, reproduced with exactness in vast numbers. Such structures must result from specific molecular interactions between cellular components and silicon, and larger scale movements of the intracellular compartment where silica polymerization occurs, the silica deposition vesicle (SDV). New insights into diatom silicification have arisen from recent characterization of the molecular components involved. We have isolated genes encoding silicic acid transporters (SITs) responsible for transport across the cell’s lipid bilayer membrane. The SITs are the only proteins shown to specifically interact with silicon, and a major goal is to identify amino acids responsible for silicic acid recognition and binding. Long-chain polyamines, both free and peptide-attached, apparently induce silica polymerization in diatoms. These compounds have not been shown to have direct control over the formation of larger-scale structure, but observations suggest some involvement. Movements and molding of the SDV during silicification, driven by the cytoskeleton, are major determinants of silica macrostructure. We have applied and are developing techniques to elucidate the molecular mechanisms underlying diatom silicification. This investigation could inspire biomimetic approaches, or lead to the specific manipulation of silicified diatom structures for direct application in nanostructured materials syntheses. These materials are not limited to being silica-based; recent work using shape-preserving displacement reactions has converted diatom silica into an inorganic metal oxide, while maintaining the detailed silica morphology.     

Synthesis and antibiofouling properties of novel crosslinkable terpolymers containing semifluoroalkyl substituted aromatic side chains

Synthesis, contact angle analysis, surface properties and biofouling characteristics of novel crosslinkable terpolymers with semifluoroalkyl substituted aromatic side chains have been described. These polymers are targeted for use as coatings to prevent marine biofouling. The marine antifouling properties of these materials were evaluated by laboratory assays employing the fouling diatom Nitzschia and ubiquitous Staphylococcus aureusi. Results indicated that the experimental coatings exhibited better antibiofouling performance than that of a standard Poly(dimethyl siloxane) (PDMS) coating. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

LOX-induced lipid peroxidation mechanism responsible for the detrimental effect of marine diatoms on zooplankton grazers

Some marine diatoms negatively affect the reproduction of dominant zooplankton grazers such as copepods, thus compromising the transfer of energy through the marine food chains. In this paper, the metabolic mechanism that leads to diatom-induced toxicity is investigated in three bloom-forming microalgae. We show that copepod dysfunctions can be induced by highly reactive oxygen species (hROS) and a blended mixture of diatom products, including fatty acid hydroperoxides (FAHs); these compounds display teratogenic and proapoptotic properties. The process is triggered by the early onset of lipoxygenase activities that elicit the synthesis of species-specific products, the basic structures of which were established (1-20); these compounds boost oxidative stress by massive lipid peroxidation. Our study might explain past laboratory and field results showing how diatoms damage zooplankton grazers even in the absence of polyunsaturated aldehydes, a class of molecules that has been formerly implicated in mediating the toxic activity of diatoms on copepods.     

Identification of the free and conjugated sterol in a non-photosynthetic diatom,Nitzschia alba,as 24-methylene cholesterol

Previous studies on the sterol fraction of the nonphotosynthetic marine diatom,Nitszchia alba, indicated the major sterol to be either brassicasterol (24R-methylcholesta-5,22-dien-3β-ol) or 22-dehydrocampesterol (24S-methylcholesta-5,22-dien-3β-ol) on the basis only of gas chromatographymass spectral analysis. The present studies using nuclear magnetic resonance, infrared, and gas chromatography-mass spectrometry on the free and bound sterol fractions isolated by preparative thin layer chromatography showed the presence in both fractions of a single sterol, with spectral and chromatographic properties identical with those reported for 24-methylenecholesterol (ergosta-5,24(28)-dien-3β-ol). This sterol may be the precursor of 24-methyl sterols found in diatoms. The bound sterol fraction was found to consist of a single compound identified as 24-methylenecholesterol sulfate. No sterol esters or sterol glycosides were detected. Presented at symposium on Marine Lipids, AOCS Meeting, New York, May 1977.