Kulikovskiyia gen. nov. (Bacillariophyceae) from the lateritic rock pools of the Western Ghats,India and from Hainan Province,China

A new triundulate naviculoid diatom genus is described from the Western Ghats of Peninsular India and Hainan Province, China. The new taxon, Kulikovskiyia gen. nov. has robust conical spines along its margin and at the apices and the external valve face has longitudinally‐oriented siliceous slat system extending the length of the valve. The external distal raphe ends bifurcate and terminates on the valve face. There appear to be superficial similarities between this Asian genus and species and Playaensis, a genus comprised of two species found only in the western USA. The systematic position of Kulikovskiyia is discussed, and other than noting its similarities to other biraphid naviculoid diatoms due to symmetry features and the position of the raphe, we are uncertain about its systematic placement at finer levels of classification.     

Size variations of planktonic Aulacoseira Thwaites (Diatomae) in water and in sediment from Finnish lakes of varying trophic state

We measured siliceous frustules of diatoms belonging to the genus Aulacoseira Thwaites in phytoplankton samples of 33 lakes in Finland, and found some significant relationships between the frustule dimensions and the concentrations of total phosphorous, phosphate phosphorus, total nitrogen and nitrate nitrogen in lake water. The size alterations appeared to be species specific and the studied taxa showed different patterns of morphometic change along the nutrient gradients. Some taxa were clearly smaller in eutrophic and mesotrophic lakes. We also observed size reductions of diatoms in the upper parts of sediment cores from two lakes which have apparently become more nutrient rich during recent decades.      

Luminescence properties of a nanoporous freshwater diatom

Freshwater diatom frustules show special optical properties. In this paper we observed luminescence properties of the freshwater diatom Cyclotella meneghiniana. To confirm the morphological properties we present scanning electron microscopy (SEM) images. X‐ray diffraction (XRD) studies were carried out to visualize the structural properties of the frustules, confirming that silica present in diatom frustules crystallizes in an α‐quartz structure. Study of the optical properties of the silica frustules of diatoms using ultra‐violet‐visible (UV‐vis) spectroscopy and photoluminescence spectroscopy confirmed that the diatom C. meneghiniana shows luminescence in the blue region of the electromagnetic spectrum when irradiated with UV light. This property of diatoms can be exploited to obtain many applications in day‐to‐day life. Also, using time‐resolved photoluminescence spectroscopy (TRPL) it was confirmed that this species of diatom shows bi‐exponential decay. Copyright © 2011 John Wiley & Sons, Ltd.     

The diversity of relationships between Antarctic sponges and diatoms: the case of Mycale acerata Kirkpatrick, 1907 (Porifera,Demospongiae)

The diatom assemblage associated with the Antarctic sponge Mycale acerata was studied through an analysis of the diatom frustule and pigment concentrations in both the sponge ectosome and choanosome. Sponges were sampled weekly from November 2001 to February 2002 at Terra Nova Bay, Antarctica, at a depth of 25–35 m. The most abundant diatoms were Porannulus contentus, Fragilariopsis curta, Thalassiosira cf. gracilis, T. perpusilla and Plagiotropis sp. High abundances of P. contentus were found on the sponge ectosome up to the beginning of November, before the ice melted, while later frustules were incorporated inside, indicating that P. contentus lives epibiontically on M. acerata and represents a potential food source for the sponge. The presence of other diatom species was mainly related to the summer phytoplankton bloom. The sponge incorporates diatoms from the water column and utilises them as a food source, accumulating frustules inside the choanosome. The lack of planktonic diatom frustules at the beginning of the summer indicates that they are expelled or dissolved during the cold season.     

The Probable Mechanism for Silicon Capture by Diatom Algae: Assimilation of Polycarbonic Acids with Diatoms—Is Endocytosis a Key Stage in Building of Siliceous Frustules?

Many organisms including unicellular (diatoms, radiolaria, and chrysophytes), higher plants (rice and horsetail) and animals (sponges) use silica as a main part of skeletons. The bioavailable form of silicon is silicic acid and the mechanism of silicic acid penetration into living cells is still an enigma. Macropinocytosis was assumed as a key stage of the silicon capture by diatoms but assimilation of monomeric silicic acid by this way requires enormous amounts of water to be passed through the cell. We hypothesized that silicon can be captured by diatoms via endocytosis in the form of partially condensed silicic acid (oligosilicates) whose formation on the diatom surface was supposed. Oligosilicates are negatively charged nanoparticles and similar to coils of poly(acrylic acid) (PAA). We have synthesized fluorescent tagged PAA as well as several neutral and positively charged polymers. Cultivation of the diatom Ulnaria ferefusiformis in the presence of these polymers showed that only PAA is able to penetrate into siliceous frustules. The presence of PAA in the frustules was confirmed with chromatography and PAA causes various aberrations of the valve morphology. Growth of U. ferefusiformis and two other diatoms in the presence of tri- and tetracarbonic fluorescent tagged acids points to the ability of diatoms to recognize substances that bear four acidic groups and to include them into siliceous frustules. Thus, partial condensation of silicic acid is a plausible first stage of silicon assimilation.     

Auxosporulation in Paralia guyana MacGillivary (Bacillariophyta) and Possible New Insights into the Habit of the Earliest Diatoms

Background

Diatoms are one of the most ecologically important aquatic micro-eukaryotes. As a group unambiguously recognized as diatoms, they seem to have appeared relatively recently with a limited record of putative remains from oldest sediments. In contrast, molecular clock estimates for the earliest possible emergence of diatoms suggest a considerably older date. Depending on the analysis, Paralia and Leptocylindrus have been recovered within the basal molecular divergences of diatoms. Thus these genera may be in the position to inform on characters that the earliest diatoms possessed.

Findings

Here we present auxospore development and structure of initial and post-auxospore cells in a representative of the ancient non-polar centric genus Paralia. Their initial frustules showed unusual, but not unprecedented, spore-like morphology. Similarly, initial frustules of Leptocylindrus have been long considered resting spores and a unique peculiarity of this genus. However, even though spore-like in appearance, initial cells of Paralia readily resumed mitotic divisions. In addition, Paralia post-auxospore cells underwent several rounds of mitoses in a multi-step process of building a typical, “perfect” vegetative valve. This degree of heteromorphy immediately post-auxosporulation is thus far unknown among the diatoms.

Implications

A spore-related origin of diatoms has already been considered, most recently in the form of the “multiplate diploid cyst” hypothesis. Our discovery that the initial cells in some of the most ancient diatom lineages are structurally spore-like is consistent with that hypothesis because the earliest diatoms may be expected to look somewhat similar to their ancestors. We speculate that because the earliest diatoms may have appeared less diatom-like and more spore-like, they could have gone unrecognized as such in the Triassic/Jurassic sediments. If correct, diatoms may indeed be much older than the fossil record indicates, and possibly more in line with some molecular clock predictions.     

Reinvestigation of Phryganella paradoxa (Arcellinida,Amoebozoa) Penard 1902

A major drawback in testate amoeba research is a general lack of scientific studies combining molecular approaches and classical laboratory experiments. We isolated five yet uncultured testate amoebae of the genus Phryganella Penard, 1902 from three different rivers and one pond in Germany. Based on established cultures we show their morphology, which we studied by light and electron microscopy, and present their unique feeding mode on abundant and common pennate diatoms like Nitzschia spp. and Synedra spp., whose frustules are bent and frequently, but not always, broken during the feeding process. We further obtained the first SSU rDNA sequences of strains of the family Phryganellidae, all of which contain introns. We used the sequences to confirm the taxonomic placement of the Phryganellidae in the Arcellinida (Amoebozoa), branching as a sister group to the Cryptodifflugiidae.     

Processing samples of benthic marine diatoms from Mediterranean oligotrophic areas

The processing of benthic diatoms is tedious and involves several potentially damaging steps for cells. Although the preservation of siliceous frustules is of paramount importance in the implementation of biotic indices, only few studies quantified treatment-induced cell losses. We assumed that commonly used treatments may lead to mechanical (centrifugation, sedimentation, boiling, sonication and mounting in Naphrax) and chemical (cold H₂O₂ digestion) damages on diatoms. We analysed the potential adverse effects of these treatments and the cleaning efficiency of H₂O₂ and incineration in order to find out the most suitable technique to process lightly silicified Mediterranean populations. Results showed that successive resuspensions of material after each concentration treatment (sedimentation and centrifugation) and low speed centrifugation did not alter the physical integrity of frustules. In contrast, boiling and sonication exhibited adverse effects especially on the preservation of large frustules and Naphrax mounting proved to be the most damaging step whatever the size of diatoms. For cleaning treatments, incineration provided the most satisfactory results and acted on a non-selective way as opposed to hydrogen peroxide which led to either a large number of non-cleaned frustules or dissolved valves. Our recommendations for processing samples of lightly silicified Mediterranean benthic diatoms include the use of low-speed centrifugations, dehydration at room temperature, incineration and dry mounting.     

DESCRIPTION OF A NEW NAVICULOID DIATOM GENUS MORENEIS GEN. NOV. (BACILLARIOPHYCEAE) FROM SAND FLATS IN KOREA1

This article describes a new diatom genus Moreneis from the Yellow Sea sand flats on the west coast of Korea. The new genus is characterized by a unique combination of morphological characteristics, including the shape of the plastids, which have not been previously observed in diatoms. The valve morphology resembles other genera belonging to Lyrellaceae, within which we place this genus. In terms of areolae structure, Moreneis resembles Petroneis and Placoneis; however, it differs from both genera with respect to the raphe system and plastid shape. Cells of Moreneis spp. have a single large plastid appressed to the girdle of the secondary side of the valve, with two lobes extended toward the primary side of the valve. Furthermore, the unique feature of Moreneis frustules is the raphe, which has both external central and apical endings bent in opposite directions. We differentiated four taxa, which we describe as new for science. However, based on our findings, several established species from Navicula should also be formally transferred to Moreneis, including N. alpha Cleve, N. besarensis Giffen, N. epsilon Cleve, N. menaiana Hendey, N. polae Heiden, and N. quadri‐undulata F. Meister. Analysis of published data revealed that species belonging to Moreneis are numerous in tropical marine littoral waters, and in moderate climate zones, especially in the western Pacific, with only a few species occurring in the Mediterranean and Atlantic.     

EVIDENCE OF AN ORGANIC MATRIX FROM DIATOM BIOSILICA1

Most biominerals appear to be composites of organic material and mineral. Whether biosilica is such a composite is unresolved because of a lack of evidence for such organic components. We present evidence that organic material exists within diatom biosilica and can be extracted using HF/NH₄F solutions from frustules isolated from Cyclotella meneghiniana Kütz and diatomaceous earth. To eliminate organic casing on the silicified frustules as a source of organic materials, the casing was removed by oxidation of frustules with NaOCl before extraction. The removal of the casing was confirmed in that oxidized frustules no longer displayed the ability to be stained with ruthenium red and fluorescamine. Frustules examined with EDXA showed an emission peak from sulfur before treatment but no peak following treatment, indicating that oxidation removed organic sulfur. The organic material obtained from extracts of fresh frustules contained both soluble and insoluble components. Only soluble material was evident in extracts from diatomaceous earth. The soluble material appears to contain glycoproteins with relatively high levels of serine and glycine. The soluble proteins from fresh frustules also appear to be phosphorylated. Indirect evidence is presented that suggests the soluble proteins may contain regions of primary structure enriched in anionic amino acids. The soluble extracts differ from general cell contents when the two fractions are compared, suggesting that frustules contain specialized organic material. The identification of silica-specific organic material suggests that mineralization in diatoms may be in part matrix-mediated.     

Phylogeny and Redescription of the Testate Amoeba Diaphoropodon archeri (Chlamydophryidae,Thecofilosea, Cercozoa), De Saedeleer 1934, and Annotations on the Polyphyly of Testate Amoebae with Agglutinated Tests in the Cercozoa

The genus Diaphoropodon, Archer 1869, comprises filose amoebae with agglutinated tests made of quartz grains, diatom frustules and other particulate materials. The key trait of the genus is a hyaline theca covered with numerous 5‐ to 10‐μm‐long, hairlike rods. Based on SSU rDNA phylogeny, we show that Diaphoropodon groups closely to Lecythium, a testate amoeba genus with a flexible but naked theca. Electron microscopic images reveal that the rods of Diaphoropodon are not perforating the test but lie randomly distributed on the surface of the amoeba. Comparing fairly naked cells from our cultures with cells from the environment leads to the conclusion that these rods play a role in agglutinating the material on the test.     

Studio Comparativo della Struttura e del Ciclo Biologico di Due Diatomee di Acqua Dolce: Navicula Minima Grun. E Navicula Seminulum Grun.: III. Esame Dei Caratteri di Navicula Minima Grun. E di Navicula Seminulum Grun

Abstract

Comparative study of the structure and of the biological cycle of two fresh water diatoms: « Navicula minima » Grun. and « Navicula seminulum » Grun. III. Examination of the characteristics of « N. minima » Grun. and « N. seminulum » Grun. — After studing separately the Navicula minima Grun. and the Navicula seminulum Grun. the various characteristics of the two have been compared and contrasted for purpose of classification. The form and dimentions of the frustules, the density and the structure of the streaks, the structure of the walls, the life circle, aspects of their growths, and some anomalies, most especially, as regards the streaks were examined. It was found the among such numerous characteristics, only one, that is, the presence of the streaks formed by double rows of pores in N. seminulum rather than of a simple file as in N. minima makes one thinks that, in spite of strong similarities existing between these two Naviculae, they are to be regarded as belonging to e different systematic classes. However, their actual positions in taxonomy May-June be defined by further research into the structures and the variabilities of the frustules of other species of Naviculae similar to those examined.     

STRUCTURE,LIFE HISTORY AND SYSTEMATICS OF RHOICOSPHENIA (BACILLARIOPHYTA). I. THE VEGETATIVE CELL OF RH. CURVATA1

Rhoicosphenia Grun. has been placed by some authors in the monoraphid group with Achnanthes Bory and Cocconeis Ehrenb., and by others near Gomphonema Ehrenb. In order to clarify the systematic position of the genus, the morphology and anatomy of the vegetative cells of Rh. curvata (Kütz.) Grun. were investigated using light and electron microscopy. The structure and formation of the two types of valve are described, and the heterovalvy shown to be of a different type from that of the monoraphids; on the basis of raphe, valve and girdle structure a close relationship between these and Rhoicosphenia is unlikely. Rhoicosphenia shows many resemblances to Gomphonema but the types of pore occlusion present, coupled with apparently slight differences in the mucilage-secreting structures and the girdle, suggest that classification in the same family is unwise. The cryptic asymmetry of the valves, and in particular of the raphe system, is noted and explained with reference to their formation; with respect to this asymmetry two configurations of the valves can occur (named cis and trans types) and the distribution of these in raphid genera is discussed briefly. In view of the lack of evidence in raphid diatoms supporting a classification of bands into copulae and pleurae, it is recommended that this practice be suspended.     

SILICON UPTAKE BY ALGAE WITH NO KNOWN Si REQUIREMENT. I. TRUE CELLULAR UPTAKE AND pH-INDUCED PRECIPITATION BY PHAEODACTYLUM TRICORNUTUM (BACILLARIOPHYCEAE) AND PLATYMONAS SP. (PRASINOPHYCEAE)1

Phaeodactylum tricornutum Bohlin, the one diatom known to lack a silicon requirement for growth, and the prasinophyte Platymonas sp. are two representatives of a taxonomically diverse group of planktonic algae that have been reported to take up Si without a demonstrable requirement for the element. For both species, removal of Si from solution during growth in batch culture has at least two components; true biological uptake throughout the growth of the culture, and spontaneous inorganic precipitation of a solid silicate phase–probably Mg₂Si₃O₈ (sepiolite)–under the elevated pH conditions that prevail late in batch growth. It is not clear to what extent previous observations of Si uptake by algae without siliceous frustules may be influenced by inorganic, non-cellular precipitation. The kinetics of true cellular uptake of Si are similar in Phaeodalylum and Platymonas, and different from those reported for the Si-requiring diatoms. Uptake follows hyperbolic saturation kinetics in both species, with half-saturation concentrations of 97.4 μM in Phaeodactylum and 80.9 μM in Platymonas, as compared to ca. 1–6 μM in diatoms that form siliceous frustules. Uptake by Phaeodactylum and Platymonas is not substrate-saturated until the dissolved Si concentration of the medium exceeds 200 μM. Concentrations this high do not occur in the surface layer of the ocean, and the kinetics suggest that both species deposit much less silica in nature than they can be induced to deposit in culture.     

IDENTIFICATION OF CULTURED PSEUDO-NITZSCHIA (BACILLARIOPHYCEAE) USING SPECIES-SPECIFIC LSU rRNA-TARGETED FLUORESCENT PROBES1

Some, but not all, marine pennate diatoms of the genus Pseudo-nitzschia H. Peragallo are associated with the production of domoic acid, a naturally occurring amino acid responsible for amnesic shellfish poisoning. Distinguishing between potentially toxic and nontoxic representatives of this genus is time-consuming and difficult because it demands scanning electron microscopy of cleaned frustules. The objective of this work is to speed and ease identification of these organisms by using whole-cell (in situ) hybridization and species-specific large-subunit ribosomal RNA (LSU rRNA)-targeted oligonucleotide probes. Toward that end, cultures of P. australis Frenguelli, P. pungens (Grunow) Hasle, P. multiseries (Hasle) Hasle, P. fraudulenta (P. T. Cleve) Heiden, P. heimii Manguin, P. delicatissima (P. T. Cleve) Heiden, P. pseudo-delicatissima (Hasle) Hasle, and P. americana (Hasle) Fryxell were screened with a suite of 15 putative species-specific probes. Of those, a subset of eight probes was found that distinguished each species tested. In addition, Pseudo-nitzschia chloroplasts were labeled with a probe directed against a eubacterial-conserved sequence. Identification of new cultures based on their reactivity toward a set of probes agreed with species designations as defined by morphological criteria. Whole-cell hybridization is a rapid, simple, and cost-effective technique for discriminating among cultured Pseudo-nitzschia species.     

PHYLOGENETIC POSITION OF ATTHEYA LONGICORNIS AND ATTHEYA SEPTENTRIONALIS (BACILLARIOPHYTA)1

The phylogenetic position of diatoms belonging to the genus Attheya is presently under debate. Species belonging to this genus have been placed in the subclasses Chaetocerotophycidae and Biddulphiophycidae, but published phylogenetic trees based on 18S rDNA, morphology, and sexual reproduction indicate that this group of diatoms may be a sister group of the pennates. To clarify the position of Attheya, we studied the morphology, 18S rDNA, 16S rDNA of the chloroplasts, the rbcL large subunit (LSU) sequences of the chloroplasts, and the sterol composition of three different strains of Attheya septentrionalis (Østrup) R. M. Crawford and one strain of Attheya longicornis R. M. Crawford et C. Gardner. These data were compared with data from more than 100 other diatom species, covering the whole phylogenetic tree, with special emphasis on species belonging to the genera that have been suggested to be related to the genus Attheya. All data suggest that the investigated Attheya species form a separate group of diatoms, and there is no indication that they belong to either the Chaetocerotophycidae or the Biddulphiophycidae. Despite applying these various approaches, we were unable to determine the exact phylogenetic position of the investigated Attheya species within the diatoms.     

管壳缝类硅藻中国新记录属种——非洲南氏藻

利用光学和电子显微镜对采自黄海水域的1个管壳缝类硅藻——非洲南氏藻进行了形态学研究,并对其地理分布进行了讨论.结果表明:(1)该种壳体带面呈矩形,壳面窄椭圆形,具有钝圆的末端.(2)壳缝居中,由两条等长的分支组成.(3)管壳缝由复杂、接合的肋突支撑,但无龙骨.(4)每条线纹仅有1个孔纹,壳套上最多有1列孔纹.(5)目前...     

Influence of bacteria and salinity on diatom biogenic silica dissolution in estuarine systems

Dissolution of diatom biogenic silica (bSiO₂) in estuaries and its control by water salinity and bacteria were investigated using the river euryhaline species Cyclotella meneghiniana as a model. Laboratory-controlled bioassays conducted at different salinities with an estuarine bacteria inoculum showed a faster dissolution of diatom bSiO₂ at the lowest salinity where bacteria were the most abundant. However in another experiment, salinity increase clearly enhanced the dissolution of cleaned frustules (organic matter free). The presence of active bacteria might therefore predominate on the effect of salinity for freshly lysed diatoms whereas salinity might rather control dissolution of organic-matter-free frustule remains. Incubation of cultivated diatoms at different protease concentrations revealed that high proteolytic activities had little effect on bSiO₂ dissolution at a 1-month scale in spite of an efficient removal of organic matter from the frustules. Altogether it is hypothesized that bacterial colonization increases bSiO₂ dissolution by creating a microenvironment at the diatom surface with high ectoproteolytic activity but also via the release of metabolic byproducts since the presence of organic matter seems generally to facilitate diatom bSiO₂ dissolution.     

Purification of biosilica from living diatoms by a two-step acid cleaning and baking method

Due to their sustainability, intact cell walls, availability of pure cultures, and others, living diatoms show a lot of promise for the application in various fields in particular for micro/nano-devices. In order to purify the biosilica structures of diatoms called frustules, a two-step acid cleaning and baking method was employed. By this path, organic matter and inorganic impurities can be removed very effectively. In addition, the highest quality of frustules was achieved when the samples were cleaned in an excess of boiling 10~15 % HCl and subsequently heated to 600 °C at a heating rate of 3 °C min^?1 for 6 h. In our operation, the native frustule morphology was maintained completely, and dry frustules with more than 90 % SiO₂ in weight can be obtained, and furthermore, the surface area of them reached a good value of 48.47 m² g^?1.