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Interactions between marine diatoms and bacteria have been studied for decades. However, the visualization of physical interactions between these diatoms and their colonizers is still limited. To enhance our understanding of these specific interactions, a new Thalassiosira rotula isolate from the North Sea (strain 8673) was characterized by scanning electron microscopy and confocal laser scanning microscopy (CLSM) after staining with fluorescently labeled lectins targeting specific glycoconjugates. To investigate defined interactions of this strain with bacteria the new strain was made axenic and co‐cultivated with a natural bacterial community and in two‐ or three‐partner consortia with different bacteria of the Roseobacter group, Gammaproteobacteria and Bacteroidetes. The CLSM analysis of the consortia identified six out of 78 different lectins as very suitable to characterize glycoconjugates of T. rotula. The resulting images show that fucose‐containing threads were the dominant glycoconjugates secreted by the T. rotula cells but chitin and to a lesser extent other glycoconjugates were also identified. Bacteria attached predominantly to the fucose glycoconjugates. The colonizing bacteria showed various attachment patterns such as adhering to the diatom threads in aggregates only or attaching to both the surfaces and the threads of the diatom. Interestingly the colonization patterns of single bacteria differed strikingly from those of bacterial co‐cultures, indicating that interactions between two bacterial species impacted the colonization of the diatom. Our observations help to better understand physical interactions and specific colonization patterns of distinct bacterial mono‐ and co‐cultures with an abundant diatom of costal seas. [ABSTRACT FROM AUTHOR]

Presented here are new insights into the marine monoraphid diatom genera Schizostauron and Astartiella, based on molecular and morphological data, including descriptions of new species. Although no unambiguous morphological synapomorphies between the two genera are currently recognized, they are closely related by DNA sequence data. Heterovalvate frustules of Schizostauron are characterized by a bifid stauros on the raphe‐bearing valve and intricate areolate occlusions on the sternum valve. In Astartiella, the raphe‐bearing valve is characterized by a process resembling a fistula by morphology, while the sternum valve presents a particular striation pattern. Observations by light and electron microscopy were made, along with a molecular phylogenetic analysis using a three‐gene (SSU, rbcL, and psbC) concatenated dataset. Three new Schizostauron species are described (S. kajotkei, S. rawaii, S. papilliareae), and two new combinations proposed (S. citronella and S. trachyderma) for species that were previously included either in Achnanthes and Cocconeis, respectively. Likewise, six new species of Astartiella (A. almalikii, A. bornmanii, A. chunlianlii, A. marksii, A. persica, and A. wangii) are described. Molecular results exclude Schizostauron and Astartiella from three clades of exclusively monoraphid diatoms, the Achnanthaceae, Cocconeidaceae, and Achnanthidiaceae, instead placing them in the Stauroneidaceae. Morphological features of Schizostauron and Astartiella, such as the stauros, fistula, and coaxial internal proximal raphe endings, are found in other genera in this clade, whereas the only common feature with monoraphid diatoms as whole group is the heterovalvy of frustules. [ABSTRACT FROM AUTHOR]

Presented here are new insights into the marine monoraphid diatom genera Schizostauron and Astartiella, based on molecular and morphological data, including descriptions of new species. Although no unambiguous morphological synapomorphies between the two genera are currently recognized, they are closely related by DNA sequence data. Heterovalvate frustules of Schizostauron are characterized by a bifid stauros on the raphe‐bearing valve and intricate areolate occlusions on the sternum valve. In Astartiella, the raphe‐bearing valve is characterized by a process resembling a fistula by morphology, while the sternum valve presents a particular striation pattern. Observations by light and electron microscopy were made, along with a molecular phylogenetic analysis using a three‐gene (SSU, rbcL, and psbC) concatenated dataset. Three new Schizostauron species are described (S. kajotkei, S. rawaii, S. papilliareae), and two new combinations proposed (S. citronella and S. trachyderma) for species that were previously included either in Achnanthes and Cocconeis, respectively. Likewise, six new species of Astartiella (A. almalikii, A. bornmanii, A. chunlianlii, A. marksii, A. persica, and A. wangii) are described. Molecular results exclude Schizostauron and Astartiella from three clades of exclusively monoraphid diatoms, the Achnanthaceae, Cocconeidaceae, and Achnanthidiaceae, instead placing them in the Stauroneidaceae. Morphological features of Schizostauron and Astartiella, such as the stauros, fistula, and coaxial internal proximal raphe endings, are found in other genera in this clade, whereas the only common feature with monoraphid diatoms as whole group is the heterovalvy of frustules. [ABSTRACT FROM AUTHOR]

Stressful environmental conditions can induce many different acclimation mechanisms in marine phytoplankton, resulting in a range of changes in their photophysiology. Here we characterize the common photophysiological stress response of the model diatom Thalassiosira pseudonana to ten environmental stressors and identify diagnostic responses to particular stressors. We quantify the magnitude and temporal trajectory of physiological parameters including the functional absorption cross‐section of PSII (σPSII), quantum efficiency of PSII, non‐photochemical quenching (NPQ), cell volume, Chl a, and carotenoid (Car) content in response to nutrient starvation (nitrogen (N), phosphorus (P), silicon (Si), and iron (Fe)), changes in temperature, irradiance, pH, and reactive oxygen species (ROS) over 5 time points (0, 2, 6, 24, 72 h). We find changes in conditions: temperature, irradiance, and ROS, often result in the most rapid changes in photophysiological parameters (<2 h), and in some cases are followed by recovery. In contrast, nutrient starvation (N, P, Si, Fe) often has slower (6‐72 h) but ultimately larger magnitude effects on many photophysiological parameters. Diagnostic changes include large increases in cell volume under Si‐starvation, very large increases in NPQ under P‐starvation, and large decreases in the σPSII under high light. The ultimate goal of this analysis is to facilitate and enhance the interpretation of fluorescence data and our understanding of phytoplankton photophysiology from laboratory and field studies. [ABSTRACT FROM AUTHOR]

A new diatom genus, Gogorevia, is described on the basis of an integrated molecular and morphological investigation. Two species are described from Vietnam: the generitype, G. rinatii sp. nov., and G. ovalis sp. nov. These species share many morphological features with Achnanthes exigua and allied taxa that were previously transferred to the genera Achnanthidium or Lemnicola. Our current molecular investigation shows that Gogorevia is distinct and phylogenetically removed from the above‐mentioned genera. Morphologically, Gogorevia differs from Achnanthidium and Lemnicola by the shape of the valves, possessing uniseriate striae, raphe morphology, and the presence of an evident sternum. The recently described species Lemnicola uniseriata is transferred to Gogorevia on the basis that it possesses the same morphological features and phylogenetic position as other members of the genus. [ABSTRACT FROM AUTHOR]

The genus Minidiscus comprises a group of ecologically‐important and globally‐distributed planktonic diatoms that are characterized by their small cell size, high mantle and processes more or less concentrated in the valve center. Monoclonal strains were established from collections along the Chinese coast. In the phylogenetic analyses inferred from a LSU and SSU dataset, six Minidiscus species clustered into two well‐supported clades. The first clade was located within a larger clade formed mainly by Thalassiosira taxa, and the second clade appeared as sister to a clade comprising the genus Skeletonema. Hence, presently known Minidiscus do not form a monophyletic clade, but rather make up a phenotypic grouping. Based on the morphology of the type species, M. trioculatus, as well as morphological characters of all taxa in the clade with M. trioculatus, Minidiscus is characterized by having fultoportula(e) in the valve center or sub‐centered close to a single rimoportula, and the cells are usually cylindrical. Mediolabrus gen. nov. is proposed to accommodate species in the second clade. The main difference between Minidiscus and Mediolabrus is the type of process found in the valve (sub‐)center, with fultoportula(e) close to a rimoportula in the former, and only a single rimoportula in the latter. According to the above criteria, previously described Minidiscus taxa were re‐examined, and either retained in Minidiscus or transferred to Mediolabrus. [ABSTRACT FROM AUTHOR]

Sea ice algae contribute up to 25% of the primary productivity of polar seas and seed large‐scale ice‐edge blooms. Fluctuations in temperature, salinity, and light associated with the freeze/thaw cycle can significantly impact the photophysiology of ice‐associated taxa. The effects of multiple co‐stressors (i.e., freezing temperature and high brine salinity or sudden high light exposure) on the photophysiology of ice algae were investigated in a series of ice tank experiments with the polar diatom Fragilariopsis cylindrus under different light intensities. When algal cells were frozen into the ice, the maximum quantum yield of photosystem II photochemistry (PSII; Fv/Fm) decreased possibly due to the damage of PSII reaction centers and/or high brine salinity stress suppressing the reduction capacity downstream of PSII. Expression of the rbcL gene was highly up‐regulated, suggesting that cells initiated strategies to enhance survival upon freezing in. Algae contained within the ice‐matrix displayed similar levels of Fv/Fm regardless of the light treatments. Upon melting out, cells were exposed to high light (800 μmol photons · m−2 · s−1), resulting in a rapid decline in Fv/Fm and significant up‐regulation of non‐photochemical quenching (NPQ). These results suggest that ice algae employed safety valves (i.e., NPQ) to maintain their photosynthetic capability during the sudden environmental changes. Our results infer that sea ice algae are highly adaptable when exposed to multiple co‐stressors and that their success can, in part, be explained by the ability to rapidly modify their photosynthetic competence – a key factor contributing to algal bloom formation in the polar seas. [ABSTRACT FROM AUTHOR]

Lake snow, caused by the freshwater centric diatom Lindavia intermedia, has become problematic in several large, oligotrophic New Zealand lakes over the past decade. Macroaggregates produced by L. intermedia foul fishing lines, intake screens, and water filters, and have a negative impact on recreational values. It was confirmed that the fibers constituting lake snow are composed of chitin, two chitin synthase genes (chs1 and 2) from L. intermedia were characterized, new qPCR‐based tools to quantify the abundance of the species and measure expression of chs2 relative to the reference gene act1 (the product of which has cytoskeletal functions) were developed. The strong heterogeneity and mucilaginous nature of lake snow samples create particular difficulties for calibrations of gene or transcript copy numbers with cell densities and obtaining high yields of mRNA. However, data collected from four lakes during November 2018 and February and May 2019 show that abundance of L. intermedia is always high when lake snow is also abundant, but that a full range of L. intermedia abundance can occur when lake snow is absent, suggesting that chitin production is not obligate in L. intermedia. This result is consistent with the available data for chs2 expression, which suggest higher transcription when lake snow is abundant. Lake snow production by L. intermedia therefore requires an as yet undetermined stimulus independent of cell abundance. [ABSTRACT FROM AUTHOR]

Lake snow, caused by the freshwater centric diatom Lindavia intermedia, has become problematic in several large, oligotrophic New Zealand lakes over the past decade. Macroaggregates produced by L. intermedia foul fishing lines, intake screens, and water filters, and have a negative impact on recreational values. It was confirmed that the fibers constituting lake snow are composed of chitin, two chitin synthase genes (chs1 and 2) from L. intermedia were characterized, new qPCR‐based tools to quantify the abundance of the species and measure expression of chs2 relative to the reference gene act1 (the product of which has cytoskeletal functions) were developed. The strong heterogeneity and mucilaginous nature of lake snow samples create particular difficulties for calibrations of gene or transcript copy numbers with cell densities and obtaining high yields of mRNA. However, data collected from four lakes during November 2018 and February and May 2019 show that abundance of L. intermedia is always high when lake snow is also abundant, but that a full range of L. intermedia abundance can occur when lake snow is absent, suggesting that chitin production is not obligate in L. intermedia. This result is consistent with the available data for chs2 expression, which suggest higher transcription when lake snow is abundant. Lake snow production by L. intermedia therefore requires an as yet undetermined stimulus independent of cell abundance. [ABSTRACT FROM AUTHOR]

Chaetoceros debilis is considered one of the most abundant and widespread diatoms in the coastal marine phytoplankton, and is often used in research studies ranging from ecophysiology and molecular biology to oceanography and aquaculture. To clarify the species delineation of C. debilis and explore the diversity among C. debilis sensu lato taxa, monoclonal strains were established from different geographical regions, including the Danish coast, close to the type locality of C. debilis, the Denmark Strait (between Iceland and Greenland) as well as the Taiwan Strait, East China Sea and Daya Bay, South China Sea. Vegetative cells and resting spores were examined using light and electron microscopy. The hypervariable D1–D3 region of the nuclear large subunit ribosomal gene and the small subunit ribosomal gene were sequenced to address phylogenetic relationships. In both SSU and LSU trees, the C. debilis sensu lato strains clustered in four distinct clades. Culture material from the type locality was, along with molecular data, used to delineate and emend the description of C. debilis. Based on molecular data and detailed morphological features, one of the clades originating from Chinese waters was described as C. galeatus sp. nov., characterized by curved and helical chains, elliptical valves, and smooth and helmet‐shaped primary valves of the resting spores. The remaining two clades, which also represent two novel taxa, C. cf. debilis‐1 and C. cf. debilis‐2, were not formally described as new species due to the insufficient information on their morphology. [ABSTRACT FROM AUTHOR]

Chaetoceros debilis is considered one of the most abundant and widespread diatoms in the coastal marine phytoplankton, and is often used in research studies ranging from ecophysiology and molecular biology to oceanography and aquaculture. To clarify the species delineation of C. debilis and explore the diversity among C. debilis sensu lato taxa, monoclonal strains were established from different geographical regions, including the Danish coast, close to the type locality of C. debilis, the Denmark Strait (between Iceland and Greenland) as well as the Taiwan Strait, East China Sea and Daya Bay, South China Sea. Vegetative cells and resting spores were examined using light and electron microscopy. The hypervariable D1–D3 region of the nuclear large subunit ribosomal gene and the small subunit ribosomal gene were sequenced to address phylogenetic relationships. In both SSU and LSU trees, the C. debilis sensu lato strains clustered in four distinct clades. Culture material from the type locality was, along with molecular data, used to delineate and emend the description of C. debilis. Based on molecular data and detailed morphological features, one of the clades originating from Chinese waters was described as C. galeatus sp. nov., characterized by curved and helical chains, elliptical valves, and smooth and helmet‐shaped primary valves of the resting spores. The remaining two clades, which also represent two novel taxa, C. cf. debilis‐1 and C. cf. debilis‐2, were not formally described as new species due to the insufficient information on their morphology. [ABSTRACT FROM AUTHOR]

Snow or glacial algae are found on all continents, and most species are in the Chlamydomonadales (Chlorophyta) and Zygnematales (Streptophyta). Other algal groups include euglenoids, cryptomonads, chrysophytes, dinoflagellates, and cyanobacteria. They may live under extreme conditions of temperatures near 0°C, high irradiance levels in open exposures, low irradiance levels under tree canopies or deep in snow, acidic pH, low conductivity, and desiccation after snow melt. These primary producers may color snow green, golden‐brown, red, pink, orange, or purple‐grey, and they are part of communities that include other eukaryotes, bacteria, archaea, viruses, and fungi. They are an important component of the global biosphere and carbon and water cycles. Life cycles in the Chlamydomonas–Chloromonas–Chlainomonas complex include migration of flagellates in liquid water and formation of resistant cysts, many of which were identified previously as other algae. Species differentiation has been updated through the use of metagenomics, lipidomics, high‐throughput sequencing (HTS), multi‐gene analysis, and ITS. Secondary metabolites (astaxanthin in snow algae and purpurogallin in glacial algae) protect chloroplasts and nuclei from damaging PAR and UV, and ice binding proteins (IBPs) and polyunsaturated fatty acids (PUFAs) reduce cell damage in subfreezing temperatures. Molecular phylogenies reveal that snow algae in the Chlamydomonas–Chloromonas complex have invaded the snow habitat at least twice, and some species are polyphyletic. Snow and glacial algae reduce albedo, accelerate the melt of snowpacks and glaciers, and are used to monitor climate change. Selected strains of these algae have potential for producing food or fuel products. [ABSTRACT FROM AUTHOR]

Snow or glacial algae are found on all continents, and most species are in the Chlamydomonadales (Chlorophyta) and Zygnematales (Streptophyta). Other algal groups include euglenoids, cryptomonads, chrysophytes, dinoflagellates, and cyanobacteria. They may live under extreme conditions of temperatures near 0°C, high irradiance levels in open exposures, low irradiance levels under tree canopies or deep in snow, acidic pH, low conductivity, and desiccation after snow melt. These primary producers may color snow green, golden‐brown, red, pink, orange, or purple‐grey, and they are part of communities that include other eukaryotes, bacteria, archaea, viruses, and fungi. They are an important component of the global biosphere and carbon and water cycles. Life cycles in the Chlamydomonas–Chloromonas–Chlainomonas complex include migration of flagellates in liquid water and formation of resistant cysts, many of which were identified previously as other algae. Species differentiation has been updated through the use of metagenomics, lipidomics, high‐throughput sequencing (HTS), multi‐gene analysis, and ITS. Secondary metabolites (astaxanthin in snow algae and purpurogallin in glacial algae) protect chloroplasts and nuclei from damaging PAR and UV, and ice binding proteins (IBPs) and polyunsaturated fatty acids (PUFAs) reduce cell damage in subfreezing temperatures. Molecular phylogenies reveal that snow algae in the Chlamydomonas–Chloromonas complex have invaded the snow habitat at least twice, and some species are polyphyletic. Snow and glacial algae reduce albedo, accelerate the melt of snowpacks and glaciers, and are used to monitor climate change. Selected strains of these algae have potential for producing food or fuel products. [ABSTRACT FROM AUTHOR]

Microalgae are a promising resource for the highly sustainable production of various biomaterials (food and feed), high‐value biochemicals, or biofuels. However, factors influencing the valued lipid production from oleaginous algae require a more detailed investigation. This study elucidates the variations in lipid metabolites between a marine diatom (Cylindrotheca closterium) and a freshwater green alga (Scenedesmus sp.) under nitrogen starvation at the molecular species level, with emphasis on triacylglycerols using liquid chromatography–electrospray ionization mass spectrometry techniques. A comprehensive analysis was carried out by comparing the changes in total lipids, growth kinetics, fatty acid compositions, and glycerolipid profiles at the molecular species level at different time points of nitrogen starvation. A total of 60 and 72 triacylglycerol molecular species, along with numerous other polar lipids, were identified in Scenedesmus sp. and C. closterium, respectively, providing the most abundant triacylglycerol profiles for these two species. During nitrogen starvation, more triacylglycerol of Scenedesmus sp. was synthesized via the "eukaryotic pathway" in the endoplasmic reticulum, whereas the increase in triacylglycerol in C. closterium was mainly a result of the "prokaryotic pathway" in the chloroplasts after 96 h of nitrogen starvation. The distinct responses of lipid synthesis to nitrogen starvation exhibited by the two species indicate different strategies of lipid accumulation, notably triacylglycerols, in green algae and diatoms. Scenedesmus sp. and Cylindrotheca closterium could serve as excellent candidates for the mass production of biofuels or polyunsaturated fatty acids for nutraceutical purposes. [ABSTRACT FROM AUTHOR]

High‐affinity nitrate transporters are considered to be the major transporter system for nitrate uptake in diatoms. In the diatom genus Skeletonema, three forms of genes encoding high‐affinity nitrate transporters (NRT2) were newly identified from transcriptomes generated as part of the marine microbial eukaryote transcriptome sequencing project. To examine the expression of each form of NRT2 under different nitrogen environments, laboratory experiments were conducted under nitrate‐sufficient, ammonium‐sufficient, and nitrate‐limited conditions using three ecologically important Skeletonema species: S. dohrnii, S. menzelii, and S. marinoi. Primers were developed for each NRT2 form and species and Q‐RT‐PCR was performed. For each NRT2 form, the three Skeletonema species had similar transcriptional patterns. The transcript levels of NRT2:1 were significantly elevated under nitrogen‐limited conditions, but strongly repressed in the presence of ammonium. The transcript levels of NRT2:2 were also repressed by ammonium, but increased 5‐ to 10‐fold under nitrate‐sufficient and nitrogen‐limited conditions. Finally, the transcript levels of NRT2:3 did not vary significantly under various nitrogen conditions, and behaved more like a constitutively expressed gene. Based on the observed transcript variation among NRT2 forms, we propose a revised model describing nitrate uptake kinetics regulated by multiple forms of nitrate transporter genes in response to various nitrogen conditions in Skeletonema. The differential NRT2 transcriptional responses among species suggest that species‐specific adaptive strategies exist within this genus to cope with environmental changes. [ABSTRACT FROM AUTHOR]

This paper explores the diversity and taxonomy of species within Fragilaria sensu stricto, an abundant and ecologically important diatom genus, taking advantage of cultured and DNA‐barcoded material. The goal is to facilitate the identification of European taxa within this complex, providing a unified view on morphological and molecular diversity. There is a general agreement that the separation of species within the group of Fragilaria is difficult because morphological descriptions of species are not consistent between authorities, ongoing taxonomic revisions have resulted in species described with standards of the late 20th and 21st centuries alongside descriptions based on 19th century (light microscopical) criteria, and because not all diagnostic characters can be seen in all specimens encountered in routine analyses. Consequent confusion could blur potentially important ecological distinctions between species. Our study demonstrated that some species defined on morphological criteria could be confirmed using the rbcL chloroplast gene as a genetic marker, for example, Fragilaria gracilis, Fragilaria tenera, Fragilaria perminuta, and Fragilaria subconstricta. However, even for those species, preliminary identifications based on morphology often differed from identifications based on phylogenetic clustering combined with detailed morphological study. Clades were well‐defined by rbcL, but based on morphology, the terminal taxa of these clades did not match the currently described Fragilaria species. To clarify recognition of these taxa, we describe three new species: Fragilaria agnesiae, Fragilaria heatherae, and Fragilaria joachimii. [ABSTRACT FROM AUTHOR]

Diatoms are one of the most abundant and arguably the most species‐rich group of protists. Diatom species delimitation has often been based exclusively on the recognition of morphological discontinuities without investigation of other lines of evidence. Even though DNA sequences and reproductive experiments have revealed several examples of (pseudo)cryptic diversity, our understanding of diatom species boundaries and diversity remains limited. The cosmopolitan pennate raphid diatom genus Pinnularia represents one of the most taxon‐rich diatom genera. In this study, we focused on the delimitation of species in one of the major clades of the genus, the Pinnularia subgibba group, based on 105 strains from a worldwide origin. We compared genetic distances between the sequences of seven molecular markers and selected the most variable pair, the mitochondrial cox1 and nuclear encoded LSU rDNA, to formulate a primary hypothesis on the species limits using three single‐locus automated species delimitation methods. We compared the DNA‐based primary hypotheses with morphology and with other available lines of evidence. The results indicate that our data set comprised 15 species of the P. subgibba group. The vast majority of these taxa have an uncertain taxonomic identity, suggesting that several may be unknown to science and/or members of (pseudo)cryptic species complexes within the P. subgibba group. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The diatoms (Bacillariophyta) from a coastal lagoon from the Diablas wetlands (Isla Isabela, the Galápagos Islands) were studied in material from surface samples and a sediment core spanning the past 2,700 years in order to examine evidence of diatom evolution under geographic isolation. The total number of taxa found was ∼100. Ultrastructural variation in valve morphology between members of Galápagos taxa was used to describe 10 species from the genus Navicula sensu stricto, which are new to science. Four taxa: N. isabelensis, N. isabelensoides, N. isabelensiformis, and N. isabelensiminor, shared several key characteristics that may be indicative of a common evolutionary heritage; these species therefore provide possible evidence for the in situ evolution of diatoms in the Galápagos coastal lagoons. Shared morphological characteristics include: (i) stria patterning in the central area, (ii) an elevated and thickened external raphe-sternum, (iii) external central raphe endings that are slightly deflected toward the valve primary side, and (iv) an arched valve surface. To explain these findings, two models were proposed. The first suggested limited lateral diatomaceous transport of Navicula species between the Galápagos and continental South America. Alternatively, these new species may be ecological specialists arising from the unique environmental conditions of the Galápagos coastal lagoons, which restrict the colonization of common diatom taxa and enable the establishment of novel, rare species. The Diablas wetlands are an important site for diatom research, where local-scale environmental changes have combined with global-scale biogeographic processes resulting in unique diatom assemblages. [ABSTRACT FROM AUTHOR]

The occurrence of cryptic and pseudocryptic species, often living in sympatry, is widespread among microalgae. This phenomenon raises important questions about niche partitioning between these closely related species. To date, however, few studies have addressed the ecological mechanisms underlying sympatry in cryptic and pseudocryptic species. As a result, we have only a limited understanding of the factors that govern their distribution along environmental gradients. Here, we used the ribosomal internal transcribed spacer (ITS), 18S rRNA gene, and the RUBISCO LSU ( rbcL) chloroplast gene sequence data together with cell wall morphology to show that estuarine populations of the widespread and common benthic diatom Navicula phyllepta Kütz. consist of pseudocryptic species. Growth rate measurements in function of salinity showed that N. phyllepta strains assigned to the different species differed in their tolerance to low salinities (<5 practical salinity units, psu), which was reflected by their different (but widely overlapping) distribution in the Westerschelde estuary (the Netherlands). Multiple regression analyses of the factors determining the abundance of the different species in field samples revealed that, in addition to salinity, sediment type and ammonium concentrations were probably equally important. Our results show that N. phyllepta sensu lato comprises different species with specialized ecophysiological characteristics rather than generalists with a broad adaptability to different environmental conditions. [ABSTRACT FROM AUTHOR]

Benthic diatoms are a commonly used food source in shellfish aquaculture. Diatoms of the genus Navicula are the most abundant benthic diatoms occurring year-round on the coast of Jeju Island, Korea. We isolated an axenic strain of N. incerta Grunow; estimated its growth characteristics under 27 different combinations of temperature, salinity, and nutrients; and determined its biochemical composition and antioxidant activities. The maximum specific growth rate (μmax), defined as the increase in cell density per unit time, was 0.81–1.04 · d−1, and the maximum cell density, 7.99 × 105 cells · mL−1, was reached at 0.88 · d−1 μmax, 20°C, 30 psu salinity, and F/2 nutrient concentration on day 12 of the culture period. The approximate cellular composition was as follows: 7.0 ± 0.04% protein, 1.7 ± 0.28% lipid, 12.8 ± 0.85% carbohydrate, 68.4 ± 0.09% ash, and 10.1 ± 0.44% moisture. The antioxidant properties of N. incerta were determined for various extracts. The rates of 1,1-diphenyl-2-picrylhydrazyl (DPPH) free-radical scavenging for Neutrase and methanol extracts were 81.6% and 62.8%, respectively. Flavourzyme extract had a superoxide-scavenging rate of 57.7%. Kojizyme and Ultraflo extracts had nitric-oxide-scavenging rates of 42.2% and 40.6%, respectively, significantly higher than commercial antioxidants, such as α-tocopherol and butylated hydroxytoluene (BHT). The metal-chelating activities of the methanol, Neutrase, and Termamyl extracts were 68.5%, 45.2%, and 41.2%, respectively, four to six times higher than commercial antioxidants. The Termamyl extract showed the highest linoleic acid peroxidation inhibition, exceeding α-tocopherol and on par with BHT. [ABSTRACT FROM AUTHOR]

Six strains of diatoms from intertidal waters were isolated as part of the SERI Aquatic Species Program collection and screening effort: Amphiprora hyaline Greville, Cyclotella cryptica Reimann, Lewin & Guillard, Navicula acceptata Hustedt (two strains, NAVIC6 and NAVIC8), Navicula saprophila Lange-Bertalot & Bonik, and Nitzschia dissipata (Kütz.) Grunow. Among numerous algal strains isolated as part of this collection effort, these six strains showed rapid growth and elevated lipid content in preliminary screening experiments and were chosen for further physiological characterization. N. dissipata grew most rapidly at 25°C, whereas the other five strains grew best at 30-35°C. salinity tolerance varied among strains, with maximal growth occurring at the following conductivities: 10-60 mS·cm[sup-1] (A. hyaline and N. saprophila), and 20-35 mS·cm[sup-1] (C. cryptica), 20-45 mS·cm[sup-1] (N. acceptata NAVIC6), 10 mS·cm[sup-1] (N. saprophila), and 20-35 mS·cm[sup-1] (N. dissipata). The diatoms also differed in their utilization of nitrogen sources with A. hyaline growing optimally with either nitrate or urea; N. acceptata NAVIC6, with either nitrate or ammonium; C. cryptica, N. acceptata NAVIC8, and N. dissipata, with nitrate; and N. saprophila, with urea. Under optimal conditions, A. hyaline grew at 2.0 doubligs·day[sup-1]; C. cryptica grew at 3.0 doublings·day[sup-1]. all six strains had lipid contents in excess of 37% ashfree dryweight (AFDW) under nutrient-limited conditions, with N. saprophila having the highest lipid content at 48% AFDW. [ABSTRACT FROM AUTHOR]

Live and prepared cells of the marine pennate diatom Navicula complanatoides Hust. were examined with light and electron microscopy. It has narrowly lanceolate valves (26-55 μm long, 4-5 μm wide) and girdles 10-24 μm in depth. Striae are parallel at the center of the valve (24-28 in 10 μm). becoming slightly convergent toward the apices. Electron microscopy, revealed that the external valve surface presents a longitudinally ribbed appearance (2028 parallel ribs at its maximum width), whereas internally, rectangular areolae are occluded by ricae. The raphe slit lies in a narrow axial area. and one side of the raphe sternum is deeper and folds over the other, obscuring the internal opening. Internally, the central virga on one side of the raphe and two virgae on the other are somewhat broader. A conspicuous pore (stigma) is present between the two broadened virgae. The girdle consists of valvocopulae, copulae, and pleurae. There are 16-20 bands per cingulum. The valvocopulae and copulne are hollow tube-like structures, with inner and outer portions contrasting in morphology. They decrease in diameter in an abvalvar direction. There are four pleurae. These are flat bands which facilitate overlap of the epicingulum and hypocingulum. Fundamental features of the valve and girdle reveal the distinctness of this species within Navicula. The areolae. external longitudinal ribs, and raphe structure suggest affinities with Pleurosigma. Gyrosigma, and Hasa. It is hypothesized that they share a derived state which indicates a recent common ancestor for these taxa. N. complanatoides and related species of the Naviculae microstigmatacae are distinctive enough to merit their own genus within the Naviculaceae. [ABSTRACT FROM AUTHOR]

This paper evaluates the utilisation of space by epibenthic diatom cells, as a response to environmental variations. The aggregation pattern of five species of epihenthic diatoms was quantified and compared to provide evidence for the significance of cell motility as an adaptive mechanism for space occupation and monopoly. The epibenthic diatoms included (1) non-mobile colonial species forming either fan-shaped (Synedra tabuiata (Ag) K[SUBz]) or arborescent (Gomphonema kamtschaticum var. californicum Grun.) colonies; (2) slow-moving (Cocconeis costata Grig. and Amphora pusio Cl.), and (3)fast-moving (Navicula directa (W. Sm.) Ra ) non-colonial species. The aggregation pattern of S. tabulata did not vary significantly among six different light intensities manipulated in nature. The major patterns of aggregation were iden- tified using analysis of covariance and dummy-variable regression. Highly mobile . directa are significantly less aggregated than the four other diatom species. Non-mobile and slow-moving species show a similar, highly aggregated pattern. The occurrence of two patterns of spatial dispersion indicates that growth forms bear far-ranging ecological implications with respect to colonization strategies, immigration, and possibly impact by grazers. An integrated model of growth form characteristics, biological properties, and ecological implications is presented for epibenthic diatoms. [ABSTRACT FROM AUTHOR]

Colonies of the tube-dwelling diatom Navicula hamulifera Grunou, living on mangrove prop rools in Indian River, Florida and at La Parguera, Puerto Rico, were studied using light and electron microscopy. Observations of the tube morphology and cell structure of this diatom from fresh samples and cultures are described, as well as the ultrastructural morphology of its fruslule. The forrnation of tubes by this diatom is reported for the first time. Comparisons are made with the closest species; Navicula delognei V.H. and Navicula pseudocomoides Hendey. [ABSTRACT FROM AUTHOR]

Describes the deposition of siliceous valves during asexual reproduction of the pannate diatom Navicula cuspidata. Emphasis on the cytoplasmic components involved; Events accompanying valve secretion that are similar to those already known from other pennate species; Implications on phycology.

Studies the valve and band morphology of freshwater diatom Navicula confervacea var. confervacea. Development of the mucilage on the outer surface; Types of nonstructural cell wall material; Morphology of the frustule; Secretion between the bands.

Studies the morphology and integration of valves and bands in diatom Navicula mutica var. mutica. Axis symmetry of frustules; Morphology of the mantle and punctum; Position of the undulate advalvar margin of valvocopula.

Studies the role of microtubule in diatom valve symmetry and pattern formation in Navicula saprophila. Inhibitory effects of microtubule drugs related to microtubule disruption; Percentage of produced aberrant valves; Characteristic aberrations of valves; Valve components affected by anti-microtubule drugs.

Describes the species of tube-dwelling diatom Navicula using light and scanning electron microscopy. Morphology of the colonies; Frustule morphology of the diatoms; Similarities of the cells with that of Schizonema smithii C. Agardh.

Epilithic and epiphylic diatoms were collected monthly from 18 June 1979 through 19 May 1980 from both shaded and unshaded sited of Sessums Creek, a shallow aligotrophic and strongly alkaline stream in northeastern Mississippi. The dominant macroalgae were filamentous green algae belonging to the non-mucilage producing genera Cladophora and Rhizoclonium. Ninety taxa were identified with Navicula minima Grun. and Nitzschia dissipata (Kütz.) Grun. accounting for 50% of all values counted. Other important taxa were Navicula menisculus var. upsaliensis (Grun.) Grun. N. cryptocephala var. veneta (Kütz.) Rabh. Achnanthes minutissima Kütz. and Cymbella turgida (Gerg.) Cl. With few exceptions, the more dominant taxa were equally abundant in the shaded and unshaded sites and also in the epilithon and epiphyton. Species diversity (H') and the number of taxa in a sample in all four habitats showed an identical pattern, being lowest in winter and highest in fall. No one pair of habitats was more structurally similar than any other pair when compared by a similarity index (SIMI). Apparently, differences in light intensity and substrate type had little effect on diatom distribution in sessums Creek and it was concluded that the locality sampled supported a single, nearly homogeneous diatom community. [ABSTRACT FROM AUTHOR]

The role of microtubules in silicon metabolism leading to valve formation was investigated in the pinnate diatom. Navicula saprophila Lange-Bertalot & Bnik. By using synchromized cells blacked after mitosis and cytokinesis but proor to cell wall formation, effects due to inhibition of mitosis were eliminated. Cells were treated with three anti-microtubule drugs to assess the role of microtubules. Chemical analogs to two of the drugs provided controls for inhibition not related to microtubule disruption. Although all three anti-microtubules drugs reduced cell separation at high concentrations (1×10[SUP-1] M), podophyllotoxin was the only drug which reduced cell separation at concentration lower 1×10[SUP-5] M. None of the drugs at any concentration tested affected cell viability. There was no differential inhibitory affect between the active and inactive drugs on silicic acid transport total uptake, incorporation.or pool formation. There was no qualitative difference between silica incorporated in treated and untreated cells. A colchicines binding component was isolated from N. saprophila. The characteristics of colchicines binding suggest this component may be tubulin. Microtubules do not appear to be involved in any of the steps of silicon metabolism leading to valve formation and yet they have profound influence on the symmetry and pattern of the mineralized product the siliceous valve. [ABSTRACT FROM AUTHOR]

The reactions and processes which underlie the silicification mechanism (incorporation of soluble material) in the diatom. Navicula pelliculosa (Bréb.) Hilse are quite sensitive to low temperature. Furthermore incororation is completely blocked in [SUP68]Ge-Si(OH)[SUB4] preloaded cells treated with an inhibitor of oxidative phosphorylation (2,4-dinitrophenol) or a sulfhydryl blocking agent (N-ethylmaleimide). De nova protein synthesis is not required for incorporation in cells preloaded 3 h, but cycloheximide added to cells preloaded 1 h inhibits incorporation after 2 h. These results are interpreted to indicate that purely chemical reactions, which are uncoupled from cellular metabolism, cannot completely account for Si(OH)[SUB4] polycondensation during silical frustule morphogenesis in the diatom. A temperature sensitive cellular process or reaction, postcytokinesis, is also postulated to be required before silicification can occur. [ABSTRACT FROM AUTHOR]

During winter (1973), a very pure natural population of the diatom Navicula glaciei Van Heurck occurred in dense concentrations (up to 244 mg.m[SUP-2] chlorophyll a) in the sea ice at Signy Island, South Orkney, Antarctica. Samples of algal material were collected for subsequent chemical analysis. The diatom had a composition of 33.77% ash, 21.81% lipid, 25.38% crude protein, 19.04% crude carbohydrate and an intact calorific value of 15.384 KJ.g[SUP-1]. Carbon, hydrogen, nitrogen and phosphorus formed 34, 5.3, 4.1 and 0.52% dry wt respectively. The material was analysed for the trace elements Na, K, Fe, Ca, Mg, Al, Zn, Cu, Pb, Mn, [SUP137]Cs. Fatty acid composition was dominated by 16.0 palmitic acid (20.46%), 16;1 palmitoleic acid (32.86%), and 20;5 docosahexaenoic acid (19.33%). To supplement a very scanty original description, a full taxonomic description is given in the text. [ABSTRACT FROM AUTHOR]

Chemically cleaned and critical-point dried cells of a clonal culture were examined with scanning electron microscopy. Cells from filaments by valve-to-valve connections maintained by organic material which adheres to the central area of the valve face. Bending of filaments is probably restricted to some extent by the articulation of overlapping spatulate marginal spines with an adjacent underlapping set of much shorter spines (ridges), and with the mantle edge itself. Cell division results in three possible spine patterns for each cell: a set of overlapping and a set of underlapping spines; no overlapping sets of spines (two underlapping); or two sets of overlapping spines (no underlapping). Each filament inherits cells with spine set patterns in the ratio of 2 (with 1 set overlapping): 1 (with no sets overlapping): 1 (with 2 sets overlapping): Valvocopulae are shaped similarly to pleurae except that the partes experiores of the valvocopulae are wider. The pars interior of both is delimited by an advalvar row of pores continuous around the cell apex. The pars exterior also has a row of pores, but it is median in the valvocopula and first pleura and does not continue around the cell apex. The valvocopulae always underlap the mantle and the pleurae always underlap their preceding band. The ends of both appeared attached, but may become free in acid-cleaned preparations. Bands alternate with each other so that the ends of the valvocopula attach to the first continuous apical portion of the first pleura; the ends of the first pleura attach in that same fashion to the second pleura but at the opposite apex; and all subsequent pleurae alternate in the same fashion with up to at least 13 pleurae alternate in the same fashion with up to at least 13 pleuraelepicingulum. The continuous apical portion of each band is formed, with the continuous apical portion of alternate bands becoming adjacent and underlapping each other only in this region. The valvocopulae in a single cell, or of adjacent cells, may have their continuous apical ends on the same or on opposite apices. It is recommended that N. confervacea var. peregrina (W. Sm.) Grun. Be merged with the nominate variety. [ABSTRACT FROM AUTHOR]

Radioactively labeled ribosomal RNA from seven species of algae was purified and hybridized to purified DNA from Chlamydomonas reinhardtii Dangeard (Chlorophyta). Delta T[subin] values for the heterologous RNA-DNA duplexes were obtained by thermal dissociation; values ranged from 3.9 to 10.9 C. Organisms traditionally considered to be less closely related to C. reinhardtii showed the greatest delta T[subm] values. Ulothrix fimbriata Bold and Klebsormidium flaccidum (Kütz.) S., M. & Bl., although similar morphologically, showed very different delta T[subm] values and would not appear to be closely related by these criteria. [ABSTRACT FROM AUTHOR]

The presence of up to 500 μg sulfur·1[sup-1] of an equimolar mixture of cysteine and methionine had virtually no effect on the SO[SUB4,SUP2-] uptake rate of Navicula pelliculosa, (Bréb.) Hilse whereas the rate of Ankistrodesmus falcutus (Corda) Ralfs was decreased by the presence of 500 μg S&middotl[sup-1] and Anabaena flos-aquae (Lyngbye) Bréb. by 50 μg S·l[sup-1]. Primary productivity int hese axenic cultures was affected (decreased) only in A. falcatus. The C:S uptake ratio was lowest in N. pelliculosa and highest in A. falcatus. Considering these species as representative of groups of naturally occurring algae, patterns of SO[sub4,sup2-] uptake and primary productivity in a eutrophic and a moderately oligotrophic lake reflected the results of the algal culturing experiments: SO[sub4,sup2-] uptake rates, relative to primary productivity, were higher in the presence of diatoms and bluegreen algae and lower when green algae were present; the addition of the cysteinelmethionine mixture to the lake waters decreased the rate of microplankton SO[sub4,sup2-] uptake in correlation with the makeup of the algal community; primary productivity decreased upon the addition of cyteine/methionine when green algae were relatively abundant. It is concluded that, in most fresh water systems, the effects of organic sulfur pollution on algal SO[sub4,sup2-] uptake and primary productivity are insignificant as compared to other ecological changes that occur due to that pollution. [ABSTRACT FROM AUTHOR]

Silicic acid taken up from the growth medium by Navicula pelliculosa (Breb.) Hilse was shown to enter at least two compartments: i) soluble pools; ii) insoluble fraction comprised predominantly of the silica frustule. Soluble Si pools were extracted by a variety of agents from cells uniformly labeled for ten generations in medium containing [sup68]Ge-Si(OH)[sub4] 1000 C water soluble and 0 C perchloric acid (PCA) soluble Si pools of 680 mM Si · I[sup-1] and 490 mM Si l[sup-1] cell water represented 13 and 9%, respectively, of total cell Si in exponential growth phase cells. Uniformly labeled cells synchronized by the combined synchronization technique accumulate at the cell cycle stage where silica frustule development is initiated. These cells contain water and PCA soluble pools of 10 nmol Si 10[sup6] cells[sup-4] and 8.8 nmol Si · 10[sup6] cells[sup-1], respectively. On addition of Si(OH)[sub4], a rapid uptake ensues allowing the Si pool to expand 2.5-fold, apparently to provide precursors of the silica frustule. [ABSTRACT FROM AUTHOR]

Navicula ulvacea (Berkeley ex Kuütz.) P. T. Cleve, a marine colonial blade-forming diatom originally discovered in Scotland was collected at North Rustico, prince Edward Island, during winter 1971. it formed dense stands of Porphyra-like fronds, ranging up to 60 mm long × 20 mm wide. These occurred under ice-covered water on rocks 1-2 m below zero tide. Comparisons made at the light and scanning electron microscope level compared favorably with original Aberdeen material. Clonal cultures established from single cells at first also formed blades, but rarely more than 10 mm long. In numerous serial subcultures made since 1971 no further blades have been formed. Instead, growth consisted of well-separated cells or short filaments scattered over the bottom and sides of the vessels. Older cultures developed prostrate sheets of filaments, embedded in ann mucilaginous matrix and occasional bubble-like eruptions. Results of the cultures suggest that N. ulvacea probably occurs in a prostrate form in nature, perhaps more commonly than in the blade form. Literature records since the original collection in 1944 are brought together but are considered doubtful. A discussion on nomenclature is included. [ABSTRACT FROM AUTHOR]

Edaphic diatoms were collected on a seasonal basis from beneath five monospecific stands of spermatophytes on Graveline Bay Marsh (Mississippi) from 14 October 1976 through 21 June 1977. Of the 119 diatom taxa encountend, only seven were restricted to a single edaphic habitat, and five of these accounted for 17.2% of the individuals comprising the community associated with Distichlis spicata (L.) Greene. The single most abundant diatom was Navicula tripunctata (Müll.) Bory, which accounted for 21.5% of all individuals counted during the study. Based on a 2-way ANOVA of species diversity (H[SUP1]) and the number of taxa in a sample, edaphic diatom community diversity was highest beneath D. spicata and Spartina patens (Ait.) Muhl. Lowest beneath Sp. Alterniflora Loisel: and Juncus roemerianus Scheele, and somewhat intermediate for the Scirpus olneyi Gray habitat. Structural differences between selected community pairs were quantified using a similarity index (SIMI) and the values generated were exceedingly variable. A multiple regression analysis revealed that structural differences amongst edaphic diatom communities were related to differences in elevation, far red light energy, ammonia nitrogen, soil moisture, and tentatively, height of the spermatophyte canopy. [ABSTRACT FROM AUTHOR]

The benthic diatom, Navicula seminulum var. hustedtii part. was isolated from the field and studied in laboratory cultures. Experiments were conducted to determine the suitability of Millipore membranes and solidified agar sustrate for diatom colonization under continuous flow conditions. Diatom colonization showed large variation and low reproducibility on Millipore membranes of different materials and pore sizes. Solidified agar substrate supported stable and reproducible colonization and is nutritionally neutral, translucent, homogeneous and easy to sample. The diatom colonization process on agar substrate involved four growth phases: I) pioneer; ii) exponential; iii) steady state; and , iv) vanishing. The culture system was also used in bioassay, testing the toxic effect of copper on the growth of benthic diatoms. The proposed method provides a useful means for studying autecology of benthic diatoms as well as for bioassay work. [ABSTRACT FROM AUTHOR]

The marine diatom Navicula incerta Hustedt and the haptophyte Isochrysis galbana Parke, both accustomed to grow on nitrate, were tested for their adaptive capacity for growth in axenic culture on 0.036-2.0 mM L-, D-, and DL-isomers of phenylalanine and tyrosine as sole nitrogen sources. The diatom showed immediate and excellent growth (superior to nitrate) on L-phenylalanine and L-tyrosine but required prolonged periods of adaptation before growing on the D-isomers, which growth was considerably slower. Isochrysis showed good growth on L-phenylalanine after short adaptation, fair growth on low but poor growth on high concentrations of L-tyrosine and no growth on the D-isomers of both amino acids. The racemate (DL-mixture) of each amino acid produced growth responses, from both algae, inferior to those of the corresponding L-isomer, indicating competitive inhibition from the D-isomer in the presence of equal amounts of its counterpart. Increasing tyrosine concentration was beneficial to growth of Navicula but markedly inhibitory or toxic to that of Isochrysis. Phenylalanine concentration appeared to benefit growth of both algae. Ecological considerations suggest that N. incerta may be habituated to utilize both aromatic amino acids in its native milieu. [ABSTRACT FROM AUTHOR]

Synchronized populations of Navicula pelliculosa (Bréb) Hilse show a 10-fold increase in Si(OH)[SUB4] transport rate during traverse through the cell division cycle. The transport activity pattern is similar to a "peak enzyme," Kinetic analysis showed there was a significant change in K[SUB8] values, indicating increased "affinity" for Si(OH)[SUB4] as cells neared maximal uptake rates. However, the dramatic changes in transport rate at various cell cycle stages were also reflected by alterations in the V[SUBmax] values of the transport process, suggesting a change in the number of functional transport "sites" in the plasma membrane. Cells in the wall forming stage, arrested from further development by Si(OH)[SUB4] deprivation, maintained high transport rates for as long as 7 h. The rates decreased rapidly if protein synthesis were blocked or if Si(OH)[SUB4] was added, the latter allowing the cells to traverse the rest of the cycle. The half-life of the transport activity ranged from 1.0 to 2.2 h when protein synthesis was inhibited at various cell cycle stages and during the natural decline of activity late in the cycle. The transport system appears to be metabolically unstable as is typical for a "peak protein." The rise in transport rate through the cell cycle did not depend on the presence of Si(OH)[SUB4] in the medium; therefore, the transport system does not appear to be induced by its substrate. The rise in transport is also observed in L:D synchronized cells developing in the presence of Si(OH)[SUB4]: neither does the transport system appear to be derepressed. The transport rate was strongly cell cycle-state dependent: the data appeared to fit the "dependent pathway" model proposed by Hart-well to explain oscillations in enzyme synthesis during the cell cycle. [ABSTRACT FROM AUTHOR]

Silicic acid transport was studied in the photosynthetic diatom Navicula pelliculosa (Bréb.) Hilse using [SUP68]Ge] germanic acid ([SUP68]Ge(OH)[SUP4]) as a tracer of silica acid (Si(OH)[SUB4]) . The initial uptake rate of Si(OH)[SUB4] was dependent on cell number, pH, temperature, light and was promoted by certain monovalent cations in the medium. Na[SUP+] was more effective than K[SUP+], whereas Li[SUP+] and NH[SUB4][SUP+] were ineffective at promoting uptake. Uncouplers and inhibitors of oxidative phosphorylation and of photophosphorylation reduced uptake by 40-99% of control values. Uptake was also especially sensitive to the sulfhydryl blacking agents at 10[SUP-5]m and tot he ionophorous compound valinomycin (10[SUP-7]m) which inhibited uptake by 82%. The Si(OH)[SUB4] transport system displayed Michaelis-Menten-type saturation kinetics with kinetic parameters of K[SUB8] = 4.4 μmol Si(OH)[SUB4]·l[SUP-1], V[SUBmax] = 334 pmol Si(OH)[SUB4]&middot10[SUP6] cells[SUP-1]·min[SUP-1]. Calculations of the acid-soluble silicic acid pool size based on 60 s uptake at 20 μm Si(OH)[SUB4] suggested that intracellular levels of Si could reach 20 mM and as much as 5 mM could exist as free silicic acid, representing maintenance of a 250-fold concentration gradient compared with the medium. Efflux from preloaded cells was dependent on temperature and the Si(OH)[SUB4] concentration of the external medium. In the presence of 100 μM "cold" Si(OH)[SUB4], approximately 30% of the Si(OH)[SUB4] in preloaded cells was exchanged in 20 min. The initial uptake rate of Si(OH)[SUB4] in logarithmic phase cells was constant, but the uptake rate increased in a linear fashion for 6 h in stationary phase cells. These results suggest that the first step in silica mineralization by diatoms is the active transmembrane transport of Si(OH)[SUB4] by an energy dependent, saturable, membrane-carrier mechanism which requires the monovalent cations Na[SUP+] and K[SUP+] and is sensitive to sulfhydryl blacking agents. Silicic acid transport activity also appears to be regulated during different growth stages of the diatom. [ABSTRACT FROM AUTHOR]

The effects of molybdenum on photosynthesis and nitrate uptake by two species of freshwater algae, Navicula pelliculosa (Bréb.) Hilse and Chlamydomonas reinhardtii Dang. Were examined. Photosynthetic rates in cells of N. pelliculosa deprived of Mo for 48 h were significantly lower than in non-deprived cells; the rates were 2.6 and 4.5 μg C/10[supn] cells/h, respectively. There was no significant reduction in photosynthetic rates of C. reinhardtii under the 2 treatments, the rates were both ca. 6.0 μg C/10[sup6] cells/h. These observed rate in the 2 species were not altered by added mo concentrations as high as 1.0 ppm. The chlorophyll a values in 48 h Mo-deprived cells were 1.15 μg/10[sup6] cells compared to 1.57 μg/10[sup6] cells provided with this metal. Molybdenum deficiency did not affect the chlorophyll a concentration in Chlamydomonas: the chlorophyll levels were 2.44 μg/10[sup6] cells. Nitrate uptake by Mo-deprived cells of N. pelliculosa was significantly lower than in cells cultured in Mo; the rates were 0.087 and 0.238 μM NO[sub3,sup-]/10[sup6] cells/h, respectively. Uptake rates by C. reinhardtii were similar with or deprived of Mo. The K[subm] values for NO[sub3] uptake were 14.9 and 148.0 μM for N. pelliculosa and C. reinhardtii, respectively. [ABSTRACT FROM AUTHOR]