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In contrast to surveys based on a few genes that often provide limited taxonomic resolution, transcriptomes provide a wealth of genomic loci that can resolve relationships among taxonomically challenging lineages. Diatoms are a diverse group of aquatic microalgae that includes important bioindicator species and many such lineages. One example is Nitzschia palea, a widespread species complex with several morphologically defined taxonomic varieties, some of which are critical pollution indicators. Morphological differences among the varieties are subtle and phylogenetic studies based on a few genes fail to resolve their evolutionary relationships. We conducted morphometric and transcriptome analyses of 10 Nitzschia palea strains to resolve the relationships among strains and taxonomic varieties. Nitzschia palea was resolved into three clades, one of which corresponds to a group of strains with narrow linear‐lanceolate valves. The other morphological group recovered in the shape outline analysis was not monophyletic and consisted of two clades. Gene‐tree concordance analyses and phylogenetic network estimations revealed patterns of incomplete lineage sorting and gene flow between intraspecific lineages. We detected reticulated evolutionary patterns among lineages with different morphologies, resulting in a putative recent hybrid. Our study shows that phylogenomic analyses of unlinked nuclear loci, complemented with morphometrics, can resolve complex evolutionary histories of recently diverged species complexes. [ABSTRACT FROM AUTHOR]

The paraphyletic diatom genus Nitzschia comprises over 1000 morphologically distinct pennate taxa, known from the benthos and plankton of freshwater, brackish, and marine environments. The principal diagnostic characters for delimitation of Nitzschia species include valve shape, the position and structure of the raphe, presence/absence and shape of the proximal raphe endings and terminal raphe fissures, areola structure, and specific morphometric features such as cell size, and stria and fibula density. In this study, we isolated 12 diatom strains into culture from samples collected at the surface or greater depths of the southeastern Adriatic Sea. Morphological analyses included LM, SEM, and TEM observations, which, along with specific morphometric features, allowed us to distinguish three new Nitzschia species. These findings were congruent with the results of phylogenetic analyses performed on nuclear‐encoded SSU (18S) rDNA and chloroplast‐encoded rbcL and psbC genes. One of the new species (Nitzschia dalmatica sp. nov.) formed a lineage within a clade of Bacillariaceae containing members of the Nitzschia sect. Dubiae, which was sister to Psammodictyon. A second lineage was part of a novel clade that is significantly distinct from other Nitzschia species sequenced so far and includes Nitzschia adhaerens sp. nov. and N. cf. adhaerens. A further new species was found, Nitzschia inordinata sp. nov., which appeared as the sister group to the N. adhaerens clade and the conopeoid Nitzschia species in our phylogenetic trees. Our findings contribute to the overall diversity of genus Nitzschia, especially in identifying some deep branches within the Bacillariaceae, and highlight under‐scoring of this genus in marine plankton. [ABSTRACT FROM AUTHOR]

During ice melt in spring, ice algae are released from the ice and could be exposed to variable temperatures and irradiances in surface water. Saroma Lagoon is an embayment with two inlets leading to the Sea of Okhotsk. With seasonal development of sea ice, its water temperature changes dramatically throughout the year. To investigate the living and photoprotective strategies of ice algae in such a coastal water system, we grew Nitzschia cf. neglecta, an ice diatom isolated from the sea ice of this lagoon, under irradiance levels of 30 and 100 lmol photons • m-2 • s-1, and temperatures of 2°C and 10°C. Then the acclimated cells were exposed to high light in order to investigate the plasticity of their photosynthetic apparatus. At 10°C, cells grew faster and showed decreased susceptibility to high light. At 2°C, an immediate decrease in all pigment content upon exposure, as well as a higher cellular content of diatoxanthin was used to compensate for the more severe excitation stress. Highly efficient photoprotection was achieved through the diadinoxanthin-diatoxanthin cycledependent nonphotochemical quenching. While regulation through psbA and rbcL at the transcription level played a minor role in the response to high light stress at both temperatures. The wide tolerance to both temperature and light changes suggest that the thinning of sea ice and higher temperatures in a warmer world will lead to more intense blooms in Saroma Lagoon. [ABSTRACT FROM AUTHOR]

Nitzschia palea is a common freshwater diatom used as a bioindicator because of its tolerance of polluted waterways. There is also evidence it may be the tertiary endosymbiont within the "dinotom" dinoflagellate Durinskia baltica. A putative strain of N. palea was collected from a pond on the University of Virginia's College at Wise campus and cultured. For initial identification, three markers were sequenced—nuclear 18S rDNA, the chloroplast 23S rDNA, and rbcL. Morphological characteristics were determined using light and scanning electron microscopy; based on these observations the cells were identified as N. palea and named strain "Wise." DNA from N. palea was deep sequenced and the chloroplast and mitochondrial genomes assembled. Single gene phylogenies grouped N. palea—Wise within a clearly defined N. palea clade and showed it was most closely related to the strain "SpainA3." The chloroplast genome of N. palea is 119,447 bp with a quadripartite structure, 135 protein‐coding, 28 tRNA, and 3 rRNA genes. The mitochondrial genome is 37,754 bp with a single repeat region as found in other diatom chondriomes, 37 protein‐coding, 23 tRNA, and 2 rRNA genes. The chloroplast genomes of N. palea and D. baltica have identical gene content, synteny, and a 92.7% pair‐wise sequence similarity with most differences occurring in intergenic regions. The N. palea mitochondrial genome and D. baltica's endosymbiont mitochondrial genome also have identical gene content and order with a sequence similarity of 90.7%. Genome‐based phylogenies demonstrated that D. baltica is more similar to N. palea than any other diatom sequence currently available. These data provide the genome sequences of two organelles for a widespread diatom and show they are very similar to those of Durinskia baltica's endosymbiont. [ABSTRACT FROM AUTHOR]

CO2 levels in freshwater systems can fluctuate widely, potentially influencing photosynthetic rates and growth of phytoplankton. Given the right conditions, this can lead to bloom formation and affect water quality. This study investigated the acquisition of dissolved inorganic carbon (DIC) by six species of microalgae, a cyanobacterium Cylindrospermopsis raciborskii, the diatoms Cyclotella sp., Nitzschia sp., and the green algae Stichococcus sp., Staurastrum sp., and Monoraphidium sp., all isolated from a subtropical reservoir in Australia. Carbon acquisition characteristics, specifically the affinity for DIC, internal pH, and internal DIC concentrations were measured. Affinities for CO2 ( K 0.5 ( CO 2 )) ranged between 0.7 and 6 μM CO2. This was considerably lower than air‐equilibrated surface water CO2 concentrations, and below reported affinities for CO2 of RuBisCO suggesting operation of active carbon dioxide concentrating mechanisms (CCMs) in all species. Internal pH was lowest for Cyclotella sp. at 7.19, and highest for Staurastrum sp., at 7.71. At 180 μM external DIC, ratios of internal:external CO2 ranged from 2.5 for Nitzschia sp. to 14 in C. raciborskii. Internal HCO3− concentration showed a linear relationship with surface area to biovolume ratio (SA:Vol). We hypothesized that species with a higher SA:Vol suffer more from diffusive escape of CO2, thus storage of DIC as bicarbonate is favored in these strains. For C. raciborskii, under stratified summer conditions, its strong CCM, and resilient photosynthetic characteristics may contribute to its bloom forming capacity. [ABSTRACT FROM AUTHOR]

The genus Pseudo-nitzschia contains potentially toxic species of problematic taxonomy, making it one of the most intensively studied diatom genera. The study of 35 clonal strains isolated from the Bilbao estuary, an area that experiences recurrent blooms of Pseudo-nitzschia, revealed the presence of two new species, P. abrensis and P. plurisecta, differing from their congeners in both morphology and gene sequence. The morphological features were analyzed by LM and EM, whereas molecular analyses were based on the internal transcribed spacer ( ITS) and large subunit ( LSU) regions of the r DNA. P. plurisecta appears closely related to P. cuspidata/ P. pseudodelicatissima in the phylogenetic tree, whereas P. abrensis forms a moderately supported clade with P. heimii/ P. subpacifica and P. caciantha/ P. circumpora. Comparison of the secondary structure of ITS2 regions reveals marked differences in the most highly conserved regions among related taxa. Morphologically, the new species differ from their closest congeners in the arrangement of the poroid sectors and the density of valve striae and fibulae. The two species share similar pigment composition, and belong to the group of Pseudo-nitzschia species containing only chlorophyll c2 and c3. [ABSTRACT FROM AUTHOR]

A study on the morphology and phylogeny of 18 strains of Pseudo-nitzschia established from the Strait of Malacca, Peninsular Malaysia, was undertaken. Morphological data combined with molecular evidence show that they constitute three new species, for which the names, P. batesiana sp. nov., P. lundholmiae sp. nov., and P. fukuyoi sp. nov., are proposed. The three new species closely resemble species in the P. pseudodelicatissima complex sensu lato. Morphologically, P. batesiana differs from other species in the complex by having a smaller part of cell overlapping in the chain, whereas P. lundholmiae differs by having fewer poroid sectors and P. fukuyoi by having a distinct type of poroid sectors. Nucleotide sequences of the LSU rDNA (D1-D3) of the three new species reveal significant nucleotide sequence divergence (0.1%-9.3%) from each other and from other species in the P. pseudodelicatissima complex s.l. The three species are phylogenetically closely related to species in the P. pseudodelicatissima complex, with P. batesiana appearing as a sister taxon to P. circumpora, P. caciantha, and P. subpacifica; whereas P. lundholmiae and P. fukuyoi are more closely related to P. pseudodelicatissima and P. cuspidata. The three species show 2-3 compensatory base changes ( CBCs) in their ITS2 transcripts when compared to the closely related species. The ITS2 with its structural information has proven its robustness in constructing a better resolved phylogenetic framework for Pseudo-nitzschia. [ABSTRACT FROM AUTHOR]

Nitzschia sublinearis Hustedt and N. pura Hustedt are common oligosaprobic freshwater diatom species that frequently occur in diatom inventories, thus being important in water quality studies. Both are considered as species with overlapping diagnostic criteria in several floras, which is typical of the whole genus Nitzschia. The type material of Hustedt of N. sublinearis and N. pura was examined using LM and EM in order to document the range of variation within the type populations and to compare it with populations occurring in different European rivers. Detailed observations allowed recognition of two new freshwater diatom species: N. alicae sp. nov., occurring in mesotrophic up to eutrophic conditions, and N. puriformis sp. nov., mostly occurring in oligotrophic habitats, both in rivers and streams at middle and high altitudes. The most reliable taxonomic features that separate both new species from the most similar taxa are the density of fibulae and striae, valve shape, and valve width as well as the shape of areolae. Morphological examination of different populations indicates that N. puriformis is relatively common in European rivers and has been overlooked to date and confounded with N. pura by several researchers. By contrast, N. alicae has, to date, been collected only in Slovakia and Northern Italy, but with a high frequency of occurrence and sometimes in high abundance at sites. [ABSTRACT FROM AUTHOR]

The growth of microalgae in hypersaline conditions requires that cells accumulate osmoprotectants. In many instances, these are polyols. We isolated the diatom Nitzschia ovalis H. J. Arn. from the saline and alkaline water body Mono Lake (CA, USA). This isolate can grow in salinities ranging from 5 to 120 parts per thousand (ppt) of salt but normally at 90 ppt salinity. In this report, we identified the major polyol osmoprotectant as 1,4/2,5 cyclohexanetetrol by electron ionization-mass spectrometry (EI–MS), 1H, 13C nuclear magnetic resonance spectroscopy (NMR), and infrared (IR) and showed an increase in cellular concentration in response to rising salinity. This increase in the cyclitol concentration was evaluated by gas chromatography of the derived tetraacetylated cyclohexanetetrol obtaining an average of 0.7 fmol · cell−1 at 5 ppt and rising to 22.5 fmol · cell−1 at 120 ppt. The 1,4/2,5 cyclohexanetetrol was also detected in the red alga Porphyridium purpureum. Analysis of the free amino acid content in N. ovalis cultures exposed to changes in salinity showed that proline and lysine also accumulate with increased salinity, but the cellular concentration of these amino acids is about 10-fold lower than the concentration of 1,4/2,5 cyclohexanetetrol. The comparison of amino acid concentration per cell with cyclitol suggests that this polyol is important in compensating the cellular osmotic pressure due to increased salinity, but other physiological functions could also be considered. [ABSTRACT FROM AUTHOR]

The diatom Nitzschia laevis Hust. is a potential producer of eicosapentaenoic acid (EPA). To elucidate its cellular response to salt stress, the effects of salinity on EPA production, lipid composition, and fatty acid distribution in the lipid pool were investigated. The highest contents of total fatty acids, EPA, and polar lipids were all obtained at NaCl of 20 g · L−1, under which 71.3% of total EPA existed in polar lipid fractions. In N. laevis, high salt concentration might induce the decrease in neutral lipids (NLs), whereas the production of polar lipids, including phospholipids (PLs) and glycolipids (GLs), was enhanced. The degree of fatty acid unsaturation of both neutral and polar lipid fractions increased sharply when NaCl concentration increased from 10 to 20 g · L−1 but decreased at NaCl concentration of 30 g · L−1. The amount of total free sterols was increased with the increase in salt concentration. All these changes in lipid and fatty acids suggested a decrease in membrane permeability and fluidity under high salt concentration, which could help the alga acclimate to the salinity stress. [ABSTRACT FROM AUTHOR]

Nitzschia fonticola (Grunow) Grunow is a member of Nitzschia sect. Lanceolatae, a group of taxonomically intractable but ecologically important and widespread diatoms. We investigated the morphology and life cycle in three clones of N. fonticola and all exhibited reduced sexuality, with pedogamous production of auxospores in unpaired gametangia. The auxospores of all clones contained tangles of striplike elements that lay outside the perizonium and were distinct from it in structure and ontogeny. We introduce a new term, incunabula, to refer to such components of the auxospore wall. Semicryptic variation was detected: one clone differed from the other two in valve size and shape, stria density, and fibula density, as well as its nuclear large subunit ribosomal DNA (LSU rDNA) sequence. The implications of reduced sexuality for the taxonomy of sect. Lanceolatae are discussed. A lectotype is designated for N. fonticola from among original material of Grunow, and the application of the name is clarified further by designating illustrations and the LSU sequence AM182191 from one of our clones as epitypes. [ABSTRACT FROM AUTHOR]

Silicon is an important element in biology, for organisms ranging from unicellular algae to humans. It acts as a structural material for both plants and animals, but can also function as a metabolite or regulator of gene expression, affecting a wide range of cellular processes. Molecular details of biological interaction with silicon are poorly understood. Diatoms, the largest group of silicifying organisms, are a good model system for studying this interaction. The first proteins shown to directly interact with silicon were diatom silicon transporters (SITs). Because the basis for substrate recognition lies within the primary sequence of a protein, identification of conserved amino acid residues would provide insight into the mechanism of SIT function. Lack of SIT sequences from a diversity of diatoms and high sequence conservation in known SITs has precluded identification of such residues. In this study, PCR was used to amplify partial SIT sequences from eight diverse diatom species. Multiple gene copies were prevalent in each species, and phylogenetic analysis showed that SITs generally group according to species. In addition to partial SIT sequences, full-length SIT genes were identified from the pennate diatom, Nitzschia alba (Lewin and Lewin), and the centric diatom Skeletonema costatum (Greville) Cleve. Comparing these SITs with previously identified SITs showed structural differences between SITs of centrics and pennates, suggesting differences in transport mechanism or regulation. Comparative amino acid analysis identified conserved regions that may be important for silicon transport, including repeats of the motif GXQ. A model for silicon uptake and efflux is presented that is consistent with known aspects of transport. [ABSTRACT FROM AUTHOR]

In 1999, a 49,000 km2 area in western Scottish waters was closed to shellfish harvesting due to the amnesic shellfish poisoning (ASP) toxin domoic acid (DA). The only previously confirmed DA producer identified had been Pseudo-nitzschia australis Frenguelli. The toxin has appeared every year since and has led to more harvesting closures. We isolated and cultured two strains of Pseudo-nitzschia seriata f. seriata (P. T. Cleve) H. Peragallo from western Scottish waters in 2001 and 2002. They were identified using TEM analysis of their morphological fine structure and sequencing of the internal transcribed spacer (ITS)1, 5.8S, ITS2, and partial large subunit (LSU) rDNA. The morphology of the Scottish P. seriata f. seriata strains differed slightly, for example, in the number of poroid rows, from descriptions in identification keys. Comparison of P. seriata sequences with those of two co-occurring Pseudo-nitzschia australis isolates showed an overall divergence of only 0.012. Sequence divergence between both species was highest in the ITS1 region (0.036). Combined morphological and genetic approaches are needed to identify closely related Pseudo-nitzschia species. The P. seriata strains grew successfully at 15°C, suggesting that although seen as a psychrophilic species, it may also occur at higher water temperatures. All isolates produced DA in stationary phase (measured on day 25): 0.16–0.23 pg DA·cell−1 in P. seriata and 0.15–1.68 pg DA·cell−1 in P. australis. Our study is the first to identify P. seriata f. seriata as a DA producer in Scottish waters and indicates that at least it and P. australis can be responsible for ASP toxicity in that region. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia seriata (Cleve) H. Peragallo isolated from Scottish west coast waters was studied in batch culture with phosphate (P) or silicate (Si) as the yield-limiting nutrient at 15°C. This species produced the neurotoxin domoic acid (DA) when either nutrient was limiting but produced more when stressed by Si limitation during the stationary phase. Under P-limiting conditions, exponential growth stopped after P was reduced to a low threshold concentration. Under Si-limiting conditions, fast exponential growth was followed by a period of slower exponential growth, until Si became exhausted. A stationary phase was observed in the P-limited but not the Si-limited cultures, the latter showing a rapid decrease in cell density after the second exponential growth phase. Si-limited cultures exhibited a further period of active metabolism (as indicated by increases in chl and carbon per cell) late in the experiment, presumably fueled by regenerated Si. DA production was low in exponential phase under both conditions. In P-limited cultures, most DA was produced during the immediate postexponential phase, with little or no new DA produced during later cell senescence. In contrast, although a substantial amount of DA was produced during the slower exponential phase of the Si-limited cultures, DA production was even greater near the end of the experiment, coincident with the period of chl synthesis and increase in carbon biomass. Comparison of the magnitude of toxin production in the two nutrient regimes indicated a greater threat of P. seriata-generated amnesic shellfish poisoning events under Si rather than P nutrient limitation. [ABSTRACT FROM AUTHOR]

A flow cytometer coupled to a scanning monochromator and a fluorescence microscope were used to characterize the fluorescence spectrum of Pseudo-nitzschia multiseries (Hasle) Hasle, a pennate diatom that produces the neurotoxin domoic acid, a lethal amnesic. In this research, we characterize the fluorescence spectrum of P. multiseries in vivo over the wavelength range of 360 to 850 nm and show that this diatom autofluoresces blue when excited with UV light (350–365 nm). The autofluorescence characterization of Pseudo-nitzschia may provide new methods for rapid in situ monitoring of diatom populations and reiterates the usefulness of flow cytometry in the analysis and study of marine phytoplankton. [ABSTRACT FROM AUTHOR]

Domoic acid (DA), a neuroexcitatory amino acid, was detected in batch culture of the newly recognized species Nitzschia navis-varingica Lundholm et Moestrup. The production of DA by this diatom was confirmed by electrospray ionization mass spectrometry. The diatom was collected from a shrimp-culture pond in Do Son, Vietnam. The production of DA (1.7 pg·cell-1) is within the levels reported for Pseudo-nitzschia multiseries (Hasle) Hasle. The DA production started during the late exponential growth phase and reached a maximum during the early stationary growth phase. Maximum DA levels in the axenic culture decreased to about half that of the nonaxenic culture (0.9 pg·cell-1 vs. 1.7 pg·cell-1), suggesting that DA production by the new species is influenced by bacteria. [ABSTRACT FROM AUTHOR]

A new marine diatom, Nitzschia navis-varingica, sp. nov., isolated from Vietnamese waters, is described by light, transmission, and scanning electron microscopy, including thin sectioning. The new species has been found to produce the neurotoxin domoic acid (DA), better known from several species of Pseudo-nitzschia Peragallo and one species of Amphora Ehrenberg. Production of DA is therefore more widespread among diatoms than previously thought. Taxonomically, the genus Nitzschia Hassall is exceptionally difficult, with about 900 described taxa. Grunow (in divided the genus into 24 sections, and this system is still used with modifications. Nitzschia navis-varingica, sp. nov. fits best into a group of sections that includes Dubiae, Bilobatae, most of the Lanceolatae, and Lineares, all sensu Grunow, as the cell is slightly indented in the middle in girdle view and has a moderately eccentric raphe and a weak longitudinal fold on the valve. Many species within these sections have features similar to N. navis-varingica, but no species seems to be identical. Because both Pseudo-nitzschia and Nitzschia belong to the family Bacillariaceae, it seems reasonable to look for further producers of DA in this family, including freshwater species, which mainly comprise species within the sections Dubiae, Bilobatae, Lanceolatae, and Lineares. [ABSTRACT FROM AUTHOR]

To better determine the ecological role of motility in pennate diatoms, we quantitatively characterized several motility and adhesion properties of four species of motile pennate diatoms (Craticula sp., Pinnularia sp., Nitzschia sp., and Stauroneis sp.) isolated from the same fresh-water pond. Using computer-assisted video microscopy, we measured speed, size/shape, functional adhesion, path curvature, and light sensitivity for these species, each of which shows a distinctive set of motile behaviors. The average speed of Stauroneis, Pinnularia, Nitzschia, and Craticula cells are 4.6, 5.3, 10.4, and 10.0 ???m s???-1, respectively. Craticula and Nitzschia cells move in a relatively straight path (<4 degrees rotation per 100μm movement), Stauroneis exhibits minor rotation (about 7 degrees per 100μm movement), and Pinnularia rotates considerably during movement (about 22 degrees per 100μm moved). Functional adhesion (as measured by the release rate of attached cells from the underside of an inverted coverslip) shows a half time for cell release of approximately 50 min for Craticula, 192 mins for Pinnularia, and >1day for Nitzschia and Stauronesis. Direction reversal at light/dark boundaries, which appears to be the main contributor to diatom photoaxis, is most responsive for Craticula, Pinnularia, and Nitzschia at wavelengths around 500 nm. Craticula and Nitzschia cells are the most sensitive to the photophobic response, with over 60& of these cells responding to a 30-lx light/dark boundary at 500 nm, whereas Pinnularia cells are only moderately responsive at this irradiance, showing a maximal response of approximately 30% of cells at 450 nm. Stauroneis cells, in contrast, had a maximal photosensitive response at 700 nm, suggesting that this cell type may use a different response mechanism than the other three cell types. In addition, Craticula and Pinnularia show a net movement out of the light spot when illuminated at 650 nm, whereas Stauroneis shows a net movement out of light spot when illuminated at 450 nm. Such quantitative characterizations of species-specific responses to environmental stimuli should give us firm foundation for future studies analyzing the behavior of interspecies diatom competition for limited light or nutrient resources. [ABSTRACT FROM AUTHOR]

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 aligonucleotide probes. Toward that end, cultures of P. australis Frenguelli, P. pungenes (Grunow) Hasle, P. multiseries (Hasle) Hasle, P. fraudulenta (P. T. Cleve) Heiden. P. heimii Mangum, P. delicatissima (P. T. Cleve) Heiden, P. pseudodelicatissima (Hasle) Hasle, and P. americana (Hastle) 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, sample, and cost-effective technique for discriminating among cultured Pseudo-nitzschia species. [ABSTRACT FROM AUTHOR]

Morphologic, diagnostic characters of the subgenus Nitzschia, genus Nitzschia Hassall 1845, and the marine planktonic genus Pseudo-nitzschia H. Peragallo in H. & M. Peragallo 1900 were compared, Colony formation by overlap of cell ends; weakely silicified, shallow, and flattened valves; an extremely eccentric raphe, not elevated above the general level of the valve; lack of conopea; and striated girdle bands characterize Pseudonitzschia as a natural group and a genus separate from Nitzschia. [ABSTRACT FROM AUTHOR]

This article describes the effect of various environmental conditions on the speed of freshwater diatoms. The diatoms display a wide distribution of cell speeds, from 0 to >20 μm·s[SUP-1], as indicated by both the distribution of speeds within a cell population as well as the distribution of 1-s interval speeds of individual cells. Cell length has little or no effect on cell speed, as the speed of large postconjugal populations of Craticula and smaller preconjugal cell populations were no significant different. The diatoms showed a broad pH tolerance, with Craticula spp. and Nitzschia spp. displaying active motility between pH 3 and 12 and pH 4 and 10, respectively, with velocity maxima for both species at approximately pH 7. In contrast to previous reports on marine diatoms, these freshwater diatoms do not require millimolar levels of external calcium for motility, as both Craticula spp. and Nitzschia spp. showed significant motility in distilled water (<0.5 μM calcium) for up to 5 h. Although addition of ≥500 μM of EGTA inhibited motility, this inhibition did not appear to be due to calcium chelation, as EGTA solutions preincubated with up to 20-fold excess calcium, magnesium, or both still inhibited motility with the same dose-dependent response as EGTA alone. Moreover, significant motility was restored by rinsing EGTA-treated cells in distilled water, Ca-free medium, or regular diatom medium. The calcium channel inhibitors lanthanum and ruthenium red also inhibited motility in a dose-dependent manner, suggesting that regulation of internal calcium stores may be important in motility. Craticula motility also declines rapidly in medium ≥ 50 mOsM while the isotonic concentration appears to be 100-120 mOsM, suggesting that movement may require the plasma membrane to be exerting a force ≥50-70 mOsM osmotic pressure (1-1.5 atm) against the cell wall. [ABSTRACT FROM AUTHOR]

Nitzschia seriata Cleve, a common member of marine, bottom ice communities in the Arctic, was grown in unialgal batch cultures to test for compensator)' mechanisms for the low temperatures (-1.8°C) typical of its natural habitat. The upper lethal limit for growth was between 12° and 15°C, and the optimum was between 6° and 12°C. The Arrhenius function adequately (R[sup2] = 73%) fitted the relationship between growth rate and temperature from -1.6° up to 10°C. with an average Q[sub10] of 1.9 over the entire range. Light-saturated and light-limited rates of photosynthesis (normalized to chlorophyll a or cell carbon) showed complete compensation from 12° to 4°C. Photosynthetic rates, especially at light saturation, declined rapidly at temperatures below 4° C. Susceptibility to photoinhibition was greatest at the lowest growth temperatures. Cellular composition (chlorophyll a, protein, polysaccharide, and lipid contents) was not systematically related to temperature in any simple way, although cell size (carbon per cell) was maximal at the lowest growth temperature. Dark respiration was unmeasurably low (<0.015 day [sup-1]) at all growth temperatures. The strategy of adaptation in N. seriata may be characterized as optimizing efficiency and compensation, rather than maximization, of growth rate. [ABSTRACT FROM AUTHOR]

Presents comments on an article related to gametogenesis in Nitzschia Pungens published in the 1991 issue of the 'Journal of Phycology.' Primary thesis of the article; Conclusions drawn in the article; Absence of sufficient evidence to prove these conclusions.

The domoic acid-producing diatom Nitzschia pungens Grunov f. multiseries Hasle, which is responsible for amnesic shellfish poisonings in Prince Edward Island, Canada, underwent gametogenesis when senescent cells (i.e. in stationary growth phase for more than 290 days) were subcultured into fresh FE medium and light intensity was increased from 33 to 530 μE m[sup2] s[sup-1]. The number of gamates produced varied with the salinity of the medium, with a maximum at 23.5%[sub0]. Cells in the exponential growth phase (0.8 div d[sup-1]) did not produce gamates, nor did senescent cells when transferred without change in light intensity. Anisogamus gamates, probably haploid, were isolated by combining conventional microscopy with flow cytometry. Zygotes resulting from syngamy yielded cigar-shaped naviculoid cells, morphologically different from parent cells (heteromorphism). These cells, with a division rate of 1.9 div d[sup-1], could serve as a seed population and explain the origin of the toxic blooms of red-water proportions that have been a public health problem in Eastern Canada. Production of domoic acid by postexponential and moribund cells but not by gamates, zygotes, or immediately resulting cells, provides an insights into the dependence on the developmental history of this diatom. [ABSTRACT FROM AUTHOR]

The enzyme activity of ribulose 1.5-bisphosphate carboxylase-oxygenase (RuBisCO) and phosphoenolpyruvate carboxylase (PEPC) was measured in four speciesof marine benthic diatoms isolated from subtidal sediments of Graveline Bayou, Mississippi. Enzyme activities were measured in cultures of Amphora micrometra Giffen, A. tenerrima Aleem and Hustedi, Nitzschia fontifuga Cholnoky, and Nitzschia vermicularis Grunow that were grown at light levels supporting μ[SUBmax] and at light-timing irradiances. All four species exhibited similar RuBisCO: PEP ratios (range = 1-1.8) at μ[SUBmax] the lowest ratio (0.4) was observed in A. micrometra. Reduced light levels increased PEPC relative to that measured at μ[SUBmax] in two species. Two-dimensional paper chromatography was used to determine the first products of carbon fixation in A. micrometra. After a 15 s incorporation period, the first product of photosynthetic carbon fixation was 3-phosphoglycerate even though this alga had a PEPC activity that was three times higher than that of RuBisCO. After 30 s, over 50% of the recovered radioactivity was still in this compound. Stable carbon isotope analyses of a mixture of the four pinnate diatoms also suggest the predominant carbon fixation pathway in these benthic diatoms was similar to C3 plants. [ABSTRACT FROM AUTHOR]

Short-term (3 day) diatom colonization of clean ceromic tiles and tiles conditioned with a thin, nonolgal biofilm was examined in fast- and slow-current outdoor experimental stream channels to assess effects of organic conditioning and current regime on diatom colonization. Colonization rates onto unconditioned tiles were 10 times lower in fast current than in slow. Substratum conditioning reduced the effects of current because organic conditioning reduced the effect of current because organic conditioning of tiles significantly enhanced colonization in fast current, but not in slow current. Two diatom taxa (Nitzschia acicularis W. Sm. and Synedra radians Kütz.) colonized unconditioned tiles more rapidly than conditioned tiles in slow current, suggesting the existence of negative interactions between these diatoms and bacteria and/or organics in conditioning films. [ABSTRACT FROM AUTHOR]

Protein synthesis in the diatom Nitzschia alba Lewin and Lewin was drastically altered when the cells were incubated at supraoptimal temperature. Quantitatively, the overall protein synthesis was greatly suppressed as indicated by the rate of ["S]methionine incorporation. The extent of suppression of protein synthesis was proportional to the severity of the heat-shock treatment which was a combination of elevated temperature and treatment duration. The in vivo synthesized proteins were also qualitatively analyzed by two-dimensional gel electrophoresis. Depending on the treatment condition, a set of heat-shock proteins (HSPs) were induced. They were best detected when the cells were subjected to shocks of 35°C for 60 min or 40°C for 10 min followed by a 60 min labeling at 30°C. the results revealed 16 HSPs which had molecular weights ranging from 24-94 kD and isoelectric points ranging from 5.50-7.10. some of the SHPs were identical in molecular weights but with different isoelectric points. The induction and accumulation of HSPs in Nitzschia alba were transitory. Prolonged heat-shock treatments resulted in a complete cessation of protein synthesis and no further induction of HSPs. In all aspects, the heat shock response of diatoms was similar to that in higher plants such as soybean, maize and tobacco but different from most animal systems. [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]

Transport of a nitrate Analogue, [SUP36]CI-CIO[SUP-][SUB3], was examined in two diatoms, Skeletonema costatum (Greve.) Cleve and Nitzschia closterium (Ehrenb) W. Sm. A dinoflagellate, Gonyaulax polyedra did not transport CIO[SUP-][SUB3] Transport of [SUP36]Cl-ClO[SUP-][SUB3] by diatoms appeared to be active and showed saturation kinetics. The data were fitted by Michaelis-Menten equation at all but the lowest chlorate concentrations (where plots ors vs. v showed a slight concave bend). Affinity of cells for nitrate was considerably higher than for chlorate. The K, for nitrate inhibition of chlorate transport was calculated assuming competitive inhibition. Light had little or no effect on chlorate transport. Pulse-chase experiments demonstrated that (1) ClO[SUP-][SUB3] (hence NO[SUP-][SUB3]) was stored in two intracellular compartments of equal size, (2) internal CIO[SUP-][SUB3] was exchangeable with external CIO[SUP-][SUB3] (rates of e]flux and influx were measured), and (3) efflux of intracellular ClO[SUP-][SUB3] showed transient states following a chase of CIO[SUP-][SUB3] or NO[SUP-][SUB3] which stabilized after 10-20 min. Transport of chlorate was a function of growth phase. [ABSTRACT FROM AUTHOR]

In benthic samples from the unchannelized Missouri River, the diatoms Nitzschia dissipata (Kütz.) Grun., N. filiformis (W. Sm. ) Schütt and N. pseudofonticola Hust. were observed within the mucilage tubes of four tube-forming diatoms: Cymbella prostrata (Berk.) Cl., C. prostrata var. auerswaidii (Rabh.) Reim., Navicula tripunctata var. schizonemoides (V.H.) Patr., and Nitzschia filiformis. Microscopical observations of live and preserved specimens indicated that "invasion" by Nitzschia occurred primarily in older tubes. Data are presented on the environmental conditions in which the tube-formers and their cohabitants have been found. [ABSTRACT FROM AUTHOR]

The lipid profile of seven species of unicellular eukaryotic microalgae grown under controlled conditions was studied with empbhasis on the hydrocarbons and the fatty acids as part of a search for oil-producing algae. Green. slo-growing colonies of Borryococcus braunii Kutz conttained the highest lipid content of 45% based on the organic weight, with an increase to 55% under nitrogen deficiency and with no effect of sodium chloride stress. Ankistrodesmus sp. Tbomas, Duznaliella spp., Isochrysis sp., Nannochloris sp. Thomas, and Nitzschia sp. Chapman contained an average of 25% lipids under nitrogen sufficient conditions, Nitrogen deficiency resulted in significant increase in the lipid content in all species but Dunaliella spp.. which praduced a higher content of carbohydrates. Significant low, amounts of acyclic hydrocarbons were detected only in Boiryococcus braunii Kutz and not in the other algae. The major hydrocarbon fractions in nitrogen deficient Botryococcus braunii Kutz. Dunaliella salina Thomas, Isochrvsis spp. and Nannochloris sp. Thomas were cyclic and branched polyunsaturated component, which were identified as various isoprenoid derivatives. The polar lipid composition of glycolipids and phosphotopids of all species investigated was fairly typical of photosynthetic eukaryntic algae. Fatty acid composition was species specific, with changes occurring in the relative amounts of individual acids of cells cultivated under different conditions and groeth phases. All species synthesized C14:0, C16:0, C18:1, C18:2 and Cl8:3 fatty acids; C16:4 in Ankistrodesmus sp. Tbomas; C18:4 a,d C22:6 in Isochrysis sp.: C16:2, C16:3 and C20:5 in Nannochloris sp. Thomas; C16:2. C16:3 and C20:5 in Nitzschia sp. Chapman. Nitrogen deficiency and salt stress induced accumulation of C18:1 in all treated species and to a lesser extent in Botryococcus braunii Kutz. The low production of hydrocarbons under optimol growth conditions and the high production of hydrocarbons under limited growth conditions cannot support the notion that microalgae can be utilized as biosolar energy converters for the production of liquid fuel, but point to the availability of a variety of neutral and polar lipid products. [ABSTRACT FROM AUTHOR]

Studies the relationship between cell organelles and valve morphogenesis in three species of diatom Nitzschia. Behavior of the microtubule center and microtubule system; Central origin of the silicalemma; Generation of nitzschioid and hantzschioid symmetry in daughter cells following cytokinesis.

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]

Cultures of freshwater algae, representing three algal divisions, Synura petersenii Korshikov; Chlamydomonas sp.; and Nitschia sp., were subjected to four different mercury-temperature shock interactions to demonstrate synergistic effects between mercury and temperature. Algal growth, measured by temporal changes in in vivo fluorescence of chlorophyll was used to ascertain the effects. Mercury addition and temperature shock had various inhibitory effects on algal growth. Prior environmental conditions influence the effect of subsequent treatments. Growth of S. petersenii was severely inhibited by mercury in all experiments. Control cultures would not grow at 30 C and died when shocked at this temperature. Chlamydomonas sp. Cultures initially inhibited by mercury were able to recover under most conditions after a period of reduced growth. Nitzschia sp. was resistant to mercury except when simultaneously shocked with temperature. Mercury analyses showed that Nitzschia cells at 25 C and 30 C contained a high percentage of the mercury initially added to the cultures. There was a significant loss of mercury at the end of each experiment from all cultures, Probably due to volatilization. [ABSTRACT FROM AUTHOR]

The marine diatom Nitzschia ovalis possesses at least 3 amino acid uptake systems, specific for transport of acidic, polybasic, and neutral amino acids. Maximum uptake velocity (V[SUBmax]) for each site is inversely related to the nitrogen content of the cell, and to the nitrogen available in the culture medium. Transport of polybasic amino acids occurs throughtout the course of growth in batch culture, but the V[SUBmax] increases dramatically as the culture ages and nitrogen/cell reaches a low value. K[SUB8] does not change significantly. Acidic and neutral amino acids are taken up only by cells harvested from nitrogen-poor culture. It appears that amino acid transport is repressed by high concentrations of nitrogen in the medium. Under natural conditions, where nitrogen concentrations are low, the contribution of amino acid uptake to the nitrogen economy of Nitzschia populations may be significant. [ABSTRACT FROM AUTHOR]

Cells of the colorless, heterotrophic diatom Nitzschia alba, after removal from the culture medium, were able to absorb silicic acid from a salt solution lacking carbon, nitrogen, and phosphorus. Silicic acid uptake continued for approximately 12 hr. At low cell densities (ca. 2.5 × 10[SUP5] cells/ml), the cell number doubled trader these conditions. At high cell densities (ca. 2 × 10[SUP6] cells/ml) no cell division resulted. When such cells were washed with a salt solution, their ability to absorb silicic acid was somewhat impaired. The degree of impairment became progressively more pronounced after subsequent washing treatments. A heat-stable factor washed from the cells and present in the first "wash water" was able to restore completely the ability of washed cells to absorb silicic acid. The factor was not identified. Aspartic acid (5 × 10[SUP-4] M) or glutamine (5 × 10[SUP-4] M) when added to the saline solution similarly promoted complete recovery. At such concentrations, these substances had only a slight effect on unwashed cells. A sollution of 5 × 10[SUP-3] M Na glutamate (or aspartic acid plus glutamine) had an even more pronounced effect, and in addition promoted cell division or "growth" of unwashed cells. Several other amino acids and other compounds tested were apparently without effect. [ABSTRACT FROM AUTHOR]

Presents a reply to comments on an article related to gametogenesis in Nitzschia Pungens published in the 1991 issue of the 'Journal of Phycology.' Main arguments that were concluded in the article; Defense of those conclusions; Objections raised by critics of the article.

Minimum phosphorus requirements of 2 marine diatomos, Cylindrotheca (Nitzschia) closterium and Cyclotella nana, were measured in axenic stcady state chemostat culture. C. closterium and C. nan required 1.055 and 1.045 × 10[SUP-15] g-at P cell[SUP-1] generation [SUP-1], respectively, with an average cell doubling time of 0.20 divisions/day. The algae were cullured at 15.5 C and exposed to 5380 lux on a light-dark cycle of 19 hr-5 hr. The phosphorus requirement per unit of cell volume was 0.0135 and 0.0129 × 10[SUP-15] g-at P/μ[SUP3] of cell volume for C. closterium and C. nana, respectively. [ABSTRACT FROM AUTHOR]