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Two morphologically similar populations of Didymosphenia were reported from the West Branch of the Farmington River, Connecticut, USA in 2014 and 2016. We described one of them as a new species, D. hullii. The other was observed subsequently in late 2016 and resembled D. geminata, but given the worldwide nuisance characteristic of this species, the identification required confirmation. In this work we used geometric morphometrics analysis to test for quantitative distinctions between the two Connecticut populations, along with two morphologically similar taxa from the literature, D. laticollis and D. pumila. We successfully separated the four entities and confirmed the identity of the second blooming diatom in the Farmington River, Connecticut, as D. geminata, which is the first confirmed report of this species for the state. We conclude that geometric morphometrics, in combination with features viewed with scanning electron microscopy and light microscopy, enhances the ability to distinguish among these morphologically similar species of Didymosphenia. We summarize these findings and pinpoint morphological distinctions that can be used to separate the taxa during routine light microscopy analyses. Geometric morphometrics was used to differentiate four Didymosphenia taxa. Morphological comparisons of D. hullii and D. geminata are shown. Didymosphenia geminata was recently reported in Connecticut, USA. [ABSTRACT FROM AUTHOR]

The presence of eukaryotic parasites (i.e. chytridiomycetes and oomycetes) infecting benthic marine diatoms was revealed by a reconnaissance survey in the Solthörn tidal flat (southern North Sea, Germany) followed by 5 months of regular monitoring in order to assess the impact of these zoosporic fungal pathogens on microphytobenthic diatom communities. Additionally, variation of environmental factors such as sediment composition and nutrient concentrations were monitored. Pre-treatment of sediment samples using short ultrasound pulses and gradient centrifugation, in combination with CalcoFluor White, were used for the visualization of both pathogen groups. The highest prevalence of infected benthic diatoms was observed in late September (6.3% of the total benthic diatom community), correlating with the highest abundance of benthic diatoms recorded during the survey (6.5 ± 1.3 × 104 cells cm-2). Most infections were caused by chytrids (up to 99.8%) and, only in a few cases, by oomycetes. The analysis of individual host abundances/infection prevalence showed in most cases a decline in cell numbers of the host species with increasing numbers of the eukaryotic parasite. Several shifts in the diatom community composition were observed. Statistical analysis revealed that the abundance of the benthic diatom hosts and their parasites was related to seasonal variation in temperature, irradiance and nutrient availability, particularly of dissolved inorganic nitrogen. [ABSTRACT FROM AUTHOR]

Two non-native stalk-forming diatoms that were recently observed in the West Branch of the Farmington River, a tributary of the Connecticut River in Connecticut (USA), are characterized morphologically and barcode marker sequences were obtained for each of them.Cymbella janischii, the dominant stalk-forming species during the summer of 2012, previously had not been found in the northeastern USA. Samples ofC. janischiiwere examined microscopically and used to obtain four sequences of the barcode marker, the V4 region of the 18S rDNA gene. Phylogenetic analysis indicated that the four independent sequences ofC. janischiiwere distinct from, but most closely related to, published sequences ofC. janischiifrom Idaho andC. mexicanafrom Texas, USA. A second non-native stalk-producing diatom, resemblingDidymosphenia geminata, was found in November 2012 – June 2013 and first reported asDidymospheniasp. Over this period, the observed cells had a compressed morphology and were consistently small compared withD. geminata. Sequences of the V4 region, obtained from three independent direct polymerase chain reactions (PCR) of single cells isolated from the Connecticut samples, indicated a close relationship to three published sequences ofD. geminatafrom Italy, New Zealand and the USA, and toD. sibericaandD. dentatafrom Russia. Frustules of the cells used in the PCR reactions were recovered and examined using scanning electron microscopy, providing a direct link between the observed morphology and sequence data. The morphology of the novel ConnecticutDidymospheniataxon was compared with that of otherDidymospheniataxa, being most similar toD. pumila,D. laticollis,D. grunowiiand smaller cells ofD. geminata. Didymospheniasp. had a triundulate morphology with a consistent length of 40–60 µm. Given the unique morphological features of this diatom, it is proposed as a new species,Didymosphenia hulliiKhan-Bureau, sp. nov. [ABSTRACT FROM PUBLISHER]

Benthic diatoms inhabiting intertidal flats face highly variable environmental conditions, due to changing water levels and exposure during low tide. The present study is the second part of a more extensive study of the adaptive potential of these species in response to varying UV radiations in the Solthörn tidal flat (Lower Saxony, southern North Sea). Five isolates (Achnanthes exigua, Amphora exigua, Cocconeis peltoides, Diploneis littoralisandNavicula digitoradiata), which were found in this area in high cell numbers in summer 2008, were used in semi-continuous cultures to study the physiological effects of UV-radiation (PAR [photosynthetically active radiation], PAR+UV-A, PAR+UV-B, PAR+UV-B+UV-A). For short- and long-term exposures (6 h, 30 days), the composition of intercellular carbohydrates, amino and fatty acids were analysed in exponential-phase cultures grown at a salinity of 30 in a 12 : 12 h light : dark cycle at 20 °C. Although all tested species showed distinct differences in their initial carbohydrate, amino and fatty acid compositions and in their responses to the different UV treatments, general response patterns could be identified. Overall physiological responses to short- and long-term UV treatments included the accumulation of proline as well as an increase in total carbohydrates and lipids, whereas significant differences in the composition of carbohydrates, amino and fatty acids occurred after long-term exposure to the UV treatments (P< 0.05). While UV-A exposure led to higher accumulations of phenylalanine, aspartic acid and saturated fatty acids, the response to UV-B long-term exposure included increases of galactose, mannose and unsaturated fatty acids in the cells. In both UV experiments there was a noteworthy accumulation of the amino acid tryptophan in most species. The combined UV-A+UV-B experiment showed a significant (P< 0.05) increase of aspartic acid, phenylalanine, galactose and saturated fatty acids in a majority of species. Overall, the results indicated significant differences in the physiological responses of the five diatom taxa during UV exposure, which suggests species-specific acclimation strategies that may explain the growth insensitivity towards at least short-term UV. [ABSTRACT FROM PUBLISHER]

The unconsolidated sediment of intertidal mudflats constitutes a highly unstable environment, due to continuously changing water levels and currents as well as temporary exposure to the air. Therefore, diatoms inhabiting marine intertidal areas are subjected to strongly changing surface light and UV intensities due to exposure at low tide. Five marine intertidal diatoms (Achnanthes exigua, Cocconeis peltoides, Diploneis littoralis, Navicula digitoradiataandAmphora exigua) were isolated from the Solthörn tidal flat (Lower Saxony, southern North Sea). Semi-continuous cultures were used to determine the effect of UV radiation (photosynthetically active radiation only [PAR], PAR+UV-B, PAR+UV-A, PAR+UV-B+UV-A) during short- and long-term exposure (6 h or 30 days). Growth rates, chlorophylla(chla), antioxidant capacities, accumulation of phenolic compounds (e.g. flavonoids) and DMSP, and activities of antioxidant enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase and glutathione reductase) were assessed. UV-A had only minor effects on cells, while growth rate, chlacontent and protein content were significantly reduced after long-term UV-B exposure.Achnanthes exiguaextracts showed the highest antioxidant capacity. The highest activity of SOD, APX and MDHAR was found under long-term combined UV exposure (PAR+UV-B+UV-A). Overall, the antioxidative defence of the five isolates was stimulated during exposure to UV radiation, as may be found during emersion. Emersion induces oxidative stress and, as a result, growth of the five diatom taxa was inhibited to suit changing environmental conditions. All five taxa tested in the present study showed species-specific acclimatization potentials, providing possible explanations for variability in population, species composition and ecosystem structures in the face of climatic variations. [ABSTRACT FROM PUBLISHER]

Although benthic diatoms are used to assess river water quality, there are few data on the rate at which diatom assemblages react to changes in water quality. The aim of this study was to assess the reaction time of diatoms and to discuss the changes occurring during water quality improvement on the basis of their autecological characteristics. In order to simulate this improvement, diatom-dominated biofilms grown on artificial sandstone substrata were transferred from several polluted rivers to an unpolluted river. They were sampled three times: before transfer and 1 and 2 months after transfer. The ecology and growth-forms of the taxa explained most of the changes in species composition observed during the experiment. Adnate diatoms gradually replaced motile and stalked taxa. Gomphonema parvulum, a stalked diatom positioned vertically in the biofilm, is adapted for light and space competition in high-density algal biofilms. When transferred to an unpolluted site, this growth-form is less competitive and does not tolerate the high grazing pressure. Fistulifera saprophila is a single celled motile diatom, living in organic matrices. When the artificial substrata were transferred to the unpolluted site, this particular ecological niche disappeared quickly. On the other hand, Achnanthidium minutissimum, which is considered to be cosmopolitan and an early colonizer, increased during the first month of transfer and then decreased. It was gradually replaced by A. biasolettianum, which was the taxon best suited to this pristine stream. The changes observed differed between treatments depending on the species composition and architecture of the biofilms. In particular, biofilms dominated by stalked and motile diatoms were more quickly modified than those dominated by small motile diatoms. The diatom index reflects these changes, and its values showed that about 60 days following a water quality improvement were necessary for transferred diatom assemblages to reach diatom index values similar as those at the unpolluted river. [ABSTRACT FROM AUTHOR]

Several recent studies have employed warm-water treatment of diatom cells to extract nominally bound extracellular polymeric substances. Where examined, the dominant neutral sugar in these extracts was glucose. In the present study, we sought to characterize the structure of the glucose-rich polymers in the water extracts of diatoms and to determine the origin of these polymers. The marine diatoms surveyed were Phaeodactylum tricornutum , Cylindrotheca fusiformis , Craspedostauros australis and Thalassiosira pseudonana . A freshwater species, Pinnularia viridis , was also investigated for the dye labelling experiments. Freshly harvested marine diatoms were extracted with water at 30°C for 1 h. Constituent monosaccharide analyses showed that glucose was the dominant neutral sugar (80 - 95 mol% of the total) in the extracts from three marine species, whereas the P. tricornutum extract contained predominantly ribose, galactose and glucose, and was inferred to be enriched in low-molecular-weight components. Linkage analysis of the constituent monosaccharides and proton nuclear magnetic resonance spectroscopy showed that the glucose in these extracts was derived primarily from 1,3-β- D -glucan. Immunocytochemistry with a monoclonal anti-1,3-β- D -glucan antibody confirmed that the glucan was localized in the vacuoles of diatom cells preserved by freeze-substitution. Nearly all diatom cells incubated with a fluorescent dye, DiBAC 4 (3), during warm water treatment at 30°C or 60°C incorporated the dye, demonstrating that the membrane integrity of the diatoms was compromised and supporting the contention that intracellular glucan was released during the treatment. In light of these data, the extracellular glucans of diatoms reported in some previous studies are re-interpreted as intracellular chrysolaminaran. [ABSTRACT FROM AUTHOR]