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This study presents five new records of diatoms based on light and electron microscopy results from the surface water of the Sea of Marmara coast during a large-scale mucilage event in 2021. Three of these diatoms are small nanoplanktic; Cyclotella cryptica, Nitzschia amabilis, Thalassiosira pseudonana, and the two of them are larger diatoms; Conticribra weissflogii and Entomoneis cf. pusilla. In addition, a species frequently seen in mucilage samples in the Adriatic Sea and the the Sea of Marmara, Cylindrotheca closterium, was also isolated and described. The chloroplast rbcL region, SSU, and 18S rDNA of C. closterium, C. cryptica and N. amabilis were amplified using primers in other previous studies. The rbcL, SSU, and 18S rDNA partial sequences were submitted to the NCBI database. Molecular phylogeny (based on 18S, rbcL, and SSU V4 DNA sequences) confirmed that the analysed species were those identified by SEM images. [ABSTRACT FROM AUTHOR]

Juvenile mussels enter the benthos after excysting from a fish host and settling to the bottom where they inhabit the interstitial zone in rivers. We examined the algal composition in the surface water and pore waters in different locations in a temperate river (Thames River) in Southern Ontario. Surprisingly, algal concentration (C) was ~9× higher in pore water versus surface water and varied spatially in the riverbed (downstream of boulders > upstream of boulders and nonbedform regions), and pennate diatoms were the most abundant taxon in the pore waters. We examined the clearance rate (CR; mass of suspended material removed from the water per unit time and mussel) of recently metamorphosed juvenile unionid mussels (3- to 4-week-old Lampsilis siliquoidea, Fatmuckets) exposed to pore water and surface water in a paddle wheel flow chamber at different water velocities (U). Juvenile CR based on Chlorophyll a fluorescence was ~2× higher on pore water versus surface water and CR based on a specific algal taxon, identified via flow cytometry, varied with its initial concentration. Chesson's feeding electivity index revealed that mussels removed five chlorophyte taxa in proportion to their concentration in the water (i.e., removed at random), but they removed five diatom taxa in greater proportion (i.e., selected for by juvenile mussels) across the range of algal flux (J = UC) examined. This study provides evidence of the importance of diatoms in pore waters to juvenile mussels. It also reveals elements of the physicochemical environment used by juvenile mussels, which should be considered in their conservation. [ABSTRACT FROM AUTHOR]

Background and aims - We examine the possibility of the independent evolution of the same features multiple times across the pennate diatom tree of life. Methods and key results - Features we have studied include symmetry, raphe number and amphoroid symmetry. Phylogenetic analysis, with both morphological and molecular data suggest in each of these cases that the features evolved from 5 to 6 times independently. We also look at the possibility of certain features having evolved once and diagnosing large genera of diatoms, suggestive of an adaptive radiation in genera such as Mastogloia, Diploneis and Stauroneis. Conclusion - Formal phylogenetic analyses and recognition of monophyletic groups allow for the recognition of homoplasious or homologous features. [ABSTRACT FROM AUTHOR]

Graphical abstract Comparison of the pseudoharmonic, Kratzer and Morse potentials for CO and NO. The potential parameters for CO and NO were taken from [5,6,45]. Highlights • Application of a novel pseudospectral method for the solution of the Schrödinger equation. • The use of nonclassical polynomials and quadratures based on the Morse potential and other weight functions. • Applications to the Kratzer and pseudoharmonic potentials. • The accurate calculation of the vibrational states of H 2 with a realistic potential. Abstract The pseudoharmonic and Kratzer potentials have been extensively employed by numerous workers to model the vibrational states of diatomic molecules. These potentials belong to SUperSYmmetric (SUSY) quantum mechanics and the eigenvalues of the Schrödinger equation are known. The energy eigenvalues of the Schrödinger equation for the pseudoharmonic and Kratzer potentials have been determined with different numerical methods as a benchmark of the numerical schemes. We employ a pseudospectral method based on a quadrature grid defined with a nonclassical polynomial basis set. This basis set is defined orthogonal with respect to the square of ground state wavefunction as the weight function. A discrete matrix representation of the Hamiltonian of dimension N is constructed and vibrational energies are calculated with the numerical diagonalization of this matrix. This pseudospectral method is employed to calculate the vibrational energy levels of H 2 , CO and NO modelled with the pseudoharmonic and Kratzer potentials in comparison with the more realistic Morse potential. The vibrational energy eigenstates for H 2 with a realistic quantum mechanical potential and an approximate Morse potential are also calculated. The oversimplified pseudoharmonic and Kratzer potentials are useful for benchmarking numerical methods. However, they represent potential energy curves that can deviate drastically from more exact potentials such as the Morse potential. [ABSTRACT FROM AUTHOR]

During the first study of the diverse diatom assemblages in Rara Lake, the largest lake in Nepal, 11 species of Gomphonema, belonging to six morphological groups, and Gomphoneis qii could be investigated using light and scanning electron microscopy. Five new Gomphonema species are described: Gomphonema subodhii, Gomphonema parasundaense, Gomphonema raraense, Gomphonema parapygmaeum and Gomphonema himalayaense. Known species included Gomphonema sublaticollum, Gomphonema cf. capitatum, Gomphonema minusculum, Gomphonema lateripunctatum, Gomphonema tergestinum (the only one previously recorded from Nepal) and Gomphonema vibrio. The history of the latter name is explained in detail. The distribution of the Gomphonema species, number of species and records in the littoral of the lake shore varied and was related to the presence of suitable substrata, land use and season, with more records and species present in spring than in autumn. This publication is dedicated to the victims of the earthquakes which hit Nepal in 2015 and to their families. [ABSTRACT FROM AUTHOR]

Silicon transporters (SIT) are the proteins, which capture silicic acid in the aquatic environment and direct it across the plasmalemma to the cytoplasm of diatoms. Diatoms utilize silicic acid to build species-specific ornamented exoskeletons and make a significant contribution to the global silica cycle, estimated at 240 ±40 Tmol a year. Recently SaSIT genes of the freshwater araphid pennate diatom Synedra acus subsp. radians are found to be present in the genome as a cluster of two structural genes (SaSIT-TD and SaSIT-TRI) encoding several concatenated copies of a SIT protein each. These structural genes could potentially be transformed into “mature” SIT proteins by means of posttranslational proteolytic cleavage. In the present study, we discovered three similar structural SuSIT genes in the genome of a closely related freshwater diatom Synedra ulna subsp. danica. Structural gene SuSIT1 is identical to structural gene SuSIT2, and the two are connected by a non-coding nucleotide DNA sequence. All the putative “mature” SITs contain conserved amino acid motifs, which are believed to be important in silicon transport. The data obtained suggest that the predicted “mature” SIT proteins may be the minimal units necessary for the transport of silicon is S. ulna subsp. danica. The comparative analysis of all available multi-SITs has allowed us to detect two conservative motifs YQXDXVYL and DXDID, located between the “mature” proteins. Aspartic acid-rich DXDID motif can, in our opinion, serve as a proteolysis site during the multi-SIT cleavage. The narrow distribution of the distances between CMLD and DXDID motifs can serve as additional evidence to the conservation of their function. [ABSTRACT FROM AUTHOR]

Reproductive development in Ardissonea crystallina revealed a unique mode of enlargement involving a combination of novel and known structures. In light microscopy, auxospores of this elongated polar centric diatom were superficially similar to the auxospores of pennates. With SEM we found three different components in the auxospore wall. In the youngest, nearly spherical cell-stage, the wall consisted only of a delicate veil containing minute siliceous spherules. Incunabular elements developed underneath this layer. Second, a previously unknown form of specifically modified incunabular scales shaped the subsequent ellipsoidal-capsule auxospore stage. Third, there was a clear contribution of scales to the development of scaly transverse perizonial bands (or scaly bands, for brevity). Such bands, although noted by previous researchers, have not been fully appreciated for the evolutionary information they may convey: possibly common among polar centrics but not pennates. Finally, we propose maintaining the term transverse perizonium to refer to these bands in polar diatoms, but to introduce the differentiation of scaly bands described here from pinnate bands (currently known as typical of pennates). Further research into band types among polar centrics may provide new insights into the relationship between the groups within polar centrics that are currently unresolved by molecular methods. [ABSTRACT FROM AUTHOR]

Incomplete reproductive isolation between genetically distinct taxa provides an interesting opportunity for speciation and adaptation studies. This phenomenon is well-described in macro-organisms, but less experimental evidence is available for unicellular eukaryotes. Here, we document the sympatric occurrence of genetically differentiated populations of the pennate model diatom Seminavis robusta in coastal subtidal biofilm communities and show widespread potential for gene flow between them. Based on sequence variation in the plastid-encoded rbc L gene, three distinct clades were identified. Morphological variation between the clades reflected their phylogenetic relationships, with subtle differences in valve morphology in the most distant clade compared to the other two clades, which were indistinguishable. Using a large number of experimental crosses we showed that, although reproductive output was significantly lower compared to the majority of within-clade crosses, approximately 34.5% of the inter-clade crosses resulted in viable and fertile progeny. While the nature of the incomplete reproductive isolation remains unknown, its occurrence in natural diatom populations represents an additional mechanism contributing to population genetic structuring and adaptation and can spur further research into the mechanisms of species divergence and the maintenance of species identity in the presence of gene flow. [ABSTRACT FROM AUTHOR]

The occurrence of the ciguatera fish poisoning (CFP) causative Gambierdiscus spp. was confirmed in the Sea of Japan for the first time in 2009. This paper reports seasonal distribution of Gambierdiscus spp. and epiphytic diatoms in the Sea of Japan. Monitoring results suggested an antagonistic interaction in abundances between epiphytic diatoms and the dinoflagellate Gambierdiscus spp. Allelopathic effects of diatoms were considered to be involved in the competitive phenomenon. Therefore it is hypothesized that cell densities of epiphytic pennate diatoms on macroalgae are a novel determinant affecting the abundance of Gambierdiscus spp. other than sea water temperature, salinity and nutrients. Monitorings of the abundance of epiphytic diatoms would lead us to predict the occurrences of Gambierdiscus spp. blooms in the CFP area, and thereby the CFP risk assessments would be developed. Phylogenetic analyses indicated that Gambierdiscus spp. in the Sea of Japan belonged to Gambierdiscus sp. type 2 which was reported to be non-toxic. Nevertheless, based on morphological characteristics, at least two types of Gambierdiscus spp. were found in the Sea of Japan. It is needed to test the toxicity of the both types of Gambierdiscus recognized in the present study for evaluation of the probability of CFP outbreak risks in the Sea of Japan in the future. [ABSTRACT FROM AUTHOR]

Diploneis species have perhaps the most complex valve structure among pennate diatoms. The development of this structure was studied in Diploneis smithii and begins with the formation of a primary band, which then develops secondary arms at both poles and the center, as in the classic Chiappino–Volcani model of raphid diatom ontogeny. Spine‐like projections grow out from the primary band and secondary arms to establish the transapical ribs (virgae) of the mature valve and themselves develop spines, which are spaced first oppositely and then alternately and fuse with each other to delimit the stria pores. Subsequently, new pattern and structures develop both externally (formation of bifurcating projections that fuse to delimit the outer, sieve‐like layer of the valve) and internally (growth and fusion of flanges from the first‐formed ribs to create the longitudinal canals and deposition of a hymenate strip over the internal face of each stria). Comparisons are made with morphogenesis in other diatoms. Diploneis smithii ontogeny suggests how very slight developmental changes might have created the very variable external morphology of Diploneis species. It also indicates that the longitudinal canals of Diploneis and Fallacia have different origins, since the porous external wall is not formed as a unilaterally attached flap in Diploneis and the canal is internal to the first‐formed rib–stria system in Diploneis, but external to it in Fallacia. [ABSTRACT FROM AUTHOR]

The diatoms are one of the most important groups of organisms for biomonitoring studies. In Turkey, most previous applications of diatoms to water quality monitoring have focused on the pennate diatoms, with almost no attention given to the centric forms. The paper presents the centric diatoms in some river catchments in Central Anatolia (Konya closed catchment and Kızılırmak) and Western Anatolia (Marmara, Sakarya, Susurluk, Akarçay, Küçük Menderes, and Meriç-Ergene in the Marmara and Aegean regions). The survey of these catchments is based on samples collected between 2009 and 2013 from 33 different locations, including some springs from Türkmen Mountain and Domaniç forest, as well as small streams and big rivers of the Anatolian Peninsula. Altogether 30 taxa were found, of which 14 are new records for the freshwater diatom flora of Turkey. [ABSTRACT FROM AUTHOR]

We examined gametogenesis and auxospore development in the cymatosiroid diatom Brockmanniella brockmannii . Our mating experiments demonstrated that the clones were homothallic, self-compatible, produced two eggs per oogonium and four hologenous uniflagellate male gametes per spermatogonium. Auxospores grew free in the culture medium and the most external layer of the auxospore wall was made up of spinescent scaly elements in their early globular stage of development. The anisodiametric expansion of the globular auxospore was rather limited, at best proceeding only to a sub-globular stage. Our data suggest that the initial epivalves, nearly pennate-like in outline, developed within such auxospores curled up against the ventral side of the auxospore wall, not across its equatorial plane, and apparently without the help of rings, hoops or bands characteristic of pennate-type transverse perizonia. Thus, B. brockmannii showed a mode of initial epivalve development thus far unknown among diatoms. We propose that progressive silicification of the initial epivalve facilitated the breakdown of the sub-globular auxospore dorsal wall to accommodate for its straightening. The structural features of the spinescent scales on the auxospore wall suggest that Cymatosiraceae could be related to the mediophycean family Eupodiscaceae, although most current molecular phylogenies do not support a direct relationship. [ABSTRACT FROM AUTHOR]

Iron availability limits primary productivity in large areas of the world's oceans. Ascertaining the iron status of phytoplankton is essential for understanding the factors regulating their growth and ecology. We developed an incubation-independent, molecular-based approach to assess the iron nutritional status of specific members of the diatom community, initially focusing on the ecologically important pennate diatom Pseudo-nitzschia. Through a comparative transcriptomic approach, we identified two genes that track the iron status of Pseudo-nitzschia with high fidelity. The first gene, ferritin ( FTN), encodes for the highly specialized iron storage protein induced under iron-replete conditions. The second gene, ISIP2a, encodes an iron-concentrating protein induced under iron-limiting conditions. In the oceanic diatom Pseudo-nitzschia granii (Hasle) Hasle, transcript abundance of these genes directly relates to changes in iron availability, with increased FTN transcript abundance under iron-replete conditions and increased ISIP2a transcript abundance under iron-limiting conditions. The resulting ISIP2a: FTN transcript ratio reflects the iron status of cells, where a high ratio indicates iron limitation. Field samples collected from iron grow-out microcosm experiments conducted in low iron waters of the Gulf of Alaska and variable iron waters in the California upwelling zone verify the validity of our proposed Pseudo-nitzschia Iron Limitation Index, which can be used to ascertain in situ iron status and further developed for other ecologically important diatoms. [ABSTRACT FROM AUTHOR]

A high-resolution diatom analysis of a varved sediment sequence from Lac Brûlé, southwestern Québec, was used to study temporal patterns of environmental change in the late Holocene. Key periods of interest in the record included theMedievalWarm Period (~800-1300 CE), the Little Ice Age (~1450-1850 CE), and post-European settlement (~1850-present). Subfossil diatom assemblages were compared to previously published pollen, cladocera, and sediment records from Lac Brûlé, revealing complex dynamics between terrestrial vegetation succession, nutrient fluxes, and trophic interactions. Generalized additive models showed a response to long-term climate variability in the diatom record, although it was not the most influential driver of community changes at Lac Brûlé. Catchment-mediated processes instead played the largest role in governing the structure of diatom assemblages in the lake. For example, nutrient loading following a local fire in the watershed at 1345 CE led to an abrupt and significant increase in Fragilaria spp. Human activity associated with deforestation and the Wallingford-Back Mine (1924-1972 CE) also had strong impacts on the landscape, which triggered further responses in the aquatic communities of Lac Brûlé. [ABSTRACT FROM AUTHOR]

Pre-ingestive selection has been identified as a feeding mechanism of oysters that may influence their uptake of particles and microalgal cells. Oysters can feed specifically on the pennate diatom Haslea ostrearia, which produces the blue pigment marennine that is responsible for the greening of oysters. Because the size of particles or cells plays a significant role in the selection process, and given that diatoms experience a decrease in size as a consequence of vegetative reproduction, H. ostrearia consumption and marennine uptake might be influenced by pre-ingestive selection. We examined the role of H. ostrearia cell size in the selective feeding of Crassostrea gigas. Individual flow-through chambers were used to deliver mixtures of H. ostrearia of varying cell length to oysters. Inflow, outflow and pseudofaecal samples were collected from chambers during oyster feeding. Video-endoscopy was used to sample material in the dorsal and ventral particle tracts. Diatom cells counts showed that pseudofaeces contained on average larger cells than the ambient medium. However, proportions of the different populations of H. ostrearia in pseudofaeces were identical to those in the ventral tracts, indicating that no selection was performed by the labial palps. Video-endoscopy, plus imaging by scanning electron microscopy, of gills and labial palps revealed that only those larger H. ostrearia that were orientated dorsoventrally could enter the principal filaments (pfs) and then access the dorsal acceptance tract. These results show that for particles like Haslea cells with only one axis exceeding the width of the pfs, the selection on the oyster gills is passive and based on cell size. [ABSTRACT FROM AUTHOR]

In the open Southern Ocean (SO), both modern and past size changes of the diatom Fragilariopsis kerguelensis appear to be strongly controlled by iron availability. Conversely, sea surface temperatures (SST) and sea ice seasonal dynamics take over in the seasonal sea-ice zone where iron is not limiting. No information exists on F. kerguelensis biometry from the subtropical SO, on the other extreme of the thermal and nutrient gradients. We present here new data on mean valve area of F. kerguelensis (FkergArea) from a sediment core covering the last ~42 cal kyrs from the southern Subtropical Front (SSTF) of the Indian sector of the SO, where iron and silica stocks are thought to have been consistently low over this period. Our results suggest that larger F. kerguelensis valves occurred during the Last Glacial period, and declined during the Holocene period. These findings indicate that more favourable SST, within the F. kerguelensis ecological range, during the Last Glacial period may have enabled F. kerguelensis to make better use of the low silica stocks prevailing in the subtropical zone leading to larger valves. Conversely, declining FkergArea during the deglacial and the Holocene periods may have been a result of higher SST which hampered the utilization of silica. [ABSTRACT FROM AUTHOR]

Three genetic sub-populations (clade I, II and III) of Pseudo-nitzschia pungens , the potential toxic marine diatom, are known to have distinguishable growth characteristics under different culture conditions and distinct distributed patterns in the world. However, to date their exact eco-physiological traits are unrevealed in fields due to lack of the method to detect and/or measure abundances of each sub-populations, hence, the qPCR (quantitative real-time polymerase chain reaction) assay was developed to detect and quantify the P. pungens cells of each clade. Designed two specific primer sets, Pcla12F/R (for clade I and II) and Pcla3F/R (for clade III) only could amplify each target genomic DNA. The, significant linear relationships (R 2 > 0.998) was established between C t (threshold cycle) value and the log of cell abundance for each clade. Through the melting curve analysis, comparisons for gene copy numbers among the three clades and spike test for field study, our qPCR assay was reliable to quantify the cell numbers of each clade. There was strong linear correlation (R 2 > 0.990) between cell abundances as estimated by qPCR assay and direct counting via light microscope in spike test, and 0.24 (clade I), 0.25 (clade II) and 0.33 (clade III) P. pungens cells per mL were detected markedly upon the use of specific two-primer set. Finally, developed qPCR assay was applied on field samples successfully. Our study implicate that our qPCR assay is an accurate and sensitive technique to estimate the cell abundances of each clade of P. pungens in field works. [ABSTRACT FROM AUTHOR]

When grown under intermittent light (IL), the pennate diatom Phaeodactylum tricornutum forms ‘super’ non-photochemical fluorescence quenching (NPQ) in response to excess light. The current model of diatom NPQ mechanism involves two quenching sites, one of which detaches from photosystem II reaction centres (RCIIs) and aggregates into oligomeric complexes. Here we addressed how antenna reorganisation controls NPQ kinetics in P. tricornutum cells grown under continuous light (CL) and IL. Overall, IL acclimation induced: (i) reorganisation of chloroplasts, containing greater pigment pools without a strongly enhanced operation of the xanthophyll cycle, and (ii) ‘super NPQ’ causing a remarkable reduction of the chlorophyll excited state lifetime at Fm′. Regardless of different levels of NPQ formed in both culture conditions, its dark recovery was rapid and similar fractions of their antenna uncoupled (~ 50%). Although antenna detachment relieved excitation pressure, it provided a minor protective contribution equivalent to NPQ ~ 1, while the largest NPQ was 4.4 ± 0.2 (CL) and 13 ± 0.8 (IL). The PSII cross-section decrease took place only at relatively low NPQ values, beyond which the cross-section remained constant whilst NPQ continued to rise. This finding suggests that the energy trapping efficiency of diatom antenna quenchers cannot over-compete that of RCIIs, similarly to what has been observed on higher plants. We conclude that such ‘economic photoprotection’ operates to flexibly adjust the overall efficiency of diatom light harvesting. [ABSTRACT FROM AUTHOR]

Several lineages of raphe-bearing diatoms possess a “stauros,” which is a transverse, usually thickened area free of pores across the center of the valve. It has been suggested that this structure has evolved several times across the raphid diatoms, but we have noticed similarities beyond the stauros between two marine genera— Craspedostauros and Staurotropis —in the structure of their pore occlusions. We have isolated, cultured and extracted DNA from several strains of both genera to infer the phylogenetic relationship between these taxa, as well as test the suggested relationship of Craspedostauros to Achnanthes and Mastogloia based on plastid morphology. DNA sequence data (nuclear-encoded rRNA SSU, plastid-encoded rbc L and psb C) suggest that, except for Mastogloia , these genera are closely-related, though not sister taxa. The DNA phylogeny also suggests that the Mastogloiales are not monophyletic, with clades containing Achnanthes and Craspedostauros sister to clades containing taxa in the Bacillariales. Using evidence from molecular and morphological data, we describe the following new taxa: Craspedostauros alyoubii and C. paradoxa from the Red Sea and Guam, respectively; Staurotropis khiyamii and S. americana from the Red Sea and the Gulf of Mexico, respectively; and Dreuhlago cuneata n. gen., n. sp. from Guam. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia is a thoroughly studied pennate diatom genus for ecological and biological reasons. Many species in this genus, including Pseudo-nitzschia multistriata, can produce domoic acid, a toxin responsible for amnesic shellfish poisoning. Physiological, phylogenetic and biological features of P. multistriata were studied extensively in the past. Life cycle stages, including the sexual phase, fundamental in diatoms to restore the maximum cell size and avoid miniaturization to death, have been well described for this species. P. multistriata is heterothallic; sexual reproduction is induced when strains of opposite mating type are mixed, and proceeds with cells producing two functionally anisogamous gametes each; however, detailed cytological information for this process is missing. By means of confocal laser scanning microscopy and nuclear staining, we followed the nuclear fate during meiosis, and using time-lapse cinematography, we timed every step of the sexual reproduction process from mate pairing to initial cell hatching. The present paper depicts cytological aspects during gametogenesis in P. multistriata, shedding light on the chloroplast behaviour during sexual reproduction, finely describing the timing of the sexual phases and providing reference data for further studies on the molecular control of this fundamental process. [ABSTRACT FROM AUTHOR]

Hannaea baicalensisis a benthic pennate diatom that predominantly grows at depths of less than a metre attached to rocks and filamentous algae in Lake Baikal, Russia. This narrow zone at the edge of the lake is subject to frequent wave action and lake level fluctuations, which combine with other factors to affect seasonal abundance. During ice cover from January to May in 2008, when lake levels decreased from 42 to 14 cm above datum,H. baicalensiscell abundance remained low (0.39 × 106cells cm–2). The main period of net cell increase occurred in autumn, when there was a period of stable lake level (±10 cm changes in water depth) that coincided with the return of nutrients during autumn overturn. Cell abundance reached 1.52 × 106cells cm–2on 31 October. Alongside the changes in abundance, cyclic size changes in cell apical lengths were found (40 to 144 µm), which were associated with timing of the length of the life cycle. Size decline occurred in both spring and autumn, with an average decrease in apical length of 36 µm per year. It took two years for the mean apical length of a single cohort to decrease from 128 µm to 56 µm, which was then below the threshold (< 65 µm) for initiation of size regeneration. [ABSTRACT FROM PUBLISHER]

We present the combined abundance of all extant fossilizable planktonic groups (Dinoflagellates, Coccolithophores, Silicoflagellates, Diatoms, Parmales, Archaeomonads and micro-zooplankton) from surface waters collected along a latitudinal transect in the western Pacific sector of the Southern Ocean, ranging from ~ 48°S, offshore New Zealand, to ~ 70°S in the Ross Sea, Antarctica. Latitudinal shifts in species' distribution correspond with the Antarctic Circumpolar Current fronts and with the seasonal position of the ice-edge. Distinct bioprovinces are defined by clustering samples with a high degree of similarity. Our data confirm the importance of previously-defined taxa as palaeoceanographic proxies but also reveal some differences: the shift in dominance between the silicoflagellates genera Dictyocha and Stephanocha , used as a proxy of palaeo sea-surface temperatures, occurs slightly north of the Southern Sub-Antarctic Front rather than at the Polar Front; the shifts in abundance between the open-ocean diatom species Fragilariopsis kerguelensis and sea-ice related F. curta and F. cylindrus , as well as the drop in the coccolithophore Emiliania huxleyi , occur at the southern Antarctic Circumpolar Front rather than at the Polar Front. Finally, we introduce the Corona-index, based on the ratio of the coronatid to non-coronatid silicoflagellates species Stephanocha speculum , as a new proxy for sea-ice and we confirm the occurrence of abundant Archaeomonads and Parmales ( Triparma laevis subsp. ramispina ) in the marginal ice-edge zone. [ABSTRACT FROM AUTHOR]

Cadmium selenide (CdSe) nanoparticles (NPs) were first synthesized in the cavity of recombinant cage-shaped protein from marine pennate diatoms. Our constructed recombinant apoferritin (FerA-dCys) from the diatoms revealed that the removal of cysteine residues on the surface of the recombinant apoferritin enhanced the CdSe NPs synthesis in the apoferritin cavity. The CdSe NPs were synthesized in the FerA-dCys with a very low concentration of cadmium ions (0.02 mM). The core formation ratio of CdSe NPs showed more than 20%. The average diameter of synthesized CdSe NPs was 7 nm with a small size distribution. The synthesized NPs were analyzed by energy-dispersive X-ray spectroscopy (EDX) and high-resolution transmission electron microscopy (HR-TEM), and it was confirmed that the synthesized NPs in the FerA-dCys were consistent with Cd and Se ions. [ABSTRACT FROM AUTHOR]

The study investigated the influence of the xanthophyll cycle pigments diadinoxanthin (DD) and diatoxanthin (Dt) on the spectroscopic characteristics, structure and protein composition of isolated fucoxanthin chlorophyll protein (FCP) complexes of the pennate diatom Phaeodactylum tricornutum . 77 K fluorescence emission spectra revealed that Dt-containing FCP complexes showed a characteristic long wavelength fluorescence emission at 700 nm at a pH-value of 5 whereas DD-enriched FCPs retained the typical 680 nm fluorescence emission maximum of isolated FCPs. The 700 nm emission in Dt-containing FCPs indicates an aggregation of antenna complexes and is a typical feature of the quenching site Q1 in recent models for non-photochemical fluorescence quenching (NPQ). A comparable long-wavelength fluorescence emission was found in FCP complexes prepared with either triton X-100 or n-dodecyl β-D-maltoside as detergent. A treatment of the FCP complexes at low pH-values in the presence of a high concentration of Mg 2+ ions showed that the extent of FCP aggregation which leads to the 700 nm fluorescence emission is different from the macro-aggregation of antenna complexes in higher plants. Protein analyses by mass spectrometry showed that the protein composition of the DD- and Dt-enriched FCP complexes was comparable. However, the Lhcf6 and Lhcr1 polypeptides were only found in Dt-enriched FCPs isolated with dodecyl maltoside whereas the Lhcf17 protein was only detected in DD-enriched FCPs prepared with triton. With respect to low pH-induced antenna aggregation it is important that the Lhcx1 protein was found in both DD- and Dt-enriched FCPs, albeit with only two peptides with confident scores. [ABSTRACT FROM AUTHOR]

The marine pennate diatom Phaeodactylum tricornutum has become a model for diatom biology, due to its ease of culture and accessibility to reverse genetics approaches. While several features underlying the molecular mechanisms of cell division have been described, morphological analyses are less advanced than they are in other diatoms. We therefore examined cell ultrastructure changes prior to and during cytokinesis. Following chloroplast division, cleavage furrows are formed at both longitudinal ends of the cell and are accompanied by significant vesicle transport. Although neither spindle nor microtubules were observed, the nucleus appeared to be split by the furrow after duplication of the Golgi apparatus. Finally, centripetal cytokinesis was completed by fusion of the furrows. Additionally, F-actin formed a ring structure and its diameter became smaller, accompanying the ingrowing furrows. To further analyse vesicular transport during cytokinesis, we generated transgenic cells expressing yellow fluorescent protein (YFP) fusions with putative diatom orthologs of small GTPase Sec4 and t-SNARE protein SyntaxinA. Time-lapse observations revealed that SyntaxinA-YFP localization expands from both cell tips toward the center, whereas Sec4-YFP was found in the Golgi and subsequently relocalizes to the future division plane. This work provides fundamental new information about cell replication processes in P. tricornutum . [ABSTRACT FROM AUTHOR]

Diatom complexes from two ponds and one lake were compared and analyzed. The samples were taken from modern bottom sediments. All water bodies are situated in Moscow oblast. The ponds in the boundaries of Dubna C. are of artificial origin, while Lake Glubokoe is a natural water body. The degree of adverse changes in the structure of diatom complexes does not depend on the origin of the water body but is determined by the overall level of anthropogenic load. The study suggests the conclusion that the results of studies of diatom complexes from natural lakes and artificial ponds can be combined. [ABSTRACT FROM AUTHOR]

The remarkable adaptability of diatoms living in a highly variable environment assures their prominence among marine primary producers. The present study integrates biochemical, biophysical and genomic data to bring new insights into the molecular mechanism of chromatic adaptation of pennate diatoms in model species Phaeodactylum tricornutum , a marine eukaryote alga possessing the capability to shift its absorption up to ~ 700 nm as a consequence of incident light enhanced in the red component. Presence of these low energy spectral forms of Chl a is manifested by room temperature fluorescence emission maximum at 710 nm (F710). Here we report a successful isolation of the supramolecular protein complex emitting F710 and identify a member of the Fucoxanthin Chlorophyll a / c binding Protein family, Lhcf15, as its key building block. This red-shifted antenna complex of P. tricornutum appears to be functionally connected to photosystem II. Phylogenetic analyses do not support relation of Lhcf15 of P . tricornutum to other known red-shifted antenna proteins thus indicating a case of convergent evolutionary adaptation towards survival in shaded environments. [ABSTRACT FROM AUTHOR]

A 45-day exposure experiment was carried out to assess whether the harmful algal blooming Pseudo-nitzschia delicatissima (i.e. needle shaped diatom and potential domoic acid producer) is involved in recurrent mass mortality events at a coastal fish farm in the southern North Sea. Juvenile sea bass ( Dicentrarchus labrax ) were exposed to different concentrations of P. delicatissima , ranging from 1 × 10 6 to 5 × 10 6 cells L − 1 . Despite exposure to high concentrations of P. delicatissima , sea bass weight and length based growth rates (0.05 ± 0.02 g d − 1 and 0.18 ± 0.05 mm d − 1 , respectively) and condition (Fulton K = 0.98 ± 0.06 mg mm − 3 ) were not significantly reduced suggesting that the fish were not affected during the 45-day exposure period. However, signs of gill mucosa irritation (i.e. mucus overproduction) were observed, showing that this diatom induced a mechanical stress, which can affect gill functions or increase susceptibility of fish to secondary infections (e.g. bacterial and viral infections, parasitism). Results are discussed with regard to consequences for wild and farmed fish, and possible synergic noxious effects when P. delicatissima is associated with other potentially harmful taxa (e.g. Phaeocystis globosa ) during the phytoplankton spring bloom in the eastern English Channel–North Sea ecosystem. [ABSTRACT FROM AUTHOR]

The article discusses research analyzing the iron contents in fresh, dried, and toasted nori Pyropia yezoensis. Topics discussed include analysis of contribution of iron storage protein ferritin to iron storage in raw and dried nori, research on mechanism for iron storage in algae mainly on prokaryotic and eukaryotic unicellular microalgae, and role of ferritin in iron storage, in the proliferation of cyanobacteria and bloomforming marine pennate diatoms.

Nucleic acid aptamers are small-size ligands that selectively bind to molecular segments even when they protrude from cell surfaces. Due to their high specificity, aptamers are widely used in biomedical research and as probes for different applications. Here, we tested whether aptamers can also discriminate among phytoplankton cells. As a proof of concept we focused on the widespread centric diatom Leptocylindrus danicus and generated two aptamers that selectively bind to its cell surface. The aptamers did not bind to other diatoms tested, which included both pennate (Pseudo-nitzschia multistriata) and centric (Skeletonema marinoi, Chaetoceros socialis) species. They also showed negative binding to closely related species (Tenuicylindrus belgicus, Leptocylindrus aporus, Leptocylindrus convexus), which are hardly recognizable with microscopy techniques. In addition, aptamers discriminated also among cells of the same clone, suggesting a potential use of aptamers as clone-specific/stage-specific probes to track phytoplankton life stages in their natural environment. While the method still needs to be tested with natural algal samples, it can complement in a unique way the existing approaches to discriminate among species and possibly life stages of marine phytoplankton. The method can find useful application in taxonomic and ecological studies as well as in environmental monitoring including early warning strategies. [ABSTRACT FROM AUTHOR]

Fatty acids ( FAs) in the body walls of sea cucumber, Apostichopus japonicus, reared under diet-administered conditions were analysed to determine the accumulative status of dietary FAs. Four test diets different in diet source and microbial degradation, that is, a diet composed of powdered pennate diatoms (diet PD), one microbially degraded of diet PD (diet PDM), one composed of brown algae [tangle weed, Saccharina ( Laminaria) longissima ( Miyabe); diet BA], and one microbially degraded of diet BA (diet BAM), were fed to juvenile A. japonicus, respectively, for 2 months and the FA composition of the juvenile body wall was determined. FAs in body wall were influenced and changed by diet source and microbial degradation of diet. Degradation significantly promoted juvenile's growth and increased iso-15:0 in the body wall; however, iso-15:0 was not a growth factor. FA 20:4n6 and 20:5n3 were dominant in all groups despite being a minor dietary constituent, suggesting that these FAs can be readily accumulated or synthesized in the animal. [ABSTRACT FROM AUTHOR]

A study on indigenous diatoms was carried out at 49 sites from November 2008 to December 2012 in the marine and brackish plankton and benthic ecosystem in Korea. The structure of small-sized pennate diatoms was examined by means of light and scanning electron microscopy. Twenty species of diatoms were newly identified and divided into five orders, 18 families, and nine genera in this study. The nomenclature, references, specimens examined, specimen descriptions, photographs, and distribution profiles are reported here. The newly reported pennate diatoms imply several reasons why these taxa have not been recorded previously in Korea and we present the strategy to understand the diversity of diatoms in Korea. [ABSTRACT FROM AUTHOR]

Fistulifera sp. strain JPCC DA0580, a marine pennate diatom, contains extremely high levels of intracellular triglyceride and has been suggested as a promising source of feedstock for biodiesel fuels. JPCC DA0580 was isolated from a mangrove swamp located in Sumiyo Bay below the mouths of the Sumiyo and Yakugachi Rivers in Amami- Ohshima, Kagoshima, Japan. In this study, the morphology and the 18S rDNA sequence of JPCC DA0580 were compared with those of other Fistulifera strains. JPCC DA0580 possesses morphological characters of the genus Fistulifera, namely lightly silicified frustules, a distinct median costa (raphe sternum), and a wart-like central pore (fistula). Morphometric analysis revealed that JPCC DA0580 differs from other Fistulifera species by the presence of a valve with coarser striation and coarser areolation. On the basis of 18S rDNA phylogeny, JPCC DA0580 formed a well-supported clade with other members of the Fistulifera species complex, although the number of nucleotide substitutions was highest in JPCC DA0580. Our results led us to propose the taxonomic name Fistulifera solaris sp. nov. for JPCC DA0580. [ABSTRACT FROM AUTHOR]

Fistulifera sp. strain JPCC DA0580 is a newly sequenced pennate diatom that is capable of simultaneously growing and accumulating lipids. This is a unique trait, not found in other related microalgae so far. It is able to accumulate between 40 to 60% of its cell weight in lipids, making it a strong candidate for the production of biofuel. To investigate this characteristic, we used RNA-Seq data gathered at four different times while Fistulifera sp. strain JPCC DA0580 was grown in oil accumulating and non-oil accumulating conditions. We then adapted gene set enrichment analysis (GSEA) to investigate the relationship between the difference in gene expression of 7,822 genes and metabolic functions in our data. We utilized information in the KEGG pathway database to create the gene sets and changed GSEA to use re-sampling so that data from the different time points could be included in the analysis. Our GSEA method identified photosynthesis, lipid synthesis and amino acid synthesis related pathways as processes that play a significant role in oil production and growth in Fistulifera sp. strain JPCC DA0580. In addition to GSEA, we visualized the results by creating a network of compounds and reactions, and plotted the expression data on top of the network. This made existing graph algorithms available to us which we then used to calculate a path that metabolizes glucose into triacylglycerol (TAG) in the smallest number of steps. By visualizing the data this way, we observed a separate up-regulation of genes at different times instead of a concerted response. We also identified two metabolic paths that used less reactions than the one shown in KEGG and showed that the reactions were up-regulated during the experiment. The combination of analysis and visualization methods successfully analyzed time-course data, identified important metabolic pathways and provided new hypotheses for further research. [ABSTRACT FROM AUTHOR]

Could the abundant sulfate salts on Mars contain microfossils and/or viable microorganisms? Here we report a variety of microorganisms trapped both as solid inclusions and as potentially viable halophilic and acidophilic prokaryotes and eukaryotes within fluid inclusions in Mars-analog gypsum. We have documented pennate diatoms, green algae, and prokaryotes in gypsum precipitated from acid (pH 1.8-4.6) saline (5%-28% total dissolved solids) waters at Salars Gorbea and Ignorado in an active volcanic terrain in the high Andes (4000+ m) of northern Chile. These salars are strikingly similar in geology and geochemistry to Mars. We propose that this discovery should serve as a model for fossilization of possible life on Mars and may inform methodologies used in future missions to Mars. Furthermore, the potential long-term viability of microorganisms within fluid inclusions in gypsum suggests the possibility of a living, yet isolated and likely dormant, microbiological community on Mars today. [ABSTRACT FROM AUTHOR]

Abstract: Diatoms are eukaryotic microalgae broadly present in freshwater and marine ecosystems. The great ecological interest about diatoms has recently led to increased efforts towards the exploration of the molecular properties of these organisms and the development of molecular tools to study the function of genes. We are using as model system two pennate diatoms, Pseudo-nitzschia multistriata and Pseudo-nitzschia arenysensis. In order to enable molecular investigations in these two species, we have made use of sequence information from transcriptomic data to identify genes that can be used as reference genes in quantitative PCR (qPCR). We have analyzed the expression of a set of genes commonly used as reference genes: histone H4, TBP (TATA binding protein), RPS (30S ribosomal protein), GAPDH (glyceraldehyde 3-phosphate dehydrogenase), TUB A and TUB B (tubulin α and tubulin β), ACT (actin), CDK A (cyclin dependent kinase A) and COPA (coatomer protein complex, subunit α). The suitability of these genes as references in qPCR has been tested in different conditions and among different strains. We have found that only TUB A, TUB B and CDK A are stable in all the conditions analyzed. These three genes, in addition to ACT and COPA, are good reference genes for P. multistriata, while GAPDH appears to be differentially expressed in the tested conditions in this species. In P. arenysensis, instead, TUB A, TUB B, CDK A, GAPDH, H4 and RPS show the highest levels of stability and can be considered reliable reference genes. [Copyright &y& Elsevier]

Highlights: [•] Microorganisms mediate processes affecting the fate and impacts of marine plastic. [•] North Pacific Gyre (NPG) plastics were examined with scanning-electron microscopy. [•] Bacillus bacteria and pennate diatoms dominated the NPG plastic fouling community. [•] Bacterial abundance was patchily distributed but increased on foamed polystyrene. [•] Diatom abundance increased on rough surfaces and at sites with high plastic density. [Copyright &y& Elsevier]

Diatoms represent an important class of aquatic phototrophs. They are not only one of the major contributors to global carbon fixation, but they also play a key role in the biogeochemical cycling of silica. Molecular identification methods based on conserved DNA sequences, such as internal transcribed spacer (ITS) have revolutionized our knowledge and understanding of conventional taxonomy. In this study, we aimed to compare the conventional identification methods with molecular identification methods. To do so, we isolated 4 diatom samples from the coast at Urla and characterized them using light microscopy (LM) and scanning electron microscopy (SEM) according to morphological features. Then we amplified ITS regions using a conventional polymerase chain reaction (PCR), sequenced the PCR products, and analyzed the sequences using bioinformatic tools. Bioinformatic analysis indicated that the isolated species had high sequence similarity to Pseudo-nitzschia delicatissima, Achnanthes taeniata, Amphora coffeaeformis, and Cylindrotheca closterium. We think that molecular identification methods enable rapid and more reliable identification of diatom species and are crucial for monitoring harmful algal blooms. [ABSTRACT FROM AUTHOR]

The influence of PBR composition [clear polyurethane (PolyU) vs. clear linear low-density polyethylene (LLDPE) (top) and black opaque high-density polyethylene (bottom)] and shape (rectangular vs. tubular) on biofouling and the influence of biofouling on algae productivity were investigated. In 9-week experiments, PBR biofouling was dominated by pennate diatoms and clear plastics developed macroalgae. LLDPE exhibited lower photosynthetic-active-radiation (PAR) light transmittance than PolyU before biofouling, but higher transmittance afterwards. Both rectangular and tubular LLDPE PBRs accumulated biofouling predominantly along their wetted edges. For a tubular LLDPE PBR after 12 weeks of biofouling, the correlation between biomass, percent surface coverage, and PAR transmittance was complex, but in general biomass inversely correlated with transmittance. Wrapping segments of this biofouled LLDPE around an algae culture reduced CO 2 and NH 3 -N utilization, indicating that external biofouling must be controlled. [ABSTRACT FROM AUTHOR]

Over recent years, several planktonic and benthic freshwater diatom taxa have been established as laboratory model strains. In common with most freshwater diatoms the pennate diatom Planothidium frequentissimum suffers irreversible cell shrinkage on prolonged maintenance by serial transfers, without induction of the sexual cycle. Therefore, alternative strategies are required for the long-term maintenance of this strain. Conventional colligative cryopreservation approaches have previously proven unsuccessful with no regrowth. However, in this study using 5% dimethyl sulfoxide (Me2SO), controlled cooling at 1°Cmin−1, automated ice seeding and cooling to −40°C with a final plunge into liquid nitrogen, viability levels were enhanced from 0.3±0.4% to 80±3%, by incorporating a 48h dark-recovery phase after rewarming. Omission, or reduction, of this recovery step resulted in obvious cell damage with photo-bleaching of pigments, indicative of oxidative-stress induced cell damage, with subsequent deterioration of cellular architecture. [ABSTRACT FROM AUTHOR]

Diatoms are one of the largest groups of primary producers in the oceans, yet despite their environmental importance little is known about their plastidial lipid biochemistry. It has been previously reported that Skeletonema species contain primarily C16/ C16 and C20/ C16 forms of mono- and digalactosyldiacylglycerol ( MGDG and DGDG, respectively). Likewise, it was also reported that Phaeodactylum tricornutum contains primarily C16/ C16 and C20/ C20 forms of MGDG and DGDG. We seek to relate their studies to other diatoms, both in the centrics and pennates, with particular focus on the marennine-producing pennate diatom, Haslea ostrearia. To this end, the composition and positional distribution of fatty acids of MGDG and DGDG were examined using positive-ion electrospray ionization/mass spectrometry ( ESI/ MS). Two centric diatoms, Skeletonema marinoi and Thalassiosira weissflogii, and the pennate diatom, P. tricornutum, contained primarily C20/ C16 ( sn-1/ sn-2) and C18/ C16 forms of MGDG and DGDG. The other pennate diatoms, H. ostrearia and Navicula perminuta, contained primarily C18/ C16 or C18/ C18 forms of MGDG and DGDG, indicating a previously unrecognized fatty acid diversity in diatom MGDG and DGDG. [ABSTRACT FROM AUTHOR]

A novel ferritin was recently found in Pseudo-nitzschia multiseries (PmFTN), a marine pennate diatom that plays a major role in global primary production and carbon sequestration into the deep ocean. Crystals of recombinant PmFTN were soaked in iron and zinc solutions, and the structures were solved to 1.65- 2.2-Å resolution. Three distinct iron binding sites were identified as determined from anomalous dispersion data from aerobically grown ferrous soaked crystals. SitesAandBcomprise the conserved ferroxidase active site, and site C forms a pathway leading toward the central cavity where iron storage occurs. In contrast, crystal structures derived from anaerobically grown and ferrous soaked crystals revealed only one ferrous iron in the active site occupying site A. In the presence of dioxygen, zinc is observed bound to all three sites. Iron oxidation experiments using stopped-flow absorbance spectroscopy revealed an extremely rapid phase corresponding to Fe(II) oxidation at the ferroxidase site, which is saturated after adding 48 ferrous iron to apo-PmFTN (two ferrous iron per subunit), and a much slower phase due to iron core formation. These results suggest an ordered stepwise binding of ferrous iron and dioxygen to the ferroxidase site in preparation for catalysis and a partial mobilization of iron from the site following oxidation. [ABSTRACT FROM AUTHOR]

We present the first study examining mtDNA transmission in diatoms, using sexual progeny of the pennate species Haslea ostrearia (Naviculaceae). A fragment of the cytochrome oxidase subunit I gene (cox1) with 7 nucleic substitutions between parental clones was used as a parental tracer in 16 F1 clones obtained from two pairs of mating crosses. Each cross involved a parental clone isolated from France (Bay of Bourgneuf) and Sweden (Kattegat Bay). We determined that all progeny possessed only one cox1 parental haplotype. These results suggest that the mitochondrial DNA transmission in H. ostrearia is uniparental. Implications and new topics of investigation are discussed. [Copyright &y& Elsevier]

Abstract: Diatoms are major contributors to the photosynthetic productivity of marine phytoplankton. In these organisms, fucoxanthin-chlorophyll proteins (FCPs) serve as light-harvesting proteins. We have explored the FCP complexes in Phaeodactylum tricornutum under low light (LL) and high light (HL) conditions. Sub-fractionating the pool of major FCPs yielded different populations of trimeric complexes. Only Lhcf and Lhc-like proteins were found in the trimers. Under LL, the first polypeptide fraction contained six different Lhcfs and was mainly composed of Lhcf10. It was characterised by the highest amount of fucoxanthin (Fx). The second was dominated by Lhcf10, Lhcf5 and Lhcf2, and had a lower Fx/Chl c ratio. Little Fx/Chl c also characterised the most abundant FCP complexes, found in fraction 3, composed mainly of Lhcf5. These FCPs bound Fx molecules with the strongest bathochromic shift. The last two fractions contained FCP complexes that were built mainly of Lhcf4, harbouring more Fx molecules that absorbed at shorter wavelengths. Under HL, the same main polypeptides were retrieved in the different fractions and spectroscopic features were almost identical except for a higher diadinoxanthin content. The total amount of Lhcf5 was reduced under HL, whereas the amount of the last two fractions and thereby Lhcf4 was increased. Lhcf11 was identified in different LL fractions, but not detected in any HL fraction, while two new Lhc-like proteins were only found under HL. This is the first report on different trimeric FCP complexes in pennate diatoms, which differ in polypeptide composition and pigmentation, and are differentially expressed by light. [Copyright &y& Elsevier]

The pennate diatom Seminavis robusta, characterized by an archetypical diatom life cycle including a heterothallic mating system, is emerging as a model system for studying the molecular regulation of the diatom cell and life cycle. One of its main advantages compared with other diatom model systems is that sexual crosses can be made routinely, offering unprecedented possibilities for forward genetics. To date, nothing is known about the genetic basis of sex determination in diatoms. Here, we report on the construction of mating type-specific linkage maps for S. robusta, and use them to identify a single locus sex determination system in this diatom. We identified 13 mating type plus and 15 mating type minus linkage groups obtained from the analysis of 463 AFLP markers segregating in a full-sib family, covering 963.7 and 972.2 cM, respectively. Five linkage group pairs could be identified as putative homologues. The mating type phenotype mapped as a monogenic trait, disclosing the mating type plus as the heterogametic sex. This study provides the first evidence for a genetic sex determining mechanism in a diatom. [ABSTRACT FROM AUTHOR]

The pennate diatom Seminavis robusta, characterized by an archetypical diatom life cycle including a heterothallic mating system, is emerging as a model system for studying the molecular regulation of the diatom cell and life cycle. One of its main advantages compared with other diatom model systems is that sexual crosses can be made routinely, offering unprecedented possibilities for forward genetics. To date, nothing is known about the genetic basis of sex determination in diatoms. Here, we report on the construction of mating type-specific linkage maps for S. robusta, and use them to identify a single locus sex determination system in this diatom. We identified 13 mating type plus and 15 mating type minus linkage groups obtained from the analysis of 463 AFLP markers segregating in a full-sib family, covering 963.7 and 972.2 cM, respectively. Five linkage group pairs could be identified as putative homologues. The mating type phenotype mapped as a monogenic trait, disclosing the mating type plus as the heterogametic sex. This study provides the first evidence for a genetic sex determining mechanism in a diatom. [ABSTRACT FROM AUTHOR]

Biomimetic fabrication of nanostructured materials has recently attracted the attention of researchers as a cost-effective and easily applicable method of nanotexturing. Different techniques and materials have been used in order to replicate natural patterns, among which polydimethylsiloxane (PDMS Sylgard 184 ® ) was recently used to replicate the micro- and nanoscale patterns from centric diatoms. In this paper, we test the reproducibility and precision of this approach using various morphologically different diatom species trying to optimize the molding parameters. The optimization process is focused on immobilization of diatoms on the glass support, which serves as a master for templating, as well as on the parameters of PDMS fabrication such as the ratio of the curing agent and elastomer, use of vacuum, curing time and temperature. The results indicate that higher ratios of curing agent and elastomer, longer curing time and lower temperature are the most favorable conditions to obtain negative diatom replicas of good quality with features of 50 nm. Although this method can give very precise results producing high-resolution molds with all micro- and nanostructures replicated, we revealed some limitations regarding the size and morphology of the species used. These results indicate that large round and flat diatom species seem to be more suitable for the cast molding. [ABSTRACT FROM AUTHOR]