Terminologia Anatomica in Latin-American countries: a systematic review.

Terminologia Anatomica (TA) is a unique collection of technical terms that allow communication in anatomy and medicine around the world. Considering this, we reviewed articles published by Latin American authors on Terminologia Anatomica and synthesized the main results found in this article. This study is a systematic review about Terminologia Anatomica that focuses on non-English-speaking countries in Latin America. The database used was Scopus via Elsevier. 207, and candidate articles were identified after applying the search strategy and with no restriction of year of publication. After the exclusion of articles whose authorship was not Latin American, 68 articles were filtered based on their titles and abstracts without the exclusion of any of them. These articles were fully evaluated resulting in 66 articles that met all the inclusion criteria of this review. We collected the following data: title of the article, year of publication, journal of publication, keywords of the study, country of origin, and aim of the article. Among the analyzed articles, 22 proposed changes to terms present in Terminologia Anatomica, 15 of them proposed the inclusion of terms for Terminologia Anatomica, and several articles sought to explain the existence of the existing terms. It is necessary to analyze the terms that are and their origins in the Latin America languages to evaluate their coherence and anatomical correspondence. A standard descriptor for Terminologia Anatomica was not obtained and it is a limitation since eventual articles may not have been obtained. As the study evaluates only articles that were published in journals indexed in Scopus, some articles published in non-indexed journals were not included.

Multiannual patterns of genetic structure and mating type ratios highlight the complex bloom dynamics of a marine planktonic diatom.

Understanding the genetic structure of populations and the processes responsible for its spatial and temporal dynamics is vital for assessing species' adaptability and survival in changing environments. We investigate the genetic fingerprinting of blooming populations of the marine diatom Pseudo-nitzschia multistriata in the Gulf of Naples (Mediterranean Sea) from 2008 to 2020. Strains were genotyped using microsatellite fingerprinting and natural samples were also analysed with Microsatellite Pool-seq Barcoding based on Illumina sequencing of microsatellite loci. Both approaches revealed a clonal expansion event in 2013 and a more stable genetic structure during 2017-2020 compared to previous years. The identification of a mating type (MT) determination gene allowed to assign MT to strains isolated over the years. MTs were generally at equilibrium with two notable exceptions, including the clonal bloom of 2013. The populations exhibited linkage equilibrium in most blooms, indicating that sexual reproduction leads to genetic homogenization. Our findings show that P. multistriata blooms exhibit a dynamic genetic and demographic composition over time, most probably determined by deeper-layer cell inocula. Occasional clonal expansions and MT imbalances can potentially affect the persistence and ecological success of planktonic diatoms.

Marine phycotoxin levels in shellfish-14 years of data gathered along the Italian coast.

Along the Italian coasts, toxins of algal origin in wild and cultivated shellfish have been reported since the 1970s. In this study, we used data gathered by the Veterinary Public Health Institutes (IZS) and the Italian Environmental Health Protection Agencies (ARPA) from 2006 to 2019 to investigate toxicity events along the Italian coasts and relate them to the distribution of potentially toxic species. Among the detected toxins (OA and analogs, YTXs, PTXs, STXs, DAs, AZAs), OA and YTX were those most frequently reported. Levels exceeding regulatory limits in the case of OA (≤2,448 µg equivalent kg-1) were associated with high abundances of Dinophysis spp., and in the case of YTXs (≤22 mg equivalent kg-1) with blooms of Gonyaulax spinifera, Lingulodinium polyedra, and Protoceratium reticulatum. Seasonal blooms of Pseudo-nitzschia spp. occur all along the Italian coast, but DA has only occasionally been detected in shellfish at concentrations always below the regulatory limit (≤18 mg kg-1). Alexandrium spp. were recorded in several areas, although STXs (≤13,782 µg equivalent kg-1) rarely and only in few sites exceeded the regulatory limit in shellfish. Azadinium spp. have been sporadically recorded, and AZAs have been sometimes detected but always in low concentrations (≤7 µg equivalent kg-1). Among the emerging toxins, PLTX-like toxins (≤971 µg kg-1 OVTX-a) have often been detected mainly in wild mussels and sea urchins from rocky shores due to the presence of Ostreopsis cf. ovata. Overall, Italian coastal waters harbour a high number of potentially toxic species, with a few HAB hotspots mainly related to DSP toxins. Nevertheless, rare cases of intoxications have occurred so far, reflecting the whole Mediterranean Sea conditions.

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov.

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

Gastroenterocolite eosinofílica - uma causa rara de diarreia / Eosinophilic gastroenterocolitis - a rare cause of diarrhea

Introdução: Colite eosinofílica é uma doença crônica rara. Pode ser idiopática ou estar associada à alergias alimentares e à doenças atópicas. Assim, a incidência é, muitas vezes, indefinida devido ao seu subdiagnóstico. Objetivo: Relatar o caso de uma paciente com colite eosinofílica e dermatite atópica. Método: Trata-se de um estudo tipo Relato de Caso utilizando dados do prontuário clínico, de uma paciente jovem que evoluiu com quadro de dor abdominal e diarreia sanguinolenta e que, após investigação por meio de exames laboratoriais, diversos exames de imagem, o resultado anatomopatológico evidenciou Ileíte eosinofílica. Resultados: O tratamento consistiu em mudança alimentar e uso de budesonida por via oral, havendo regressão do quadro e melhora da dermatite atópica. Conclusão: É necessário excluir a Colite Eosinofílica secundária, pois pode ser uma manifestação à diversas patologias, já que tem apresentação clínica inespecífica

Introducion: Eosinophilic colitis is a rare chronic disease. It may be idiopathic or associated with food allergies and atopic diseases. Thus, the incidence is often undefined due to underdiagnosis. Objective: To report the case of a patient with eosinophilic colitis and atopic dermatitis. Method: This is a case report study using data from the clinical record, of a young patient who developed abdominal pain and bloody diarrhea and who, after investigation through laboratory tests, several imaging tests, the result pathology showed eosinophilic ileitis. Results: Treatment consisted of dietary changes and oral budesonide, resulting in regression of the condition and improvement in atopic dermatitis. Conclusion: It is necessary to exclude secondary Eosinophilic Colitis, as it can be a manifestation of several pathologies, as it has a nonspecific clinical presentation

Introducción: La colitis eosinofílica es una enfermedad crónica rara. Puede ser idiopática o estar asociada a alergias alimentarias y enfermedades atópicas. Por tanto, la incidencia suele estar indefinida debido a un infradiagnóstico. Objetivo: Reportar el caso de un paciente con colitis eosinofílica y dermatitis atópica. Método: Se trata de un estudio de reporte de caso, utilizando datos de la historia clínica, de un paciente joven que desarrolló dolor abdominal y diarrea sanguinolenta y quien, luego de la investigación mediante pruebas de laboratorio, varias pruebas de imagen, el resultado de la patología arrojó ileítis eosinofílica. Resultados: El tratamiento consistió en cambios dietéticos y budesonida oral, lo que resultó en regresión del cuadro y mejoría de la dermatitis atópica. Conclusión: Es necesario excluir la Colitis Eosinofílica secundaria, ya que puede ser manifestación de varias patologías, al tener una presentación clínica inespecífica

The pennate diatom Pseudo-nitzschia multistriata as a model for diatom life cycles, from the laboratory to the sea.

Phytoplankton dynamics are regulated by external cues, such as light and nutrients, as well as by biotic interactions and endogenous controls linked to life cycle characteristics. The planktonic pennate diatom Pseudo-nitzschia multistriata, with a heterothallic mating system with two opposite mating types (MTs), represents a model for the study of diatom life cycles. P. multistriata is a toxic species, able to produce the neurotoxin domoic acid. First described in Japan in 1993, it was detected at the long-term monitoring station MareChiara (Gulf of Naples, Italy) in 1995. Since then, P. multistriata has been reported from several worldwide coastal sites. A large body of knowledge has been produced on its ecology, genetic diversity, and life cycle characteristics. The availability of these data, the ecological relevance of the Pseudo-nitzschia genus, and its controllable life cycle with a short generation time made it an ideal species to develop a genetic model system for diatoms. To enable functional studies, a 59 Mb genome sequence and several transcriptomic data were produced, and genetic transformation was optimized. These tools allowed the discovery of the first mating-type determining gene for diatoms. Gene expression studies and metabolomics analyses defined genes and molecules underpinning different phases of the process of sexual reproduction. This model system, developed to explore the genetics of diatom life cycles, offers the opportunity to parallel experimental observations in the laboratory using in situ meta-omics analyses along space and time, empowering knowledge on the biology and ecology of the genus.

Gene expression during the formation of resting spores induced by nitrogen starvation in the marine diatom Chaetoceros socialis.

BACKGROUND: Dormancy is widespread in both multicellular and unicellular organisms. Among diatoms, unicellular microalgae at the base of all aquatic food webs, several species produce dormant cells (spores or resting cells) that can withstand long periods of adverse environmental conditions. RESULTS: We present the first gene expression study during the process of spore formation induced by nitrogen depletion in the marine planktonic diatom Chaetoceros socialis. In this condition, genes related to photosynthesis and nitrate assimilation, including high-affinity nitrate transporters (NTRs), were downregulated. While the former result is a common reaction among diatoms under nitrogen stress, the latter seems to be exclusive of the spore-former C. socialis. The upregulation of catabolic pathways, such as tricarboxylic acid cycle, glyoxylate cycle and fatty acid beta-oxidation, suggests that this diatom could use lipids as a source of energy during the process of spore formation. Furthermore, the upregulation of a lipoxygenase and several aldehyde dehydrogenases (ALDHs) advocates the presence of oxylipin-mediated signaling, while the upregulation of genes involved in dormancy-related pathways conserved in other organisms (e.g. serine/threonine-protein kinases TOR and its inhibitor GATOR) provides interesting avenues for future explorations. CONCLUSIONS: Our results demonstrate that the transition from an active growth phase to a resting one is characterized by marked metabolic changes and provides evidence for the presence of signaling pathways related to intercellular communication.

Encapsulated in sediments: eDNA deciphers the ecosystem history of one of the most polluted European marine sites.

The Anthropocene is characterized by dramatic ecosystem changes driven by human activities. The impact of these activities can be assessed by different geochemical and paleontological proxies. However, each of these proxies provides only a fragmentary insight into the effects of anthropogenic impacts. It is highly challenging to reconstruct, with a holistic view, the state of the ecosystems from the preindustrial period to the present day, covering all biological components, from prokaryotes to multicellular eukaryotes. Here, we used sedimentary ancient DNA (sedaDNA) archives encompassing all trophic levels of biodiversity to reconstruct the two century-natural history in Bagnoli-Coroglio (Gulf of Pozzuoli, Tyrrhenian Sea), one of the most polluted marine-coastal sites in Europe. The site was characterized by seagrass meadows and high eukaryotic diversity until the beginning of the 20th century. Then, the ecosystem completely changed, with seagrasses and associated fauna as well as diverse groups of planktonic and benthic protists being replaced by low diversity biota dominated by dinophyceans and infaunal metazoan species. The sedaDNA analysis revealed a five-phase evolution of the area, where changes appear as the result of a multi-level cascade effect of impacts associated with industrial activities, urbanization, water circulation and land-use changes. The sedaDNA allowed to infer reference conditions that must be considered when restoration actions are to be implemented.

Trade-off between sex and growth in diatoms: Molecular mechanisms and demographic implications.

Diatoms are fast-growing and winning competitors in aquatic environments, possibly due to optimized growth performance. However, their life cycles are complex, heteromorphic, and not fully understood. Here, we report on the fine control of cell growth and physiology during the sexual phase of the marine diatom Pseudo-nitzschia multistriata. We found that mating, under nutrient replete conditions, induces a prolonged growth arrest in parental cells. Transcriptomic analyses revealed down-regulation of genes related to major metabolic functions from the early phases of mating. Single-cell photophysiology also pinpointed an inhibition of photosynthesis and storage lipids accumulated in the arrested population, especially in gametes and zygotes. Numerical simulations revealed that growth arrest affects the balance between parental cells and their siblings, possibly favoring the new generation. Thus, in addition to resources availability, life cycle traits contribute to shaping the species ecological niches and must be considered to describe and understand the structure of plankton communities.

Molecular characterization of extrahepatic cholangiocarcinoma: perihilar and distal tumors display divergent genomic and transcriptomic profiles.

BACKGROUND: Extrahepatic cholangiocarcinoma (ECC) is classified into two subtypes based on anatomic origin: distal extrahepatic (DECC) and perihilar (PHCC) cholangiocarcinoma. This study aimed to shed light on its genomic and transcriptomic profiles. RESEARCH DESIGN AND METHODS: The genomic alterations of 99 ECC (47 PHCC and 52 DECC) were investigated by next-generation sequencing of 96 genes. A subgroup of cases, representative of each subtype, was further investigated using transcriptomic analysis. Bioinformatics tools were applied for clustering and pathway analysis and defining the immune composition of the tumor microenvironment. RESULTS: PHCC had more frequent KRAS mutations (p = 0.0047), whereas TP53 mutations were more common in DECC (p = 0.006). Potentially actionable alterations included high-tumor mutational burden and/or microsatellite instability (7.1%), PI3KCA mutations (8.1%), and MYC (10.1%) and ERBB2 amplification (5.1%). The transcriptomic profiles showed the presence of three distinct clusters, which followed the anatomic origin and differed in immune microenvironment. DECC appeared to contain two distinct tumor subgroups, one enriched for druggable alterations and one lacking actionable opportunities. CONCLUSIONS: This study provides new insights into the molecular landscape and the actionable alterations of ECC. Our findings represent a step toward improved ECC molecular taxonomy and therapeutic strategies for precision oncology.

New alleles in the mating type determination region of West Atlantic strains of Pseudo-nitzschia multistriata.

The cosmopolitan, species-rich diatom genus Pseudo-nitzschia represents a good system for the study of speciation, evolution and diversity. Understanding elements linked to population dynamics and life cycle regulation for these species is of particular importance in view of their ability to produce the toxin domoic acid and cause harmful blooms. Pseudo-nitzschia multistriata, one of the toxic species that represents a model for the study of life cycle related questions, is the only diatom for which a sex determination mechanism has been described. Populations in the Gulf of Naples (Mediterranean Sea), can share four different allelic variants (A, M, B, N) of the mating type determination region, and one of them (A) is responsible for the determination of the mating type + (MT+), defined by the MT+ restricted expression of the gene MRP3. Here, we analysed the sex determination genomic region in three new strains isolated from the Gulf of Mexico and compared it to the alleles previously described in the Mediterranean strains. We first show that these geographically distant strains of P. multistriata belong to different populations but can interbreed. Next, we show that the two populations share an overall similar structure of the genomic locus although differences can be seen in the polymorphic regions upstream of MRP3. In strain P4-C1, we amplified and sequenced an allele (M) identical to one of those previously characterized in the Mediterranean strains. In the other two strains, P4-C2 and P4-C5, we identified three new alleles, which we named A2, B2 and N2. P4-C2 and P4-C5 are heterozygous and share the common allele A2 linked to the monoallelic expression of the MT+ specific sex determining gene MRP3. Our results expand information on the global distribution of P. multistriata and on the level of conservation of the sex determination region in different populations. The definition of the extent of intra- and inter-specific conservation of this region would be a relevant addition to our understanding of Pseudo-nitzschia diversity and evolution.

Toxic marine microalgae and noxious blooms in the Mediterranean Sea: A contribution to the Global HAB Status Report.

We review the spatial distribution of toxic marine microalgal species and the impacts of all types of harmful algal events (Harmful Algal Blooms, HABs) in the Mediterranean Sea (MS), including the Black Sea, the Sea of Marmara, coastal lagoons and transitional waters, based on two databases compiled in the Ocean Biogeographic Information System (OBIS). Eighty-four potentially toxic species have been detected in the MS (2,350 records), of which 16 described from these waters between 1860 and 2014 and a few suspected to have been introduced. More than half of these species (46) produce toxins that may affect human health, the remainders ichthyotoxic substances (29) or other types of toxins (9). Nevertheless, toxicity-related events are not frequent in the MS (308 records in 31 years), and mainly consist of impacts on aquaculture, caused by the dinoflagellates Dinophysis and Alexandrium, along with a few actual shellfish poisoning cases. Pseudo-nitzschia blooms are widespread, but domoic acid in shellfish rarely exceeds regulatory levels. Fish kills are probably less sporadic than reported, representing a problem at a few places along the southern MS coasts and in the Ebro River Delta. Since the last decade of the 20th century, blooms of the benthic dinoflagellates Ostreopsis cf. ovata have regularly occurred all along rocky shores of the MS, at times with human health problems caused by toxic aerosol. New records of Gambierdiscus and Fukuyoa, until now reported for the westernmost and easternmost MS coasts, raise concerns about the risk of ciguatera, a syndrome so far known only for subtropical and tropical areas. Recent discoveries are the dinoflagellates Vulcanodinium rugosum, responsible for the presence of pinnatoxins in French lagoons' shellfish, and the azaspiracid-producers Azadinium spp. Mucilages and discolorations have a major impact on tourism in summer. Reports of toxic species and HABs have apparently increased in the MS over the last half century, which is likely related to the increased awareness and monitoring operations rather than to an actual increase of these phenomena. Indeed, while the case of Ostreopsis appears as a sudden upsurge rather than a trend, no actual increase of toxic or noxious events has so far emerged in intensively studied areas, such as the French and Spanish coasts or the Adriatic Sea. Moreover, some cases of decrease are reported, e.g., for Alexandrium minutum blooms disappearing from the Harbour of Alexandria. Overall, main HAB risks derive from cases of massive development of microalgal biomass and consequent impacts of reduced coastal water quality on tourism, which represents the largest part of the marine economy along the MS coasts.

Virus-induced spore formation as a defense mechanism in marine diatoms.

Algal viruses are important contributors to carbon cycling, recycling nutrients and organic material through host lysis. Although viral infection has been described as a primary mechanism of phytoplankton mortality, little is known about host defense responses. We show that viral infection of the bloom-forming, planktonic diatom Chaetoceros socialis induces the mass formation of resting spores, a heavily silicified life cycle stage associated with carbon export due to rapid sinking. Although viral RNA was detected within spores, mature virions were not observed. 'Infected' spores were capable of germinating, but did not propagate or transmit infectious viruses. These results demonstrate that diatom spore formation is an effective defense strategy against viral-mediated mortality. They provide a possible mechanistic link between viral infection, bloom termination, and mass carbon export events and highlight an unappreciated role of viruses in regulating diatom life cycle transitions and ecological success.

Morphological and phylogenetic data do not support the split of Alexandrium into four genera.

A recently published study analyzed the phylogenetic relationship between the genera Centrodinium and Alexandrium, confirming an earlier publication showing the genus Alexandrium as paraphyletic. This most recent manuscript retained the genus Alexandrium, introduced a new genus Episemicolon, resurrected two genera, Gessnerium and Protogonyaulax, and stated that: "The polyphyly [sic] of Alexandrium is solved with the split into four genera". However, these reintroduced taxa were not based on monophyletic groups. Therefore this work, if accepted, would result in replacing a single paraphyletic taxon with several non-monophyletic ones. The morphological data presented for genus characterization also do not convincingly support taxa delimitations. The combination of weak molecular phylogenetics and the lack of diagnostic traits (i.e., autapomorphies) render the applicability of the concept of limited use. The proposal to split the genus Alexandrium on the basis of our current knowledge is rejected herein. The aim here is not to present an alternative analysis and revision, but to maintain Alexandrium. A better constructed and more phylogenetically accurate revision can and should wait until more complete evidence becomes available and there is a strong reason to revise the genus Alexandrium. The reasons are explained in detail by a review of the available molecular and morphological data for species of the genera Alexandrium and Centrodinium. In addition, cyst morphology and chemotaxonomy are discussed, and the need for integrative taxonomy is highlighted.

Species detection and delineation in the marine planktonic diatoms Chaetoceros and Bacteriastrum through metabarcoding: making biological sense of haplotype diversity.

High-throughput sequencing (HTS) metabarcoding is commonly applied to assess phytoplankton diversity. Usually, haplotypes are grouped into operational taxonomic units (OTUs) through clustering, whereby the resulting number of OTUs depends on chosen similarity thresholds. We applied, instead, a phylogenetic approach to infer taxa among 18S rDNA V4-metabarcode haplotypes gathered from 48 time-series samples using the marine planktonic diatoms Chaetoceros and Bacteriastrum as test case. The 73 recovered taxa comprised both solitary haplotypes and polytomies, the latter composed each of a highly abundant, dominant haplotype and one to several minor, peripheral haplotypes. The solitary and dominant haplotypes usually matched reference sequences, enabling species assignation of taxa. We hypothesise that the super-abundance of reads in dominant haplotypes results from the homogenization effect of concerted evolution. Reads of populous peripheral haplotypes and dominant haplotypes show comparable distribution patterns over the sample dates, suggesting that they are part of the same population. Many taxa revealed marked seasonality, with closely related ones generally showing distinct periodicity, whereas others occur year-round. Phylogenies inferred from metabarcode haplotypes enable delineation of biologically meaningful taxa, whereas OTUs resulting from clustering algorithms often deviate markedly from such taxa.

Effects of small-scale turbulence on two species of Dinophysis.

Dinoflagellate species of Dinophysis, in particular D. acuminata and D. acuta, produce lipophilic toxins that pose a threat to human health when concentrated in shellfish and jeopardize shellfish exploitations in western Europe. In northwestern Iberia, D. acuminata has a long growing season, from spring to early autumn, and populations develop as soon as shallow stratification forms when the upwelling season begins. In contrast, D. acuta blooms in late summer, when the depth of the pycnocline is maximal and upwelling pulses are moderate. In situ observations on the hydrodynamic regimes during the two windows of opportunity for Dinophysis species led us to hypothesize that D. acuta should be more sensitive to turbulence than D. acuminata. To test this hypothesis, we studied the response of D. acuminata and D. acuta to three realistic turbulence levels low (LT), ε ≈ 10-6 m2 s-3; medium (MT), ε ≈ 10-5 m2 s-3 and high (HT), ε ≈ 10-4 m2 s-3generated by Turbogen, a highly reproducible, computer-controlled system. Cells of both species exposed to LT and MT grew at rates similar to the controls. Marked differences were found in the response to HT: D. acuminata grew slowly after an initial lag phase, whereas D. acuta cell numbers declined. Results from this study support the hypothesis that turbulence may play a role in shaping the spatio-temporal distribution of individual species of Dinophysis. We also hypothesize that, in addition to cell disturbance affecting division, sustained high shear generated by microturbulence may cause a decline in Dinophysis numbers due to decreased densities of ciliate prey.

Correction to: Identification of the meiotic toolkit in diatoms and exploration of meiosis-specific SPO11 and RAD51 homologs in the sexual species Pseudo-nitzschia multistriata and Seminavis robusta.

Following the publication of this article [1], the authors reported that the link to Additional file 11 linked to the wrong set of data. The correct supplementary data is provided in this Correction article (Additional file 11).

Exploring Molecular Signs of Sex in the Marine Diatom Skeletonema marinoi.

Sexual reproduction plays a fundamental role in diatom life cycles. It contributes to increasing genetic diversity through meiotic recombination and also represents the phase where large-sized cells are produced to counteract the cell size reduction process that characterizes these microalgae. With the aim to identify genes linked to the sexual phase of the centric planktonic diatom Skeletonemamarinoi, we carried out an RNA-seq experiment comparing the expression level of transcripts in sexualized cells with that of large cells not competent for sex. A set of genes involved in meiosis were found upregulated. Despite the fact that flagellate gametes were observed in the sample, we did not detect the expression of genes involved in the synthesis of flagella that were upregulated during sexual reproduction in another centric diatom. A comparison with the set of genes changing during the first phases of sexual reproduction of the pennate diatom Pseudo-nitzschiamultistriata revealed the existence of commonalities, including the strong upregulation of genes with an unknown function that we named Sex Induced Genes (SIG). Our results further broadened the panel of genes that can be used as a marker for sexual reproduction of diatoms, crucial for the interpretation of metatranscriptomic datasets.

Diatom diversity through HTS-metabarcoding in coastal European seas.

Diatoms constitute a diverse lineage of unicellular organisms abundant and ecologically important in aquatic ecosystems. Compared to other protists, their biology and taxonomy are well-studied, offering the opportunity to combine traditional approaches and new technologies. We examined a dataset of diatom 18S rRNA- and rDNA- (V4 region) reads from different plankton size-fractions and sediments from six European coastal marine sites, with the aim of identifying peculiarities and commonalities with respect to the whole protistan community. Almost all metabarcodes (99.6%) were assigned to known genera (121) and species (236), the most abundant of which were those already known from classic studies and coincided with those seen in light microscopy. rDNA and rRNA showed comparable patterns for the dominant taxa, but rRNA revealed a much higher diversity particularly in the sediment communities. Peculiar to diatoms is a tight bentho-pelagic coupling, with many benthic or planktonic species colonizing both water column and sediments and the dominance of planktonic species in both habitats. Overall metabarcoding results reflected the marked specificity of diatoms compared to other protistan groups in terms of morphological and ecological characteristics, at the same time confirming their great potential in the description of protist communities.