Search

271 p., La mayoría de los eucariotas son organismos unicelulares (protistas), muchos de ellos pertenecientes a linajes que divergieron temprano en la historia evolutiva de este Dominio de organismos nucleados. Microscópicos, enormemente diversos y fenotípicamente convergentes, su clasificación cladística ha sido históricamente compleja, dejando atrás un extenso registro de taxones y de términos parafiléticos y polifiléticos. Teniendo que investigar atributos estructurales, celulares, biológicos y ecológicos en un mundo de rápidas interacciones y difícilmente accesible a simple vista, la protistología es particularmente dependiente de la sistemática. Ésta permite inferir rasgos de especies crípticas a partir de especies evolutivamente relacionadas.Las moléculas de ADN (y ARN), representan un "registro" preciso de estos eventos de diversificación, que preceden incluso a los más antiguos registros fósiles. En los últimos años, la maduración de los métodos de filogenia molecular, catalizados por una mayor accesibilidad a la secuenciación de próxima generación (NGS), está permitiendo resolver preguntas e hipótesis sobre la evolución y la especiación de estos organismos micro-eucariotas que no se habían podido responder mediante otros métodos. Por una parte, arboles filogenéticos construidos mediante concatenaciones de cientos, incluso miles de genes, están permitiendo rastrear la historia evolutiva de los linajes protistas hasta el último ancestro común de todos los eucariotas (LECA). Concomitantemente, análisis moleculares basados en genes e incluso fragmentos cortos (especialmente 18S rRNA), recuperados principalmente de matrices ambientales u orgánicas (eDNA o ADN ambiental), están revelando una ¿caja de Pandora¿ de diversidad micro-eucariota. Ésta diversidad ¿oculta¿ está transformando nuestra percepción de los protistas en la cadena trófica y la estructura ecológica. En el medio marino, sus papeles como autótrofos, heterótrofos (predadores, saprófitos, parásitos) o mixótrof

Agapollen is a traditional heliothermic marine oyster lagoon in western Norway, representing the northernmost site of any Marteilia sp. protists detected in Europe. The semi-closed lagoon is a unique site to study the life cycle and development of M. pararefringens in naive mussels. Two baskets with uninfected mussels were deployed in the lagoon outlet in May and October 2018, respectively, and sampled every 6 wk. The parasite was first detected in the mussels by PCR in early July and by histology in late August. By then, M. pararefringens had developed into mature stages, indicating a rapid development during mid-summer. Sporulation occurred during autumn. Mussels deployed in October never became infected, indicating that transmission was restricted to the warmest period of the year. Pronounced pathology was observed in infected mussels, including degenerated digestive tubules and infiltration of haemocytes. Mussel mortality was observed in the baskets, but whether this was due to infections of M. pararefringens or other environmental factors could not be determined. Plankton samples from the lagoon were also collected for PCR analysis. These samples, dominated by copepods, were positive for M. pararefringens in summer. In sorted samples, M pararefringens was detected in the Acartia spp. and Paracartia grani fractions between July and October. These plankton copepods are therefore potentially involved in the life cycle of M. pararefringens.

This study provides a morphological, ultrastructural, and phylogenetic characterization of a novel micro-eukaryotic parasite (2.3–2.6 µm) infecting amphipod genera Echinogammarus and Orchestia. Longitudinal studies across two years revealed that infection prevalence peaked in late April and May, reaching 64% in Echinogammarus sp. and 15% in Orchestia sp., but was seldom detected during the rest of the year. The parasite infected predominantly hemolymph, connective tissue, tegument, and gonad, although hepatopancreas and nervous tissue were affected in heavier infections, eliciting melanization and granuloma formation. Cell division occurred inside walled parasitic cysts, often within host hemocytes, resulting in hemolymph congestion. Small subunit (18S) rRNA gene phylogenies including related environmental sequences placed the novel parasite as a highly divergent lineage within Class Filasterea, which together with Choanoflagellatea represent the closest protistan relatives of Metazoa. We describe the new parasite as Txikispora philomaios n. sp. n. g., the first confirmed parasitic filasterean lineage, which otherwise comprises four free-living flagellates and a rarely observed endosymbiont of snails. Lineage-specific PCR probing of other hosts and surrounding environments only detected T. philomaios in the platyhelminth Procerodes sp. We expand the known diversity of Filasterea by targeted searches of metagenomic datasets, resulting in 13 previously unknown lineages from environmental samples.

271 p., La mayoría de los eucariotas son organismos unicelulares (protistas), muchos de ellos pertenecientes a linajes que divergieron temprano en la historia evolutiva de este Dominio de organismos nucleados. Microscópicos, enormemente diversos y fenotípicamente convergentes, su clasificación cladística ha sido históricamente compleja, dejando atrás un extenso registro de taxones y de términos parafiléticos y polifiléticos. Teniendo que investigar atributos estructurales, celulares, biológicos y ecológicos en un mundo de rápidas interacciones y difícilmente accesible a simple vista, la protistología es particularmente dependiente de la sistemática. Ésta permite inferir rasgos de especies crípticas a partir de especies evolutivamente relacionadas.Las moléculas de ADN (y ARN), representan un "registro" preciso de estos eventos de diversificación, que preceden incluso a los más antiguos registros fósiles. En los últimos años, la maduración de los métodos de filogenia molecular, catalizados por una mayor accesibilidad a la secuenciación de próxima generación (NGS), está permitiendo resolver preguntas e hipótesis sobre la evolución y la especiación de estos organismos micro-eucariotas que no se habían podido responder mediante otros métodos. Por una parte, arboles filogenéticos construidos mediante concatenaciones de cientos, incluso miles de genes, están permitiendo rastrear la historia evolutiva de los linajes protistas hasta el último ancestro común de todos los eucariotas (LECA). Concomitantemente, análisis moleculares basados en genes e incluso fragmentos cortos (especialmente 18S rRNA), recuperados principalmente de matrices ambientales u orgánicas (eDNA o ADN ambiental), están revelando una ¿caja de Pandora¿ de diversidad micro-eucariota. Ésta diversidad ¿oculta¿ está transformando nuestra percepción de los protistas en la cadena trófica y la estructura ecológica. En el medio marino, sus papeles como autótrofos, heterótrofos (predadores, saprófitos, parásitos) o mixótrof

Intracellular microcolonies of bacteria (IMC), in some cases developing large extracellular cysts (bacterial aggregates), infecting primarily gill and digestive gland, have been historically reported in a wide diversity of economically important mollusk species worldwide, sometimes associated with severe lesions and mass mortality events. As an effort to characterize those organisms, traditionally named as Rickettsia or Chlamydia-like organisms, 1950 specimens comprising 22 mollusk species were collected over 10 countries and after histology examination, a selection of 99 samples involving 20 species were subjected to 16S rRNA gene amplicon sequencing. Phylogenetic analysis showed Endozoicomonadaceae sequences in all the mollusk species analyzed. Geographical differences in the distribution of Operational Taxonomic Units (OTUs) and a particular OTU associated with pathology in king scallop (OTU_2) were observed. The presence of Endozoicomonadaceae sequences in the IMC was visually confirmed by in situ hybridization (ISH) in eight selected samples. Sequencing data also indicated other symbiotic bacteria. Subsequent phylogenetic analysis of those OTUs revealed a novel microbial diversity associated with molluskan IMC infection distributed among different taxa, including the phylum Spirochetes, the families Anaplasmataceae and Simkaniaceae, the genera Mycoplasma and Francisella, and sulfur-oxidizing endosymbionts. Sequences like Francisella halioticida/philomiragia and Candidatus Brownia rhizoecola were also obtained, however, in the absence of ISH studies, the association between those organisms and the IMCs were not confirmed. The sequences identified in this study will allow for further molecular characterization of the microbial community associated with IMC infection in marine mollusks and their correlation with severity of the lesions to clarify their role as endosymbionts, commensals or true pathogens.

Intracellular microcolonies of bacteria (IMC), in some cases developing large extracellular cysts (bacterial aggregates), infecting primarily gill and digestive gland, have been historically reported in a wide diversity of economically important mollusk species worldwide, sometimes associated with severe lesions and mass mortality events. As an effort to characterize those organisms, traditionally named as Rickettsia or Chlamydia-like organisms, 1950 specimens comprising 22 mollusk species were collected over 10 countries and after histology examination, a selection of 99 samples involving 20 species were subjected to 16S rRNA gene amplicon sequencing. Phylogenetic analysis showed Endozoicomonadaceae sequences in all the mollusk species analyzed. Geographical differences in the distribution of Operational Taxonomic Units (OTUs) and a particular OTU associated with pathology in king scallop (OTU_2) were observed. The presence of Endozoicomonadaceae sequences in the IMC was visually confirmed by in situ hybridization (ISH) in eight selected samples. Sequencing data also indicated other symbiotic bacteria. Subsequent phylogenetic analysis of those OTUs revealed a novel microbial diversity associated with molluskan IMC infection distributed among different taxa, including the phylum Spirochetes, the families Anaplasmataceae and Simkaniaceae, the genera Mycoplasma and Francisella, and sulfur-oxidizing endosymbionts. Sequences like Francisella halioticida/philomiragia and Candidatus Brownia rhizoecola were also obtained, however, in the absence of ISH studies, the association between those organisms and the IMCs were not confirmed. The sequences identified in this study will allow for further molecular characterization of the microbial community associated with IMC infection in marine mollusks and their correlation with severity of the lesions to clarify their role as endosymbionts, commensals or true pathogens.