Detailed morphological documentation in LM and SEM is provided for Proschkinia taxa, including the generitype P. bulnheimii and P. complanata, P. complanatula, P. complanatoides and P. hyalosirella, as well as six new species. All established taxa are characterized from original material from historical collections. The new species described in this paper-P. luticola, P. staurospeciosa, P. impar, P. modesta, P. fistulispectabilis and P. rosowskiiwere isolated from from the Western Pacific (Yellow Sea coast of Korea) and across the Atlantic (Scottish and Texas coasts). Thorough documentation of the frustule, valve and protoplast architecture revealed the revealed the combination of characters diagnostic of the genus Proschkinia: a single lobed chloroplast, girdle composed of U-shaped, perforated bands, the position of the conopeate raphe-sternum relative to the external and internal valve surface, and the presence of an occluded process through the valve, termed the "fistula". Five strains of Proschkinia were harvested for DNA and sequenced for nuclear ribosomal SSU and plastid-encoded rbcL. Phylogenetic analysis recovered a clade of Proschkinia with Fistulifera, another fistula-bearing diatom genus, and these were sister to a clade formed of the Stauroneidaceae; in turn, all these were sister to a clade composed of Parlibellus and data from two monoraphid genera Astartiella and Schizostauron. Despite morphological similarities between Proschkinia and the Naviculaceae (Navicula, Haslea), these two taxa are distant in our analysis. We documented the morphology of Proschkinia, including variability in fistula, suggesting that fistula ultrastructure might be the key feature for species identification within the genus.
Dinoflagellates of the family Kryptoperidiniaceae, known as “dinotoms”, possess diatom-derived endosymbionts and contain individuals at three successive evolutionary stages: a transiently maintained kleptoplastic stage; a stage containing multiple permanently maintained diatom endosymbionts; and a further permanent stage containing a single diatom endosymbiont. Kleptoplastic dinotoms were discovered only recently, in Durinskia capensis; until now it has not been investigated kleptoplastic behavior and the metabolic and genetic integration of host and prey. Here, we show D. capensis is able to use various diatom species as kleptoplastids and exhibits different photosynthetic capacities depending on the diatom species. This is in contrast with the prey diatoms in their free-living stage, as there are no differences in their photosynthetic capacities. Complete photosynthesis including both the light reactions and the Calvin cycle remain active only when D. capensis feeds on its habitual associate, the “essential” diatom Nitzschia captiva. The organelles of another edible diatom, N. inconspicua, are preserved intact after ingestion by D. capensis and expresses the psbC gene of the photosynthetic light reaction, while RuBisCO gene expression is lost. Our results indicate that edible but non-essential, “supplemental” diatoms are used by D. capensis for producing ATP and NADPH, but not for carbon fixation. D. capensis has established a species-specifically designed metabolic system allowing carbon fixation to be performed only by its essential diatoms. The ability of D. capensis to ingest supplemental diatoms as kleptoplastids may be a flexible ecological strategy, to use these diatoms as “emergency supplies” while no essential diatoms are available.
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