Publications by authors named "Yuichiro Kashiyama"

Chlorophylls (Chls) are ubiquitous photosynthetic pigments with inherent potential to generate cytotoxic reactive oxygen species. Therefore, all phototrophs and any phagotrophs that attempt to digest phototrophic cells have presumably developed mechanisms to mitigate this phototoxicity. In aquatic environments, the Chls produced by the dominant producers, microalgae, are catabolized into nonphototoxic pigments, cyclopheophorbide enols (CPEs), either by microalga-feeding protists or autonomously, particularly by those carrying secondary chloroplasts during the dismantling of their chloroplasts.

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While photoautotrophic organisms utilize inorganic nitrogen as the nitrogen source, heterotrophic organisms utilize organic nitrogen and thus do not generally have an inorganic nitrogen assimilation pathway. Here, we focused on the nitrogen metabolism of Rapaza viridis, a unicellular eukaryote exhibiting kleptoplasty. Although belonging to the lineage of essentially heterotrophic flagellates, R.

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Green photosynthetic bacteria, one of the phototrophs, have the largest and most efficient light-harvesting antenna systems, called chlorosomes. The core part of chlorosomes consists of unique bacteriochlorophyll // molecules. In the biosynthetic pathway of these molecules, a BciC enzyme catalyzes the removal of the C13-methoxycarbonyl group of chlorophyllide .

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Kleptoplasts (kP) are distinct among photosynthetic organelles in eukaryotes (i.e., plastids) because they are routinely sequestered from prey algal cells and function only temporarily in the new host cell.

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Secondary loss of photosynthesis is observed across almost all plastid-bearing branches of the eukaryotic tree of life. However, genome-based insights into the transition from a phototroph into a secondary heterotroph have so far only been revealed for parasitic species. Free-living organisms can yield unique insights into the evolutionary consequence of the loss of photosynthesis, as the parasitic lifestyle requires specific adaptations to host environments.

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Euglena gracilis produces ATP in the anaerobic mitochondria with concomitant wax ester formation, and NADH is essential for ATP formation and fatty acid synthesis in the mitochondria. This study demonstrated that mitochondrial cofactor conversion by nicotinamide nucleotide transhydrogenase (NNT), converting NADPH/NAD to NADP /NADH, is indispensable for sustaining anaerobic metabolism. Silencing of NNT genes significantly decreased wax ester production and cellular viability during anaerobiosis but had no such marked effects under aerobic conditions.

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Production of valuable compounds including biofuels and pharmaceutical precursors derived from microalgae has garnered significant interest. Stable production of algal biomass is essential to make the microalgal industry commercially feasible. However, one of the largest issues is severe biological contamination by predators grazing the algal biomass, resulting in the crash of outdoor cultures.

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Microbial rhodopsins, comprising a protein moiety (rhodopsin apoprotein) bound to the light-absorbing chromophore retinal, function as ion pumps, ion channels, or light sensors. However, recent genomic and metagenomic surveys showed that some rhodopsin-possessing prokaryotes lack the known genes for retinal biosynthesis. Since rhodopsin apoproteins cannot absorb light energy, rhodopsins produced by prokaryotic strains lacking genes for retinal biosynthesis are hypothesized to be non-functional in cells.

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Article Synopsis
  • - The study investigates non-photosynthetic plastids in green algae, specifically a strain of Chlamydomonas, which retains some components of electron transport systems despite lacking photosynthesis-related structures.
  • - Researchers found that this alga has retained the ability to synthesize carotenoids and plastoquinol, but not chlorophyll, and identified key genes involved in electron transport and redox homeostasis.
  • - The findings suggest that the electron sink system, crucial for managing excess electrons, is more widespread in non-photosynthetic plastids across various algal and plant species than previously understood.
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Article Synopsis
  • The order Trypanosomatida, known for its pathogenicity and unique mitochondrion biology, contains four distinct DNA polymerases localized within its mitochondria.
  • These polymerases (PolIA, PolIB, PolIC, and PolID) are evolutionarily different from other known DNA polymerases found in other organisms, like humans and plants.
  • This study identifies various types of mitochondrion-localized DNA polymerases across three major classes of Euglenozoa, revealing specific patterns of presence and evolution among PolIA-D in Kinetoplastea, Diplonemea, and Euglenida.
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Compound-specific isotope analyses of geoporphyrins, which are derivatives of chloropigments possessed by phototrophs, provide essential records of the biogeochemical cycle of past aquatic environments. Here, we evaluated uncertainties in carbon and nitrogen isotopic compositions (δC and δN) associated with high-performance liquid chromatography (HPLC) purification and isotopic measurements of geoporphyrins. Evaluation of total blank carbon and nitrogen for the HPLC and our sensitivity-improved elemental analyzer/isotope ratio mass spectrometer (nano-EA/IRMS) analysis confirmed that blank carbon can be corrected and that blank nitrogen is negligible compared to the mass of geoporphyrins required for the isotopic measurement.

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Loss of photosynthesis is a recurring theme in eukaryotic evolution. In organisms that have lost the ability to photosynthesize, nonphotosynthetic plastids are retained because they play essential roles in processes other than photosynthesis. The unicellular algal genus Cryptomonas contains both photosynthetic and nonphotosynthetic members, the latter having lost the ability to photosynthesize on at least three separate occasions.

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Article Synopsis
  • Eukaryotic ecology mainly relies on oxygenic photosynthesis, driven by chlorophylls, which can be both beneficial for energy harvesting and harmful due to reactive oxygen species.
  • The research shows that a widespread process called chlorophyll catabolism converts chlorophylls into non-toxic forms (CPEs) among various microeukaryotes, except for Archaeplastida.
  • This catabolism likely evolved in algivorous microeukaryotes to detoxify chlorophylls and played a crucial role in photosynthetic endosymbiosis, enabling the diversification of eukaryotes following increased oxygen levels in the environment.
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For photosynthetic organisms that nourish the earth's biosphere, chlorophylls (Chls) are the major pigments utilized for light harvesting and primary charge separation. Although Chl molecules are effective photosensitizers, they are inevitably phototoxic to living organisms due to the facile generation of highly oxidative singlet oxygen (O) through triplet energy transfer from their photoexcited states to oxygen molecules. Such phototoxicity of Chls is a major problem for translucent microbes that feed on photosynthetic algae.

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Article Synopsis
  • Divinyl-13,17-cyclopheophorbide-a enol is a compound produced both naturally by protists and synthetically in the lab from a derivative of divinyl-chlorophyll-a.
  • Analysis using H NMR spectroscopy revealed that this compound primarily exists in its enol form in solution.
  • The process of intramolecular cyclization at specific positions altered the compound's optical properties, leading to a lack of fluorescent emission from the enol form.
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The evolution of mitochondria and plastids from bacterial endosymbionts were key events in the origin and diversification of eukaryotic cells. Although the ancient nature of these organelles makes it difficult to understand the earliest events that led to their establishment, the study of eukaryotic cells with recently evolved obligate endosymbiotic bacteria has the potential to provide important insight into the transformation of endosymbionts into organelles. Diatoms belonging to the family Rhopalodiaceae and their endosymbionts of cyanobacterial origin (i.

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Both 13(2),17(3)-cyclopheophorbide a and b enols were produced along with ingestion of green microalgae containing chlorophylls a and b by a centrohelid protist (phycophagy). The results suggest that chlorophyll b as well as chlorophyll a were directly degraded to colored yet non-phototoxic catabolites in the protistan phycophagic process. Such a simple process by the predators makes a contrast to the much sophisticated chlorophyll degradation process of land plants and some algae, where phototoxicity of chlorophylls was cancelled through the multiple enzymatic steps resulting in colorless and non-phototoxic catabolites.

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Chlorophylls are essential components of the photosynthetic apparati that sustain all of the life forms that ultimately depend on solar energy. However, a drawback of the extraordinary photosensitizing efficiency of certain chlorophyll species is their ability to generate harmful singlet oxygen. Recent studies have clarified the catabolic processes involved in the detoxification of chlorophylls in land plants, but little is understood about these strategies in aquatic ecosystem.

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We have established a procedure for removing interfering materials from extracts of geological and biological samples, in order to determine precise compound-specific nitrogen isotopic compositions of amino acids. We employed cation-exchange chromatography of protein and non-protein amino acids prior to derivatization for gas chromatographic separation. The average recovery of a standard amino acid solution was better than 94%, without nitrogen isotope fractionation during the cation-exchange chromatography.

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We describe an improved method for purification of sedimentary vanadyl and nickel porphyrins (i.e., naturally occurring metalloalkylporphyrins).

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