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Tsukubamonas globosa n. gen., n. sp., A Novel Excavate Flagellate Possibly Holding a Key for the Early Evolution in “Discoba”

Authors

  • AKINORI YABUKI,

    1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
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  • TAKESHI NAKAYAMA,

    1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
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  • NAOJI YUBUKI,

    1. Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada
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  • TETSUO HASHIMOTO,

    1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
    2. Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
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  • KEN-ICHIRO ISHIDA,

    1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
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  • YUJI INAGAKI

    1. Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan
    2. Center for Computational Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8577, Japan
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Corresponding Author: Y. Inagaki, Center for Computational Sciences and Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennoudai, Tsukuba, Ibaraki 305 8572, Japan—Telephone number: +81 29 853 6483; FAX number: +81 29 853 6406; e-mail: yuji@ccs.tsukuba.ac.jp

Abstract

ABSTRACT. We report the ultrastructure and phylogenetic position of a free-living heterotrophic flagellate, Tsukubamonas globosa n. gen., n. sp. This flagellate was isolated from a pond in the University of Tsukuba, Japan. Under light microscopy, the spherical vegetative cells were naked and highly vacuolated, and always swam with rotating motion. Electron microscopic observations revealed that T. globosa possessed a ventral feeding groove, which is one of the hallmark characteristics of the supergroup Excavata. The position of T. globosa was unresolved in the small subunit ribosomal RNA phylogeny. On the other hand, a multigene phylogeny using α-tubulin, β-tubulin, actin, heat shock protein 90, and translation elongation factor 2 robustly united T. globosa with members of the “Discoba” clade of Excavata, composed of jakobids, euglenozoans, and heteroloboseans, although the precise position of T. globosa in this clade remained unresolved. Our detailed morphological comparisons elucidated that T. globosa possessed a novel set of morphological features, and could not be classified into any taxa in the Discoba clade. Instead we classified T. globosa into Tsukubamonadidae n. fam. under Tsukubamonadida n. ord.

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