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Diseases of Aquatic Organisms

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DAO 116:143-148 (2015)  -  DOI:

Cellulose is not degraded in the tunic of the edible ascidian Halocynthia roretzi contracting soft tunic syndrome

Satoshi Kimura1,2,*, Kei Nakayama3,*, Masahisa Wada2,4, Ung-Jin Kim2, Kaoru Azumi5,8, Takao Ojima6, Akino Nozawa3, Shin-Ichi Kitamura3,**, Euichi Hirose7,**

1Department of Biomaterial Science, Graduate School of Agricultural and Life Science, The University of Tokyo, Bunkyo, Tokyo 113-8657, Japan
2Department of Plant and Environmental New Resources, College of Life Sciences, Kyung Hee University, Seocheon-dong, Giheung-gu, Yongin-si, Gyeonggi-do 606-8502, Republic of Korea
3Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime 790-8577, Japan
4Division of Forest and Biomaterials Science, Graduate School of Agriculture, Kyoto University, Kitashirakawa-Oiwakechou, Sakyo-ku, Kyoto 606-8502, Japan
5Department of Biochemistry, Graduate School of Pharmaceutical Sciences, Hokkaido University, Sapporo, Hokkaido 060-0812, Japan
6Laboratory of Marine Biotechnology and Microbiology, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Hokkaido, Japan
7Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
8Present address: Clinical Research and Medical Innovation Center, Hokkaido University Hospital, Sapporo, Hokkaido 060-8648, Japan
*These authors contributed equally to this work**
Corresponding authors: ,

ABSTRACT: Soft tunic syndrome is a fatal disease in the edible ascidian Halocynthia roretzi, causing serious damage to ascidian aquaculture in Korea and Japan. In diseased individuals, the tunic, an integumentary extracellular matrix of ascidians, softens and eventually tears. This is an infectious disease caused by the kinetoplastid flagellate Azumiobodo hoyamushi. However, the mechanism of tunic softening remains unknown. Because cellulose fibrils are the main component of the tunic, we compared the contents and structures of cellulose in healthy and diseased tunics by means of biochemical quantification and X-ray diffractometry. Unexpectedly, the cellulose contents and structures of cellulose microfibrils were almost the same regardless of the presence or absence of the disease. Therefore, it is unlikely that thinning of the microfibrils occurred in the softened tunic, because digestion should have resulted in decreases in crystallinity index and crystallite size. Moreover, cellulase was not detected in pure cultures of A. hoyamushi in biochemical and expressed sequence tag analyses. These results indicate that cellulose degradation does not occur in the softened tunic.

KEY WORDS: Cellulose content · Cellulase · X-ray diffractometry · EST analysis · Azumiobodo hoyamushi · Ascidian aquaculture

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Cite this article as: Kimura S, Nakayama K, Wada M, Kim UJ and others (2015) Cellulose is not degraded in the tunic of the edible ascidian Halocynthia roretzi contracting soft tunic syndrome. Dis Aquat Org 116:143-148.

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