DAO 115:253-262 (2015)  -  DOI: https://doi.org/10.3354/dao02897

Encystment and excystment of kinetoplastid Azumiobodo hoyamushi, causal agent of soft tunic syndrome in ascidian aquaculture

Akatsuki Nawata1, Euichi Hirose2, Shin-Ichi Kitamura3,4, Akira Kumagai5,*

1Miyagi Prefecture Fisheries Technology Institute, Ishinomaki, Miyagi 986-2135, Japan
2Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
3Department of Biology, Faculty of Science, Ehime University, Matsuyama, Ehime 790-8577, Japan
4Center for Marine Environmental Studies (CMES), Ehime University, Matsuyama, Ehime 790-8577, Japan
5Miyagi Prefecture Fisheries Technology Institute, Kesennuma Fisheries Experimental Station, Kesennuma, Miyagi 988-0181, Japan
*Corresponding author:

ABSTRACT: Soft tunic syndrome in the edible ascidian Halocynthia roretzi is caused by the kinetoplastid flagellate Azumiobodo hoyamushi, which was found to assume a fusiform cell form with 2 flagella in axenic, pure culture. When the flagellate form was incubated in sterilized artificial seawater (pH 8.4), some of the cells became cyst-like and adhered to the bottom of the culture plate. The cyst-like forms were spherical or cuboidal, and each had 2 flagella encapsulated in its cytoplasm. Encystment was also induced in culture medium alkalified to the pH of seawater (8.4) but not in unmodified (pH 7.2) or acidified media (pH 6.4). More than 95% of the cyst-like cells converted to the flagellate form within 1 d following transfer to seawater containing ascidian tunic extracts from host ascidians. The cyst-like cells were able to survive in seawater with no added nutrients for up to 2 wk at 20°C and for a few months at 5 to 15°C. The survival period in seawater depended on temperature: some cyst-like cells survived 3 mo at 10°C, and ca. 95% of these converted to flagellate forms in seawater containing tunic extracts. Thus, A. hoyamushi is able to persist under adverse conditions in a cyst-like form able to adhere to organic and inorganic substrata for protracted periods of time.

KEY WORDS: Kinetoplastid flagellate · Halocynthia roretzi · Soft tunic syndrome · Tunic extract · Temporary cyst · In vitro culture · pH

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Cite this article as: Nawata A, Hirose E, Kitamura SI, Kumagai A (2015) Encystment and excystment of kinetoplastid Azumiobodo hoyamushi, causal agent of soft tunic syndrome in ascidian aquaculture. Dis Aquat Org 115:253-262. https://doi.org/10.3354/dao02897

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