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Diseases of Aquatic Organisms

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DAO 129:207-214 (2018)  -  DOI: https://doi.org/10.3354/dao03253

Tunic extract of the host ascidian attracts the causal agent of soft tunic syndrome, Azumiobodo hoyamushi (Kinetoplastea: Neobodonida)

Akatsuki Nawata1,5,*, Euichi Hirose2, Shin-Ichi Kitamura3,4

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
3Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan
4Center for Marine Environmental Studies, Ehime University, Matsuyama, Ehime 790-8577, Japan
5Present address: Department of Agriculture, Forestry and Fisheries, Miyagi Prefectural Government, Sendai, Miyagi 980-8570, Japan
*Corresponding author:

ABSTRACT: Azumiobodo hoyamushi, a kinetoplastid flagellate, is the causative agent of soft tunic syndrome, an infectious disease of the edible ascidian Halocynthia roretzi. The flagellate is thought to invade the tunic matrix via a damaged area of the tunic on the siphon wall. We hypothesized that the flagellate locates the tunic entry site by a chemotactic response to soluble substances diffused from the host ascidians. To investigate this hypothesis, we examined whether the flagellate shows a chemotactic response to tissue extracts (tunic and other tissues) from the host ascidian H. roretzi. We tested extracts from 5 tissues as well as hemolymph. Only the tunic extract showed significant positive chemotactic activity, and the activity decreased with increasing dilution. Furthermore, autoclaved tunic extract, extracts from diseased individuals, and extract from the styelid ascidian Styela clava also had chemotactic activity, although the activities were lower than that of tunic extract from healthy H. roretzi. Ultrafiltration of the tunic extract through a 3 kDa cutoff membrane completely abrogated the activity; the ultrafiltration retentate still showed activity. Thus, the soluble factors that attract the flagellate are present exclusively in the tunic extract, and the chemotactic factors are larger than 3 kDa. Our experiments also suggested that the tunic extract contains both heat-stable and heat-labile factors. We conclude that the flagellate locates the tunic entry site by chemotaxis toward soluble factors that diffuse from a damaged area of the tunic on the siphon wall.


KEY WORDS: Chemotaxis · Halocynthia roretzi · Kinetoplastid flagellate · Tunic extract


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Cite this article as: Nawata A, Hirose E, Kitamura SI (2018) Tunic extract of the host ascidian attracts the causal agent of soft tunic syndrome, Azumiobodo hoyamushi (Kinetoplastea: Neobodonida). Dis Aquat Org 129:207-214. https://doi.org/10.3354/dao03253

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