title: The kinetoplastid parasite Azumiobodo hoyamushi, the causative agent of soft tunic syndrome of the sea squirt Halocynthia roretzi, resides in the East Sea of Korea.
abstract: Mass mortality of the edible sea squirt Halocynthia roretzi since the 1990s in the southern and eastern seas of Korea has caused large economic losses. The disease is characterized by symptoms of initially softened and thinned tunics that eventually rupture. Thus, the disease is called soft tunic syndrome (STS); however, the causative agent in these regions is unknown. In the present study, two kinetoplastid organisms were isolated from STS sea squirts collected from culture farms in Tongyeong located in the East Sea of Korea. Phylogenetic analysis of 18S rRNA sequences identified these organisms as Azumiobodo hoyamushi and Procryptobia sorokini. These kinetoplastids were injected into healthy sea squirts and cultured at 15°C for 13days. Sea squirts injected with A. hoyamushi showed 100% STS whereas, P. sorokini did not induce disease, thereby confirming A. hoyamushi as the causative agent of STS. A. hoyamushi flourishes in vitro at 10-15°C, and dies at temperatures below 5°C or above 20°C. The optimum salinity level for growth is 30-35psu, and death occurs below 25psu. These optima coincide with marine temperature and salinity levels between March and June on the southern coasts of Korea, the period when the syndrome occurs at the highest frequency. The identification here of A. hoyamushi as the causative agent of STS and our findings regarding its optimum growth conditions should lead to methods for reducing the incidence of STS.
authors.affiliation: Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University, 558 Daehakno, Gunsan 573-701, Republic of Korea.
authors.forename: Hyoun-Joong
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Oceanography, Kyungpook National University, Sangju 742-711, Republic of Korea.
authors.forename: Jong Soo
authors.initials: JS
authors.lastname: Park
authors.affiliation: Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University, 558 Daehakno, Gunsan 573-701, Republic of Korea.
authors.forename: Kwan Ha
authors.initials: KH
authors.lastname: Park
authors.affiliation: National Fisheries Research and Development Institute, 216 Haean-ro, Busan 619-705, Republic of Korea.
authors.forename: Yun-Kyung
authors.initials: YK
authors.lastname: Shin
authors.affiliation: Department of Aquatic Life Medicine, College of Ocean Science and Technology, Kunsan National University, 558 Daehakno, Gunsan 573-701, Republic of Korea. Electronic address: kipark@kunsan.ac.kr.
authors.forename: Kyung-Il
authors.initials: KI
authors.lastname: Park
mesh_terms: D000818:Animals; D016830:Kinetoplastida / Q000145:classification / Q000302:isolation & purification / Q000472:pathogenicity* / Q000502:physiology; D010802:Phylogeny; D012337:RNA, Ribosomal, 18S / Q000737:chemistry; D056910:Republic of Korea; D017422:Sequence Analysis, DNA; D014561:Urochordata / Q000469:parasitology*
chemical_list: D012337:RNA, Ribosomal, 18S
keywords: Aquaculture; Azumiobodo hoyamushi; Halocynthia roretzi; Korea; Soft tunic syndrome