Genetic investigation of Babesia parasites in Japan

2023 Fiscal Year Final Research Report

• Project/Area Number: 18K06398
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 45030:Biodiversity and systematics-related
• Research Institution: National Institute of Infectious Diseases
• Principal Investigator: Niikura Aya 国立感染症研究所, 安全管理研究センター, 主任研究官 (10392325)
• Project Period (FY): 2018-04-01 – 2024-03-31
• Keywords: Babesia

Outline of Final Research Achievements

We analyzed the genomes of three strains of Babesia microti (Hobetsu, US, and Kobe), which were isolated from field mice and transmitted by different vectors ticks in Japan. The sister species, B. rodhaini, was included in this study. The number of chromosomes was the same as that of the previously reported smallest apicomplexan, B. microti RI strain (6.5 Mb). However, their sizes differed greatly, with a 13.5% gap (6.0 Mb minimum). Gene prediction revealed the presence of tiny introns (19-25 nt), which were scattered throughout the genome. There were differences in size distribution among the strains. This study reveals for the first time the genomic diversity of the B. microti group.

Free Research Field

獣医学

Academic Significance and Societal Importance of the Research Achievements

Babesia microtiは約6億年前に　ピロプラズマ目（赤血球に感染し、ダニが媒介する寄生虫）の他の原虫よりも早く共通祖先から分化した。日本で分離された複数のB. microtiゲノム解析から、そのサイズが約6.0Mbとアピコンプレックス門最小であること、僅かな真核生物種でしか見つかっていない～25ntの極小イントロンがゲノム全体に散在していること、特有のミトコンドリア構造をもつこと、これらは系統間で多様であることなどが明らかとなった。さらに解析を進めることで、原虫が効率の良い代謝・増殖能力を獲得し、環境変化に柔軟に適応してきたプロセスを、ゲノム進化から解明できる可能性が見えてきた。