Analysis of conjugation system in obligate intracellular bacteria (Rickettsia) and its application to the gene manipulation system

2020 Fiscal Year Final Research Report

• Project/Area Number: 19K22536
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 49:Pathology, infection/immunology, and related fields
• Research Institution: Kyushu University
• Principal Investigator: Hayashi Tetsuya 九州大学, 医学研究院, 教授 (10173014)
• Project Period (FY): 2019-06-28 – 2021-03-31
• Keywords: リケッチア / ゲノム解析 / プラスミド / ICE / 接合伝達 / 遺伝子改変系

Outline of Final Research Achievements

We analyzed a novel Rickettsia species (Ca, R. longicornis) and its plasmid (pRlon) to show the presence of plasmid-mediated conjugation systems in obligate intracellular bacteria, develop a gene manipulation system based on the conjugation system of pRlon, and systematically identify the Rickettsia genes essential for their growth in host cells. We found that a conjugation system different from that of pRlon is encoded by an integrative conjugative element (ICE) called Rickettsia Amplified genetic element (RAGE) in Rickettsia. However, systematic comparison of conjugation systems of all conjugation systems so far found in Rickettsia revealed that all conjugation systems, including those found in Ca. R. longicornis, contained multiple pseudogenes. This result indicates that all conjugation systems present in Rickettsia currently circulating in the world have been inactivated.

Free Research Field

細菌学分野

Academic Significance and Societal Importance of the Research Achievements

本研究では、偏性細胞内寄生菌であるリケッチアの新菌種のゲノム解析によって見出したプラスミドに着目し、これまでに報告の無い偏性細胞内寄生菌での接合による遺伝子伝達系の存在の証明、さらにこのプラスミドの接合系を利用したリケッチアでの遺伝子改変系の開発とこれを用いた増殖必須遺伝子の網羅的同定に挑戦した。染色体上のRAGEと呼ばれる遺伝因子上にも新たな接合伝達系を同定できたが、既知のリケッチアのRAGEやプラスミドと比較解析を行った結果、解析した全ての接合系には複数の偽遺伝子（失活した遺伝子）が存在することが明らかとなった。この知見は、現存するリケッチアの接合伝達系は機能を失っていることを示唆する。