2022 Fiscal Year Final Research Report
Study of the origin and evolution of symbiosis using an in-vitro synthetic ecosystem
| Project/Area Number |
20K06769
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 45020:Evolutionary biology-related
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| Research Institution | Ehime University |
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Principal Investigator |
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| Project Period (FY) |
2020-04-01 – 2023-03-31
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| Keywords | 共生 / 実験進化 / 生態系 / ゲノム / クロレラ / 大腸菌 / テトラヒメナ |
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| Outline of Final Research Achievements |
A synthetic ecosystem composed of Chlorella (Micractinium sp.), a bacterium (E. coli), and a ciliate (Tetrahymena thermophila) has been cultured for 13 years to understand the origin and evolution of symbioses. In analyzing the isolates and their co-cultures, we revealed the following processes and their mechanisms: (i) Chlorella evolved two different types: one forms cell aggregates incorporating E. coli cells, and the other enters Tetrahymena cells forming an endosymbiotic association. (ii) A filament-cell type of E. coli has evolved, not forming a symbiotic association with Chlorella. The gene that cause this phenotype was identified. (iii) E. coli isolates that require amino acids can survive and reproduce by being incorporated into a Chlorella cell aggregate. (iv) The whole genome sequences of the ancestral Chlorella and isolates from 5, 6, 8, and 13-year-old cultures were determined, and genes that can be possibly related to the cell-aggregation formation were identified.
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| Free Research Field |
進化生態学，理論生物学
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| Academic Significance and Societal Importance of the Research Achievements |
本研究は、実験合成生態系の13年間の長期培養を解析し光栄養生物(藻類)と従属栄養生物(細菌及び繊毛虫)との間の共生の進化過程をを実証的に解析したものである．このような解析は国内外で他に例がない.従来の研究が共生をすでに進化させた生物を用いた解析であるのに対し，本研究ではこのモデル生態系において構成種間に共生が起源し，進化する過程を追跡した.このモデルは、進化対象を切り取って解析するのではなく，分子，細胞，個体群，生態系過程全体を捉え，各階層間関係の中で構成種の進化を明らかにするという全く新しい手法である．この手法は還元主義的方法と全体論的方法を統合した検証可能な新しい進化研究手法となるだろう．
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