著者

玉木 秀幸 鎌形 洋一

出版者

公益社団法人 日本農芸化学会

雑誌

化学と生物 (ISSN:0453073X)

巻号頁・発行日

vol.50, no.10, pp.730-741, 2012-10-01 (Released:2013-10-01)

参考文献数

62

被引用文献数

2

---

21世紀最初の10年は,環境微生物学・微生物生態学における第二の革命期であったと言えるだろう.言うまでもなく,それは次世代シークエンサーの登場とそれを活用した環境ゲノム解析技術の驚くべき発展によるものである.1990年代の16S rRNA遺伝子に基づいた培養に依存しない複合微生物系解析技術の誕生による第一の革命期から,大規模シークエンシング技術による環境ゲノム科学の時代を経て,今後期待される第三の革命は何であろうか.筆者らは,環境微生物の分離培養技術の革新がそれにあたるのではないか,と考えている.本稿では,環境ゲノム解析の現状を概観しつつ,この大規模シークエンス解析時代の中で少しずつ光の見えてきた未知微生物探索の現状と課題について述べる.

著者

中井 亮佑 玉木 秀幸

出版者

日本微生物生態学会

雑誌

日本微生物生態学会誌 (ISSN:24241989)

巻号頁・発行日

vol.32, no.2, pp.43-50, 2017-09-01 (Released:2017-10-27)

参考文献数

53

著者

戎崎 俊一 西原 秀典 黒川 顕 森 宙史 鎌形 洋一 玉木 秀幸 中井 亮佑 大島 拓 原 正彦 鈴木 鉄兵 丸山 茂徳

出版者

公益社団法人 東京地学協会

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.129, no.6, pp.779-804, 2020-12-25 (Released:2021-01-18)

参考文献数

94

被引用文献数

2

---

Previously proposed hypotheses on the origin of life are reviewed and it is demonstrated that none of them can provide the energy flux of ionizing radiation (UV/X/γ photons, and high-energy charged particles and neutrons) required to synthesize organic materials as demonstrated by the experiments by Miller and Urey in 1953. In order to overcome this difficulty, Ebisuzaki and Maruyama, in 2017, proposed a new hypothesis called the “Nuclear Geyser Model” of the origin of life, in which high-energy flux from a natural nuclear reactor drives chemical reactions to produce major biological molecules, such as amino acids, nucleotides, sugars, and fatty acids from raw molecules (H2O, N2, and CO2). Natural nuclear reactors were common on the surface of Hadean Earth, because the 235U/238U ratio was as high as 20%, which is much higher than the present value (0.7%), due to the shorter half-life of 235U than 238U. Ebisuzaki and Maruyama further posited that aqueous electrons and glyceraldehyde play key roles in the networks of chemical reactions in a nuclear geyser and suggested that primordial life depended on glyceraldehyde phosphate (GAP) from the nuclear geyser system as energy, carbon, and phosphate sources, pointing to a possible parallelism with the anaerobic glycolysis pathway; in particular, the lower stem path starting from GAP through Acetyl Coenzyme A to produce ATP and reduction power. It is shown that microbes (members of candidate division OD1) inhabiting high alkali hot springs, a modern analogue of the Hadean Earth environment, do not possess genes associated with conventional metabolisms, such as those of the TCA cycle, but only have genes in the lower stem path of the glycolysis. This is named the “Hadean Primordial Pathway”, because it is believed that this striking result points to a plausible origin of metabolic pathways of extant organisms. Also proposed is a step-by-step scenario of the evolution of the metabolism: 1) Chemical degradation of GAP supplied from the nuclear geyser to lactate; 2) Catalytic reactions to produce reductive power and acetyl coenzyme A (or its primitive form) and self-reproductive reactions by ribozymes on the surface of minerals (pyrite and struvite), which precipitate in a nuclear geyser (RNA world); 3) Enzymatic reactions by proteins with pyrites and the struvite in their reaction centers (RNP world); and, 4) Metabolism of extant organisms with the full assembly of enzymes produced by translating molecular machines with information stored in DNA sequences (DNA world). It is further inferred that relics of primordial metabolic evolution in the Hadean nuclear geyser can be seen at the reaction centers of enzymes of both pyrite and struvite types, nucleotide-like molecules as a cofactor of the enzymes, Calvin Cycle of photosynthesis, and chemical abundance of cytoplasm.