報告書番号

V05031

タイトル（和文）

電気による微生物の制御（その9） -―キノン化合物を用いた微生物の電気培養―-

タイトル（英文）

Electrochemical control of microorganisms (Part 9) -Electrochemical cultivation of bacteria using a quinine compound.-

概要 （図表や脚注は「報告書全文」に掲載しております）

地下土壌環境中に生息する難培養性微生物の獲得と土壌中での微生物の生育環境を明らかにするために、土壌中に豊富に存在するキノン化合物を用いた電気培養を実施した。環境微生物を含む土壌試料を、水溶性のキノン化合物であるアントラキノンを含む培養液中で、水素ガスを充填した嫌気状態で２週間培養した結果、キノンの還元に伴う複数種の微生物の増殖が確認された。この微生物群に対し、キノンの酸化反応が生じる+0.1V(vs. Ag/AgCl)の電位で水素ガス嫌気環境で５日間電気培養を実施したところ、通常の7倍に当たる4×10^8cells/mLの高密度菌体を得ることができた。さらにこの中から、2種類のキノン還元活性を有する微生物株が単離され、いずれも新種の可能性が示された。嫌気度に対するそれぞれの微生物の性質の違いから、一方は微好気環境を、他方は絶対嫌気的環境を好み棲み分けしていると考えられた。

概要 （英文）

Subterranean microorganisms affect several geochemical factors such as redox potential because of their activities. Therefore, understanding the behavior of these microorganisms is crucial for evaluating the condition of the subterranean regions for industrial use. However, over 90% of those microorganisms are categorized as "unculturable," and hence, we have been unable to elucidate the subterranean biochemical effects. Recently, soil materials containing quinone groups such as humic acid have been considered as energy transporters for subterranean microorganisms. Hence, we attempted to detect quinone reducing microorganisms in environmental samples and cultivate these microorganisms using electrochemical methods. To obtain quinone reducing microorganisms from the environment, batch cultivation was performed under anaerobic conditions using hydrogen gas with 0.2 mM anthraquinone disulfonate (AQDS). After two weeks of cultivation, cell growth was obtained along with AQDS reduction. Growth of more than two strains of microorganisms was obtained, and the cultivation of these microorganisms was carried out to isolate the AQDS reducing microorganisms. Electrochemical cultivation of these microorganisms was performed under anaerobic conditions in order to accumulate the AQDS reducing microorganisms. The subcultured cell suspension was inoculated into an electrochemical chamber and a current of +0.1 V (vs Ag/AgCl) was applied under the anaerobic condition in the presence of hydrogen gas. The cell density after electrochemical cultivation with 5-day electrolysis reached 4×10^8 cells/mL, and this cell density was 7 times higher than that obtained during normal batch cultivation. This was the first attempt at electrochemical cultivation using an organic compound as an electrochemical mediator instead of metal elements. Plate cultivations were performed to isolate the strains of AQDS reducing microorganisms. Two types of microorganisms were isolated from a colony and these strains were identified as Desulfitobacter sp. and Enterobacter sp. The Desulfitobacter group includes dechlorination bacteria, and these are usually obligate anaerobes. On the other hand, the Enterobacter group includes intestinal bacteria, and these are usually facultative anaerobes. From these results, it is suggested that the two strains segregate their habitat in response to oxygen concentration.

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