報告書番号

U01052

タイトル（和文）

電気による微生物の制御（その６） -－嫌気鉄呼吸を適用した自然界からの新規微生物検索－-

タイトル（英文）

Electrochemical control of bacteria (6). Cell screening from natural samples using anaerobic electrochemical cultivation.

概要 （図表や脚注は「報告書全文」に掲載しております）

自然界に存在する微生物の中で、従来法では培養が不可能だった種類について、多くの微生物に潜在するといわれる太古の呼吸形態である嫌気鉄呼吸を導入した電気培養で増殖させる事を試みた。初めに自然界の多くの試料に嫌気的電気培養を適用するため、鉄(III)錯体を用いた中性pH環境下での電気培養法を検討した。本条件下で太古の細菌、好熱性水素細菌を供試した結果、通常の培養の10倍濃度の菌体増殖が確認でき、汎用的な電気培養法が提示できた。次に３種の環境試料（下水処理場流入水、湖沼底泥、地底軟岩）に対し同手法による嫌気的電気培養を実施した。7日から10日間培養した結果、通常の嫌気培養に比べ4倍から100倍濃度の菌が得られた。これらのDNA配列による遺伝子解析を行った結果、合計6種類の微生物が同定された。この中には培養に成功していない難培養微生物も含まれており、本法による新種微生物増殖の有効性が確認された。

概要 （英文）

Although huge kinds of bacteria exist in natural environment, only few of them can be cultivated artificially. One of the reasons at present cultivation is that an enriched medium is used to cultivate bacterium and, therefore, only the species that could adopt such conditions would dominantly grow. To develop a new cultivation technique for those un-cultured species will provide another possibility of bio-remediation or bio-production. We have succeeded an electrochemical cultivation of bacteria under anaerobic condition with Fe(III), which is known as ancient respiration way for livings. It was expected new species of bacteria grow by applying the electrochemical cultivation with iron respiration to environmental samples. Since previous electrochemical cultivation was taken place under low pH condition which allows iron ions dissolve into the medium easily, it can not introduce directly to the most of natural samples because these pH is neutral. First, we then developed a method for electrochemical cultivation under a normal pH condition. To make Fe(III) ions solve in normal pH solution, EDTA was introduced. As an model cultivation of anaerobic electrochemical cultivation under medium pH, we used Hydrogenobacter thermophyrus, which is well known as an ancient bacterium closed to the common ancestor. After 6 days cultivation, the density increased to 8.2 x 10^8 cells/mL, which corresponded to 10-fold high density of normal anaerobic cultivation. This result indicated a possibility of the anaerobic electrochemical cultivation for universal usage. Next, we applied the anaerobic electrochemical cultivation under normal pH to three kinds of natural samples. Those are taken from water at municipal sewage center, sludge precipitated bottom of the lake, and a core sample collected under deep ground. After 7 to 10 cultivation of those samples with the same technique mentioned above, growth of bacteria was observed in each samples, and reached to 4 to 10-fold high density of normal anaerobic cultivation. From a 16S rDNA sequence to those newly cultivated bacteria, six species were identified and five of them were new species. Furthermore, one difficult-culture species was included in them. Thus, the effectiveness of this method to a screening of new species in natural samples was indicated.

報告者

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