報告書番号

V07011

タイトル（和文）

電気による微生物の制御(その10) －電気培養技術の汎用化に向けた培養装置の開発－

タイトル（英文）

Electrochemical control of bacteria (Part 10). - Development of prototype system for electrochemical cultivation -

概要 （図表や脚注は「報告書全文」に掲載しております）

電気を用いて微生物の生育を促進する当所独自の培養法の普及を目指し、市販型電気培養装置の試作を行った。製作にあたっては、イオン交換膜にナフィオンを用いることで、多価イオン透過性及び電気抵抗性能を維持しつつ高温滅菌が可能となった。また、安価で耐食性及び加工性に優れた白金メッキチタン材を培養向けの電極として使用できることが分かった。さらに、上記のイオン交換膜及び電極を装着しうる繰り返し使用が可能な培養槽も合わせて試作した。この試作機により、培養性能の指標として用いた鉄酸化細菌を高密度まで電気で培養できた。以上、試作機の製作と性能評価により、市販型電気培養装置を提案できた。

概要 （英文）

The advantages of the electrochemical cultivation technique developed by our institute are that it allows high-density cell growth of chemoautotrophic bacteria and enables cultivation of previously uncultured bacteria. These advantages are applicable not only for understanding of environmental microorganisms living underground, but also for the screening of environmental bacteria useful for the degradation of toxic materials. In order to utilize the electrochemical cultivation technique for these purposes, it is necessary to develop a generalized model for a stable supply. However, the previous electrochemical cultivation system was not a generalized model because of following reasons. First, it could not be applied for sterilization because the ion-exchange membrane was not heat-resistant. Second, the platinum used for the electrode was expensive. Third, the system could not be reused because of its structure.
In this report we attempted to establish a generalized model of the electrochemical cultivation system by examining the materials used for the membranes and the electrodes, and design an electrode bath that can be reused.
For the heat resistant ion-exchange membrane, Nafion (N-117), which is one of the materials used in a fuel cell, was selected. The ion-exchange characteristics and electrochemical resistance ability of N-117 after sterilization were similar to the previous heat-sensitive membrane K-192. Therefore, N-117 was selected as the substitute membrane, which could be used for electrochemical cultivation and sterilization.
To find an economical and electrochemically stable material for the electrode instead of platinum, 11 types of alloys with high corrosion resistance were chosen. In addition, titanium coated with Pt by electroplating was also investigated for the purpose. All 11 types of alloys were dissolved or insulated during the 1 h of electrolysis with a constant current of 20 mA in the test electrolyte (0.1 mol/L NaCl). However, no damage was observed on the Pt-coated titanium electrode. Based on these results, the Pt-coated titanium was selected as the candidate economical electrode due to its electrochemical stability.
In order that the electrode bath be reused and sterilized, pyrex glass was selected as the material. Based on these results, the generalized electrochemical cultivation system was proposed with N-117 as the ion-exchange membrane, Pt-coated titanium as the electrode, and pyrex glass for the electrode bath.
To confirm the performance of this system, electrochemical cultivation of iron-oxidizing bacteria was conducted. During the 2 week-cultivation, the cell density of the culture grown in the electrochemical bath was 100 times higher than that grown without electrolysis.

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