報告書番号

V08038

タイトル（和文）

電気による微生物の制御(その13) - 環境微生物の菌叢に与える電子メディエータと酸化還元電位の効果 -

タイトル（英文）

Electrochemical control of bacteria (Part 13).- Effect of electron mediators and redox potential on the flora of environmental microbes -

概要 （図表や脚注は「報告書全文」に掲載しております）

当所の電気培養法では、培地に電位調整のための物質(電子メディエータ)を加えるが、その種類が微生物増殖へ与える影響は検討されていない。そこで、6種類の電子メディエータを用いた培地の電位条件(-0.6V、-0.2V、+0.2V、+0.6V(vs. Ag/AgCl)、調整無し)を変え、環境微生物の培養を行った。その結果、鉄、キノン、マンガン、コバルト含有培地では電位調整により、電位調整無しに比べ微生物の増殖が促進したが、硝酸塩、亜ヒ酸塩含有培地では、電位調整の効果はみられなかった。また、菌叢解析の結果、鉄、マンガン、硝酸塩、コバルト含有培地の電位調整下で、電位調整無しと異なる微生物が集積され、マンガン含有培地の-0.6Vでは顕著な集積がみられた。電気培養で集積された微生物は、自然環境中で非優占的な微生物であった。以上の結果、電気培養では、電子メディエータの種類も微生物の増殖に影響を与えており、環境微生物を、適切な物質を電子メディエータとし、任意の電位で電気培養することで、非優先的な微生物を集積培養できる可能性が示された。

概要 （英文）

The optimal redox potential for growth may vary according to the bacterial species. Thus far, we have successfully enhanced the growth of iron-oxidizing and chromium-reducing bacteria using potential-controlled cultivation. Here, we electrochemically cultivated a consortium of environmental bacteria to understand the effect of redox potential on the microbial flora during cultivation.
A bacterial sample was collected from anaerobic sediments at the bottom of a pond. The sample was filtered to remove soil and then suspended in a culture medium based on inorganic materials. For potential-controlled electrochemical cultivation, 2 mM of Fe(III) or Mn(II) was mixed into the microbial suspension as an electron mediator.
Electrochemical cultivation was performed using a chamber containing 2 baths separated by an ion-exchange membrane. For cultivation, the bacterial suspension was poured into the electrochemical chamber. All the samples were cultured for 2 weeks in an anaerobic chamber at 30 degrees C with varied redox potential. After cultivation, the microbial floras in each sample were analyzed by density gradient gel electrophoresis (DGGE).
Potential-controlled cultivation at +0.2 V with Fe(III) and at --0.6V with Mn(II) yielded remarkable bands on a DGGE image. The organisms from the former and latter bands were identified as members of the genera Bacillus and Rhizobium, respectively. Since some Bacillus spp. are known to reduce iron, it was suggested that the growth of the bacteria cultured at +0.2 V with Fe(III) was enhanced by using Fe(III) generated on the electrode at +0.2 V. The growth of some Rhizobium spp. is known to be affected by the presence of Mn(II). Thus, the Mn(II) generated on the electrode at --0.6 V might have also affected the growth of the bacteria in our experiment.
Specific bacteria that could not be grown under conventional conditions could be cultured by potential-controlled cultivation. This technique is thought to be effective for finding previously unknown bacteria in the environment.

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