第 4 章 結論
4.2. 今後の展望
4.2.1. 産業系排水の生物処理活性の向上
第 2 章において，食品系工場排水，化学系工場排水，半導体工場排水で用いられる活性 汚泥サンプルを対象に菌叢解析およびAHL合成細菌のスクリーニングを行った．下水汚泥 と比較して微生物の構成は異なるものの，主たるAHL合成細菌はAeromonas属細菌である ことが分かった．また，本研究で分離した，新規AHL合成細菌であるAlicycliphilus 属細菌 についても，遺伝学的解析を行った結果，他種からAHL合成遺伝子を獲得している可能性 が示唆された．これらの結果は，産業系排水の生物処理における種汚泥として下水汚泥が 用いられていることと関係があるかもしれない．すなわち，産業系排水の多様な基質によ って馴養された微生物群についても，反応槽内における定着という基本的な機能について は下水汚泥の微生物群と共通な機構が働いているのではないかと推察される．このような 考えに立てば，産業系排水における AHL 合成細菌の多様性を明らかにしていくと同時に，
モデル細菌としての Aeromonas 属細菌に関するバイオフィルム形成能の機構解明を進めて いくことも重要である．産業系排水の生物処理では，下水汚泥と比較して，より負荷の変 動が大きかったり，より分解性の低い化合物が流入する場合がある．たとえば，AHL 合成 遺伝子を伝播し易い Aeromonas 属細菌の活用により，増殖の遅い硝化細菌や難分解性物質 の分解菌を早く担体に定着させることができれば，負荷の変動や流入基質の変化にいち早 く対応できるようになり，安定した処理が可能になるかもしれない．
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4.2.2. 産業系用水におけるバイオファウリング抑制
第3章において，5種の工場冷却水を対象にAHL合成細菌のスクリーニングを行った結 果，C工場とE工場ではそれぞれAeromonas属細菌とMethylobacterium属細菌に近縁な新規 AHL 合成細菌が分離され，生産する AHL の化学構造を明らかにした．しかしながら，
Aeromonas属細菌とLysobacter sp. F13株に共通なAHL合成遺伝子は確認されず，また，B.
massiliensis E9株においてもMethylobacterium属細菌と同様に多様なAHLを合成しているこ とが分かった．これらの結果から，冷却水におけるAHL合成細菌は多様性に富んでいる可 能性が考えられる．このため，個々の遺伝子を制御する方法でバイオフィルム形成を抑制 することは，非常に困難と考えられる．したがって，AHL そのものに対する作用，例えば 第1章で上げた阻害剤の添加や，AHLの不活性化といった手法のさらなる検討が期待され る．このようなAHLに対する直接的な操作が，冷却水の分野でどの程度広く利用できるか を把握するという目的に立てば，本研究で行ったAHL合成細菌のスクリーニングは今後も 継続していく価値があると言えよう．
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