Mechanistic Insights into Indigo Reduction in Indigo Fermentation: A Voltammetric Study

• Main Authors: Kasumi NAKAGAWA, Michiki TAKEUCHI, Mayu KIKUCHI, Suzuna KIYOFUJI, Masami KUGO, Takaiku SAKAMOTO, Kenji KANO, Jun OGAWA, Eiji SAKURADANI
• Format: Article
• Language: English
• Published: The Electrochemical Society of Japan 2021-01-01
• Series: Electrochemistry
• Subjects: indigo reduction mechanism; acetaldehyde; bioelectrocatalysis; mediator
• Online Access: https://www.jstage.jst.go.jp/article/electrochemistry/89/1/89_20-00123/_pdf/-char/en

Indigo is one of the oldest natural blue dyes. Microorganisms and their enzymatic activities are deeply involved in the traditional indigo staining procedure. To elucidate the mechanism of the microbial indigo reduction, we directly performed cyclic voltammetry on alkaline fermenting dye suspensions. A pair of characteristic redox peaks of leuco-indigo was observed in a supernatant fluid of the fermenting dye suspension. On the other hand, it was found that the indigo/leuco-indigo redox couple mediated two-way microbially catalyzed oxidation and reduction in a sediment-rich suspension of the fermenting suspension. Acetaldehyde was supposed to be the electron donor and acceptor of the catalytic reactions. In order to verify the bioelectrocatalytic reaction, we isolated indigo-reducing bacterium K2-3′ from the fermenting suspension, and the two-way bioelectrocatalysis was successfully restaged in a model system containing K2-3′ and methyl viologen (as a soluble mediator instead of indigo) as well as acetaldehyde at pH 10.