Effect of Fermentation Scale on Microbiota Dynamics and Metabolic Functions for Indigo Reduction

Area of Science:

• Microbiology
• Biotechnology
• Textile Chemistry

Background:

• Indigo dyeing fermentation relies on microbial reduction of indigo particles under anaerobic, alkaline conditions.
• Optimizing the microbial community in sukumo (composted indigo plant) is crucial for efficient indigo reduction via extracellular electron transfer (EET).

Purpose of the Study:

• To analyze microbiota convergence mechanisms for indigo reduction.
• To understand the microbial physiological basis for indigo reduction.
• To investigate microbiota dynamics and redox potential (ORP) changes at different fermentation scales.

Main Methods:

• Analysis of microbiota composition and convergence under varying fermentation scales.
• Functional analysis of microbiota involved in indigo reduction.
• Genomic identification of extracellular electron transfer (EET) related genes in *Alkalibacterium pelagium*.

Main Results:

• A rapid ORP decrease was achieved in large-scale fermentation, favoring *Alkalibacterium* and excluding *Actinomycetota*.
• Carbohydrate metabolism, prokaryotic defense systems, and gene regulatory functions were identified as important for strong indigo reduction.
• Genes for FAD transportation, NADH to FMN electron transfer, and DMK synthesis were found in *Alkalibacterium pelagium*, linked to EET.

Conclusions:

• Environmental factor adjustment can guide microbiota towards efficient indigo reduction.
• *Alkalibacterium pelagium* plays a significant role in indigo reduction through identified EET gene sets.
• Metabolic functions, including V/A-type H+/Na+-transporting ATPase and NAD(P)H-producing enzymes, drive the EET system in indigo fermentation.