Isolation and characterization of alkaliphilic and thermotolerant bacteria that reduce insoluble indigo to soluble leuco-indigo from indigo dye vat

Abstract

Indigo dye has been used in the textile dye industry for long period. Insoluble indigo are reduced to soluble leuco-indigo before dying textiles. A traditional process for solubilization of indigo using microbial reduction metabolism has been considered as environmentally benign method and as alternative to faster chemical reactions. Thus, fermentation liquor aged for 6 years with Polygonum tinctorium (indigo plant) extracts was used to isolate bacteria able to reduce insoluble indigo. Two bacterial isolates, A1 and G5, showed indigo-reducing activity, and were identified as Alkalibacterium sp. and Pseudomonas sp. respectively, with 99% sequence similarity by 16S rDNA sequence analyses. Based on the concentrations of leuco-indigo reduced from indigo, Alkalibacterium sp. A1 and Pseudomonas sp. G5 showed alkaliphilic and thermotolerant charactertistics, optimally functioning at pH 10.0 and 50°C. Isolation of alkaliphilic and thermotolerant bacterial strains, which can reduce insoluble indigo into leuco-indigo, from Korean traditional fermentation liquor could provide a biological tool to enhance efficiency in the traditional indigo dye by an environmentally friendly manner.