Reductive decolorization of indigo carmine dye with Bacillus sp. MZS10

• The bacterium Bacillus sp. MZS10 effectively decolorizes indigo carmine dye.
• Reductive decolorization of indigo carmine was firstly proposed in this work.
• Indoline sulfonic acid was one of indigo carmine decolorization metabolites.

Decolorization of indigo carmine (IC) dye with strain Bacillus sp. MZS10 and its mechanism was evaluated in the present study. The decolorization ratio of 87.31  ±  2.04% was achieved after cultivation of IC (0.1 g L−1) with Bacillus sp. MZS10 for 15 h in a 5 L stirred-tank fermenter. In the process of decolorization, metabolites derived from IC decolorization were analyzed by ultraviolet–visible spectroscopy, mass spectroscopy, and Fourier transform infrared spectroscopy, respectively. Based on the analyses of metabolites, a novel mechanism of decolorization of IC was suggested as follows: the CC and CO bonds of IC were broken and –CH bonds were generated via a reductive process. Then an indoline derivative, indoline sulfonic acid was produced during biotransformation of IC. Decolorization efficiency and mechanism shown by the strain provides insight on its potential application for the bioremediation of IC and production of indoline derivative.