Bacterial decolorization of textile dyes is an extracellular process requiring a multicomponent electron transfer pathway

Abstract

SummaryMany studies have reported microorganisms as efficient biocatalysts for colour removal of dye‐containing industrial wastewaters. We present the first comprehensive study to identify all molecular components involved in decolorization by bacterial cells. Mutants from the model organism Shewanella oneidensis MR‐1, generated by random transposon and targeted insertional mutagenesis, were screened for defects in decolorization of an oxazine and diazo dye. We demonstrate that decolorization is an extracellular reduction process requiring a multicomponent electron transfer pathway that consists of cytoplasmic membrane, periplasmic and outer membrane components. The presence of melanin, a redox‐active molecule excreted by S. oneidensis, was shown to enhance the dye reduction rates. Menaquinones and the cytochrome CymA are the crucial cytoplasmic membrane components of the pathway, which then branches off via a network of periplasmic cytochromes to three outer membrane cytochromes. The key proteins of this network are MtrA and OmcB in the periplasm and outer membrane respectively. A model of the complete dye reduction pathway is proposed in which the dye molecules are reduced by the outer membrane cytochromes either directly or indirectly via melanin.

The Escherichia coli Azoreductase AzoR Is Involved in Resistance to Thiol-Specific Stress Caused by Electrophilic Quinones

“…Similar results were obtained in the study of an azoR homolog from Shewanella oneidensis (6). In conclusion, the well-studied azoreductase AzoR has no contribution to dye reduction in vivo and is actually a quinone reductase playing a role in protection against thiol-specific stress.…”

Bacterial diversity and composition in major fresh produce growing soils affected by physiochemical properties and geographic locations

“…This implies that the dye decolorization process is mainly dependent on oxygen concentration, not on microbial biomass. Similarly, the process is also very much dependent on the availability and nature of electron donors (Brige et al, 2008;Hong et al, 2008;Modi et al, 2010). Most of the anaerobic reduction processes are location specific but can take place both in cytoplasmic and membrane fractions isolated from bacterial cells (Kudlich et al, 1997).…”

Bioaugmentation of Azo Dyes

“…This hypothesis is supported by the findings that microbial excreted or artificial redox mediators catalyze the dye decolorization process [105,106,108]. [81] (continued) Recently, Brigé et al [109] demonstrated that dye decolorization is an extracellular reduction process requiring a multicomponent electron transfer pathway that consists of cytoplasmic membrane, periplasmic, and outer membrane components. Similarly, we have demonstrated the ability of bacteria to remove the color of azo dyes from solid agar medium, which suggested the accumulation of redox active enzymes or biochemical substances that were released into the medium during growth of the bacterial cells [40].…”