Bio-bleaching of Dyed Cotton Fabric Using a Bacterial Catalyst

Abstract

Anaerobically grown cells of Shewanella strain J18 143 were able to bio-bleach the color from cotton fabric that was dyed with Remazol Black B (C.I. Reactive Black 5), a common diazo reactive dye. This bio-bleaching process, involving a bacterial catalyst, offers potential benefits to the color industry as the removal of color from dyed fabric opens up the potential for fabric re-use. Growing cells removed the color with greater efficiency than that achieved using pre-grown “resting” cells. Assays of resting cells were used to determine the effect of cell concentration and depth of shade of the dyeing on the color removal process. Further resting cell assays were carried out to ascertain if an electron donor was required for the color removal process, and suggested that the cotton substrate could supply some reducing power to the biocatalyst, although dye reduction rates were maximal with added electron donor (formate). The Shewanella cells were also able to remove the color from dyed cotton fabric that was isolated inside a dialysis membrane to prevent contact with the cells. This indicates that Shewanella strain J18 143 is able to synthesize and excrete endogenous extracellular electron shuttles, eliminating the need for direct contact between the intracellular electron transport components and the extracellular terminal electron acceptors. The dyed cotton fabric was assessed visually, and by reflectance spectroscopy and environmental scanning electron microscopy.