Fast Light-Driven Biodecolorization by a Geobacter sulfurreducens–CdS Biohybrid

Conventional biodecolorization of azo dyes is often limited by the lack of sustainable and bioavailable electron donors in aqueous environments. This limitation may be overcome by light-excited photoelectrons that drive the microbial reduction of azo dyes. Here, we innovatively developed a surface-precipitated Geobacter sulfurreducens–CdS biohybrid for the bioreduction of methyl orange (MO), a typical azo dye, driven by light. This biohybrid system exhibited the maximum kinetic constant at 1.441 h–1, which is, to the best of our knowledge, the highest value reported thus far for MO biodecolorization. The intermittent illumination results indicated that G. sulfurreducens could directly use extracellular photoelectrons (rather than electrons from organics oxidization by strains) in order to perform decolorization on the bacterial cell surface. This can be attributed to the direct electron transfer from CdS nanoparticles to G. sulfurreducens. In addition, OmcB was identified as a key outer-membrane protein that may act as a capacitor to modulate electron transfer from CdS to MO. This biohybrid catalytic approach may serve as a new strategy for azo dye degradation in oligotrophic surface waters and can deepen our knowledge on interactions between light, semiconductors and micro-organisms.