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

Abstract

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 outermembrane 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.

Recent advances in the roles of minerals for enhanced microbial extracellular electron transfer

“…For instance, Ye et al [131] revealed that high methane production rates comparable to that of plants or algae when using an innovative biohybrid system consisting of CdS NPs and Methanosarcina barkeri. Similarly, rapid light-driven decolorization of methyl orange was achieved by a G. sulfurreducens-CdS NPs biohybrid [132]. The highest maximum kinetic rate constant (1.441 h − 1 ) was the highest reported in the literature for methyl orange biodecolorization.…”

“…Considering that c-Cyts are critical for electron transfer [16,129], the accessibility of c-Cyts for photoelectron transfer requires more careful consideration and experimental investigation. In recent studies by Zhou et al [130][131][132][133], markedly higher transcription levels for c-Cyts in G. sulfurreducens and functional ferredoxin-dependent hydrogenase in Methanosarcina barkeri (M. barkeri) were all found in response to illuminated cultured systems. This suggests that a c-Cyts-mediated mechanism was also important in the photoelectron transfer pathway in a majority of electrogenesis strains.…”

“…Due to interactions between enhanced electrical conductivity and mineral photoelectrons, the produced synergistic effects are conducive to nonphototrophic microorganisms that gain light energy through semiconductive CdS NPs, thereby improving the ICP-MR performance in biohybrids. Outer membrane-bound cytochromes of engineered biohybrids were shown to participate in photoelectron transport by acting as the terminal reductase [131][132][133], indicating good biocompatibility of CdS NPs for biohybrid construction. Thus, biohybrids constructed through in situ grafting of nanosized semiconductive mineral Table 3 Selected applications of illuminated engineered biohybrids by superficial precipitation of semiconductive minerals onto nonphototrophic microorganisms.…”

Material–Microbe Interfaces for Solar-Driven CO2 Bioelectrosynthesis

“…In the same year, a living quantum dot (QD) bacterial hybrid was constructed through the self-assembly of biocompatible QD and specific enzymes inside the living cells [62]. See [30][31][32]41,[52][53][54][55][56]63,68,70]. efficiency in CO 2 photoreduction is to combine inorganic and biological systems as hybrid systems.…”

“…Further, they found a synergistic effect where the photocatalytic efficiency of the G. sulfurreducens-CdS biohybrid is higher than CdS and microbe alone. The efficient electron transfers from CdS to G. sulfurreducens through a key membrane protein OmcB, (a family of cytochrome c) are found to be the reason for efficient azo dye degradation [63].…”