Carbon quantum dot-induced bio-hybrid of Shewanella oneidensis MR-1 for enhanced extracellular hexavalent chromium reduction

The extracellular hexavalent chromium (Cr(VI)) reduction and stabilization capabilities of Shewanella oneidensis MR-1 have garnered significant scientific interest due to their ability to bypass intracellular limitations. Herein, we demonstrated that the extracellular deposition of reductive species of Cr(VI) dynamically encapsulated bacterial cells and prevent the further reduction of Cr(VI) by S. oneidensis MR-1 with a limited Cr(VI) reduction efficiency of <50%. Carbon quantum dots (CQDs) supplementation triggered a 25-fold nanowire proliferation and a 2.6-fold elevation in extracellular riboflavin concentration, driving bacterial aggregation into conductive biohybrid. The conductive biohybrids circumvented the chromium-derived “shell barrier” through transcellular bulk electron transfer. Furthermore, CQDs augmented the anaerobic metabolism of lactate by S. oneidensis MR-1, boosting electron generation and increasing electron flux toward Cr(VI) reduction. Our findings elucidate the mechanistic role of CQDs in enhancing the biological transformation process of insoluble minerals, offering a transformative strategy for optimizing Cr(VI) bioremediation.