Sustainable Electron Shuttling Processes Mediated by In Situ-Deposited Phenoxazine

Phenoxazine and quinone are typical electron mediators in natural and engineered systems. Although the electron shuttling process of quinone has been well studied, phenoxazine is poorly characterized. Here, a model phenoxazine (resazurin) was examined as an electron mediator in a bioelectrochemical system with Shewanella oneidensis MR-1. Results showed that the current generation was substantially enhanced by the presence of phenoxazine, and was almost unaffected even after replacing the original medium with a fresh medium without phenoxazine. This is completely different to the well-known quinones used as electron mediators. Further study suggested that, resorufin (RR), as an intermediate product, was deposited in situ onto the electrode. The RR deposition was suggested to be a dominant mechanism for stabilizing the electron shuttling efficiency by phenoxazine. This study proposed a novel electron shuttling mechanism of phenoxazine and may provide a new insight into the extracellular electron transfer.