Optogenetics for Control of Biofilm Deposition and Extracellular Electron Transfer in Shewanella Oneidensis MR-1

<i>Shewanella oneidensis</i> MR-1 is a model electroactive bacterium, whose extracellular electron transfer (EET) pathway includes a network of multiheme <i>c</i>-type cytochromes to route electrons from the cellular interior to external, solid electron acceptors. <i>S. oneidensis</i> MR-1 is able to form living conductive biofilms on electrode surfaces for long-distance electron transport. Optogenetics circuits combine the light-sensitive proteins and transcription factors for spatiotemporal control of gene expression within living organisms as a response to illumination with light. Here, we introduced optogenetic circuits into <i>S. oneidensis </i>to control the electron transfer with different scales. We first developed a lithographic strategy to pattern conductive biofilms of <i>S. oneidensis</i> by controlling expression of the aggregation protein CdrAB with the blue light-induced genetic circuit pDawn. This controlled deposition enabled <i>S. oneidensis</i> biofilm patterning on transparent electrode surfaces and electrochemical measurements allowed us to demonstrate tunable conduction of living biofilms dependent on pattern geometry. Next, we developed a red light-induced genetic circuit in <i>S. oneidensis</i> based on a reported iLight system. This red light-induced genetic circuit was used to control the cytochromes expression in <i>S. oneidensis</i> which allowed<i> </i>us to<i> </i>adjust the extracellular electron transfer activity of <i>S. oneidensis</i> with light. Overall, these two new genetic tools enabled the control of biofilm conduction and EET activity by light which could have implications for both studying and harnessing bioelectronics.