Synthetic biology tools to create electroactive biofilms*

Many bacterial species are naturally capable of extracellular electron transfer, leading to long-distance electron transport and the formation of electrically conductive biofilms. Shewanella oneidensis is one such exoelectrogenic organism, which uses a network of multiheme c-type cytochromes to transfer electrons from the cellular interior to external surfaces, including adjacent cells. Synthetic biology tools to manipulate such exoelectrogens are largely lacking, especially when compared to the toolbox available for more traditional laboratory strains. To address this need, we have adapted several synthetic biology constructs to enable light-induced gene expression within the bacteria Shewanella oneidensis. Light was used to regulate the expression of genes involved in cell-cell adhesion and biofilm formation. An adhesion protein native to another species of bacteria was identified that led to light-controlled patterning of biofilms. Such biofilms were thicker and more uniform than wildtype biofilms formed by S. oneidensis and exhibited extracellular redox activity similar to the wildtype strain. Using these tools, conductive biofilms could be patterned on surfaces with controlled geometry and placement. The engineered strains were used to characterize the intrinsic conductivity of living S. oneidensis biofilms and demonstrate new applications involving the precise placement of electrically active biofilms on electronic devices.