Phenazine oxidation by a distal electrode modulates biofilm morphogenesis

Microbes living in biofilms, dense assemblages of cells, experience limitation for resources such as oxygen when cellular consumption outpaces diffusion. The pathogenic bacterium Pseudomonas aeruginosa has strategies for coping with hypoxia that support cellular redox balancing in biofilms; these include (1) increasing access to oxygen by forming wrinkles in the biofilm surface and (2) electrochemically reducing endogenous compounds called phenazines, which can shuttle electrons to oxidants available at a distance. Phenazine-mediated extracellular electron transfer (EET) has been shown to support survival for P. aeruginosa cells in anoxic liquid cultures, but the physiological relevance of EET over a distance for P. aeruginosa biofilms has remained unconfirmed. Here, we use a custom-built electrochemistry setup to show that phenazine-mediated electron transfer at a distance inhibits wrinkle formation in P. aeruginosa biofilms. This result demonstrates that phenazine-dependent EET to a distal oxidant affects biofilm morphogenesis.