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Abstract Redox is a unique, programmable modality capable of bridging communication between biology and electronics. Previous studies have shown that theE. coliredox-responsive OxyRS regulon can be re-wired to accept electrochemically generated hydrogen peroxide (H₂O₂) as an inducer of gene expression. Here we report that the redox-active phenolic plant signaling molecule acetosyringone (AS) can also induce gene expression from the OxyRS regulon. AS must be oxidized, however, as the reduced state present under normal conditions cannot induce gene expression. Thus, AS serves as a “pro-signaling molecule” that can be activated by its oxidation—in our case by application of oxidizing potential to an electrode. We show that the OxyRS regulon is not induced electrochemically if the imposed electrode potential is in the mid-physiological range. Electronically sliding the applied potential to either oxidative or reductive extremes induces this regulon but through different mechanisms: reduction of O₂to form H₂O₂or oxidation of AS. Fundamentally, this work reinforces the emerging concept that redox signaling depends more on molecular activities than molecular structure. From an applications perspective, the creation of an electronically programmed “pro-signal” dramatically expands the toolbox for electronic control of biological responses in microbes, including in complex environments, cell-based materials, and biomanufacturing. 

Melanins have complex structures, difficult-to-characterize properties, and poorly understood biological functions. Electrochemical methods are revealing how melanin's redox-state molecular-switching is coupled to its electron-transfer activities.