Our group has sought to design hybrid cell-based devices which combine the information-rich processing capabilities of cellular life with the robust control schemes of electronics. To do this, we have sought to manipulate the flow of information between biology and electronics through the use of reversible redox-shuttles. These mediators are capable of reversibly donating and accepting electrons between electrodes and molecules containing redox-active moieties, such as the iron-sulfur core of the SoxR transcription factor. When coupled together, these mediators can direct the flow of electrons between electron-acceptors and electron-donors based upon the Nernst potential of each mediator. We previously used this technique to electrochemically control gene expression of SoxR-mediated gene circuits by using a redox mediator to enhance the oxidative cycling of pyocyanin. In this work we have coupled this activity with an artificial melanin-mimetic polymer which contains reversible redox-activity to create a form of binary information storage which can be written to and accessed by genetically modified <i>E. coli</i>. Our group has shown that the soluble eumelanin-like polymer produced by the enzymatic oxidation of tyrosine and L-DOPA is capable of storing and donating electrons.  In this system, eumelanin can serve as an intermediary to transfer electrons between reduced pyocyanin and oxidized ferrocene. The reduced ferrocene is then capable of shuttling electrons to a positively-biased electrode where the mediator is re-oxidized, thus creating a cycle to achieve enhanced pyocyanin oxidation.  By regulating the potential applied at the electrode, we demonstrate either reductive or oxidative potential can be stored in the soluble melanin. This stored potential can then be interpreted electronically by recording the current at an oppositely biased electrode, or biologically using an electrogenetic gene-circuit based around the interaction of SoxR and pyocyanin. These two interactions serve as the basis for our bio-electronic cell-factory where we demonstrate directed information flow to both guide and measure cellular metabolism.

Design of an electronic gene-expression control scheme with the capability to store and direct information flow

2019 Spring National Meeting

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