Living Electronics: Microbial Metabolism as Batteries, Resistors, and Capacitors

Conventional electronics owe their reliability to materials engineered to ignore their surroundings; living systems owe their resilience to materials that respond to them. Here we integrate three biohybrid circuit elements on paper, assigning distinct microbial species to energy generation, light‐responsive charge transport, and electrochemical charge storage. A biobattery switches on only when dormant Bacillus subtilis spores are fed and germinate; a bioresistor's value is set by the color and intensity of light striking a photosynthetic Synechocystis biofilm; and a biocapacitor stores charge in the redox chemistry of respiring Shewanella oneidensis . Co‐printed on a single sheet of paper, they form an environment‐responsive living circuit—battery, resistor, and capacitor—governed by biological activity rather than fixed material constants. Germination raises the biobattery's peak power more than 30‐fold; colored light sweeps the resistance from 96.7 to 6.4 kΩ; and electrode spacing tunes a 0.762–2.173 mF charge store—so that light, acting through living matter alone, programs how fast the circuit charges. Remarkably, this circuit of cells charges reproducibly under designable RC rules, recasting a photosynthetic action spectrum as an engineering transfer function. The result is a printable, disposable route to electronics powered, regulated, and stored by life itself.