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Recently, hybrid structures of microorganisms with inorganic nanoscale moieties have received great interest due to their potential in fabricating electronic systems. Electronic properties of metal nanoparticles, due to single electron transport of current, make them ideal material for nanodevices. Concomitantly, the nanostructure of microorganisms such as bacteria, viruses[3;4] and yeast are attractive scaffolds for nanoparticle templating due to surface charge and biological affinities for specific molecules [2-7]. However, the key challenges in building hybrid devices are patterning nanostructures without destroying the biological construct of the microorganism and achieving active integration of biological response to the electrical transport in nanoparticle device. Here we present a simple method to build hybrid devices that use biological response of the microorganism to control the electrical properties of the system. In our design, a monolayer of gold nanoparticles is deposited on the peptidoglycan membrane of a live gram-positive bacterium. The hydrophilic peptidoglycan membrane is then actuated by humidity, to modulate the electron tunnelling barrier width between the metallic nanoparticles. A decrease in inter-particle separation by < 0.2 nm (for humidity excursion from 20% to ~0%) causes a > 40-fold increase in tunnelling current. Vapour sensors based on the increase in resistance due to separation of Au nanoparticles have been reported in three-dimensional (3D) clusters of Au nanoparticle/organic composite films[8-10]. In this study, the coupling between large expansion of an underlying hygroscopic bacterium membrane and the Au particle monolayer is the key to achieving an order of magnitude larger change in current compared to the above-mentioned 3D nanocomposite devices where the change is due to the swelling of an inter-particle organic phase. The method shown here could be used to pattern various nano-scale inorganics, whose optical, electrical and magnetic properties could be biologically controlled, bringing a prominent advancement in the present technology.