Electric wiring of bacteria using redox polymers and selective measurement of metabolic activity in the presence of surrounding planktonic bacteria.

Non-electroactive bacteria (n-EAB), constituting the majority of known bacteria to date, have been underutilized in electrochemical conversion technologies due to their lack of direct electron transfer to electrodes. In this study, we established an electric wiring between n-EAB (gram-positive Bacillus subtilis and gram-negative Escherichia coli) and an extracellular electrode via a ferrocene-polyethyleneimine-based redox polymer (Fc-PEI). Chronoamperometry recordings indicated that Fc-PEI can transfer intracellular electrons to the extracellular electrode regardless of the molecular organization of PEI (linear or branched) and the membrane structure of bacteria (gram-positive or -negative). As fluorescence staining suggested, Fc-PEI improves the permeability of the bacterial cell membrane, enabling electron carriers in the cell to react with Fc. In addition, experiments with Fc-immobilized electrodes without PEI suggested the existence of an alternative electron transfer pathway from B. subtilis to the extracellular Fc adsorbed onto the cell membrane. Furthermore, we proposed for the first time that the bacteria/Fc-linear PEI modified structure enables selective measurement of immobilized bacterial activity by physically blocking contact between the electrode surface and planktonic cells co-existing in the surrounding media. Such electrodes can be a powerful analytical tool for elucidating the metabolic activities of specific bacteria wired to the electrode even within complex bacterial communities.

Minimally invasive current-controlled electrical stimulation system for bacteria using highly capacitive conducting polymer-modified electrodes.

This paper proposes a minimally invasive current-controlled electric stimulation system based on a poly(3,4-ethylenedioxythiophene) (PEDOT)-modified electrode to characterize the dynamics of the membrane potential in Bacillus subtilis. A highly capacitive PEDOT-modified electrode enabled the injection of a large ionic charge to the surface of the cells suppressing cytotoxic pH change in the vicinity of the electrode. The current pulse induced a hyperpolarization response in B. subtilis around the electrode. Using quantitative charge injection through current-controlled electrical stimulation, the threshold charge density to excite B. subtilis was roughly estimated to be 530.8 µC cm-2 (of electrode surface area) for the first time. Our results provide the minimum electrical stimulation conditions necessary to minimal invasively control the bacterial membrane potential.