PEDOT:PSS Porous Electrodes for Probing Cohort Signaling in Escherichia Coli

Bacteria are known to coordinate gene expression to control their phenotypic characteristics to the most favourable condition in harsh environments. This smart communication mechanism enables the bacteria cells to efficiently manage the behaviour of their surrounding community. One important mediator of communication processes in bacteria is the dynamics of their membrane potential, mainly studied through single-cell patch-clamp - which is difficult due to bacteria small size, and through the use of genetic modified bacteria that produce changes in fluorescence intensity as a function of membrane polarization. Despite being a direct response to the external electric stimuli and chemical agents (such as ion channel inhibitors, stimulants or antibiotics) these fluorescence methods usually require toxic fluorescent probes hindering stress-free long-term recordings and fail to probe important sub-thresholds regimes in the measuring cell or cellular cohort.<br/>Non-invasively sensing the minuscule electrical activity of bacteria populations is therefore a major challenge in bioelectronics and microbiology. To overcome this challenge, we have devised a highly sensitive transducer based on Au/Polyurethane(PU)/poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) electrodes, to visualize the electrogenic activity of cohorts of bacteria without the need of gene modification or the use of stimuli to address intercellular communication.<br/>For the first time, the electrical activity of large <i>Escherichia coli </i>populations is directly measurable. By submerging the recording electrodes into LB broth with the model bacteria <i>E. coli </i>MG1655, we were able to sense the bacterial electrical behaviour without any physical disruption or interference into their physiology. <i>E. coli</i> demonstrated fluctuations of their basal voltage level, which is much higher in amplitude than the background acquisition noise of about 1 µV. The extracellular analysis reveals asynchronous and synchronous electrical spikes, with amplitudes ranging from 10 µV up to 100 µV, spike widths from 50 ms to 2 s and sporadic events of quasi-periodic bursts with interspike intervals mostly between 0.5 to 10 s, which can be attenuated by using a protonophore carbonyl cyanide m-chlorophenylhydrazine (CCCP).<br/>The electric noise analysis combined with compound screening indicated that the <i>E. coli</i> likely communicate through a diffusion-limited paracrine signalling mechanism where the diffusion of H⁺ plays an important role.<br/>Our ultra-sensitive transducer is a unique screening tool to study the electrophysiological properties of large bacterial populations under different pharmacological compounds effects and metabolic states contributing to more effective drug developments.