Biofilms as Bioelectric Networks. Understanding Their Response to Neural Signals

Abstract

Information processing in biological systems presupposes communication, whether with other organisms, the environment (learning and stigmergy), or one’s past or future selves (memory and prediction). How do individual cells (neurons, bacteria) use communication to build emergent complex beings like brains and colonial superorganisms? How does information within a whole, such as a vertebrate animal or biofilm, relate to the information processed by its individual components (cells)? Given that both neurons and bacteria utilize bioelectrical signals, could this serve as a mechanism for intercellular communication between these two entities? Our previous studies demonstrated that bacteria respond specifically to neurotransmitter cues. We analyzed Escherichia coli, Limosilactobacillus reuteri, and Enterococcus faecalis, key members of the human microbiota, with the latter two species capable of transitioning to pathogenic states. Neural-type stimuli altered bacterial membrane potential (Vmem) without affecting growth or viability, indicating that bacteria can depolarize or hyperpolarize in response to external signals. However, whether biofilms—structured bacterial communities with enhanced information processing capabilities—exhibit dynamic responses to neural signals remains unknown. In this study, we investigated the bioelectrical responses of bacterial biofilms to neural stimuli. Using the Vmem-sensitive fluorescent dye thioflavin T, which indicates hyperpolarization, we monitored 24-hour-old biofilms over three hours under confocal microscopy, comparing untreated biofilms to those exposed to glutamate (Glu). Our results reveal that bacterial biofilms exhibit a coordinated bioelectrical response to Glu exposure, distinct from planktonic cultures. Unlike individual bacterial cells, which respond independently, biofilms displayed a synchronized shift in Vmem upon exposure to neurotransmitters, suggesting intercellular communication within the biofilm structure. These findings suggest that biofilms, much like neural networks, utilize dynamic and synchronized bioelectrical signals to process external stimuli. This opens new avenues for understanding bacterial behavior and targeting bioelectric signaling at the interface of bacteria and neurons, particularly in systems such as the microbiota-Gut-brain axis.