Identification of Clostridium cochlearium as an electroactive microorganism from the mouse gut microbiome.

Microbial electroactivity, the metabolically relevant transfer of electrons between microorganisms and solid conductors, was first discovered for now well characterized model organisms from hypoxic or anaerobic water or sediment samples. Recent findings indicate that the metabolic trait of electroactivity might as well be important within the microbiome of the mammalian gut. Based on a pre-selection from the mouse intestinal bacterial collection five microorganisms originating from diverse parts of the gut were screened for electroactivity. As there is no marker gene for electroactivity, the ability to synthesize cytochromes and metabolize redox-mediators was studied in-silico. Clostridium cochlearium showed highest electroactivity and Lactobacillus reuteri as well as Staphylococcus xylosus show putative electroactivity, as well. The maximum current density of C. cochlearium of 0.53 ± 0.02 mA cm after only 5.2 h of incubation was clearly linked to growth and glucose consumption. Cyclic voltammetric analysis on C. cochlearium revealed a formal potential of the extracellular electron transfer (EET) site of +0.22 ± 0.05 V versus Ag/AgCl sat. KCl (and + 0.42 V versus SHE) and indicates that EET is not based on biofilm formation, but the involvement of either redox-active molecules or planktonic cells. The potential of the gut as habitat for electroactives and their physiological role are discussed.