Enrichment of Novel Electroactive Bacteria from Equatorial Climate Sediments Via Potentiostatic Growth and Subsequent Characterisation Via Metagenomics, Metatranscriptomics, Voltammetry and Electrochemical Impedance Spectroscopy

Electrochemically-active microorganisms couple the degradation of organic matter to the production of electricity via extracellular electron transfer. They are usually enriched from sediments via growth at certain potentials, either in microbial fuel cells or in potentiostat-controlled electrochemical cells. Despite the great microbial diversity of sediments from natural and man-made environments, most electrochemical enrichments select a small group of dissimilatory metal-reducing microorganisms.

In this study, we aim to enrich novel electrochemically-active strains in sediments from various equatorial environments. Sediment inocula from urban waterways and mangroves were tested in long-term enrichment experiments at controlled anodic potentials. In addition to the conventional voltamperometric characterisation, the biofilm formed at the working electrode was subjected to electrochemical impedance spectroscopy (EIS) over a wide range of potentials. EIS of the biofilms revealed several charge transfer routes at different potentials and with different characteristic times. Furthermore, EIS enabled monitoring of the long-term changes of the electroactive biofilm and quantification of the effect of biofilm accumulation on the conductivity of the biofilm/electrode interface. 

Electrochemical analysis was coupled to metagenomics and metatranscriptomics to reveal novel electrochemically-active microorganisms and to understand their charge-transfer mechanism. The understanding of the microbe/electrode interaction in the sediments will assist in controlling the dynamic of metal cycling in urban sediments. Furthermore, novel electrochemically-active microorganisms will find application in bioremediation and environmental sensing applications.