Electrotrophs and Electricigens; Key Players in Microbial Electrophysiology

A wide range of microbes belonging to all three domains of life is known to generate electrical current and transfer electrons to anodes within a bioelectrochemical system. Typically these exoelectrogens are iron-reducing bacteria (e.g., Geobacter sulfurreducens) that are capable of producing high power density at moderate temperatures. Under nutrient sufficient conditions, other microbes ranging from extremophiles to yeasts can also produce high current densities. On the other hand, electrotrophic microbes grow on electrons derived from the cathode, but such microbes are less diverse and have uncommon traits. Electrotrophs shows low current densities (well below representative exoelectrogens) and utilizes several terminal electron acceptors for cell respiration. Thus, there is a vast diversity of electroactive microbes and their cultivation conditions that opens-up a new avenue for electrochemical devices particularly for H and CH production. The microbial fuel cell has been considered as an eco-friendly technology to harvest electricity harvesting from a variety of carbonaceous substrates. Here, microorganisms can be used as biocatalysts. This chapter provides an introduction to the currently identified electricigens, their taxonomical groups, and electricity-producing abilities. The mechanism of electron transfer from electricigens to electrodes is also discussed.