Electromicrobiology is a new discipline that investigates the ability of microbial species to interact with insoluble exter-nal electron acceptors and donors. This ability has most commonly been studied through microbial communities found in association with electrodes as part of a microbial electrolysis cell (MEC). MECs are devices that employ bac-teria capable of utilising either an anode as an electron acceptor or a cathode as an electron donor to carry out biologically driven processes. In effect, these devices make use of microbes that are eating and breathing electricity. Potential applications for MECs are ever expanding and currently include bioremediation, biosensing, biofuel pro-duction and power generation. MECs that produce overall net power are referred to as microbial fuel cells (MFCs) and have helped to generate much of our initial knowledge regarding electroactive bacteria. Energy consuming MECs have more recently expanded our knowledge on microbial electrosynthesis pathways, whereby microbes reduce CO 2 using electrons provided by an electrode. Furthering of our knowledge on electrode-associated microbes has in turn led us to an increased understanding of how microbes in the environment have been developing, powering and utilis-ing their own electricity grids all along. These electrical interactions, between microbes and components of their living and non-living environment, are potentially very im-portant but have been overlooked until very recently. nota notae est nota rei ipsius – in as much as chemical change being a sign of life, and electrical change a sign of chemical change, it follows that electrical change is a sign of life. Waller 1 Electron transfer from microbes to electrodes The electrical nature of living organisms was eloquently summarised in lectures by Augustus Waller in 1903 1 and the ability to use an anode to detect an electrical current in a microbial culture during the decomposition of organic compounds was demonstrated by Potter in 1911 2 . However, it was not until half a century later that this knowledge was implemented into the first reported studies using a MFC. In the past 10 years research into electric bacteria has expo-nentially expanded. Defining microbial fuel cells A MFC is typically a two-chambered system containing an anaerobic anode chamber and an oxic cathode chamber, separated by an ion permeable membrane, and is capable of utilising electrons from microbial central metabolism for a net energy gain. Electric microbes in the anode chamber utilise the anode as a final electron acceptor for the anaerobic respiration of organic electron donors such as acetate. Electrons donated to the anode flow to the cathode through electrical wires, where they are reunited with the protons generated in the anode chamber and combine with oxygen or other electron acceptors to form reduced products. The reported anodic power density has increased from initial power outputs of 0.1 W/m 2 to more recent reports of 6.9 W/m 2 of anode surface area. Despite the many improvements made to MFC electrical current produc-tion, these systems do not yet produce enough power for commer-cially viable large-scale power production applications, but are able to reduce the energy demands of wastewater treatment as well as provide small scale power outputs to power remote sensing devices. Many physical, chemical and biological discoveries remain Under the Microscope MICROBIOLOGY AUSTRALIA * 2014 10.1071/MA14065 A