Thermodynamics of interspecies electron transfer: from syntrophy to parasitism

Abstract : Interspecies Electron Transfer (IET) is a mechanism that allows energetic coupling between two microorganisms. It plays a key role in a wide range of environmental and biotechnological microbial ecosystems and stimulation of Direct Interspecies Electron Transfer (DIET) appears as an attractive way to boost anaerobic digestion. However, studies dealing with IET have, so far, mostly restrained on the possible syntrophic interactions supported by this mechanism. In the present work, the case of a fermentative bacterium receiving extracellular electrons while fermenting a substrate is considered. By applying microbial thermodynamics to experimental data previously published, we show that IET can promote a wide range of interactions such as mutualism, commensalism or parasitism. In the case of glycerol fermentation IET indeed leads to a diminution of bacterial biomass production concomitantly with an increased production of reduced compounds such as 1,3-propanediol. Thus, our study indicates that IET probably plays an important role nowadays underestimated in microbial interactions networks giving interesting perspectives for the optimization and control of bioprocesses using IET stimulation.