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. Recently, we studied the case of a fermentative bacterium receiving extracellular electrons from an electroactive bacterium while fermenting glycerol. In that case IET leads to a diminution of bacterial biomass production concomitantly with an increased production of reduced compounds such as 1,3-propanediol. This demonstrated that IET could also promote competitive and even parasitic behavior and could lead to interesting improvements in industrial fermentations. In my talk, I will show recent results of a bioaugmentation experiment where we introduced an electroactive species in a mixed microbial consortia fermenting glucose. The bioaugmentation led to shifts in products yields but also in microbial diversity. The interpretation of the results thus require disentangling possible metabolic shifts from changes in products associated with shifts in microbial abundances. I will discuss how linear programming gives us insight into this complex problem. I will finally highlight how such non-mutualistic IET could be widespread and of particular significance for the shaping of complex microbial communities.