In the context of Stefan’s joint PhD at the ULB (with D. Gonze) and VUB (with J. Danckaert) in Brussels, he has theoretically studied the dynamics of two interacting microbial species in the chemostat. These species are competitors for a common resource, as well as mutualists due to cross-feeding. He demonstrated that this system has a rich repertoire of dynamical behavior, including bistability, and showed that the different steady state solutions can be well captured by an extended Lotka-Volterra model. This work was published in PLoS One.