Here we studied a microbial community with more than 100 different types of species in a biofilm that evolved during 15-years in a bioreactor system with benzene as the main carbon and free energy source and nitrate as the terminal electron acceptor.

A key question in microbial ecology is what the driving forces behind the persistence of large biodiversity in natural environments are. Here we studied a microbial community with more than 100 different types of species in a biofilm that evolved during 15-years in a bioreactor system with benzene as the main carbon and free energy source and nitrate as the terminal electron acceptor. We demonstrate that only a few community members are able to degrade benzene, and that most others feed on the metabolic left-overs or on the contents of dead cells making up an extended food web with different trophic levels. As a result of niche partitioning, a high species richness can be maintained and the complexity of a natural community can be stabilized in a relatively simple environment. This view highlights the importance of species interactions and inter-dependencies, which drive microbial community structure and function, and, more importantly, that these mechanisms may well be conserved across ecosystems.