Multispecies biofilms are hubs for metabolic interactions leading to ecologically and biotechnologically relevant emergent properties

In nature, the majority of bacteria live in structured communities, called biofilms. The biofilm environment gives rise to community-intrinsic and biofilm-associated emergent properties. Through interactions between the indwelling bacteria, the biofilm and its environment, different matrix components, as well as interactions between the bacteria and the EPS matrix, the biofilm environment provides distinct environmental and ecological niches for its inhabitants. Through the creation of subniches within the biofilm environment, multispecies biofilms represent highly heterogeneous ecosystems. Here, we discuss how multispecies biofilms can host and reinforce a variety of different metabolic interactions and, conversely, how metabolic interactions shape community properties and functionality. We provide examples on how co-metabolism and cross-feeding of metabolites, as well as sharing of resources and other public goods, can facilitate the coexistence of different species, while competition for resources, as well as other direct or indirect forms of competition, can result in the exclusion of others. We also outline how the metabolic interactions within multispecies biofilms can give rise to novel phenotypes and emergent properties that may be useful for applications in biotechnology and the bioremediation of polluted ecosystems.