Bacterial–fungal interactions: connections and consequences

In nature, microorganisms exist in multispecies microbial communities containing bacteria, fungi, archaea, and viruses. The organisation, behaviour, and ecological impact of these communities are very much defined by the various interactions between bacteria and fungi within the community, with physical associations, chemical communication, metabolic exchange, and genetic regulation collectively shaping how these interkingdom communities assemble, adapt, and influence their hosts and habitats. Methods of interaction are widely shared across the microbiota of plants, animals, and the built environment; however, interkingdom microbial communities have environmentally specific outcomes, meaning it is critically important to understand bacterial-fungal interactions (BFIs) within the host or environmental context. With recent advances in BFI analysis now providing increasingly detailed resolution of BFIs and their function in the dialogue between interkingdom microbial communities and their growth environment, we can now gain better insight into these fundamental processes. In the present mini-review, we detail the main BFIs observed in these interkingdom microbial communities, and their implications in the context of plant, human, and the health of the built environment. We also discuss tools and methodologies for their analysis and potential use in the development of microbially derived technologies to improve health and well-being. Finally, we endorse the perspective that interkingdom microbial communities should be considered as structured, interdependent networks with analogy to multicellular organisation.