exploration is triggered by fungal interactions and volatile signals.

It has long been thought that the life cycle of bacteria encompasses three developmental stages: vegetative hyphae, aerial hyphae and spores. Here, we show interactions between and fungi trigger a previously unobserved mode of development. We term these cells 'explorers', for their ability to adopt a non-branching vegetative hyphal conformation and rapidly transverse solid surfaces. Fungi trigger exploratory growth in part by altering the composition of the growth medium, and explorer cells can communicate this exploratory behaviour to other physically separated streptomycetes using an airborne volatile organic compound (VOC). These results reveal that interkingdom interactions can trigger novel developmental behaviours in bacteria, here, causing to deviate from its classically-defined life cycle. Furthermore, this work provides evidence that VOCs can act as long-range communication signals capable of propagating microbial morphological switches.