A new study on the coexistence of bacteria and fungi shows that a mutually beneficial, functioning symbiosis can be very fragile. Researchers at the Leibniz Institute for Natural Product Research and Infection Biology (Leibniz-HKI) in Jena found out that the bacterial species Mycetohabitans rhizoxinica lives happily in the hyphae of the fungus Rhizopus microsporus only when the bacteria produce a certain protein.