Predation by Myxococcus xanthus induces Bacillus subtilis to form spore-filled megastructures

Biofilm formation is a common mechanism for surviving environmental stress and can be triggered by both intraspecies and interspecies interactions. Prolonged predator-prey interactions between the soil bacterium Myxococcus xanthus and Bacillus subtilis were found to induce the formation of a new type of B. subtilis biofilm, termed megastructures. Megastructures are tree-like brachiations that are as large as 500 μm in diameter, are raised above the surface between 150 and 200 μm, and are filled with viable endospores embedded within a dense matrix. Megastructure formation did not depend on TasA, EpsE, SinI, RemA, or surfactin production and thus is genetically distinguishable from colony biofilm formation on MSgg medium. As B. subtilis endospores are not susceptible to predation by M. xanthus, megastructures appear to provide an alternative mechanism for survival. In addition, M. xanthus fruiting bodies were found immediately adjacent to the megastructures in nearly all instances, suggesting that M. xanthus is unable to acquire sufficient nutrients from cells housed within the megastructures. Lastly, a B. subtilis mutant lacking the ability to defend itself via bacillaene production formed megastructures more rapidly than the parent. Together, the results indicate that production of the megastructure facilitates B. subtilis escape into dormancy via sporulation.