SummaryIn ever-changing natural environments, bacteria are continuously challenged with numerous biotic and abiotic stresses. Accordingly, they have evolved both specific and more general mechanisms to counteract stress-induced damage and ensure survival. In the soil habitat of Bacillus subtilis, peptide antibiotics and bacteriophages are among the primary stressors that affect the integrity of the cytoplasmic membrane. Dynamin-like proteins (DLPs) play a major role in eukaryotic membrane re-modelling processes, including antiviral activities, but the function of the corresponding bacterial homologues was so far poorly understood. Here, we report on the protective function of a bacterial DLP, DynA from B. subtilis. We provide evidence that DynA plays an important role in a membrane surveillance system that counteracts membrane pore formation provoked by antibiotics and phages. In unstressed cells, DynA is a highly dynamic membrane-associated protein. Upon membrane damage, DynA localizes into large and static assemblies, where DynA acts locally to counteract stress-induced pores, presumably by inducing lipid bilayer fusion and sealing membrane gaps. Thus, lack of DynA increases the sensitivity to antibiotic exposure and phage infection. Taken together, our work suggests that DynA, and potentially other bacterial DLPs, contribute to the innate immunity of bacteria against membrane stress.