Bacteria exist in highly competitive environments that require them to interact with a range of organisms. To mediate these interactions, bacteria employ different types of contractile injection systems (CIS). CIS particles function as specialised secretion systems to transfer cytoplasmic proteins from the cell into the environment or directly into the cytoplasm of eukaryotic or prokaryotic cells. While CIS are widespread across microbial phyla, representative examples from Gram-positive bacteria have remained poorly characterised.

We recently showed that CIS particles from multicellular Streptomyces bacteria are functionally distinct from related CIS and have an intracellular role. Using a combination of cryo-electron microscopy, live-cell imaging and in vivo assays, we determined the cryoEM structure of the extended CIS particle from Streptomyces coelicolor and propose a model of how these CIS particles mediate cell death in response to diverse stress conditions and impact the timely progression of the Streptomyces life cycle.