Structure of a thylakoid-anchored contractile injection system in multicellular cyanobacteria

By G. L. Weiss, Fabian Eisenstein, Ann-Katrin Kieninger, Jingwei Xu, Hannah A. Minas, Milena Gerber, Miki Feldmüller, I. Maldener, K. Forchhammer, M. Pilhofer. 2022

39 citations recorded by the source corpus.

Contractile injection systems (CISs) mediate cell–cell interactions by phage tail-like structures, using two distinct modes of action: extracellular CISs are released into the medium, while type 6 secretion systems (T6SSs) are attached to the cytoplasmic membrane and function upon cell–cell contact. Here, we characterized a CIS in the multicellular cyanobacterium Anabaena, with features distinct from extracellular CISs and T6SSs. Cryo-electron tomography of focused ion beam-milled cells revealed that CISs were anchored in thylakoid membrane stacks, facing the cell periphery. Single particle cryo-electron microscopy showed that this unique in situ localization was mediated by extensions of tail fibre and baseplate components. On stress, cyanobacteria induced the formation of ghost cells, presenting thylakoid-anchored CISs to the environment. Functional assays suggest that these CISs may mediate ghost cell formation and/or interactions of ghost cells with other organisms. Collectively, these data provide a framework for understanding the evolutionary re-engineering of CISs and potential roles of these CISs in cyanobacterial programmed cell death. The characterization of a contractile injection system anchored in the thylakoid membrane of Anabaena reveals structural features linked to the unique localization and function of this cyanobacterial nanomachine.

Subfields: Cell Biology, Ecology, Endocrinology