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

Abstract

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.

Cytoplasmic contractile injection systems mediate cell death inStreptomyces

“…The comparison of the sheath (domains 1/2) in the extended vs. the contracted states revealed an increase in diameter and shortening of the length upon contraction, similar to other CISs (Fig. 2b/e) 14,19,24,18,27 .…”

“…The absorbance was normalized by weight of the wet pellet. 14,63 . Asterisks indicate gene products that were detected by mass spectrometry after CISs purification (Supplementary Table 1).…”

“…By contrast, eCIS are assembled in the bacterial cytoplasm of the donor cell and are subsequently released into the extracellular space, where they can bind to the surface of a target cell, contract and puncture the cell envelope 13 . Recently, a third mode of action was described in multicellular Cyanobacteria 14 . This system is also assembled in the bacterial cytoplasm and it then attaches to the thylakoid membrane where it potentially induces lysis of the cell upon stress, resulting in the formation of "ghost cells" which may in turn proceed to interact with other organisms 14 .…”

“…Recently, a third mode of action was described in multicellular Cyanobacteria 14 . This system is also assembled in the bacterial cytoplasm and it then attaches to the thylakoid membrane where it potentially induces lysis of the cell upon stress, resulting in the formation of "ghost cells" which may in turn proceed to interact with other organisms 14 .…”

Parallel cryo electron tomography on in situ lamellae

“…This requires precise modelling of sample movements as has previously been done for relatively flat samples (Bouvette et al, 2021; Zheng et al, 2004). However, in situ cellular samples elucidating the interactions of macromolecular complexes with each other and with the cellular architecture are becoming increasingly popular (Albert et al, 2020; Gupta et al, 2021; Mahamid et al, 2016; Schaffer et al, 2019; Weiss et al, 2022). Unfortunately, these samples are neither homogeneous nor flat due to their more complex sample preparation methods.…”