DPANN archaea encompass a widespread and highly diverse group of archaea characterised by their small size, reduced genome, and symbiotic existence. Known DPANN species are predominantly obligate ectosymbionts that depend on their host for their survival and proliferation. Despite their importance, the structural and molecular details of host recognition, host-DPANN intercellular communication, and host adaptation in response to DPANN attachment remain unknown.
CryoET is an ideal method to study genetically intractable microbial communities as it can determine high-resolution cellular details and macromolecular structures in situ without recombinant expression systems. We used electron cryo-ET to observe the intercellular interactions of DPANNs with their hosts. Tomographic reconstructions combined with 3D segmentation revealed that host cells can use intercellular nanotubes to facilitate interactions with their DPANN symbionts. Using sub-tomogram averaging we determined the in situ architectures of host and DPANN S-layers and the structures of the nanotubes in their primed and extended states. In another DPANN-host system, we observed an enormous attachment organelle embedded in DPANN cell envelope that makes intricate connections with the host.
Our work shows the vast the resources that both host and DPANN commit to this symbiosis and provides mechanistic insights the DPANN-host relationship