DPANN archaea account for half of all archaeal diversity in the biosphere and are characterized by their small size, reduced genome, and limited metabolic capabilities. Consequently, most members of the DPANN superphylum live in a mutualistic, commensal, or parasitic relationship with diverse archaeal and bacterial hosts. Despite their widespread occurrence and significant role in microbial ecology and the environment, very little is known about their cell biology, metabolic potential, and the molecular/structural basis of their host interactions. A significant hurdle in the study of DPANNs lies in the formidable difficulty of isolating and establishing new co-culture systems.
We used cryo-electron tomography (cryoET) to image three different host-DPANN co-cultures. Tomographic reconstructions combined with 3D segmentation uncovered two novel molecular machines that facilitate intercellular interaction between the host and DPANN. In one co-culture, we show that host cells can make extensive protein nanotubes to interact with their DPANNs. In another host-DPANN system, we observed DPANN cells assemble an enormous attachment organelle that makes intricate connections with the host, bridging the two cytoplasms. Our work shows the vast resources that both host and DPANN commit to this symbiosis and provides mechanistic insights into the DPANN-host relationship.
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