9/ We propose a novel model of viral egress in sheathed archaea. We hypothesize that secreted viral SH-like proteins may decrease the stability of the host sheath. Alternatively, they may disrupt sheath assembly, competing with the host SH monomers.

8/ Interestingly, we found SH-like proteins in viruses infecting sheathed archaea and we use them as markers to assign 580 new viral OTUs to sheathed hosts! What is the function of these viral SH-proteins? Using AlphaFold, we infer that they can form dimers with the host SH-proteins!

7/ Viruses employ sophisticated mechanisms to breach the cell walls of their hosts. However, it is unknown how they can break through the robust amyloid structure of the sheath. We searched for potential lysis-related genes in viruses infecting sheathed archaea.

6/ Phylogenetic analysis reveals that the current distribution of the sheath was shaped by a complex pattern of transfers and lineage-specific losses. These events indicate an active dynamic of the sheath in archaeal communities, which may have accompanied environmental adaptations.

5/ We find that sheaths are widespread across ANME-1 archaea. Sequence similarity suggests multiple acquisitions via recent horizontal gene transfers from Methanothrix and Methanospirillum.

4/ We reveal a large diversity of cap domains, which might adapt the sheath structure to specific environmental or physiological needs. For example, SH proteins with a long chain of Ig-like domains could form sheaths with adhesion properties.

3/ Using Foldseek we searched for structural homologues of SH proteins in archaeal genomes. We found them in four lineages, and for the first time in the ecologically important ANME-1 (methane oxidizers). SH proteins are present in multiple copies per genome (up to 40) and are highly expressed.

2/ Sheaths are made of SH proteins, organized into rings. SH protein consists of an amyloid domain (facing the interior of the sheath tube) and a “cap” domain. SH proteins of Methanospirillum and Methanothrix have no sequence similarity, so how can we identify sheath in other archaea?

1/ Sheaths were first discovered in two archaeal methanogens: Methanospirillum and Methanothrix. They are tube-like surface structures, shared by multiple cells within a filament, which remain largely understudied.

4/ We reveal a large diversity of cap domains, which might adapt the sheath structure to specific environmental or physiological needs. For example, SH proteins with a long chain of Ig-like domains could form sheaths with adhesion properties.

3/ Using Foldseek we searched for structural homologues of SH proteins in archaeal genomes. We found them in four lineages, and for the first time in the ecologically important ANME-1 (methane oxidizers). SH proteins are present in multiple copies per genome (up to 40) and are highly expressed.

2/Sheaths are made of SH proteins, organized into rings. SH protein consists of an amyloid domain (facing the interior of the sheath tube) and a “cap” domain. SH proteins of Methanospirillum and Methanothrix have no sequence similarity, so how can we identify sheath in other archaea?

1/ Sheaths were first discovered in two archaeal methanogens: Methanospirillum and Methanothrix. They are tube-like surface structures, shared by multiple cells within a filament, which remain largely understudied.