A Micrarchaeon Isolate Is Covered by a Proteinaceous S-Layer

Area of Science:

• Microbiology
• Archaea
• Cell Biology

Background:

• The DPANN superphylum, including Micrarchaeota, is poorly understood due to reliance on cultivation-independent methods.
• Previous hypotheses suggested Micrarchaeota possess two membrane systems.
• Understanding archaeal symbiont surface structures is crucial for deciphering host-parasite interactions.

Purpose of the Study:

• To investigate the surface structure of the cultivated archaeon "Candidatus Micrarchaeum harzensis A_DKE."
• To confirm the presence and nature of the S-layer in Micrarchaeota.
• To explore the implications for host-symbiont interactions in DPANN archaea.

Main Methods:

• Proteomic analysis to identify abundant surface proteins.
• In silico analysis of protein homology to known S-layer proteins.
• Electron microscopy of freeze-etched samples to visualize cell surface structures.

Main Results:

• A highly abundant protein in "Ca. Micrarchaeum harzensis A_DKE" shows homology to known S-layer proteins.
• Electron microscopy confirms an S-layer covering the cytoplasmic membrane of "Ca. Micrarchaeum harzensis A_DKE."
• Homologues of the S-layer protein are present in other Micrarchaeota genomes, suggesting a common trait.

Conclusions:

• "Candidatus Micrarchaeum harzensis A_DKE" possesses a surface S-layer, validating previous hypotheses.
• The S-layer may be a common feature among Micrarchaeota, impacting their interactions.
• This research provides critical insights into the cell surface and symbiotic lifestyle of DPANN archaea.