Cell Structure Changes in the Hyperthermophilic Crenarchaeon Sulfolobus islandicus Lacking the S-Layer

Area of Science:

• Microbiology
• Archaeal Cell Biology
• Evolutionary Biology

Background:

• The S-layer is a common cell wall component in Archaea, but its in vivo function remains largely unknown.
• Understanding archaeal cell biology is vital due to their ancient evolutionary relationship with eukaryotes.
• Sulfolobales, within Crenarchaeota, possess S-layers and exhibit features linked to the archaea-eukaryote common ancestor.

Purpose of the Study:

• To investigate the architecture and cellular roles of the S-layer in the hyperthermophilic archaeon Sulfolobus islandicus.
• To identify novel proteins associated with the S-layer and their contribution to its stability.
• To elucidate the function of the S-layer in cell morphology, division, and stress response.

Main Methods:

• Electron microscopy of wild-type and mutant Sulfolobus islandicus strains (ΔslaA, ΔslaB).
• Genetic analysis to identify and characterize S-layer-associated proteins.
• Phenotypic analysis of mutants under various stress conditions (e.g., hyperosmotic stress).

Main Results:

• Mutants lacking the outermost S-layer protein (SlaA) exhibited significant cell aggregation and size increase (up to six times wild-type diameter).
• A novel S-layer-associated protein (M164_1049) was identified, likely assisting SlaB in stabilizing SlaA.
• ΔslaA mutants showed increased sensitivity to hyperosmotic stress and aberrant chromosome copy numbers, suggesting cell fusion or division irregularities.

Conclusions:

• The S-layer, particularly the SlaA component, is a key determinant of cell morphology in Sulfolobus.
• The SlaA protein plays a critical role in regulating cell division and/or preventing cell fusion.
• This study provides the first genetic evidence for the essential functions of the S-layer in Sulfolobus physiology and cell integrity.