Assembly and function of cell surface structures of the thermoacidophilic archaeon Sulfolobus solfataricus

PhD ceremony: Mr. B. Zolghadr, 13.15 uur, Academiegebouw, Broerstraat 5, Groningen

Thesis: Assembly and function of cell surface structures of the thermoacidophilic archaeon Sulfolobus solfataricus

Promotor(s): prof. A.J.M. Driessen

Faculty: Mathematics and Natural Sciences

Sulfolobus solfataricus belongs to the group of hyperthermoacidophilic archaea and grows optimally under extreme conditions of high temperature (80˚C) and low pH value (pH 3). Archaea forms a separate form of life and distinct from the bacteria and eukaryotes. A central question in the research of Behnam Zolghadr was how these microorganisms are adapted to thrive under extreme environment circumstances.

S. solfataricus secretes large quantities of proteins that constitute the cell surface and other cell associated structures. The so-called S-layer forms an essential component of the cell surface. Its two protein components assemble spontaneously in a semi-crystalline layer. This S-layer is very stable and resists the extreme environment circumstances. It is associated with the cytoplasmic membrane yielding a very stable cell surface.

Detailed investigations of the cell surface of S. solfataricus by means of electron microscopy shows that the outside is decorated wire-like structures. The flagella are responsible for motility of the cells as well as the initial colonization of solid surfaces. The pili are shorter appendices and necessary for a stable adherence to such surfaces.

Another surface structure is the bindosome. The exact composition of this structure is not known but it contains sugar-binding proteins that are intimately associated with the cell wall.Sugar-binding proteins are important for the cellular uptake of sugars. The natural environment of S. solfataricus is relatively poor in organic substrates. The bindosome is important for the efficient uptake of sugars from the medium under extreme environmental conditions.