| Abstract: | Attachment of microorganisms to surfaces is a prerequisite for colonization and biofilm formation. The hyperthermophilic crenarchaeote Sulfolobus solfataricus was able to attach to a variety of surfaces, such as glass, mica, pyrite, and carbon-coated gold grids. Deletion mutant analysis showed that for initial attachment the presence of flagella and pili is essential. Attached cells produced extracellular polysaccharides containing mannose, galactose, and N-acetylglucosamine. Genes possibly involved in the production of the extracellular polysaccharides were identified.In microbiology, organisms are isolated from their natural habitats and typically cultivated in the laboratory as planktonic species. Though this method has been essential for understanding the concept of life, it remains unclear how microbial ecosystems operate. For bacteria, it is well known that they are able to form large cellular communities with highly complex cellular interactions and symbioses between different microbial or eukaryotic species. Biofilm formation is an essential component of such communities, and studies have shown that bacteria within biofilms are physiologically different from planktonic ones (20, 21). They can exhibit extensive networks of pili on their surfaces and produce and secrete extracellular polysaccharides (EPS), their growth rate is decreased, and cells are much more resistant to physical stresses and antibiotics (19).The study of surface colonization and cellular communities of archaea is crucial for understanding their ecological properties. The only detailed study showed that the hyperthermophilic organism Archaeoglobus fulgidus produced biofilms when challenged with heavy metals and pentachlorophenol (10). Pyrococcus furiosus was able to adhere to different surfaces, such as mica and carbon-coated gold grids, and cells were connected via cable-like bundles of flagella (12). Methanopyrus kandleri was shown to adhere to glass, but P. furiosus could colonize only by attaching to M. kandleri cells, using flagella and direct cell contacts (16).Here we report on the function of cell surface appendages in initial attachment to surfaces of archaea, using directed gene inactivation mutants. The crenarchaeote Sulfolobus solfataricus P2 is a thermoacidophile which grows optimally at 80°C and pH values of 2 to 4 (22). S. solfataricus possesses cell surface structures such as flagella and UV-induced pili (1, 2). The flagellum operon of S. solfataricus encodes, in addition to the structural subunit FlaB, four proteins of unknown function, the ATPase FlaI, and the only integral membrane protein, FlaJ. Previously, we isolated a ΔflaJ mutant which was nonflagellated and had lost its ability for surface motility on Gelrite plates (17). Recently, we described UV-inducible pili in S. solfataricus that directed cellular aggregation after UV stress (8). Deletion of the central ATPase UpsE, responsible for pilus assembly, rendered cells devoid of pili and defective in cellular aggregation after UV treatment (8). In this study, wild-type cells and deletion strains were tested for the ability to attach to a variety of surfaces and the formed structures and extracellular material were analyzed. |
