Sulfolobus solfataricus
Members of the group Sulfolobales are found in solfataric fields, acidophilic mud springs and thermal active areas all around the world. Famous strains include e.g. Sulfolobus acidocaldarius from Yellowstone Nationalpark, described by T. Brock as the first hyperthermophilic microorganism (Brock et al. 1972), and Sulfolobus solfataricus strain P2, which was isolated from a solfataric field near Naples, Pisciarelli (Italy; Zillig et al. 1980). Sulfolobus strains are hyperthermophilic crenarchaea that optimally grow around 75-80°C and a pH between 2.5 - 3.5. Since Sulfolobus spp. are grown aerobically and are quite easy to cultivate in a laboratory scale, these organisms have developed into a model system for studies on different aspects of microbial adaptation to extreme environments in metabolism, DNA translation and transcription, cell division and many other cellular aspects. Membranes of Sulfolobus strains contain tetraether lipids and their content can be up to 98% of all lipids. These lipids have been found to be highly proton impermeable allowing Sulfolobus to keep an internal pH of 6.5 in an acidic surrounding (Van de Vossenberg et al. 1995; Moll & Schäfer 1988).
Some Sulfolobus strains are able to oxidize iron in the presence of sulphur; however most of them can also grow heterotrophically. S. solfataricus grows on a variety of different carbon sources like trypton, various sugars or amino acids (Grogan 1989). The organism has been chosen as a model system for our study not only because the whole genome sequence information (She et al. 2001) is available, but it also harbors special metabolic features like an unusual branched Entner-Doudoroff (ED) pathway for glucose catabolism (Ahmed et al. 2005). Furthermore, the strain is attractive as genetic tools like a deletion mutant strain and a virus based vector system are available (Wagner et al. 2009).