At the optimum growth temperature, doubling time of P. fumarii is 60 minutes [1]. The pH range for growth is 4.0-6.5, with an optimum pH of 5.5 [1]. The strain forms white colonies (1 mm in diameter) on Gelrite-containing media [1]. Like in Hyperthermus, no cell-to-cell network is formed and the S-layer exhibits a central depression, most likely kinase inhibitor DAPT secretase a pore [1,32]. Such networks of extracellular tubules appear to be characteristic for members of the genus Pyrodictium. P. fumarii strain 1AT is able to grow on medium that contains 1%-4% NaCl, with an optimum salinity at 1.7% [1]. The organism uses CO2 as the single carbon source and H2 as the obligate electron donor [1]. The organism is tolerant to high pressure condition (25,000 kPa) [1]. Under anaerobic and microaerophilic conditions, P.

fumarii is obligately chemolithoautotroph and is able to oxidize H2 coupled with NO3-, S2O32- and O2 as electron acceptors [1]. Nitrate is reduced to ammonia [1]. Organic compounds do not stimulate the growth of P. fumarii [1]. P. fumarii does not grow in media containing acetate, pyruvate, glucose, starch and elementary sulfur [1]. A highly selective enrichment method for P. fumarii in comparison to other members of the family Pyrodictiaceae is based on the use of nitrate as the sole electron acceptor [32]. Crude extracts of P. fumarii strain 1AT cells show a strong cross-reaction with antibodies prepared against the thermosome of Pyrodictium occultum [32], which could suggest highly similar chaperonin protein complexes.

Furthermore, a membrane-associated hydrogenase with an optimum reaction temperature of 119��C is found in cells grown on molecular hydrogen and nitrate [32]. Interestingly, succinyl-CoA reduction in P. fumarii is not NAD(P)H-dependent, but requires reduced methyl viologen as in Ignicoccus hospitalis [33,34]. In the RNA of hyperthermophiles, posttranscriptional modification has been identified as a leading mechanism of structure stabilization [35-39]. Twenty-six modified nucleosides of P. fumarii are detected, 11 of which are methylated in ribose [38]. P. fumarii exhibits a novel RNA nucleosides characterized as 1,2��-O-dimethylguanosine (m1Gm) [38]. Figure 2 Scanning electron micrograph of P. fumarii 1AT Table 1 Classification and general features of P. fumarii 1AT according to the MIGS recommendations [22] and the NamesforLife database [23].

Chemotaxonomy The S-layer of strain 1AT exhibits p4 Drug_discovery symmetry with a lattice of 18.5 nm that encloses a 40-nm-wide ��quasi-periplasmic space�� [1]. The major core lipids of strain 1AT are uncyclized glycerol-dialkyl-glycerol-tetraether (GDGT) and traces of 2,3-di-O-phytanyl-sn-glycerol (diether) [1]. Cells of strain 1AT do not contain C20 C25 diethers and cyclized GDGT [1]. Non-hydrolyzed lipids contain a main spot on TLC staining blue (instead of violet) by anisaldehyde [1]. The major organic solute of strain 1AT is di-myo-inositol phosphate (DIP) [40].