1%) and ‘hot/spring’ (32.9%). Figure 1 shows the phylogenetic neighborhood of H. thermophilus TK-6T in a 16S rRNA based tree. The sequence of the single 16S rRNA gene sellekchem in the genome differs by one nucleotide from the previously published 16S rRNA sequence (“type”:”entrez-nucleotide”,”attrs”:”text”:”Z30214″,”term_id”:”520869″,”term_text”:”Z30214″Z30214), which contains 31 ambiguous base calls. Figure 1 Phylogenetic tree highlighting the position of H. thermophilus TK-6T relative to the type strains of the other species within the genus and to the type strains of the other genera within the family Aquificaceae. The trees were inferred from 1,423 aligned … Cells of strain TK-6T are Gram-negative, nonmotile straight rods of 0.3 to 0.5 ��m by 2.0 to 3.0 ��m occurring singly or in pairs [1] (Figure 2 and Table 1).

Molecular oxygen is used as an electron acceptor for respiratory metabolism [1]. However, strain TK-6T can grow anaerobically on nitrate as an electron acceptor when molecular hydrogen is used as an energy source [33]. Strain TK-6T does not form colonies on agar plates, but does form colonies on plates solidified with GELRITE, a polysaccharide produced by Pseudomonas species [34]. The optimal temperature for autotrophic growth on H2-O2-CO2 was between 70oC and 75��C, no growth being observed at 37��C or 80��C [1]. A neutral pH 7.2 was suitable for growth of the strain TK-6T [1]. One important feature of the strain TK-6T is a generation time that is faster by about 1h compared to other autotrophs, suggesting that this strain has an efficient hydrogen-oxidizing ability [35].

No spore formation was observed [1]. Strain TK-6T assimilates carbon dioxide via the reductive tricarboxylic acid cycle [10,36,37]. This is also true when the strain TK-6T grows anaerobically on nitrate [10]. Cytochromes b and c were found in strain TK-6T [1]. Interestingly, cytochrome C552 of H. thermophilus TK-6T is extremely thermostable and can restore its conformation even after being autoclaved for 10 minutes at 121oC [30]. One of the denitrification enzymes of the strain TK-6T, cytochrome cd1 nitrite reductase has been isolated and analyzed [38]. Optimum temperature for the activity of this enzyme was found to range between 70oC-75oC [38]. Moreover, this enzyme was found to be of the heme cd1-type [33]. Ammonium and nitrate were utilized as nitrogen sources [1,33], Cilengitide but not urea and N2. Growth was inhibited by nitrite [1]. Nitrate reduction and peroxidase were positive, while urease was negative [1].