Aquifex pyrophilus gen. nov. sp. nov., Represents a Novel Group of Marine Hyperthermophilic Hydrogen-Oxidizing Bacteria

Summary From hot marine sediments (depth: 106 m) at the Kolbeinsey Ridge, Iceland, novel bacterial hyperthermophiles were isolated. Cells were Gram-negative highly motile rods exhibiting a complex envelope consisting of murein, an outer membrane and a surface protein layer. Growth occurred between 67 and 95 °C (opt.: 85 °C; 75 min doubling time), pH 5.4 and 7.5 (opt.: pH 6.8), and 1 to 5% NaCl (opt.: 3% NaCl). The novel isolates were strict chemolithoautotrophs. They used molecular hydrogen, thiosulfate and elemental sulfur as electron donors and oxygen (low concentrations) and nitrate as electron acceptors. During growth, sulfuric acid was formed from S° and thiosulfate. In the late logarithmic growth phase, H2S was formed from S° and H2. The core lipids consisted mainly of alkyl ethers of glycerol. The GC content of the DNA was 40 mol%. By 16S rRNA comparisons, the new isolates did not belong to any of the phyla known and represent the deepest phylogenetic branch-off within the Bacteria domain. Based on the physiological and molecular properties of the new isolates, we describe here a new genus, which we name Aquifex (the “water-maker”). The type species is Aquifex pyrophilus (type strain: Kol5a; DSM 6858).