Ferroplasma acidiphilum gen. nov., sp nov., an acidophilic, autotrophic, ferrous-iron-oxidizing, cell-wall-lacking, mesophilic member of the Ferroplasmaceae fam. nov., comprising a distinct lineage of the Archaea

An isolate of an acidophilic archaeon, strain Y-T, was obtained from a biol eaching pilot plant. The organism oxidizes ferrous iron as the sole energy source and fixes inorganic carbon as the sole carbon source. The optimal ph for growth is 1.7, although growth is observed in the range ph 1.3 to 2.2. The cells are pleomorphic and without a cell wall. 16S rRNA gene sequence analysis showed this strain to cluster phylogenetically within the order 'T hermoplasmales' sensu Woese, although with only 89.9 and 87.2% sequence ide ntity, respectively, to its closest relatives, Picrophilus oshimae and Ther moplasma acidophilum. Other principal differences from described species of the 'Thermoplasmales' are autotrophy (strain Y-T is obligately autotrophic ), the absence of lipid components typical of the 'Thermoplasmales' (no det ectable tetraethers) and a lower temperature range for growth (growth of st rain Y-T occurs between 15 and 45 degrees C). None of the sugars, amino aci ds, organic acids or other organic compounds tested was utilized as a carbo n source. On the basis of the information described above, the name Ferropl asma acidiphilum gen. nov., sp. nov. is proposed for strain Y-T within a ne w family, the Ferroplasmaceae fam. nov. Strain Y-T is the type and only str ain of F. acidiphilum. This is the first report of an autotrophic, ferrous- iron-oxidizing, cell-wall-lacking archaeon.