Acidiplasma aeolicum gen. nov., sp. nov., a euryarchaeon of the family Ferroplasmaceae isolated from a hydrothermal pool, and transfer of Ferroplasma cupricumulans to Acidiplasma cupricumulans comb. nov.

A novel acidophilic, cell-wall-less archaeon, strain V(T), was isolated from a hydrothermal pool on Vulcano Island, Italy. The morphology of cells was observed to vary from pleomorphic to coccoid. The temperature range for growth of strain V(T) was 15-65 degrees C with an optimum at 45 degrees C. The pH for growth ranged from pH 0 to 4 with an optimal at pH 1.4-1.6. Strain V(T) was able to grow aerobically and anaerobically, oxidizing ferrous iron and reducing ferric iron, respectively. The isolate grew chemo-organotrophically with yeast extract and yeast extract with glucose as the sources of energy and carbon. The molar G+C content in the DNA was 36 mol%. 16S rRNA gene sequence analysis demonstrated that strain V(T) was a member of the family Ferroplasmaceae, order Thermoplasmatales, phylum Euryarchaeota, showing sequence identities of 100 % with Ferroplasma cupricumulans BH2(T), 95.4 % with Ferroplasma acidiphilum Y(T), 94 % with Picrophilus torridus DSM 9790(T) and 92 % with Picrophilus oshimae DSM 9789(T). 16S rRNA gene sequence-based phylogenetic analysis showed that strain V(T) formed a monophyletic cluster together with F. cupricumulans BH2(T) and all other thermophilic isolates with available 16S rRNA gene sequences, whereas F. acidiphilum Y(T) formed another cluster with mesophilic isolates within the family Ferroplasmaceae. DNA-DNA hybridization values between strain V(T) and F. cupricumulans BH2(T) were well below 70 %, indicating that the two strains belong to separate species. Principal membrane lipids of strain V(T) were dibiphytanyl-based tetraether lipids containing pentacyclic rings. The polar lipids were dominated by a single phosphoglycolipid derivative based on a galactosyl dibiphytanyl phosphoglycerol tetraether, together with smaller amounts of monoglycosyl and diglycosyl dibiphytanyl ether lipids and the corresponding phosphoglycerol derivatives. The major respiratory quinones present were naphthoquinone derivatives. Given the notable physiological and chemical differences as well as the distinct phylogenetic placement of the new isolate relative to the type species of the genus Ferroplasma, we propose strain V(T) as a member of a new genus and species, Acidiplasma aeolicum gen. nov., sp. nov. The type strain of Acidiplasma aeolicum is strain V(T) (=DSM 18409(T) =JCM 14615(T)). In addition, we propose to transfer Ferroplasma cupricumulans Hawkes et al. 2008 to the genus Acidiplasma as Acidiplasma cupricumulans comb. nov. (type strain BH2(T) =DSM 16551(T) =JCM 13668(T)).