Caldisphaera lagunensis gen. nov., sp. nov., a novel thermoacidophilic crenarchaeote isolated from a hot spring at Mt Maquiling, Philippines

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Abstract
Four novel, thermoacidophilic, crenarchaeotic cocci that grew anaerobically and heterotrophically were isolated from an acidic hot spring in the Philippines; two representative strains were characterized in detail. Most cells were regular cocci, 0·8–1·1 μm in width, which occurred singly or in pairs. They were non-motile and grew at 45–80 °C (optimum 70–75 °C) and pH 2·3–5·4 (optimum 3·5–4·0). They utilized starch, glycogen, gelatin, beef extract, yeast extract and peptone as carbon and energy sources. Growth was stimulated by the presence of sulfur as an electron acceptor. The lipid fraction contained cyclic and acyclic tetraether core lipids. The DNA G+C content was 31 mol%; phylogenetic analysis based on 16S rDNA sequences showed that the novel cocci represent an independent lineage in the phylum Crenarchaeota, distantly related to Acidilobus aceticus and an allied strain, NC12. Caldisphaera lagunensis gen. nov., sp. nov. is proposed to accommodate the four strains. The type strain is IC-154T(=JCM 11604T =MCC-UPLB 1331T =ANMR 0165T).