Pyrobaculum Igneiluti Sp Nov., A Novel Anaerobic Hyperthermophilic Archaeon That Reduces Thiosulfate And Ferric Iron

A novel anaerobic, hyperthermophilic archaeon was isolated from a mud volcano in the Salton Sea geothermal system in southern California, USA. The isolate, named strain 521(T), grew optimally at 90 degrees C, at pH 5.5-7.3 and with 0-2.0%(w/v) NaCl, with a generation time of 10 h under optimal conditions. Cells were rod-shaped and non-motile, ranging from 2 to 7 mu m in length. Strain 521(T) grew only in the presence of thiosulfate and/or Fe(III) (ferrihydrite) as terminal electron acceptors under strictly anaerobic conditions, and preferred protein-rich compounds as energy sources, although the isolate was capable of chemolithoautotrophic growth. 16S rRNA gene sequence analysis places this isolate within the crenarchaeal genus Pyrobaculum. To our knowledge, this is the first Pyrobaculum strain to be isolated from an anaerobic mud volcano and to reduce only either thiosulfate or ferric iron. An in silico genome-to-genome distance calculator reported <25% DNA-DNA hybridization between strain 521(T) and eight other Pyrobaculum species. Due to its genotypic and phenotypic differences, we conclude that strain 521(T) represents a novel species, for which the name Pyrobaculum igneiluti sp. nov. is proposed. The type strain is 521(T) (= DSM 103086(T) = ATCC TSD-56(T)).