Caloranaerobacter longqiensis sp. nov., a novel thermophilic member of the family Thermohalobacteraceae with the ability of ferric iron reduction from deep-sea hydrothermal sulphide

A thermophilic, strictly anaerobic, Gram-stain-negative and ferric iron-reducing bacterium, designated as DY30410^T, was isolated from a hydrothermal sulphide sample collected from the Southwest Indian Ocean Ridge during the cruise DY30 of R/V <i>Da Yang Yi Hao</i>. Cells of strain DY30410^T were rod-shaped with rounded ends and motile with one or more laterally inserted flagellum (flagella). Strain DY30410^T grew optimally at pH 6.5-7.0, 50 °C, with salinity (sea salts) of 35-45 g l^-1. Ferric oxyhydroxide, ferric chloride, thiosulphate and elemental sulphur can be used as electron acceptors. Glucose and starch are used for growth. Elemental sulphur or yeast extract is not necessary. The principal fatty acids of strain DY30410^T were iso-C_15:0, C_16:0, 3OH-iso-C_14:0 and anteiso-C_15:0. No respiratory quinone was detected. Phylogenetically, strain DY30410^T branched within the family <i>Thermohalobacteraceae</i> with <i>Caloranaerobacter ferrireducens</i> DY22619^T being its closest phylogenetic relative (98.4% similarity), followed by the type species <i>Caloranaerobacter azorensis</i> MV1087^T (97.2%). Strain DY30410^T has a draft genome size of 2.57 Mbp and has 2,852 predicted coding sequences. The genome DNA G+C content of strain DY30410^T was 29.2 mol%. The <i>in silico</i> DNA-DNA hybridization between strain DY30410^T and its closest relatives, <i>C. ferrireducens</i> DY22619^T or <i>C. azorensis</i> MV1087^T, was all 45.5%. The average nucleotide identity values between strain DY30410^T and <i>C. ferrireducens</i> DY22619^T and <i>C. azorensis</i> MV1087^T were 91.9 and 91.3%, respectively. Phylogenomic analysis also showed that strain DY30410^T branched within the family <i>Thermohalobacteraceae</i> with <i>C. ferrireducens</i> DY22619^T and <i>C. azorensis</i> MV1087^T being its closest relatives. On the basis of phenotypic, phylogenetic and chemotaxonomic characteristics, we propose a representative of a new species in the genus <i>Caloranaerobacter</i>, for which the name <i>Caloranaerobacter longqiensis</i> sp. nov. is proposed. The type strain is DY30410^T (=KCTC 25912^T=MCCC 1A01531^T).