A novel nitrogen-fixing fermentative bacterium, designated as YA01T, was isolated from Nakabusa hot springs in Japan. The short-rod cells of strain YA01T were Gram-positive and non-sporulating. Phylogenetic trees of the 16S rRNA gene sequence and concatenated sequences of 40 single-copy ribosomal genes revealed that strain YA01T belonged to the genus
Caldicellulosiruptor
and was closely related to
Caldicellulosiruptor hydrothermalis
108T,
Caldicellulosiruptor bescii
DSM 6725T and
Caldicellulosiruptor kronotskyensis
2002T. The 16S rRNA gene sequence of strain YA01T shares less than 98.1 % identity to the known
Caldicellulosiruptor
species. The G+C content of the genomic DNA was 34.8 mol%. Strain YA01T shares low genome-wide average nucleotide identity (90.31–91.10 %), average amino acid identity (91.45–92.10 %) and <70 % digital DNA–DNA hybridization value (41.8–44.2 %) with the three related species of the genus
Caldicellulosiruptor
. Strain YA01T grew at 50–78 °C (optimum, 70 °C) and at pH 5.0–9.5 (optimum, pH 6.5). Strain YA01T mainly produced acetate by consuming d(+)-glucose as a carbon source. The main cellular fatty acids were iso-C17 : 0 (35.7 %), C16 : 0 (33.3 %), DMA16 : 0 (6.6 %) and iso-C15 : 0 (5.9 %). Based on its distinct phylogenetic position, biochemical and physiological characteristics, and the major cellular fatty acids, strain YA01T is considered to represent a novel species of the genus
Caldicellulosiruptor
for which the name Caldicellulosiruptor diazotrophicus sp. nov. is proposed (type strain YA01T=DSM 112098T=JCM 34253T).
Cellular fatty acids as chemotaxonomic markers of the genera Anabaena, Aphanizomenon, Microcystis, Nostoc and Planktothrix (cyanobacteria).
