Calditerricola satsumensis gen. nov., sp. nov. and Calditerricola yamamurae sp. nov., extreme thermophiles isolated from a high-temperature compost

Two novel thermophilic micro-organisms, designated YMO81(T) and YMO722(T), were isolated from a high-temperature compost (internal temperature > 95 °C). The isolates were able to grow at 80 °C in a nutrient broth and in a synthetic medium. Cells were aerobic, Gram-negative rods (0.3 x 4.0 μm). Spore formation was not observed. Strain YMO81(T) grew at 83 °C and pH 6.9-8.9 and grew optimally at 78 °C and pH 7.5 with 2 % NaCl. For growth in a synthetic minimal medium at 70 °C, the vitamins biotin, folic acid and thiamine and the amino acids glutamine and methionine were essential for growth of both strains; at 80 °C, strain YMO81(T) also required histidine, isoleucine, leucine, lysine, phenylalanine, serine, tryptophan and valine. Cellular fatty acids of the isolates comprised mainly iso-C₁₇:₀ and anteiso-C₁₇:₀. The DNA G+C contents of strains YMO81(T) and YMO722(T) were 70 and 64 mol%, respectively. When the 16S rRNA gene sequences of the isolates were compared with those of other bacteria, highest similarity was observed with Planifilum yunnanense LA5(T) (90 % 16S rRNA gene sequence similarity). DNA-DNA relatedness between strain YMO722(T) and strain YMO81(T) was 55 %. N⁴-Aminopropylspermine was identified as a major polyamine, which suggested that the isolates were distinct from other related taxa. On the basis of phylogenetic, phenotypic and chemotaxonomic analyses, we propose a new genus, Calditerricola gen. nov., and two novel species, the type species Calditerricola satsumensis sp. nov., with type strain YMO81(T) (=ATCC BAA-1462(T) =JCM 14719(T) =DSM 45223(T)), and Calditerricola yamamurae sp. nov., with type strain YMO722(T) (=ATCC BAA-1461(T) =JCM 14720(T) =DSM 45224(T)).