A slightly thermophilic bacterial strain, designated AT-A2 T , was isolated from a hot spring water sample taken from the Antun hot spring in Taiwan and characterized using a polyphasic taxonomic approach. Cells of strain AT-A2 T were aerobic, Gram-negative, motile by a single polar flagellum and formed non-pigmented colonies. Growth occurred at 35-60 6C (optimum, 55 6C), with 0-1.0 % NaCl (optimum, 0.2 %) and at pH 7.0-9.0 (optimum, pH 7.0). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain AT-A2 T belonged to the genus Tepidimonas and its closest neighbour was Tepidimonas thermarum AA-1 T with a sequence similarity of 97.5 %. The predominant cellular fatty acids were C 16 : 0 (40.2 %), summed feature 3 (C 16 : 1 v7c and/or C 16 : 1 v6c; 20.1 %) and C 17 : 0 cyclo (11.5 %). The major respiratory quinone was Q-8. The polar lipid profile consisted of phosphatidylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, an uncharacterized aminolipid and several uncharacterized phospholipids. The DNA G+C content of strain AT-A2 T was 70.1 mol%. The mean level of DNA-DNA relatedness between strain AT-A2 T and Tepidimonas thermarum AA-1 T was 23.9 %. On the basis of the phylogenetic and phenotypic data, strain AT-A2 T should be classified as representing a novel species, for which the name Tepidimonas fonticaldi sp. nov. is proposed. The type strain is