A facultatively anaerobic, halotolerant, moderately thermophilic and non-sporulating bacterium, designated strain 10C(T), was isolated from deep-sea hydrothermal vent samples collected on the 13 degrees N East Pacific Rise at a depth of approximately 2600 m. Cells of strain 10C(T) were Gram-positive, motile rods, and grew optimally at 45 degrees C (range 12-49 degrees C), pH 7.0 (range pH 5.5-9.5) and 0-2 % NaCl (range 0-11 %). (+)-L-Lactate was the main organic acid detected from carbohydrate fermentation with traces of formate, acetate and ethanol. Strain 10C(T) was catalase-positive, oxidase-negative and reduced nitrate to nitrite under anaerobic conditions. The DNA G+C content was 50.4 mol%. Its closest phylogenetic relatives were Exiguobacterium aestuarii TF-16(T) and Exiguobacterium marinum TF-80(T) (16S rRNA gene sequence similarity >99 %). However, strain 10C(T) differed genotypically from these two Exiguobacterium species as indicated by DNA-DNA relatedness data. Therefore, on the basis of phenotypic, genotypic and phylogenetic characteristics, strain 10C(T) is considered to represent a novel species of the genus Exiguobacterium, for which the name Exiguobacterium profundum sp. nov. is proposed. The type strain is 10C(T) (=CCUG 50949(T)=DSM 17289(T)).