A Gram-negative, strictly anaerobic, halophilic, motile, sporulating and rod-shaped bacterium, T designated strain HY-42-06(T), was isolated from tidal flat sediment from Ganghwa Island in South Korea. The isolate produced glycerol, ethanol and CO2 as fermentation end-products from glucose. Strain HY-42-06(T) grew optimally at 35 degrees C, pH 7(.)5 and 3% (w/v) artificial sea salts. No growth was observed in the absence of sea salts. In phylogenetic analyses based on 16S rRNA gene sequence, strain HY-42-06(T) showed a distinct phyletic line within the members of cluster I of the order Clostridiales. The closest phylogenetic neighbour to strain HY-42-06(T) was Clostridium novyi ATCC 17861(T) (94(.)91% 16S rRNA gene sequence similarity). Several phenotypic characters readily differentiate the tidal flat isolate from phylogenetically related clostridia. On the basis of polyphasic evidence, strain HY-42-06(T) should be classified as a representative of a novel species, for which the name Clostridium ganghwense sp. nov. is proposed. The type strain is HY-42-06(T) (=IMSNU 40127(T) = KCTC 5146(T)=jCM 13193(T)).