Description of Caldanaerobius fijiensis gen. nov., sp. nov., an inulin-degrading, ethanol-producing, thermophilic bacterium from a Fijian hot spring sediment, and reclassification of Thermoanaerobacterium polysaccharolyticum and Thermoanaerobacterium zeae as Caldanaerobius polysaccharolyticus comb. nov. and Caldanaerobius zeae comb. nov.

An obligately anaerobic, spore-forming, Gram-type-positive but Gram-staining-negative thermophilic bacterium, strain JW/YJL-F3(T), was isolated from a Fijian hot spring sediment sample. Cells of strain JW/YJL-F3(T) were straight to slightly curved rods, 0.5-1.2 microm in diameter and 1.5-19 microm long. The temperature range for growth was between 40 and 67 degrees C, with an optimum at 60-63 degrees C. The pH(25 degrees C) range for growth was 4.5-8.4 with an optimum of 6.8. The salinity range for growth was 0-0.5 %. Strain JW/YJL-F3(T) utilized a range of substrates including arabinose, cellobiose, galactose, glucose, inulin, lactose, maltose, mannose, raffinose, ribose, trehalose, xylose and yeast extract as carbon and energy sources. The major fermentation end products from glucose were ethanol, acetate and formate. Strain JW/YJL-F3(T) converted thiosulfate to elemental sulfur, producing sulfur globules. The DNA G+C content was 37.6 mol% as determined by HPLC. Phylogenetic analysis using the 16S rRNA gene sequence indicated that the isolate is distantly related to the clade of the genus Thermoanaerobacterium. However, Thermoanaerobacterium polysaccharolyticum (96.7 % similarity to the type strain) and Thermoanaerobacterium zeae were the closest relatives, forming a separate, well-supported clade together with the novel isolate. Because Thermoanaerobacterium polysaccharolyticum, Thermoanaerobacterium zeae and strain JW/YJL-F3(T) have different features from other Thermoanaerobacterium species, including a higher G+C content and formate production, and are placed distantly from the remaining species of Thermoanaerobacterium (greater than 10 % distance) in the 16S rRNA gene sequence analysis, we propose to place the new isolate JW/YJL-F3(T) and Thermoanaerobacterium polysaccharolyticum and Thermoanaerobacterium zeae into the novel genus Caldanaerobius gen. nov. as Caldanaerobius fijiensis gen. nov., sp. nov. (the type species), Caldanaerobius polysaccharolyticus comb. nov. and Caldanaerobius zeae comb. nov., respectively. The type strain of Caldanaerobius fijiensis is JW/YJL-F3(T) (=ATCC BAA-1278(T) =DSM 17918(T)).