Seven closely related xylanolytic, thermophilic bacilli were isolated from mud and water samples from the Gionen and Diyadin hot springs, respectively located in the Turkish provinces of Balikesir and Agri. On the basis of morphology and biochemical characteristics, one of the isolates, designated strain G2(T), was studied further. Strain G2(T) is a xylanolytic, sporulating, Grampositive, rod-shaped bacterium. The isolate is a thermophilic (optimum temperature for growth, 55-60degreesC, facultative anaerobe that grows on a wide range of carbon sources, including glucose, starch, xylose and mannitol. It expressed a high level of xylose isomerase activity on xylose and also on glucose. 16S rRNA gene sequence analysis showed that this isolate resembled Anoxybacillus flavithermus DSM 2641(T) (> 97 % similarity), but 16S-23Sr DNA internally transcribed spacer polymorphism PCR showed variation between DSM 2641(T) and isolate G2(T). However, it is also known that analysis of 16S rRNA gene sequences may be insufficient to distinguish between some species. In DNA-DNA hybridization, thermophilic isolate G2(T) showed relatedness of 53.4% to A. flavithermus and about 45.0% to Anoxybacillus pushchinoensis, indicating that it is distinct at the species level. On the basis of the evidence presented, it is proposed that strain G2(T) (=NCIMB 13933(T) =NCCB 100040(T)) be designated as the type strain of Anoxybacillus gonensis sp. nov.