An acidophilic, slightly thermophilic bacterium, designated strain NTAP-1T, that produces a thermostable extracellular acid collagenase activity with potential industrial applications was isolated from soil of Aoba-yama Park, Sendai, Japan. The temperature range for growth was 40-65 degrees C, with an optimum at 55 degrees C, and the pH range for growth was 2.5-6.5, with an optimum at pH 5.5. Analysis of the 16S rDNA sequence of strain NTAP-1T showed that it is most closely related to strains of the genus Alicyclobacillus. Consistently, the major constituents of the cell-membrane lipid of strain NTAP-1T were omega-alicyclic fatty acids. However, DNA-DNA reassociation studies showed only low similarities (less than 33%) to any type strain of Alicyclobacillus. On the basis of the phenotypic and genotypic properties, a novel species is proposed, Alicyclobacillus sendaiensis sp. nov., represented by strain NTAP-1T (=JCM 11817T=ATCC BAA-609T).