A polyphasic taxonomic study of thermophilic bacilli from a wide geographical area

Two hundred and thirty-four thermophilic Bacillus strains isolated from geographically widespread locations were examined by phenotypic characterisation followed by numerical analysis. The strains were distributed between eighteen cluster-groups which were subsequently evaluated in DNA base composition and DNA sequence homology studies. The inclusion of type and reference strains unambiguously identified strains related to B. licheniformis, B. pallidus, B. smithii, B. stearothermophilus, B. thermocloacae and B. thermoglucosidasius. Other reference strains included in distinctive groups were 'B. caldotenax', together with 'B. caldovelox' and 'B. caldolyticus', B. kaustophilus and 'B. thermodenitrificans'. An emended description of B. kaustophilus is provided. It is proposed that 'B. caldotenax' and 'B. thermodenitrificans' should be accepted as validly described species. Members of other clusters that appeared to have distinctive characteristics, including beta-glucanase production and the ability to degrade tyrosine, may provide the nuclei of further novel species.