16s rRNA (genes coding for rRNA) sequence comparisons were conducted with the following three psychrophilic strains: Bacillus globisporus W25* (T = type strain) and Bacillus psychrophilus W16AT, and W5.These strains exhibited more than 99.5 % sequence identity and within experimental uncertainty could be regarded as identical. Their close taxonomic relationship was further documented by phenotypic similarities. In contrast, previously published DNA-DNA hybridization results have convincingly established that these strains do not belong to the same species if current standards are used. These results emphasize the important point that effective identity of 16s rRNA sequences is not necessarily a sufficient criterion to guarantee species identity. Thus, although 16s rRNA sequences can be used routinely to distinguish and establish relationships between genera and well-resolved species, very recently diverged species may not be recognizable.

Comparative 16s rRNA (rDNA) sequence analyses performed on the thermophilic Bacillus species Bacillus acidocaldarius, Bacillus acidoterrestris, and Bacillus cycloheptanicus revealed that these organisms are sufficiently different from the traditional Bacillus species to warrant reclassification in a new genus, Alicyclobacillus gen. nov. An analysis of 16s rRNA sequences established that these three thermoacidophiles cluster in a group that differs markedly from both the obligately thermophilic organism Bacillus stearothermophilus and the facultatively thermophilic organism Bacillus coagulans, as well as many other common mesophilic and thermophilic Bacillus species. The thermoacidophilic Bacillus species B. acidocaldarius, B. acidoterrestris, and B. cycloheptanicus also are unique in that they possess w-alicylic fatty acid as the major natural membranous lipid component, which is a rare phenotype that has not been found in any other Bacillus species characterized to date. This phenotype, along with the 16s rRNA sequence data, suggests that these thermoacidophiles are biochemically and genetically unique and supports the proposal that they should be reclassified in the new genus Alicyclobacillus.

The sequence of the major portion of a Bacillus cycloheptanicus strain SCH(T) 16S rRNA gene is reported. This sequence suggests that B. cycloheptanicus is genetically quite distinct from traditional Bacillus strains (e.g., B. subtilis) and may be properly regarded as belonging to a different genus. The sequence was determined from DNA that was produced by direct amplification of ribosomal DNA from a lyophilized cell pellet with straightforward polymerase chain reaction (PCR) procedures. By obviating the need to revive cell cultures from the lyophile pellet, this approach facilitates rapid 16S rDNA sequencing and thereby advances studies in molecular systematics.

No abstract

No abstract