Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/1999
Publication Date: N/A
Interpretive Summary: Some aerobic spore-forming bacteria are so closely related that they have identical biochemical and genetic traits. Because of this situation, difficulties are encountered in classifying these closely related organisms sby presently accepted techniques including biochemical evaluation, analysi of DNA similarity, and comparison of the DNA sequence of a gene called rRNA. The present work showed that closely related organisms can be classified by comparing the inferred DNA sequence of several genes different from the rRNA gene.
Technical Abstract: Bacillus globisporus and B. psychrophilus are one among many pairs of ecologically distinct taxa that cannot be distinguished by 16S rRNA sequence data. This study has investigated whether the failure of 16S to distinguish these taxa stems from this molecule's unusually slow rate of evolution or whether other factors might be preventing neutral sequence divergence at 16S as well as every other gene. B. globisporus and B. psychrophilus were each surveyed for restriction-site variation in two protein-coding genes. These species were easily distinguished as separate DNA sequence clusters for each gene. The failure of 16S to distinguish these species is, therefore, a consequence of the extremely slow rate of 16S evolution. The present results and previous results, involving two Mycobacterium species, demonstrate that there exist closely related species which have diverged long enough to have formed separate clusters for protein-coding genes but not for 16S rRNA. These results support an earlier argument that sequence clustering in protein-coding genes should be a primary criterion for identifying ecologically distinct groups and classifying them as separate species.