rRNA sequencing has shown that Leuconostocs comprise three distinct phylogenetic lineages which have been designated separate genera (viz., the genera sensu stricto, , and ). In addition, the 16S rRNA line formed by (formerly ) is exceptionally long: This fact, together with variations in the compositions of conserved positions in the 16S rRNA, has led to the hypothesis (D. Yang and C. R. Woese, Syst. Appl. Microbiol. 12:145-149, 1989) that this organism is a fast-evolving bacterium. Previous evidence that the leuconostocs should be divided into three genera and that is an example of tachytelic evolution has come solely from rRNA analyses. In this study we sequenced the gene encoding the β' subunit of DNA-dependent RNA polymerase of leuconostocs and performed a comparative phylogenetic analysis. The subdivision of the leuconostocs into three distinct lineages was confirmed by the gene data, but no evidence that indicated that is evolving at an extraordinary rate was found. If is truly tachytelic, then fast-evolving phenomena would be expected to occur throughout the whole genome, including this independent molecular chronometer.


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