|Van Berkum, Peter|
Submitted to: North American Conference on Symbiotic Nitrogen Fixation
Publication Type: Abstract Only
Publication Acceptance Date: 11/21/2000
Publication Date: N/A
Technical Abstract: It is common practice to reconstruct bacterial evolutionary histories from sequence divergence of the 16S rRNA genes. The objective is to trace ancestral lineages, which are used in taxonomy to support decisions of nomenclature. Use of the 16S rRNA genes relies on assumptions that are increasingly in question. The concern is that each bacterial cell may harbor multiple divergent copies of the 16S rRNA gene and that the evolutionary pattern of the 16S rRNA gene sometimes may have been reticulate in part instead of strictly hierarchical (Yap et al., J. Bacteriol. 181:5201-5209). To address this issue we compared evolutionary histories of the rhizobia reconstructed from sequence divergence of 16S rRNA genes and three other loci. Placement of the genus Sinorhizobium was nested within the genus Rhizobium in reconstructions made from 23S rRNA and RnaseP gene sequence divergence. The phototrophic isolates of Aeschynomene indica were placed outside instead of within the genus Bradyrhizobium in reconstructions made from sequence divergence of the Internally Transcribed Space (ITS) region and the RnaseP gene. Therefore, it may be inappropriate to use sequence divergence of the 16S rRNA gene alone for reconstructing rhizobial phylogeny and use results in decisions of nomenclature.