Evolution of the RNA polymerase B' subunit gene (rpoB') in Halobacteriales: a complementary molecular marker to the SSU rRNA gene
Abstract
Many prokaryotes have multiple ribosomal RNA operons. Generally, sequence differences between small subunit (SSU) rRNA genes are minor (<1%) and cause little concern for phylogenetic inference or environmental diversity studies. For Halobacteriales, an order of extremely halophilic, aerobic Archaea, within-genome SSU rRNA sequence divergence can exceed 5%, rendering phylogenetic assignment problematic. The RNA polymerase B' subunit gene (rpoB') is a single-copy conserved gene that may be an appropriate alternative phylogenetic marker for Halobacteriales. We sequenced a fragment of the rpoB' gene from 21 species, encompassing 15 genera of Halobacteriales. To examine the utility of rpoB' as a phylogenetic marker in Halobacteriales, we investigated three properties of rpoB' trees: the variation in resolution between trees inferred from the rpoB' DNA and RpoB' protein alignment, the degree of mutational saturation between taxa, and congruence with the SSU rRNA tree. The rpoB' DNA and protein trees were for the most part congruent and consistently recovered two well-supported monophyletic groups, the clade I and clade II haloarchaea, within a collection of less well resolved Halobacteriales lineages. A comparison of observed versus ...Continue Reading
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