Candidate phyla radiation

Although there are a few exceptions, members of the candidate phyla radiation generally lack several biosynthetic pathways for several amino acids and nucleotides. To date, there has been no genomic evidence that indicates that they are capable of producing the lipids essential for cell envelope formation. Furthermore, CPR members have unique ribosomal features. While the members of CPR are generally uncultivable, and therefore missed in culture-dependent methods, they are also often missed in culture-independent studies that rely on 16S rRNA sequences. Their rRNA genes appear to encode proteins and have self-splicing introns, features that are rarely seen in bacteria, although they have previously been reported. Owing to these introns, members of CPR are not detected in 16S-dependent methods. Additionally, all CPR members are missing the L30 ribosomal protein, a trait that is often seen in symbionts. Many of its characteristics are similar or analogous to those of ultra-small archaea (Nanobdellati). == Phylogeny ==

The Candidate phyla radiation was found to be sister to all other bacteria according to some early phylogenetic analyses of this group based on ribosomal proteins and protein family occurrence profiles. These studies found the following phylogeny between phyla and superphyla. The superphyla are shown in bold. The evolutionary relationships that are typically supported by these studies are as follows. }} == Provisional taxonomy ==

Because many CPR members are uncultivable, they cannot be formally put into the bacterial taxonomy, but a number of provisional, or Candidatus, names have been generally agreed on. As of 2017, two superphyla are generally recognized under CPR, Parcubacteria and Microgenomates. == See also ==