Whole-genome reciprocal BLAST analysis reveals that planctomycetes do not share an unusually large number of genes with Eukarya and Archaea.

The genome sequences of Rhodopirellula baltica, formerly Pirellula sp. strain 1, Blastopirellula marina, Gemmata obscuriglobus, and Kuenenia stuttgartiensis were used in a series of pairwise reciprocal best-hit analyses to evaluate the contested evolutionary position of Planctomycetes. Contrary to previous reports which suggested that R. baltica had a high percentage of genes with closest matches to Archaea and Eukarya, we show here that these Planctomycetes do not share an unusually large number of genes with the Archaea or Eukarya, compared with other Bacteria. Thus, best-hit analyses may assign phylogenetic affinities incorrectly if close relatives are absent from the sequence database.