Phylogenetic relationships and uncertain taxonomy of Pedomicrobium species

The phylogenetic relationships among the species of the genus Pedomicrobium were studied by comparing their 16S rRNA sequences. The Pedomicrobium species form a coherent phylogenetic cluster within the genera of the hyphal budding bacteria in the alpha-Proteobacteria. The sequences of two strains of Pedomicrobium australicum were obtained from DNAs extracted from nonviable freeze-dried cells, which are the only source of material available, and were found to be almost identical (level of similarity, 99.9%). Overall, the Pedomicrobium species are closely related, with sequence similarities ranging from 96.2 to 99.9%. Pedomicrobium manganicum is phylogenetically the most distantly related species and exhibits the lowest similarity (96.2%) with Pedomicrobium americanum. Australian isolate Pedomicrobium sp. strain ACM 3067, P. americanum, and P. australicum are all very highly related, with similarities greater than 99%. Pedomicrobium sp. strain ACM 3067 is most closely related to P. australicum (level of similarity, 99.6%) and P. americanum (99.4%). These manganese-oxidizing species are more closely related to the iron-oxidizing species Pedomicrobium ferrugineum than to the other manganese-oxidizing species, P. manganicum. Taxonomic uncertainties resulting from the loss of the type culture of P. australicum are discussed.