Unraveling the extent of diversity within the order Planctomycetales

The phylogenetic positions of 22 isolates that morphologically resemble members of the family Planctomycetaceae were determined by sequence analysis of genes coding for 16S rRNA. While nine and eight isolates could be assigned to the genera Planctomyces and Pirellula, respectively, three strains grouped near Isosphaera pallida and one strain was closely related to Gemmata obscuriglobus. No isolate was found to be related to a previously described species of any of the four genera at the species level. Morphological characters and sequence idiosyncrasies of genes coding for 16S rRNA of the isolates generally correlated with features described for the four genera to which the isolates could be assigned. One strain stands phylogenetically isolated and may be representative of a novel genus of the family. Comparison with environmental clone sequences representing planctomycetes in soil and water revealed that three of the novel isolates were related to one clone of soil origin, but no close relationships between clones and the other new strains were found. The study reveals that the biodiversity of planctomycetes is significantly greater than was previously determined.