UNRAVELING THE EXTENT OF DIVERSITY WITHIN THE ORDER PLANCTOMYCETALES

The phylogenetic positions of 22 isolates that morphologically resembl e members of the family Planctomycetaceae were determined by sequence analysis of genes coding for 16S rRNA. While nine and eight isolates c ould be assigned to the genera Planctomyces and Pirellula, respectivel y, three strains grouped near Isosphaera pallida and one strain was cl osely related to Gemmata obscuriglobus. No isolate was found to be rel ated to a previously described species of any of the four genera at th e 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 repr esentative of a novel genus of the family. Comparison with environment al clone sequences representing planctomycetes in soil and water revea led that three of the novel isolates were related to one clone of soil origin, but no close relationships between clones and the other new s trains were found. The study reveals that the biodiversity of planctom ycetes is significantly greater than was previously;determined.