Phylogeny of the filamentous bacterium 'Nostocoida limicola' III from activated sludge

Five strains of the filamentous bacterium 'Nostocoida limicola' III were su ccessfully isolated into pure culture from samples of activated sludge biom ass from five plants in Australia. 16S rRNA gene sequence analyses showed t hat all isolates were members of the Planctomycetales, most closely related to Isosphaera pallida, but they differed phenotypically from this species in that they did not glide and were not thermotolerant. The ultrastructure of these 'N. limicola' III isolates was also consistent with them being Pla nctomycetales, in that they possessed complex intracellular membrane system s compartmentalizing the cells. However, the arrangements of these intracel lular membranes differed between isolates. These data confirm that 'N. limi cola' III is phylogenetically unrelated to both 'N. limicola' I and 'N. lim icola' II, activated sludge filamentous bacteria which share morphological features in common with 'N. limicola' III and which have been presumed hist orically to be the same or very similar bacteria.