Isolates of eight bacterial filaments fitting the published morphological description of 'Nostocoida limicola' I were obtained from the mixed liquor of four different Australian and one Czech Republic activated sludge plants by micromanipulation. On the basis of their near complete (Ben 200 and Ben 201), or partial (Ben 77, Ben 78, Ben 202, Ben 203, Ben 204 and Ben 205) 16S rRNA gene sequences, six of these isolates were 99.3-100% similar to Lactosphaera pasteurii and Trichococcus flocculiformis, a bulking filament only reported previously in Germany. The other two (Ben 203 and Ben 204) were 99.9% similar to Streptococcus suis. Hence, all are in the low mol % G+C gram-positive bacteria division of the Bacteria. On this evidence 'N. limicola' I is phylogenetically unrelated to 'Nostocoida limicola' II, which is now known to be in the Actinobacteria, even though these two filamentous bacteria appearing in activated sludge systems have been considered to be closely related to each other historically.