'Candidatus Nostocoida limicola', a filamentous bacterium from activated sludge

Five strains of 'Candidatus Nostocoida limicola' were isolated by micromani pulation from two activated sludge plants. Two (Ben17 and Ben18) were from Sunbury, Victoria, Australia, and three (Ben67, Veri and Ver2) were from Ve rona, Italy. The near complete 16S rDNA sequences were determined for five strains and the phylogenetic location of this important bulking filament in the actinomycete subphylum is reported for the first time. Phylogeneticall y, the Ben strains formed one group with 99.4% 16S rDNA similarity, and the Ver strains formed another with 99.9 % 16S rDNA similarity. The mean simil arity between the two groups was 97.4%. By 16S rDNA comparison, the closest relative to all strains was Terrabacter sp. strain DPO1361 (95.0-95.5% ide ntical). On R2A medium, all strains generally grew as short filaments or cl umps of cocci, whereas on glucose sulfide (GS) medium, all grew as irregula r twisting filaments comprising Cram-positive and Gramnegative cells, which is close to their in situ morphology, Polyphosphate was stored either as g ranules (R2A) or throughout the trichomes (GS), None of the strains could g row without added nitrogen, reduce nitrate to nitrogen gas or grow anaerobi cally, whereas all could grow at 15-30 degrees C, produce catalase and redu ce nitrate to nitrite. All were inactive in the Hugh & Leifson test. This p aper describes 'Candidatus Nostocoida limicola'.