Diversity and distribution of a deeply branched novel proteobacterial group found in anaerobic–aerobic activated sludge processes

Summary A novel coccobacilli group found previously in enhanced biological phosphorus removal (EBPR) systems was further revealed to have a high degree of diversity and distribution in various activated sludge systems. Phylogenetic analysis based on 14 existing and 18 newly retrieved 16S rRNA sequences revealed that these sequences formed a novel cohesive cluster with seven subgroups in the γ‐ Proteobacteria . Fluorescence in situ hybridization with a set of probes designed specifically targeting the novel group at different hierarchical levels showed that the novel group with a coccoid (2–4 µm) to occasionally long‐rod (up to 20 µm) shape widely distributed and in some cases predominated in sludge samples taken from nine lab‐ and full‐scale EBPR systems (10–50% of total cells) and four conventional activated sludge systems (1–10%). Variation of predominance was also observed among those subgroups in systems showing deteriorated or effective EBPR activity.