Identification of ciliate grazers of autotrophic bacteria in ammonia-oxidizing activated sludge by RNA stable isotope probing

An rRNA-derived eukaryote clone library was constructed to identify the active protozoan phylotypes present in activated sludge and RNA-SIP was used to track carbon from bicarbonate and acetate into protozoa under ammonia-oxidizing and denitrifying conditions. The results from RNA-SIP analysis indicated that the peritrich ciliate Epistylis galea dominated the acquisition of carbon from bacteria with access to C[O.sub.2] under ammonia-oxidizing conditions, while no evidence was found for the specific grazing on acetate consumers under denitrifying conditions.