The Microbial Community Composition of a Nitrifying-Denitrifying Activated Sludge from an Industrial Sewage Treatment Plant Analyzed by the Full-Cycle rRNA Approach

Summary The composition of the microbial community present in the nitrifying-denitrifying activated sludge of an industrial wastewater treatment plant connected to a rendering facility was investigated by the full-cycle rRNA approach. After DNA extraction using three different methods, 94 almost full-length 16S rRNA gene clones were retrieved and analyzed phylogenetically. 59% of the clones were affiliated with the Proteobacteria and clustered with the β- (29 clones), α- (24), and δ-class (2 clones), respectively. 15 clones grouped within the green nonsulfur (GNS) bacteria and 11 clones belonged to the Planctomycetes . The Verrucomicrobia , Acidobacteria, Nitrospira , Bacteroidetes , Firmicutes and Actinobacteria were each represented by one to five clones. Interestingly, the highest “species richness” [measured as number of operational taxonomic units (OTUs)] was found within the α-class of Proteobacteria , followed by the Planctomycetes , the β-class of Proteobacteria , and the GNS-bacteria. The microbial community composition of the activated sludge was determined quantitatively by using 36 group-, subgroup-, and OTU-specific rRNA-targeted oligonucleotide probes for fluorescence in situ hybridization (FISH), confocal laser scanning microscopy and digital image analysis. 89% of all bacteria detectable by FISH with a bacterial probe set could be assigned to specific divisions. Consistent with the 16S rRNA gene library data, members of the β-class of Proteobacteria dominated the microbial community and represented almost half of the biovolume of all bacteria detectable by FISH. Within the β-class, 98% of the cells could be identified by the application of genus- or OTU-specific probes demonstrating a high in situ abundance of bacteria related to Zoogloea and Azoarcus sensu lato. Taken together, this study provides the first encompassing, high-resolution insight into the in situ composition of the microbial community present in a full-scale, industrial wastewater treatment plant.