Disentangling Community Structure of Ecological System in Activated Sludge: Core Communities, Functionality, and Functional Redundancy

The microbial ecosystems of the sludge were characterized in terms of the core community structure, functional pathways, and functional redundancy through Illumina MiSeq sequencing and PICRUSt analysis on the activated sludge (AS) samples from an extended activated aeration process. Based on the identified OTU distribution, we identified 125 core community genera, including 3 abundant core genera and 21 intermittent abundant core genera. Putative genera Nitrosomonas, Nitrotoga, Zoogloea, Novosphingobium, Thermomonas, Amaricoccus, Tetrasphaera, Candidatus Microthrix, and Haliscomenobacter, which are associated with functions of nitrifying, denitrifying, phosphorus accumulating, and bulking and foaming, were found to present as the core community organisms in the AS sampled from the conventional extended aeration AS processes. The high-abundant nitrogen metabolic pathways were associated with nitrate reduction to ammonium (DNRA and ANRA), denitrification, and nitrogen fixation, while the ammonia oxidation-related genes (amo) were rarely annotated in the AS samples. Strict functional redundancy was not found with the AS ecosystem as it showed a high correlation between the community composition similarity and function similarity. In addition, the classified dominant core genera community was found to be sufficient to characterize the functionality of AS, which could invigorate applications of 16S rDNA MiSeq sequencing and PICRUSt for the prediction of functions of AS ecosystems.