Ecophysiology of novel core phylotypes in activated sludge wastewater treatment plants with nutrient removal

An in depth understanding of the ecology of activated sludge nutrient removal wastewater treatment systems requires detailed knowledge of the community composition and metabolic activities of individual members. Recent 16S rRNA gene amplicon surveys of activated sludge wastewater treatment plants with nutrient removal in Denmark indicate a core set of bacterial genera. These core genera are suggested to be responsible for the bulk of nutrient transformations underpinning the functions of these plants. While we know the basic in situ activities of some of these genera, there is little to no information for the majority, and thus no indication as to their relevance to the ecology of these systems. The next logical step will therefore be to systematically characterize each of these organisms. To this end, this study applied in situ FISH based methods to characterize a selection of these phylotypes for which limited to no information is available for their ecophysiology in activated sludge. A combination of MAR-FISH and SIP was applied to identify members of the genera Rhodoferax, Dechloromonas and Sulfuritalea, all within the class Betaproteobacteria, to be core denitrifiers in these systems. Similar analysis was performed for novel core genera within Sub-group 10 of the phylum Acidobacteria, and the SC-I-84 lineage within the Betaproteobacteria. These two genera appear to be highly specialized, giving negative results for the multiple heterotrophic and autotrophic physiologies assessed so far, which may explain why many of these core organisms have not attracted attention during the many years of research into the ecology of these systems. The future goal will be to obtain genome sequences for members of these core genera, applying recently developed protocols for the assembly of genomes from metagenomes; incorporating genomics, transcriptomics and in situ based methods to develop and validate detailed metabolic models for each of these suggested core genera.