Publication
Wastewater resulting from human activities must be treated to minimize the impact on the receiving ecosystems. One of such potential impacts in lakes and other water bodies is eutrophication, an excessive increase in their nitrogen and phosphorus content. Eutrophication promotes the excessive growth of algae and plants, which lead to oxygen depletion and the death of aquatic life. Therefore, nitrogen and phosphorus need to be removed from wastewater in the treatment plants releasing to sensitive water bodies. Phosphorus, in particular dissolved phosphate, can be removed chemically or in the biological treatment step in wastewater treatment plants. Enhanced biological phosphorus removal (EBPR) processes rely on so-called polyphosphate-accumulating organisms (PAOs), which take up phosphate from the medium not only for growth but also for storage and energy in specific metabolic processes. Among these, members of genus Candidatus Accumulibacter were the first to be discovered, and their physiology during the EBPR operation cycle is the best described so far, so much so they are designated as classical PAOs. While Accumulibacter enrichments can be obtained in laboratory-scale reactors, they have not been isolated in pure culture, which is an indication of the incomplete knowledge on its requirements and the reason why culture-independent methods have been key to advance in the understanding of EBPR. Furthermore, species and strains within the genus (hereafter referred to as populations) have been reported to differ in their metabolic capabilities. To gain a broader understanding on the metabolic capabilities of Accumulibacter populations, genome-scale metabolic models (GEMs) were reconstructed for several representatives. The process revealed potential auxotrophies and differences in the uptake of small molecules or the synthesis of extracellular polysaccharides, particularly relevant for the formation of the extracellular matrix that characterizes wastewater treatment biofilms. The systematic extraction and comparison of their core networks revealed that the highest diversity affected the tricarboxylic acid cycle and electron transfer reactions. Despite this, clear differences with the non-Accumulibacter populations analyzed were observed. In addition, comprehensive metatranscriptomic and metabolomic datasets of the EBPR cycle were obtained from a laboratory-scale reactor enriched with Accumulibacter. Multiple changes in gene transcription and metabolite abundance were detected. Transcriptional changes between selected time points were integrated in one of the GEMs to understand their global effect. Finally, the transcriptome of Accumulibacter within the complex community of a reactor performing EBPR under different influents was analyzed. Two populations were transcriptionally active in the simplest influent, and showed differences in transcription despite their high genetic similarity. In addition, one of the populations was active in the medium