Ecophysiology of putative polyphosphate-accumulating organisms revealed by FISH-Raman

Phosphate is a vital, but limited resource, so recycling is crucial to support the increasing demand. The enhanced biological phosphorus removal process in wastewater treatment plants can ensure recycling of phosphate from the wastewater by the use of polyphosphate-accumulating organisms, such as certain Candidatus Accumulibacter, Tetrasphaera, and Dechloromonas species. They all store phosphate intracellularly as polyphosphate, depending on alternating anaerobic and aerobic conditions, although with diverse metabolisms. Recent mass-balance studies of full-scale enhanced biological phosphorus removal plants indicate the presence of several unknown polyphosphate-accumulating organisms. In order to get a comprehensive overview of all abundant polyphosphate-accumulating organisms for surveillance and optimization of phosphorus removal, it is important to identify these and elucidate their physiology.
The aim was to investigate whether members of Rhodoferax, Tessaracoccus, and Sulfuritalea, could be polyphosphate-accumulating organisms. We used 16S rRNA gene sequencing to describe their global abundance, metagenomics to retrieve high-quality metagenome-assembled genomes for annotation of metabolic pathways, and quantitative FISH-Raman analysis of polyphosphate and other intracellular storage polymers to verify the hypotheses.
Rhodoferax and Sulfuritalea were observed in both Danish and global plants with up to 5.8% and 2.8% of total biomass, respectively, while Tessaracoccus was less abundant. FISH-Raman analysis of Tessaracoccus and Rhodoferax showed signs of polyphosphate storage. These results were supported by the retrieved metagenome-assembled genomes, which showed genes typical for the phosphate-accumulation and cycling in polyphosphate-accumulating organisms.
Mapping the ecophysiology of these three genera can contribute to the search of finding the last important polyphosphate-accumulating organisms for phosphorus removal in wastewater.