The Composition and Implications of Polyphosphate-Metal in Enhanced Biological Phosphorus Removal Systems

The individual cellular level and quantitative Polyphosphate (PolyP)-metal compositions in EBPR (enhanced biological phosphorus removal) systems have hardly been investigated and its potential link to EBPR performance therefore remain largely unknown. In this study, we applied scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDX) method that enabled detection and semiquantification of metal elemental compositions in intact intracellular PolyP granules in individual PAO (polyphosphate accumulating organism) cells. We, for the first time, revealed diverse and dynamic distributions of different metals ions in the PolyP-metal granules in different EBPR systems operated with the same influent metal composition but varying SRT of 5-30 days. We further demonstrated that the PolyP-metal composition diversity correlated with 16S rRNA gene based PAO phylogenetic diversity, suggesting the possible phylogeny-dependent PolyP-metal composition variation. The impact of PolyP metal composition in EBPR system, especially the Mg content in PolyP granules, was evidenced by the significant and strong positive correlation between PolyP-Mg content and the long-term stability of the four EBPR systems with varying SRTs. The PolyP-Mg content can therefore possibly serve as an indicator for EBPR performance monitoring. The results demonstrated that phenotyping techniques, such as PolyP-metal-based profiling, in compliment, or combined with genotyping techniques such as phylogenetic and functional gene sequencing, can provide more insights into the mechanisms and performance prediction of this important microbial ecosystem.