Synthesis and degradation of polyphosphate: scaling-up of molecular reactions to understand phosphorus removal in a wastewater treatment plant

Jaisi, DebPolyphosphate (poly-P) is a ubiquitous long-chain phosphorous (P) compound that has many biological functions and plays an important role in the environmental P cycling. Poly-P responds strongly to oxic-anoxic conditions and P availability, however its synthesis and degradation mechanisms remain largely understudied. This research investigated the mechanisms of poly-P cycling at different scales from enzyme-substrate reaction to bacterial cell culture and to field study in a wastewater treatment plant (WWTP). It included measurements of P speciation [orthophosphate (PO4) and poly-P], enzyme activity, microbial gene expression, and phosphate oxygen isotope ratios (δ 18OP). Enzyme reaction results show that both acidic phosphatase and alkaline phosphatase enzymes are capable of catalyzing poly-P degradation, with contrasting efficiency of > 70% and < 18%, respectively. Isotope fractionation factors during enzymatic degradation of poly-P varied from +1.63‰ to +4.39‰, a positive fractionation factor, which is uncommon and hence distinct from degradation of many other organic P compounds. Results from bacterial incubations (Escherichia coli JM103 and Pseudomonas putida KT2440) suggest that poly-P synthesis and degradation is strongly associated with cell growth stage: poly-P is synthesized during exponential growth, causing an apparent isotope fractionation (~+5‰) in the residual PO4 in E. coli incubation. Degradation of poly-P in late stationary phase, however, leads to a lighter δ 18OP values. Poly-P cycling in WWTP responded strongly to variations in dissolved oxygen concentrations: under oxic condition high amount of poly-P suggest poly-P synthesis, while the lighter δ 18OP values suggest rapid microbial P cycling potential via organic matter degradation. Under anoxic condition, degradation of poly-P was accompanied by continued assimilation of PO4, suggested by decrease in its concentration and heavier δ18OP values. Overall these findings indicate towards alternative poly-P cycling mechanism in the WWTP in this study that some microorganisms may continue to take up PO4 under anoxic condition even though degradation of poly-P and release of PO4 are otherwise common processes under this condition.University of Delaware, Department of Plant and Soil SciencesM.S