Phenotypic dynamics in polyphosphate and glycogen accumulating organisms in response to varying influent C/P ratios in EBPR systems

Abstract

This study employed molecular tools and single cell Raman micro-spectroscopy techniques to reveal the single cell- and population-level phenotypic dynamics and changes in functionally relevant organisms, namely polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), in response to influent loading readily biodegradable carbon to phosphorus ratio (C/P) changes in enhanced biological phosphorus removal (EBPR) systems. The results, for the first time, provided direct and cellular evidence confirming the adaptive anaerobic metabolic pathway shifts in PAOs in response to influent loading variations. Increase in influent readily biodegradable carbon to phosphorus (C/P) ratio from 20 to 50 led to nearly 50% decline in polyphosphate content and drastic rise of intracellular polyβhydroxybutyrate (PHB) to polyphosphate (polyP) ratio by nearly 6 times in PAOs, indicating corresponding diminishing reliance on polyP hydrolysis for energy as P becomes limiting. Influent carbon availability surge also impacted the intracellular carbon polymers in GAOs, with significant increase in the mean PHB content level but no observed changes in the intracellular glycogen level. Furthermore, the Raman-based quantification of differentiated intracellular polymer content associated with PAOs and GAOs, revealed new insights into the quantitative shift in intracellular carbon storage distribution between the two populations and their variations between the two carbon polymers (PHB, Glycogen). In summary, this investigation revealed high-resolution cellular level information regarding the metabolic flexibility in PAOs, phenotypic stoichiometry changes and carbon flux and distribution among PAOs and GAOs, in response to influent loading conditions. The new information will contribute to improvement in mechanistic EBPR modeling and design.