Disruption in gene expression cycles of polyphosphate-accumulating organisms is associated with a full-scale enhanced biological phosphorus removal instability event

Abstract

Enhanced biological phosphorus removal (EBPR) enriches polyphosphate-accumulating organisms (PAOs) via alternating anaerobic/aerobic feast–famine cycles to remove phosphorus from wastewater. EBPR can be prone to instability, although the causes are often unclear. Genome-centric metatranscriptomics was used to investigate an EBPR instability event at a full-scale facility that typically experiences a winter instability event to identify changes in microbial community composition and gene expression characteristic of reduced EBPR performance. The facility sampled operates an anaerobic/anoxic/oxic (A2O) EBPR process. Notably, the process monitoring data indicated few process changes beyond increased effluent phosphorus (>3 mg L⁻¹ compared to typical concentrations <0.5 mg L⁻¹) and lower water temperatures during the instability event. Microbial community composition remained consistent before, during, and after the instability event. Two PAO MAGs, Ca. Accumulibacter phosphatis and Ca. Accumulibacter propinquus, were the most abundant and transcriptionally active PAOs. DESeq2 analyses of significantly (adjusted p-value < 0.01) and differentially (|log₂(FoldChange)| >1) expressed genes revealed that the expression of key carbon metabolism, energy metabolism, and denitrification genes that typically peak in the anaerobic zone under anaerobic, high carbon conditions shifted to peak in the anoxic zone during the instability. These results demonstrate a shift in PAO activity, and not community composition, associated with a full-scale EBPR instability event.