Quantitative DNA Stable Isotope Probing Identifies Active Microorganisms Assimilating Volatile Fatty Acids in Full-Scale Enhanced Biological Phosphorus Removal Processes

Enhanced biological phosphorus removal (EBPR) systems
often rely
on exogenous carbon sources, such as volatile fatty acids (VFAs),
to achieve higher P removal. Here, we employed DNA quantitative stable
isotope probing (qSIP) using two VFAs, acetate and propionate, in
cyclic anaerobic/aerobic incubations to assess their effects on P
cycling and microbial activity with biomass from two full-scale EBPR
water resource-recovery facilities that utilize VFA addition. We found
that anaerobic VFA uptake preferences differed within known groups
of PAOs, such as Candidatus Accumulibacter and Tetrasphaera-affiliated members (e.g., Ca. Phosphoribacter), between the two biomasses. The combination of
qSIP with metagenomics identified isotopically labeled phages that
were linked to active PAOs, highlighting their potential roles in
modulating EBPR community composition and activity. The highest levels
of anaerobic labeling from acetate were in genomes belonging to Saccharimonadales and Rickettsiales, which
are generally host-associated with bacteria and eukaryotes, respectively.
This finding highlights the possibility of cross-feeding between PAO
hosts and their parasites or predators, as well as the role of so-far
uncharacterized organisms participating in carbon cycling under EBPR
conditions. Collectively, these results expand our understanding of
the ecological interactions involved in communities anaerobically
uptaking VFAs and cycling P that are central to EBPR.