Multiple extracellular polymeric substances pathways expressed by Accumulibacter and the flanking community during aerobic granule formation and after influent modification

Aerobic granular sludge is a biological wastewater treatment process in which a microbial community forms a granular biofilm. The role of Candidatus Accumulibacter in the production of a biofilm matrix composed of extracellular polymeric substances was studied in a sequencing batch reactor enriched with polyphosphate-accumulating organisms. The metabolisms of the microbial populations were investigated using de novo metatranscriptomics analysis. Finally, the effect of decreasing the influent phosphate concentration was investigated.

A few weeks after the reactor start-up, the microbial community was dominated by Accumulibacter . Up to nine species were active in parallel. However, the most active species differed according to sampling time. Reducing the phosphate concentration led to a dominance of the glycogen-accumulating organism Propionivibrio , with some Accumulibacter species still abundant. De novo metatranscriptomic analysis indicated a high diversity of potential extracellular substances produced mainly by Azonexus, Accumulibacter, Candidatus Contendobacter, and Propionivibrio . Moreover, the results suggest that Azonexus, Contendobacter and Propionivibrio recycle the neuraminic acid produced by Accumulibacter . Changes in the microbial community did not cause the granules to disintegrate, indicating that a Propionivibrio -dominated community can maintain stable granules.