Multiple extracellular polymeric substances pathways expressed byAccumulibacterand 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 ofCandidatusAccumulibacter 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 byAccumulibacter. 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 organismPropionivibrio, with someAccumulibacterspecies still abundant.De novometatranscriptomic analysis indicated a high diversity of potential extracellular substances produced mainly byAzonexus, Accumulibacter, CandidatusContendobacter, andPropionivibrio. Moreover, the results suggest thatAzonexus, ContendobacterandPropionivibriorecycle the neuraminic acid produced byAccumulibacter. Changes in the microbial community did not cause the granules to disintegrate, indicating that aPropionivibrio-dominated community can maintain stable granules.