Microbial communities, extracellular proteomics and polysaccharides: A comparative investigation on biofilm and suspended sludge

•The S-sludge had a more flexible and loose spatial structure than the biofilm.•Denitrification was mainly performed in the S-sludge.•103 and 126 proteins were classified in biofilm and S-sludge, respectively.•The results could elucidate the why of the two aggregate architectures diversity.

Biofilm and suspended sludge (S-sludge) floc exhibit distinct physicochemical properties and process performances in an integrated fixed-film and suspended growth sequencing batch reactor. However, the mechanisms of governing these differences between the two aggregates were unknown. Current work evaluated the diversity of morphologies, microbial communities, extracellular proteins and polysaccharides between the biofilm and S-sludge. Contrast to biofilm, the denitrification was much more extensive performed in S-sludge. Furthermore, many microbial cells in the biofilm acted as the backbone of aggregates and maintained the structure stability. An extracellular protein observed only in the biofilm can promote the cell adhesion. In contrast, more extracellular proteins related to catalytic activity in the S-sludge could decrease the compactness of floc. In addition, the monosaccharide compositions from the two aggregates were various. These results could elucidate how the diversities of architecture and biochemical process between the two aggregates occurred.

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