Harnessing membrane segregation of polysaccharide-degrading strains to mitigate fouling in membrane bioreactors: Insights from bacterial community ecology and metabolomics.

Polysaccharides are key biopolymers driving membrane fouling in membrane bioreactors (MBRs), and enhancing their in situ degradation represents a promising strategy for long-term fouling control. Here, we employed a "top-down" approach to isolate an efficient polysaccharide-degrading strain, Pseudonocardia sp. P-1, from activated sludge, and engineered a membrane-based segregator to retain the target strain while allowing metabolite exchange. When applied in an aerobic MBR (MBR-E, 1.66 kPa/day), the segregator markedly reduced fouling rates compared to the control MBR (MBR-C, 3.69 kPa/day, p < 0.05) over 130 days of operation. MBR-E bulk sludge exhibited lower concentrations of polysaccharides in both soluble microbial products and extracellular polymeric substances (EPS) (both p < 0.05). Protein content in the bulk sludge EPS was also reduced (p < 0.01), with a more compact structure characterized by a higher α-helix/(β-sheet + random coil) ratio, suggesting weaker membrane-foulant interactions. The results of 16S rRNA gene sequencing indicated that the Pseudonocardia sp. P-1 segregator had minimal impact on α- and β-diversity of the bulk sludge but selectively enriched bacteria associated with fouling mitigation, as revealed by random forest analysis. Co-occurrence network analysis showed that while bacterial interaction patterns remained unchanged, the segregator altered network modularity and keystone taxa. Non-targeted metabolomics further confirmed upregulation of pathways related to carbohydrate metabolism, amino acid metabolism, and cofactor/vitamin metabolism in MBR-E relative to MBR-C, consistent with the enhanced biopolymer biodegradation. Overall, this study demonstrates an effective strategy for fouling mitigation and provides novel insights into the ecological role of biopolymer-degrading bacteria in sustaining MBR performance.