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Deciphering rapid proliferation of filamentous bacteria in activated sludge community via cross-feeding of public goods mediated by diffusible signal factor.

Huan Liu,Jie Li,Shao-Yang Liu,Jin-song Guo,You-Peng Chen,Peng Yan

Published 2025 in Bioresource Technology

ABSTRACT

The induced mechanisms underlying filamentous bulking by quorum sensing (QS) remain unclear. This study investigated how diffusible signal factors (DSF)-mediated QS facilitates filamentous bacterial proliferation via public goods cross-feeding. The results indicated that DSF concentrations increased by 4.32- and 5.03-fold in the aqueous and solid phases, respectively, correlating positively with the proliferation of the filamentous bacterium Thiothrix and upregulation of DSF-related genes (rpfF, rpfC, rpfG). Activation of the DSF-QS system stimulated threonine and serine biosynthesis and extracellular protease secretion, supporting the auxotrophic growth of Thiothrix. Correlation and phylogenetic analyses suggested that DSF-QS regulates the cross-feeding of these metabolites between Thiothrix, Acinetobacter bohemicus B and Ca. Competibacter B. Excessive proliferation of Thiothrix disrupted the physicochemical properties of sludge flocs and impaired aggregation, leading to sludge bulking. This study reveals that DSF-QS promotes filamentous bulking in activated sludge by regulating the cross-feeding of public goods.

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