Insights into the suppression of filamentous bulking by quorum quenching in the activated sludge process with low dissolved oxygen: Endogenous quorum quenching mediated multi-enzymatic degradation of AHLs and carbon-flux redistribution.

Deciphering the synergistic mechanism of quorum sensing and sulfate-reducing bacteria for directed acetate conversion during sludge fermentation.

The restricted bioconversion of C3-C5 short-chain fatty acids (SCFAs) to acetate due to thermodynamic limitations is the main bottleneck during sludge fermentation. To alleviate this constraint, this study developed an optimized approach by integrating quorum sensing regulation with incomplete-oxidation sulfate-reducing bacteria (io-SRB) to improve the selective conversion of carbon towards acetate. The results revealed that the addition of 5 μM C8-HSL combined with io-SRB led to the highest SCFAs and acetate production at 141.9 mg COD/g VSS and 87.2 mg COD/g VSS at 5 d, which was 37% and 37% higher than the group without C8-HSL addition, while increase the C8-HSL dosage had no significant promotion of SCFAs production. C8-HSL effectively accelerated the efficient utilization of soluble carbohydrates and proteins during sludge fermentation, and functional group analysis further confirmed its promotional effect on the biotransformation of macromolecular organic matter throughout the fermentation process. Functional microbes, i.e., hydrolytic bacteria, acid-producing bacteria, and io-SRB (e.g., Desulfobulbus and Desulfovibrio), were enriched in the 5 μM C8-HSL system. The molecular ecological network and Mantel analysis revealed cooperative interactions among these functional microorganisms. Moreover, the synergistic effects of exogenous C8-HSL with io-SRB enhanced the expression of key functional genes involved in glycolysis, amino-acid metabolism, and acetate synthesis pathways. These findings may improve the understanding of the biological transformation mechanisms of sludge organic matter, and provide useful theoretical support for the efficient production of value-added products from sludge fermentation.

In situ fermentation-coupled symbiosis of polyphosphate-accumulating organisms and microalgae for efficient nutrient removal and sludge reduction in low carbon-to-nitrogen ratios wastewater.

Microalgae-bacteria consortia (MBC) integrated with polyphosphate-accumulating organisms (PAOs) treat wastewater sustainably, but face excess sludge and light-dark mismatch issues. This study developed in situ fermentation-coupled photo simultaneous nitrification-denitrification phosphorus removal (F/P-SNDPR) systems by incorporating fermentative PAOs into MBC for low carbon-to-nitrogen ratios (C/N) wastewater. The effects of light-dark cycles on nutrient removal, sludge fermentation, and microbial dynamics were investigated. Under an optimal 16 h dark/8h light cycle, the F/P-SNDPR system achieved > 83% nitrogen and > 95% phosphorus removal, with low sludge production (312.21 mgVSS/d) and low net CO2 emissions. Prolonged light and dark phases promoted early microbial apoptosis and subsequent cell lysis, respectively, thereby facilitating fermentation. Combined dark duration and photoinhibition suppress nitrite-oxidizing bacteria, enabling stable partial nitrification. Flow cytometry and metagenomic results identified Candidatus Phosphoribacter as the primary fermentative microorganism. Its fermentation-associated genes, including LivFGHMK and Pta, facilitated volatile fatty acid (VFA) production during the dark phase. The generated VFA supported Candidatus Accumulibacter/Candidatus Competibacter to enhance nutrient removal, driven by key functional genes for polyphosphate metabolism (Ppk and Ppx) and denitrification (NirS, NirK, and NosZ). Overall, The F/P-SNDPR system offers a low-carbon strategy for efficient low C/N wastewater treatment without mechanical aeration or external carbon addition, while reducing sludge production.

Characterization of a Novel Quorum Quencher Acinetobacter schindleri Strain XJ-10: AHL Degradation Capability, Metabolic Pathways and Its Role in Soft Rot Disease Biocontrol

While strain XJ-10 showed no detectable acylase activity, it exhibited significant degradation activity against AHL, suggesting a distinct QQ mechanism, and these findings broaden the scope of QQ-based biocontrol strategies and enhance mechanistic insights into managing bacterial diseases through QS modulation.

Genomic and physiological characterization of newly isolated nitrous oxide-reducing bacterium Stutzerimonas frequens strain E49 from landfill leachate-treating activated sludge

Quorum sensing-driven riboflavin-hyperproducing electroactive bacteria for enhanced bioelectricity generation from sludge: From modular optimization to process performance

Waste activated sludge (WAS) represents a significant byproduct of wastewater treatment and a renewable resource for bioenergy. Bioelectrochemical systems (BESs), which couple microbial metabolism with electrochemical processes, can directly convert the organic matter in WAS into electricity. However, their performance is often constrained by the limited extracellular electron transfer (EET) capacity of electroactive bacteria. To overcome this constraint, we designed a quorum sensing-driven synthetic strategy to create self-regulated, riboflavin-hyperproducing Shewanella oneidensis. By engineering an Esa quorum-sensing circuit to autonomously control riboflavin biosynthesis, coupled with promoter tuning and codon optimization, we developed the strain SQR2, which produced 269.9 mg/L riboflavin under bioreactor conditions without impairing bacterial growth. The enhanced riboflavin production substantially improved BES performance, increasing the current density and power output by 22.2- and 11.6-fold over the control, respectively. In hybrid BESs treating WAS, the introduction of the SQR2 strain further promoted electricity generation, reduced charge-transfer resistance, and selectively enhanced electroactive microbial taxa. Our study demonstrates a scalable, inducer-free strategy—from genetic design to process application—that strengthens sludge-based bioelectricity generation and supports sustainable wastewater resource recovery.

Mitigation of membrane biofouling by a novel Pseudomonas knackmussii HITSZ-Q1 immobilized in biochar-reinforced beads: Quenching mechanism and MBR performance.

The application of quorum quenching (QQ) bacteria for fouling control in membrane bioreactors (MBRs) is often hampered by the gradual loss of biological activity during operation. Here, this limitation is overcome by combining a newly isolated QQ bacterium (Pseudomonas knackmussii HITSZ-Q1) with a low-cost biochar-reinforced polyvinyl alcohol/sodium alginate (PVA/SA/BC) immobilization matrix. The strain completely degraded N-octanoyl-l-homoserine lactone (C8-HSL) and N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C12-HSL) within 2 h via intracellular acylase, maintained stable QQ activity at 30-40 °C and pH 6-8, and inhibited Pseudomonas aeruginosa biofilm formation by approximately 30%. Biochar incorporation enhanced the hydrogen-bonding network, compressive strength, and adsorption capacity of the matrix, providing a protective microenvironment for strain Q1. In flask tests, the PVA/SA/BC QQ beads maintained integrity over six reuse cycles and retained >40% degradation activity for both AHLs after 90 days of storage at 4 °C. When applied in lab-scale MBRs, the QQ beads delayed membrane fouling by 69% without compromising effluent quality, which correlated with a 50% reduction in C8-HSL, decreased polysaccharide and protein contents in extracellular polymeric substances, and an altered microbial community. Notably, after 34 days of continuous operation, the recovered PVA/SA/BC QQ beads showed increased quenching activity, with degradation rates for C8-HSL and 3-oxo-C12-HSL rising by a further 13% and 4%, respectively, a phenomenon rarely reported in QQ systems. This work offers a practical and durable QQ strategy that turns the activity decay problem into sustained, and even slightly enhanced, biofouling control.