Alleviating acid inhibition in anaerobic digestion via a quorum-sensing strain addition: Performance enhancement and microbial mechanism analysis.

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.

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.

A Review on Effects of Sulfate in Anaerobic Digestion and Effect of Auto Generative Pressure on Biogas Production

Suppression of quorum sensing-mediated cell autolysis for highly efficient lactic acid production by Lactobacillus paracasei LYS2.

Lactic acid (LA) is an important platform chemical with diverse applications and growing market demand. Microbial fermentation using Lactobacillus paracasei is a major route for LA production. However, L. paracasei fermentation often suffers from decreased cell biomass and viability due to cell autolysis, limiting LA production. Quorum sensing (QS) mediates bacterial communication and population behavior, but its role in regulating cell autolysis during LA fermentation remains unclear. In this study, QS inhibition in L. paracasei LYS2 is shown to alleviate cell autolysis, increases biomass, and enhances LA production. The underlying molecular mechanism of QS-mediated regulation was also explored. This fermentation strategy is applicable to the strain using sweet sorghum juice to replace glucose as the carbon source, achieving 206.1 g/L of LA, the highest reported from this substrate to date. This work provides a promising strategy for LA production.

Mitigating the inhibition of organic matter to mainstream anammox system via electrolytic-enhanced strategy: Efficacy and underlying mechanisms.

The organic matter poses a considerable challenge to the stability and broad-scale application of anaerobic ammonium oxidation (anammox) process in mainstream wastewater treatment. In this study, an electrolytic-enhanced anammox biofilm reactor (E-ABR) was developed to fortify the resilience of anammox system against inhibition of organic matter. E-ABR demonstrated superior nutrient removal when treating domestic wastewater, achieving a total nitrogen and phosphate removal efficiencies of 83.80 ± 3.70% and 94.17 ± 7.23%, respectively. Transmission electron microscopy and cell damage detection revealed extensive membrane rupture and intracellular enzyme leakage in ABR. Conversely, the anammox bacteria-denitrifier symbiotic community established under electrolytic conditions could effectively resist the invasion of excessive heterotrophic bacteria under organic shock loads. The electron transfer (ETSA activity increased by 32.26%) and energy synthesis (ATP synthase content increased by 182.37%) were marked enhanced in E-ABR than that of control reactor (ABR). These benefits enabled the maintenance of an NH4+-N removal efficiency of 82.11% in E-ABR, in stark contrast to the mere 44.46% observed in ABR with an influent C/N ratio of 3.0. This study enhanced the theoretical understanding of the mechanisms underlying resistance to organic inhibition within electrochemical bioaugmented anammox systems, thereby offering novel theoretical underpinnings for the application of anammox in mainstream wastewater treatment.

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.

Low dissolved oxygen (DO) operation can substantially reduce aeration energy consumption in activated sludge systems but often induces filamentous sludge bulking dominated by Sphaerotilus natans (S. natans). This study isolated endogenous quorum quenching (QQ) bacteria from activated sludge and evaluated their potential to control low-DO bulking. Three endogenous QQ strains were newly isolated, among which Pseudochrobactrum sp. (P. sp.) showed excellent environmental adaptability and broad-spectrum N-acyl homoserine lactone degradation through multi-enzyme synergy, quenching C6-HSL, C8-HSL, and C14-HSL by 93.1%, 94.2%, and 93.0% within 24 h, respectively. Crude QQ enzymes inhibited the filamentous differentiation of S. natans, reduced peak C8-HSL concentration by 47%, and weakened ATP levels and electron transport chain activity. 13C metabolic flux analysis showed that QQ redirected carbon flux from biomass synthesis (via the glyoxylate shunt) toward energy metabolism (via the tricarboxylic acid cycle). However, the decreased ATP level and electron transport chain activity indicate that the enhanced TCA cycle flux may represent a compensatory metabolic adjustment under energy stress, ultimately leading to an inefficient energy-cycling state. Meanwhile, carbon skeleton loss restricted the supply of biosynthetic precursors and consequently inhibited filament elongation. P. sp. was then immobilized in optimized gel beads (P-gel) and applied in sequencing batch reactors (SBRs). Under low-DO operation, the SBR supplemented with P-gel effectively suppressed sludge bulking, prevented biomass loss, and sustained stable nutrients removal by regulating physicochemical properties of activated sludge. This study provides an environmentally friendly in-situ strategy for controlling S. natans-type bulking in low-DO activated sludge systems.