Key Takeaways & Executive Findings
- •• • Combined C6-HSL and C12-HSL (T3) achieved the highest SMX removal increase of 10.67% and methane yield improvement of 23.1% relative to control, demonstrating synergistic enhancement of MEC-AD performance. • • Single C6-HSL (T1) increased SMX removal by 9.26% and methane yield by 20.4%, while C12-HSL (T2) showed lower gains (7.44% and 16.9%), indicating chain-length-dependent efficacy. • • AHLs promoted electroactive biofilm formation via enhanced EPS production, with Georgenia abundance increasing by 16.77% (T1) and 36.47% (T3) but decreasing by 15.99% (T2), highlighting species-specific responses to signaling molecules. • • Combined AHLs (T3) reduced sul2 gene abundance by 4.92% compared to control, whereas single AHLs increased intI1, sul1, and sul2 abundances, suggesting that synergistic signaling mitigates ARG amplification risk.
Abstract
High-strength sulfamethoxazole (SMX) wastewater severely inhibits anaerobic microorganisms, reducing organic degradation and methane yield. This study investigated the effects of short-chain (C6-HSL) and long-chain (C12-HSL) N-acyl-homoserine lactone (AHL) signaling molecules, individually and in combination, on the construction, performance, and antibiotic resistance gene (ARG) profiles of anaerobic electroactive biofilms within a microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system. Compared to the control (no AHLs), SMX removal efficiency increased by 9.26%, 7.44%, and 10.67% for C6-HSL (T1), C12-HSL (T2), and combined (T3) treatments, respectively. Methane production rates rose by 20.4%, 16.9%, and 23.1% for T1, T2, and T3, respectively. AHLs promoted extracellular polymeric substance secretion, enhancing electroactive microbe attachment to the anode. Microbial community analysis revealed increased diversity and modulated key functional genera. Notably, Georgenia abundance increased by 16.77% (T1) and 36.47% (T3) but decreased by 15.99% (T2). ARG analysis showed that single AHLs elevated intI1, sul1, and sul2 abundances, whereas combined AHLs (T3) exhibited a milder response, with sul2 abundance reduced by 4.92% relative to control. This suggests synergistic AHLs suppress ARG host proliferation. This study first demonstrates that combined short- and long-chain AHLs enhance electroactive biofilm formation, maintain microbial community stability, and modulate ARG dissemination risk, offering a quorum sensing-based strategy for antibiotic wastewater treatment and risk management.
1. Introduction
Antibiotic-laden wastewater, particularly from pharmaceutical manufacturing, poses a dual threat: the inherent toxicity of antibiotics inhibits anaerobic digestion, and the selective pressure accelerates the spread of antibiotic resistance genes (ARGs). Conventional anaerobic treatments often fail to achieve adequate removal of recalcitrant antibiotics like sulfamethoxazole (SMX) while maintaining stable methane production. The microbial electrolysis cell coupled anaerobic digestion (MEC-AD) system offers enhanced electron transfer and degradation efficiency, yet its performance is limited by suboptimal biofilm formation and the risk of ARG proliferation. Existing strategies, such as bioaugmentation or electrical stimulation, have shown inconsistent results and do not address the ecological balance of the microbial community.
This study introduces a novel quorum sensing (QS)-based approach to overcome these bottlenecks. By exogenously supplying short-chain (C6-HSL) and long-chain (C12-HSL) N-acyl-homoserine lactones, the authors aimed to stimulate biofilm development and metabolic activity in MEC-AD systems. The rationale is that QS molecules regulate extracellular polymeric substance (EPS) production and microbial community structure, potentially enhancing SMX degradation and methane yield while controlling ARG dissemination. The experimental design systematically compares single and combined AHL additions, providing quantitative evidence of synergistic effects. This work addresses the critical need for a dual-objective strategy that simultaneously boosts treatment efficiency and mitigates resistance risks, offering a promising path for antibiotic wastewater management.
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LONG Xi, ZHANG Baowen, TIAN Jing, XIONG Jianbing, SUN Wenyu, WANG Tao (2026). Synergistic Regulation by Long- and Short-Chain Quorum Sensing Signaling Molecules Enhances Sulfamethoxazole Metabolism in Electroactive Biofilms within a Microbial Electrolysis Cell Coupled Anaerobic Digestion System. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202604006
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Frequently Asked Questions
What is the optimal concentration range of C6-HSL and C12-HSL for maximizing SMX degradation without causing microbial inhibition?
The study did not specify the exact concentrations used, but the results indicate that combined addition (T3) achieved the highest SMX removal increase (10.67%) and methane yield improvement (23.1%) relative to control. This suggests that a balanced ratio of short- and long-chain AHLs is critical. Further dose-response studies are needed to determine the optimal concentrations and ratios for scale-up.
How does the combined AHL treatment mechanistically reduce sul2 gene abundance while single AHLs increase it?
The combined AHLs (T3) likely promote a more stable microbial community that suppresses the proliferation of ARG-carrying bacteria. The reduction in sul2 abundance by 4.92% compared to control suggests that synergistic signaling may alter the competitive dynamics among microbial populations, favoring non-host species. This contrasts with single AHLs, which may selectively enrich certain hosts, leading to increased ARG abundance.
What are the long-term stability and performance of the MEC-AD system with continuous AHL supplementation?
The study did not report long-term continuous operation data. However, the observed improvements in SMX removal and methane yield over the experimental period suggest that AHLs can enhance system performance. Long-term stability would depend on factors such as AHL degradation rates, microbial adaptation, and potential resistance to QS signals. Pilot-scale studies are required to assess sustained efficacy and economic feasibility.
How does the addition of AHLs affect the electrochemical activity and electron transfer efficiency of the electroactive biofilm?
AHLs promoted EPS production, which likely improved biofilm formation and extracellular electron transfer. The enhanced SMX removal and methane production indicate improved metabolic activity. However, direct measurements of current density or cyclic voltammetry were not reported. Future studies should quantify electrochemical parameters to correlate AHL-induced biofilm changes with electron transfer efficiency.
What is the cost-effectiveness of using AHLs compared to conventional bioaugmentation or electrochemical stimulation in antibiotic wastewater treatment?
The study did not provide a cost analysis. AHLs are relatively expensive, but their use at low concentrations (likely micromolar range) may be economically viable if they significantly enhance treatment efficiency and reduce ARG dissemination. A techno-economic assessment comparing AHL supplementation to other enhancement strategies is necessary to determine practical applicability.
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