Pluripotency of endogenous AHL-mediated quorum sensing in adaptation and recovery of biological nitrogen removal system under ZnO nanoparticle long-term exposure

Quorum sensing mediated response mechanism of anammox consortia to anionic surfactant: Molecular simulation and molecular evidence

The widespread use of surfactants raise challenges to biological wastewater treatment. Anaerobic ammonium oxidation (anammox) process has the potential to treat wastewater containing anionic surfactants, but the response of anammox consortia at the molecular level under long-term exposure is unclear. Using high-throughput sequencing and gene quantification, combined with molecular docking, the effect of sodium dodecyl sulfonate (SDS) on anammox consortia were investigated. Levels of reactive oxygen species (ROS) might be lower than the threshold of oxidative damage, while the increase of lactate dehydrogenase (LDH) represented the cell membrane damage. Decreased abundance of functional genes (hdh, hzsA and nirS) indicated the decrease of the anammox bacterial abundance. Trace amounts of N-acyl homoserine lactone (AHL, C6-HSL, C8-HSL and C12-HSL) contained in influent could induce endogenous quorum sensing (QS), which could regulate the correlation between functional bacteria to optimize the microbial community and strengthen the resistance of anammox consortia to SDS. In addition, the proliferation of disinfectant resistance genes might increase the environmental pathogenicity of sewage discharge. This work highlights the potential response mechanism of anammox consortium to surfactants and provides a universal microbial-friendly bioenhancement strategy based on QS.

Recovery strategies and mechanisms of anammox reaction following inhibition by environmental factors: A review

Anaerobic ammonium oxidation (anammox) is a promising biological method for treating nitrogen-rich, low-carbon wastewater. However, the application of anammox technology in actual engineering is easily limited by environmental factors. Considerable progress has been investigated in recent years in anammox restoration strategies, significantly addressing the challenge of poor reaction performance following inhibition. This review systematically outlines the strategies employed to recover anammox performance following inhibition by conventional environmental factors and emerging pollutants. Additionally, comprehensive summaries of strategies aimed at promoting anammox activity and enhancing nitrogen removal performance provide valuable insights into the current research landscape in this field. The review contributes to a comprehensive understanding of restoration strategies of anammox-based technologies.

The effect of quorum sensing on cadmium- and lead-containing wastewater treatment using activated sludge: Removal efficiency, enzyme activity, and microbial community

Quorum sensing (QS) is prevalent in activated sludge processes; however, its essential role in the treatment of heavy metal wastewater has rarely been studied. Therefore, in this study, acyl homoserine lactone (AHL)-mediated QS was used to regulate the removal performance, enzyme activity, and microbial community of Cd- and Pb-containing wastewater in a sequencing batch reactor (SBR) over 30 cycles. The results showed that exogenous AHL strengthened the removal of Cd(II) and Pb(II) in their coexistence wastewater during the entire period. The removal of NH4+-N, total phosphorus, and chemical oxygen demand (COD) was also enhanced by the addition of AHL despite the coexistence of Cd(II) and Pb(II). Meanwhile, the protein content of extracellular polymeric substances was elevated and the microbial metabolism and antioxidative response were stimulated by the addition of AHL, which was beneficial for resistance to heavy metal stress and promoted pollutant removal by activated sludge. Microbial sequencing indicated that AHL optimized the microbial community structure, with the abundance of dominant taxa Proteobacteria and Unclassified_f_Enterobacteriaceae increasing by 73.9% and 59.2% maximally, respectively. This study offers valuable insights into the mechanisms underlying Cd(II) and Pb(II) removal as well as microbial community succession under AHL availability in industrial wastewater.

Insights into the response of electroactive biofilm with petroleum hydrocarbons degradation ability to quorum sensing signals

Bioelectrochemical technologies based on electroactive biofilms (EAB) are promising for petroleum hydrocarbons (PHs) remediation as anode can serve as inexhaustible electron acceptor. However, the toxicity of PHs might inhibit the formation and function of EABs. Quorum sensing (QS) is ideal for boosting the performance of EABs, but its potential effects on reshaping microbial composition of EABs in treating PHs are poorly understood. Herein, two AHL signals, C4-HSL and C12-HSL, were employed to promote EABs for PHs degradation. The start-times of AHL-mediated EABs decreased by 18-26%, and maximum current densities increased by 28-63%. Meanwhile, the removal of total PHs increased to over 90%. AHLs facilitate thicker and more compact biofilm as well as higher viability. AHLs enhanced the electroactivity and direct electron transfer capability. The total abundance of PH-degrading bacteria increased from 52.05% to 75.33% and 72.02%, and the proportion of electroactive bacteria increased from 26.14% to 62.72% and 63.30% for MFC-C4 and MFC-C12. Microbial networks became more complex, aggregated, and stable with addition of AHLs. Furthermore, AHL-stimulated EABs showed higher abundance of genes related to PHs degradation. This work advanced our understanding of AHL-mediated QS in maintaining the stable function of microbial communities in the biodegradation process of petroleum hydrocarbons.

Regulation of extracellular polymers based on quorum sensing in wastewater biological treatment from mechanisms to applications: A critical review

Extracellular polymeric substances (EPS) regulated by quorum sensing (QS) could directly mediate adhesion between microorganisms and form tight microbial aggregates. Besides, EPS have redox properties, which can facilitate electron transfer for promoting electroactive bacteria. Currently, the applications research on improving wastewater biological treatment performance based on QS regulated EPS have been widely reported, but reviews on the level of QS regulated EPS to enhance EPS function in microbial systems are still lacking. This work proposes the potential mechanisms of EPS synthesis by QS regulation from the viewpoint of material metabolism and energy metabolism, and summarizes the effects of QS on EPS synthesis. By synthesizing the role of QS in EPS regulation, we further point out the applications of QS-regulated EPS in wastewater biological treatment, which involve a series of aspects such as strengthening microbial colonization, mitigating membrane biofouling, improving the shock resistance of microbial metabolic systems, and strengthening the electron transfer capacity of microbial metabolic systems. According to this comprehensive review, future research on QS-regulated EPS should focus on the exploration of the micro-mechanisms, and economic regulation strategies for QS-regulated EPS should be developed, while the stability of QS-regulated EPS in long-term production experimental research should be further demonstrated.

Potential role of AgNPs within wastewater in deteriorating sludge floc structure and settleability during activated sludge process: Filamentous bacteria and quorum sensing

Excellent sludge floc structure and settleability are essential to maintain the process stability and excellent effluent quality during the activated sludge process. The underlying effect of silver nanoparticles (AgNPs) within wastewater on sludge floc structure and settleability is still unclear. The potential role of AgNPs in promoting filamentous bacterial proliferation and deteriorating sludge floc structure and settleability based on quorum sensing (QS) were investigated in this study. The results indicated that N-acyl homoserine lactose (AHL) concentration sharply increased from 23.56 to 108.41 ng/g VSS in the sequencing batch reactor with 1 mg/L AgNPs. AgNPs strengthened communication between filamentous bacteria, which triggered the filamentous bacterial QS system involving the synthetic gene hdtS and sensing genes traR and lasR. Filamentous bacterial proliferation was promoted by the triggered QS via positively regulating its cell cycle progression including chromosomal replication and divisome formation. In addition, extracellular protein production was obviously increased from 43.56 to 97.91 mg/g VSS through QS by regulating arginine and tyrosine secretion during filamentous bacterial proliferation under 1 mg/L AgNPs condition, which led to an increase in the negative charge and hydrophily at the cell surface. AgNPs resulted in an obvious increase in the surface energy barrier (WT) between bacteria. The change in the physicochemical properties of extracellular polymeric substance (EPS) induced by QS among filamentous bacteria obviously inhibited bacterial aggregation between filamentous bacteria and floc-forming bacteria under AgNPs condition, thus resulting in serious deterioration of the sludge floc structure and settleability. This study provided new insights into the microcosmic mechanism for the effect of AgNPs on sludge floc structure and settleability.

Autoinducer-2 quorum sensing regulates biofilm formation and chain elongation metabolic pathways to enhance caproate synthesis in microbial electrochemical system

Quorum sensing (QS) have been explored extensively. However, most studies focused on N-acyl homoserine lactones (AHLs) participating in intraspecies QS. In this study, autoinducer-2 (AI-2, participating in interspecies QS) with different concentration was investigated for chain elongation in microbial electrosynthesis (MES). The results demonstrated that the R3 treatment, which involved adding 10 μM of 4,5-dihydroxy-2,3-pentanedione (DPD) in the reactor, exhibited the best performance. The concentration of caproate was increased by 66.88% and the redox activity of cathodic electroactive biofilms (EABs) was enhanced. Meanwhile, microbial community data indicated that Negativicutes relative abundance was increased obviously in R3 treatment. In this study, the transcriptome Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) databases were used to analyze the metabolic pathway of chain elongation involving fatty acid biosynthesis (FAB) pathway and reverse β-oxidization (RBO) pathway. KEGG analysis revealed that fatty acid elongation metabolism (p < 0.001), tryptophan metabolism (p < 0.01), arginine and proline metabolism (p < 0.05) were significantly improved in R3 treatment. GO analysis suggested that R3 treatment mainly upregulated significantly transmembrane signaling receptor activity (p < 0.01), oxidoreductase activity (p < 0.05), and phosphorelay signal transduction (p < 0.05). Moreover, metatranscriptomic analyses also showed that R3 treatment could upregulate the LuxP extracellular receptor, LuxO transcriptional activator, LsrB periplasmic protein, and were beneficial to both FAB and RBO pathways. These findings provided a new insight into chain elongation in MES system.

Dissolved oxygen benefits N-decanoyl-homoserine lactone regulated biological nitrogen removal system to resist acute ZnO nanoparticle exposure

The beneficial effects of N-decanoyl-homoserine lactone (C₁₀-HSL), one of the typical N-acyl-homoserine lactones on biological nitrogen removal (BNR) system to resist the acute exposure of zinc oxide nanoparticles (ZnO NPs) has attracted extensive attentions. Nevertheless, the potential impact of dissolved oxygen (DO) concentration on the regulatory capacity of C₁₀-HSL in the BNR system has yet to be investigated. This study conducted a systematic investigation of the impact of DO concentration on the C₁₀-HSL-regulated BNR system against short-term ZnO NP exposure. Based on the findings, sufficient DO played a crucial role to improve the BNR system's resistance capacity to ZnO NPs. Under the micro-aerobic condition (0.5 mg/L DO), the BNR system was more sensitive to ZnO NPs. The ZnO NPs induced increased intracellular reactive oxygen species (ROS) accumulation, reduced antioxidant enzyme activities, and decreased specific ammonia oxidation rates in the BNR system. Furthermore, the exogenous C₁₀-HSL had a positive effect on the BNR system's resistance to ZnO NP-induced stress, primarily by decreasing ZnO NPs-induced ROS generation and improving ammonia monooxygenase activities, especially under low DO concentrations. The findings contributed to the theoretical foundation for regulation strategy development of wastewater treatment plants under NP shock threat.

Insights into heavy metals shock on anammox systems: Cell structure-based mechanisms and new challenges

Anaerobic ammonium oxidation (anammox) as a low-carbon and energy-saving technology, has shown unique advantages in the treatment of high ammonia wastewater. However, wastewater usually contains complex heavy metals (HMs), which pose a potential risk to the stable operation of the anammox system. This review systematically re-evaluates the HMs toxicity level from the inhibition effects and the inhibition recovery process, which can provide a new reference for engineering. From the perspective of anammox cell structure (extracellular, anammoxosome membrane, anammoxosome), the mechanism of HMs effects on cellular substances and metabolism is expounded. Furthermore, the challenges and research gaps for HMs inhibition in anammox research are also discussed. The clarification of material flow, energy flow and community succession under HMs shock will help further reveal the inhibition mechanism. The development of new recovery strategies such as bio-accelerators and bio-augmentation is conductive to breaking through the engineered limitations of HMs on anammox. This review provides a new perspective on the recognition of toxicity and mechanism of HMs in the anammox process, as well as the promotion of engineering applicability.

Quorum sensing signals stimulate biofilm formation and its electroactivity for chain elongation: System performance and underlying mechanisms

Quorum sensing signals have been widely explored in microbial communities. However, the impact of chain elongation microorganisms by quorum sensing signals of acyl homoserine lactones (AHLs) is still unclear. Here, chain elongation consortia under conditions of AHLs addition were examined in microbial electrosynthesis (MES) through 16S rRNA microbial community and metatranscriptomic analyses. The research found that N-octanoyl-L-homoserine lactone (C8-HSL) increased the caproate concentration by 61.48 % as relative to the control and showed the best performance among all the tested AHLs in MES. AHLs enhanced the redox activity of cathodic electroactive biofilms (EABs), which could be due to increased attachment of electrode microorganisms and ratios of live/dead cells. Microbial community analysis showed that AHLs increased the relative abundance of Negativicutes obviously. Meanwhile, metatranscriptomic analysis revealed that C8-HSL significantly improved CoA - transferase activity and regulated valine, leucine, isoleucine biosynthesis, and carbon metabolism. Besides, C8-HSL was beneficial to the chain elongation metabolic pathways, especially the fatty acid biosynthesis (FAB) pathway. These results not only provide metabolic insights into AHLs regulating chain elongation consortia, but also propose potential strategies for speeding up the formation of MES cathodic biofilm.

New insights into exogenous N-acyl-homoserine lactone manipulation in biological nitrogen removal system against ZnO nanoparticle shock

The effects and mechanisms of three N-acyl-homoserine lactones (AHLs) (C₄-HSL, C₆-HSL, and C₁₀-HSL) on responses of biological nitrogen removal (BNR) systems to zinc oxide nanoparticle (NP) shock were investigated. All three AHLs improved the NP-impaired ammonia oxidation rates by up to 50.0 % but inhibited the denitrification process via regulating nitrogen metabolism-related enzyme activities. C₄-HSL accelerated the catalase activity by 13.2 %, while C₆-HSL and C₁₀-HSL promoted the superoxide dismutase activity by 26.6 % and 18.4 %, respectively, to reduce reactive oxygen species levels. Besides, the enhancements of tryptophan protein and humic acid levels in tightly-bound extracellular polymeric substance by AHLs were vital for NP toxicity attenuation. The metabonomic analysis demonstrated that all three AHLs up-regulated the levels of lipid- and antioxidation-related metabolites to advance the system's resistance to NP shock. The "dual character" of AHLs emphasized the concernment of legitimately employing AHLs to alleviate NP stress for BNR systems.

Advances in AHLs-mediated quorum sensing system in wastewater biological nitrogen removal: mechanism, function, and application

Biological nitrogen removal process is to convert organic nitrogen and ammonia nitrogen into nitrogen via a series of reactions by microorganisms, and is widely used in wastewater treatment for its costless, high-effective, secondary pollution-free characteristics. Quorum sensing (QS) is a communication mode for microorganisms to regulate bacteria's physiological behaviors in response to environmental changes. N-acyl-homoserine lactones (AHLs)-mediated QS system is widespread in nitrogen removal-related functional bacteria and promotes biological nitrogen removal performance by regulating bacteria behavior. Recently, there has been an increasingly investigated AHLs-mediated QS system in wastewater biological nitrogen removal process. Consequently, the AHLs-mediated QS system is considered a promising regulatory strategy in the biological nitrogen removal process. This article reviewed the QS mechanism in various nitrogen removal-related functional bacteria and analyzed its effect on biological nitrogen removal performance. Combined with the application research of the QS system for enhanced biological nitrogen removal, it further put forward some prospects and suggestions which are of practical significance in practical application.