Role Of N-acyl Homoserine Lactone (AHL)-Mediated Quorum Sensing In Filamentous Bacteria Bulking Within Activated Sludge

The activated sludge process has the advantages of low cost,simple operation and high efficiency,so it has been widely used in municipal sewage treatment.In the activated sludge process,filamentous bacteria bulking is a problem that occurs frequently.The excessive proliferation of filamentous bacteria leads to the deterioration of the sedimentation performance of activated sludge,and a large number of functional microorganisms are lost with the effluent,which further leads to the reduction of the sewage treatment performance of the reactor and even the collapse of the entire system.How to effectively prevent and control filamentous bacteria bulking has always been a scientific frontier issue in the field of sewage treatment.Unfortunately,due to the lack of scientific understanding of the microscopic mechanism of filamentous bacteria bulking,this problem has not yet been able to find effective methods and strategies to prevent and control filamentous bacteria bulking.Quorum sensing(QS)is an important mechanism for microorganisms to realize self-proliferation and regulate growth in response to population density.The proliferation of filamentous bacteria has population density-dependent characteristics.Therefore,QS may be closely related to the filamentous bacteria bulking.This study focuses on the QS to study the microscopic mechanism of filamentous bacteria bulking,reveals the potential role of the QS in the process of filamentous bacteria bulking,and provides new micro-theoretical support for the prevention and control of filamentous bacteria bulking.This paper creates conditions conducive to the proliferation of filamentous bacteria to induce filamentous bacteria bulking,and studies the changes in the microstructure,surface characteristics,community structure and signal molecule concentration of the sludge during the process of filamentous bacteria bulking.Based on the characteristics of proteomics and metagenomics,it reveals the mechanism of QS promoting the proliferation of filamentous bacteria and the mechanism of quorum quenching(QQ)inhibiting the proliferation of filamentous bacteria.Based on the above-mentioned mechanism,a control strategy of filamentous bacteria bulking based on the QS and QQ is proposed.The main conclusions obtained are as follows:(1)Proliferation rate of filamentous bacteria in the serious filamentous bulking(SFB)(SVI>250 mL/g)stage was 16.04 times faster than that of average proliferation rate of filamentous bacteria in the no filamentous bulking(NFB)(SVI<150 mL/g)and limited filamentous bulking(LFB)(150 mL/g<SVI<250 mL/g)stage,which indicates that the proliferation of filamentous bacteria is population density-dependent characteristics.(2)Under the condition of low dissolved oxygen,the concentration of C₆-HSL increased from 31.39±3.52 ng/g VSS to 125.29±6.70 ng/g VSS with the increased in the abundance of filamentous bacteria(AF),and the concentration change trend of C₆-HSL is significantly related to the change trend of AF.Proteomics analysis indicated that relative abundance of the metabolic pathway matched QS increased from 1.10%to 7.50%during filamentous bulking.Simultaneously,the abundance of proteins involved in signal transducer activity,signaling receptor activity and electron transfer activity significantly increased as the AF increased.In addition,by adding exogenous AHLs(C₆-HSL,C₈-HSL and C₁₄-HSL)to the reactor,it was found that the signal molecule significantly promoted the proliferation of filamentous bacteria,and C₆-HSL had the strongest promotion effect.Metagenomics analysis showed that the hdt S genes related to the synthesis AHLs and the lasR and cciR genes related to receptor significant increased during filamentous bulking process.Finally,adding an appropriate concentration of QQ enzyme to the reactor significantly inhibited the proliferation of filamentous bacteria.So,the proliferation of filamentous bacteria is positively regulated by QS system.(3)In the process of low dissolved oxygen induced filamentous bacteria bulking,the protein(PN)content extracellular polymeric substances(EPS)increased from 40.06±2.41mg/g to 110.01±3.26 mg/g VSS,and there is no significant correlation between the content of polysaccharides(PS)and the degree of sludge bulking.At the same time,the PN/PS ratio increased from 3.64 to 5.57.Pearson correlation analysis showed that there is a strong correlation between C₆-HSL and PN(R²>0.90,P<=0.05).Therefore,in the process of filamentous bacteria bulking,the QS-AHL system plays an important role in the regulation of EPS components.(4)The zeta potential and hydrophilicity of sludge flocs decreased significantly during filamentous bulking.Bacteria must overcome a stronger electrostatic barrier and interfacial free energy to adhere to each other.Variation in the physicochemical properties of EPS induced by QS markedly restrained adhesion between filamentous bacteria and floc-forming bacteria.And metagenomics analysis showed that the relative abundance of isoleucine,leucine,and valine in the hydrophobic amino acids of the synthetic protein during the filamentous bacteria bulking process would be significantly reduced.(5)In the process of adding exogenous AHLs to promote the filamentous bacteria bulking,metagenomics analysis showed that the relative abundance of QQ enzymes(acyltransferase and lactonase)was significantly reduced,and the abundance of QQ system may have a significant inhibitory effect on the filamentous bacteria bulking.And the filamentous bacteria bulking can be significantly inhibited by adding the quorum quenching enzyme.Therefore,the regulation strategy of filamentous bacteria bulking based on the QQ and QS is an effective and promising new method.