Effects Of Quorum Sensing On Antibiotic Resistome Promotion In Drinking Water During Biological Activated Carbon Treatment

The discovery of antibiotics stands out as one of the most notable milestones in the process of modern science events in the 20th century.Antibiotics have been wide-ly applied to preventing humans and livestock from diseases.Since penicillin,the first antibiotic,found in 1929,antibiotics have effectively controlled a number of infec-tions in a short term and saved millions of lives around the world.However,ARGs(Antibiotic resistance genes)is rapidly developing and spreading with the abuse of antibiotics.Currently bacterial resistance has already become one of the world's most urgent public health problems,more and more studies have emphasized on the ARGs in the environment.As known to all,drinking water closely bounds up with our daily lives,therefore more attention should be paid to the ARGs pollution in drinking water.BAC(Biological activated carbon)is a common advanced water treatment technology in drinking water treatment plants.As researches shown,both the aggregation of bac-teria and the formation of biofilm are related to QS(Quorum sensing),so the surface biofilm on BAC should be attached attention,for its influence on ARGs in drinking water.There is a gene exchange between bacterial communities,which may result in the further spread of ARGs.To evaluate the formation of biofilm on BAC,the change of QS in biofilm and the fate of ARGs are both helpful to guarantee drinking water safety and protect human health.In this study,quantitative PCR,16sRNA gene sequencing and HPLC-MS/MS were used for the purpose of investigating the fate of ARGs in BAC and the relation-ship between microbial communities and QS.Conjugation transfer experiment and active carbon small-scale study were combined to explore the effect and mechanism of QS on conjugation transfer.Several common natural QSIs(quorum sensing inhibi-tors)were selected to study their effects on the bacteria which secret signal molecules,the formation of biofilm and the regulating effect on transfer conjugation.This study provides theoretical supporting for the control of ARGs in the practical BAC tech-nology.The research results were as follows:(1)BAC(Biological Activated Carbon)in drinking water treatments causes the en-richment of ARGs(Antibiotic Resistance Genes),as the abundance of ARGs increases evidently,among which blaTEM and tetQ increased the most notably,after BAC.The relative abundance of blarrEM has been increased from 1.70x10-1copies/16S rRNA copies to 3.07x100copies/16S rRNA copies and the relative abundance of tetQ was from 1.79x10-4copies/16S rRNA copies to 1.22x10-3copies/16S rRNA copies after the process.After the treatment,the bacterial community structure altered,the change of bacterial community structure was significantly correlated with the structural change of ARGs,of which the most closely was related to Firmicutes and Cyanobacteria;(2)There are 6 kinds of signal molecules(C6-HSL,C8-HSL,C10-HSL,C12-HSL,30C8-HSL,30C12-HSL)could be detected on the biological activated carbon,whose concentrations range from 0.01-0.76ng/ml.Ten kinds of bacteria which can secret signal molecules have been detected on the BAC samples,which include Proteus,Firmicutes and Bacteroides.In particular,the Fusarium can produce all the 10 detected signal molecules except C10-HSL,therefore quorum sensing is closely relevant to the transfer and spread of ARGs;(3)The signal molecules have been evidenced to be effective in promoting the horizontal transfer of ARGs between the same species of bacteria.The most signifi-cant is C8-HSL,which can promote up to 28.60 times.When the exogenous concen-tration reaches l0Ong/L,the transfer efficiency can be increased about 60 times.The bacteria which secret exogenous signal molecules can also enhance the level of the horizontal gene transfer to varying degrees,among which the most increased is Pae-nibacillus chibensis,can promote 17.40 times,and in a small-scale experiment of BAC,when the dosing ratio is 2:5 the transfer efficiency could be up to 21.02 times;(4)Signal molecules could promote bacterial secretion of more EPS and the for-mation of biofilm.In the continuous activated carbon system,the signal molecules play a significant catalytic role in the formation of EPS(P<0.05),and the highest content of polysaccharide in the exogenous signal molecules was 24.33 mg/L and the highest protein content was 125.20 mg/L,the highest content of polysaccharide in the bacteria which could secret signal molecules could reach up to 26.48mg/L and the protein content was up to 142.94mg/L,both of them were higher than the control group;(5)QSI could inhibit the quorum sensing system of bacteria which secreted signal molecules,and QSI could also significantly inhibit the biofilm formation of signal molecules than that of planktonic bacteria(P<0.05).For the strongest QSI 2(5H)-furanone,the inhibitory rate was only 33.86%for the planktonic bacteria Paenibacil-lus chibensis and for Bacillus subtilis was 28.53%,but the inhibitory rate of the bio-film formation was as high as 90%.QSI showed different degrees of inhibition on the formation of extracellular polymers and hydrophobicity.On the other hand,QSI could also inhibit the promotion of horizontal gene transfer of signal molecules.The effect of 2(5H)-furanone and furanone was better than indole and coumarin under the same concentration.