Effect Of Tetracycline Antibiotic On The Corresponding Resistance Of Degrading Bacteria And Community Structure In An Activated Sludge System

In recent years, with the increase of tetracycline antibiotics usage, it not only increased theresidues of tetracycline antibiotics in the environment, but also induced the generation andtransmission risk of tetracycline antibiotic resistance genes and tetracycline antibiotic resistantbacterias. It has been the major threat to the human health. Tetracycline antibiotics have beenwidely administered to treat and control diseases due to their effective antimicrobial actions andthe lack of major side effects. The sewage treatment plants have attracted much attention as one ofthe main point-sources of pollution with respect to tetracycline antibiotics and tetracyclineresistance genes. Researching on the residue and removal of tetracycline antibiotics and itspollution situation of TET-ARGs and ARBs in urban sewage treatment plant has significancemeaning to find out the rules of their generation, migration and evolution, which are veryimportant to prevent and control such pollution from the perspective of the sewage treatmentsystem.Anaerobic-aerobic (A/O) activited sewage treatment process is traditional method inwastewater treatment. The removal and degradation of tetracycline in sewage and its influencingfactors and behavior on TET-ARGs and ARBs are studied. For observing and analyzing theremoval effect of A/O process on tetracycline solid phase extraction and high performance liquidchromatography (SPE-HPLC) was used to detect the tetracycline’s concentration. In order toinvestigating the pollution characteristics and migration behavior of TET-ARGs in the wastewatertreatment process, the absolute quantitative and relative quantitative analysis by real-timefluorescent quantitative PCR was used to quantitative analysis the distributed situation of TET-ARGs in A/O reactors. In addition, the change of microbial communities’ diversity in A/O activated sludge in the pressure of tetracycline was determined by the combination of PCR-DGGEand high-throughput sequencing technologies.The results showed that trace TC has a certain role to the operation efficiency of A/Osystem.When the influent concentration of TC is500μg/L, the removal rate of conventionalpollutants reduced significantly. The overall removal efficiency of TC by A/O system is relativelystable, and the total removal rate is between84.8%~94.7%. Compared to aerobic segment, theimpact on the operating results of anaerobic by TC is more significant, indicating that TCinhibited anaerobic microorganisms. By biological degradation in A/O system, TC mainly turnedinto two degradation products, which are TC dehydration product, have no significant toxicity.By qPCR,7target TET-ARGs (tetA, tetC, tetG, tetM, tetO, tetW and tetX),16S rRNA andintegron I were detected in anaerobic and aerobic section. Concentration of TET-ARGs inanaerobic sludge was significantly higher than the concentration of TET-ARGs in aerobicactivated sludge. TET-ARGs concentrations in anaerobic stage ranges from9.56×104copies/g(tetM)~1.03×107copies/g(tetC), and TET-ARGs law exists to: tetC>tetA>tetO>tetG>tetW>tetX>tetM. TET-ARGs concentrations in aerobic stage ranges from8.11×102copies/g(tetW)~2.05×106copies/g(tetA), and TET-ARGs law exists to: tetC>tetG>tetA>tetM>tetO>tetX>tetW. The concentrations of TET-ARGs (tetM, tetO and tetW), which belongs to ribosomalprotection mechanisms, were low. So it can indicate that the evolution and propagation is inhibitedunder aerobic environmental conditions.TC can induce the generation and change of TET-ARGs, the study found that adding TCcreated different effects on the TET-ARGs in anaerobic and aerobic activated sludge. Pearsoncorrelation analysis was using to analysis the relative expression of the relationship between TCand TET-ARGs. In the anaerobic stage, tetC, tetG and tetM showed a significant positivecorrelation with TC (0.964≤r≤0.991, P<0.05). In aerobic stage, only tetG showed significantpositive correlation with TC (r=0.961, P<0.05). It indicated TC has some selective pressure on thegeneration and evolution of tetC, tetG and tetM. A/O system showed a significantremoval effecton tetA, and tetA was less sensitive to high concentrations of TC, it proved that high concentrationof TC will produce a pressure on tetA.Integron I is one of the important reasons for resistant bacterias rapidly generation andmigration. In this study, the correlation between TET-ARGs and integrin I in the A/O system was analysis. In the anaerobic stage, tetC, tetG, tetM and integrin I presented significant positivecorrelation (0.824≤r≤0.916, P<0.05); and in the aerobic stage, only tetA exists significantpositive correlation with integron I (r=0.587, P<0.05). There is also a certain correlation betweenTET-ARGs. However, the relationship between TET-ARGs is more complex, and the correlationof TET-ARGs in different environment is different, and the relationship of the same resistancemechanism is more remarkable.Finally, the results of high throughput sequencing showed that the dominant bacterias in theanaerobic stage of A/O system were Proteobacteria, Bacteroidetes and Firmicutes, and thedominant bacterias in aerobic stage were Proteobacteria and Bacteroidetes. The addition of TChad a certain effect on the microbial community structure in A/O system. The low concentrationof TC had no inhibition to the growth of bacteria, but it could promote the diversity of microbialflora. The high concentrations of TC have significantly inhibited or killed the anaerobic andaerobic microbial populations, which makes the diversity of the bacteria decreased. However, thedifference of the microorganisms in the anaerobic stage and aerobic stage was big, and thepollution stress of TC changed the composition of the microbial community in the activatedsludge, and decreased the similarity of the microbial community structure. Changes of aerobicmicrobial community structure were bigger than changes in the anaerobic activated sludgemicrobial community structure, but the ability to resisting and adaptating TC of microbialcommunities in aerobic stage is stronger than in the anaerobic microbial. TC changed themicrobial community structure in aerobic activated sludge, inducing predominant bacterias toadapt the TC environmental pollution.