Effects Of Chloramphenicol And Heavy Metals On Chloramphenicol Resistance And Microbial Community Structure In AAO Process

Antibiotics and heavy metals are two types of common pollutants in urban wastewater treatment plants.It is important to study their influence on the sewage treatment process and its pollution control.The effects of different concentrations of chloramphenicol（CAP）and heavy metals on the distribution of chloramphenicol resistant bacteria（CRB）and chloramphenicol resistance genes（CRGs）were studied under simulated wastewater conditions.The changes of CRB,CRG and integrons in the system were analyzed,and the correlations analysis of CRB,CRGs and integrons were discussed,and the community structure characteristics of microbes were compared.Firstly,the effects of drug resistance and microbial community structure at low concentration of CAP（350μg/L）in AAO process were studied.The levels of CRGs and Class I integrons in AAO process were significantly higher than those without CAP.The correlation between CRB and total bacteria was as good as that of CRGs and catB（p<0.01）,while CRB and total bacteria was not correlated with other genes.Compared with the control group without CAP,the most common populations of AAO system at the phylum level were Bacteroidetes and Proteobacteria.The low concentration of CAP had a certain effect on the microbial community structure in AAO process,and the shonnon index decreased from 5.01 to 4.35,and the microbial diversity was decreased.Sencondly,the effects of different concentrations of Cu²⁺ and Cr⁶⁺ and 350μg/L CAP on the CRB and CRGs of AAO were investigated.When the concentration of Cu²⁺ and Cr⁶⁺ was1mg/L-3mg/L,the AAO system was running normally.When the dosage was 4mg / L,the removal rate of CAP was significantly decreased.Compared with the addition of CAP,the number of CRB in each reaction of AAO process was reduced after adding 3mg/LCu²⁺ and 3mg/LCr⁶⁺concentration.The contents of catB and cmlA in each reaction of AAO process were significantly reduced,while ClassI was significantly increased.The dominant populations of AAO process were Bacteroidetes and Proteobacteria at the phylum level,and the dominant species were changedfrom Acinetobacter to Acidovorax at the genus level.The shonnon index decreased from4.35 to 2.37,and the microbial diversity was significantly decreased.Then,under the impact load CAP（3500μg/L）,the AAO system could’t work normally,the removal rate of CAP was not ideal,the number of CRB was greatly reduced and the contents of catB,cmlA and ClassI in each reaction pool were obviously reduced.There was a significant correlation between CRB,CRGs,catB gene,cmlA gene and ClassI integrin（p<0.05）.The Chlamydiae and the denitrification of the Arenimonas could’t be detected,the shonnon index was reduced from 2.37 to 1.90,and the microbial diversity was reduced.On the basis of the above experiments,effects of actual wastewater on CRGs and microbial community structure were investigated in AAO process.Compared with the simulated wastewater group,the number of resistant bacteria in the anaerobic and hypoxic stages was higher than the simulated wastewater group.After the hypoxia stage,the aerobic stage and the secondary sedimentation stage,the number of CRB should be lower than the simulated wastewater group.And the average content of cmlA in each stage was higher than that of simulated wastewater group.With the operation of AAO system,the content of CRGs in the actual wastewater group was a gradual increase process compared with the simulated wastewater group,especially in the secondary effluent stage.The average content of catB,cmlA and ClassI in the actual wastewater group was more much more than that of the simulated wastewater system.CRGs,catB and cmlA had a significant correlation with each other,while CRGs had a better correlation with cmlA（p<0.01）.The abundance of dominant species in the actual wastewater system include the proportion of Gemmatimonadetes and Gemmatimonadetes was higher than simulated wastewater experiment group.The shonnon index of actual wastewater pollution group was 6.05,and the biodiversity was significantly better than that of the process feeded by simulated wastewater.