Effects Of Chlortetracycline And Tellurate On Enriched Denitrifying Anaerobic Methane Oxidation Microorganisms

Denitrifying anaerobic methane oxidation?DAMO?is widely distribute in natural anaerobic environments and is significant for carbon cycle and nitrogen cycle of ecosystem.Its discovery and application play an important role in controlling environmental eutrophication and releasing of methane.In addition,the extensive use of antimicrobials in industry and agriculture could lead to the discharge of wastewater containing antimicrobials and would affect the processing of denitrification and anaerobic methane oxidation.Therefore,exploring the effects of antimicrobials on the DAMO microorganisms will help evaluating the impact of using antimicrobials on environment and provide a reference for the use of DAMO to treat wastewater-containing antimicrobials.In this thesis,an anaerobic sequencing batch bioreactor?SBR?was constructed and used to enrich the DAMO microorganisms from the anaerobic layer of composting cattle manure.The effects of antimicrobial chlortetracycline and tellurium oxyanion on the DAMO microorganisms were studied and the mechanism of the effects were explored.The main research contents and conclusions of this thesis are as follows:?1?The construction of an anaerobic sequencing batch bioreactor and the enrichment of DAMO microorganisms.A laboratory scale anaerobic SBR was constructed and used to enrich DAMO microorganisms from the agricultural composting anaerobic layer.During 163 d reactor operation,the varying nitrate and nitrite,the denitrifying efficiency and percentage,the proportion of volatile suspended solids,the abundance of related DAMO functional genes were analyzed.The results showed that the denitrification for nitrate and nitrite in the stable phase was 0.69±0.40mg-N/L/d NO₃^-and 1.27±0.78 mg-N/L/d NO₂^-,respectively.The removal efficiency of nitrogen after each cycle was completed and up to about 100%.Moreover,the proportion of volatile suspended solids in total suspended solids and the relative abundance of the functional genes of archaea and bacteria in DAMO were increasing.These results indicate the DAMO microorganisms grew stably in the SBR reactor.The SBR reactor has the advantages of long-term operation stably and high biomass retention percentage,and is suitable for enrichment and quantitative study of slow-growing DAMO microbials.?2?The effect of chlortetracycline on DAMO microorganisms.This study conducted in established anaerobic SBR through introducing various concentrations of chlortetracycline.The denitrification efficiency and average nitrogen removal rate were analyzed.Relative abundance of DAMO functional genes,integron gene intI and antibiotic resistence gene tet were also performed by qPCR.The results confirm that the addition of chlortetracycline would reduce the denitrification rate at different concentrations,and also inhibit the expression of 16S rRNA and the functional genes,pmoA and mcrA.The concentration of chlortetracycline is not directly related to the abundance of the resistance gene.Therefore,chlortetracycline inhibite the activity of M.oxyfera,and M.nitroreducens is less affected.Both of these two microbials belong to DAMO consortium.Furthermore,chlortetracycline also cause the relative abundance of intI1 to increase,which induce the gene transfer and expression of tet gene,and may be one of the ways in which DAMO microorganisms resist chlortetracycline inhibition.?3?The effect of antibacterial tellurate on DAMO microorganisms.These experiments were carried out in a newly constructed anaerobic SBR reactor with a nitrate removal efficiency of up to 1.6 mg-N/L/d and a removal percentage of 100%.Tellurate instead of nitrate was added to the SBR reactor to investigate the effect of tellurate on the DAMO microorganisms and the behavior of tellurate in the SBR.The bioreduction of tellurate occurred after its addition,the removal amount reached 0.65mg-Te/L/d,and the removal rate was about 66%.The results indicate that addition of tellurate inhibite the metabolic activity of M.oxyfera and M.nitroreducens.Combined with XRD results,it is shown that the resistant of DAMO microorganisms for antibacterial tellurate is to detoxify it to elemental Te.Besides,CH₄ is the electron donor and responsible for tellurate bioreduction.Nitrate as a competitive electron acceptor affects the bioreduction of tellurate.The bioreduction of tellurate is likely to be driven by the DAMO microorganisms.All results show that the established anaerobic SBR reactor is suitable for enriching the slow growing DAMO microorganisms.The antibacterial chlortetracycline and tellurate have inhibitory effects on the DAMO microorganisms,and the DAMO microorganisms have different mechanisms for treating the pressure of the foreign antimicrobial agent.The study also show that antimicrobial contamination in the environment affect eutrophication and accelerated methane release.At the same time,this reaserch provide reference for the treatment of wastewater containing chlortetracycline and tellurium oxyanion by DAMO microorganisms.The bioreduction and detoxification behavior of tellurate by DAMO microorganisms enriches the understand of geochemical cycle of telluirum.