Insights Into Nitrogen Removal Through Marine Anammox Bacteria(MAB) Under Ampicillin Stress

For its excellent resistance to salt and low temperature,marine anammox bacteria?MAB?have lots of advantages to treat rich-nitrogen high salinity wastewater.However,the sensitivity of MAB to various inhibitors?e.g.heavy metal and antibiotics?limits its large-scale application in Engineering.Ampicillin?AMP?,a common broad-spectrum?-lactam antibiotic which has the advantages of low cost,high-effective antibacterial activity,and low toxicity to human body,is widely used in medical industry,fisheries,and aquaculture.However,the work with the effects of various AMP in high salinity wastewater on MAB is lacking on a long-term basis.In this experiment,a sequencing batch reactor?SBR?was used to study the effects of AMP on high salinity wastewater treatment for the first time.The results showed that under AMP stress,cell lysis occurred in the reactor and the mixed liquid volatile suspended solids?MLVSS?was reduced to1.677 g/L,while the content of the extracellular polymeric substances?EPS?such as proteins and polysaccharides,rose to 325.50 and 111.81 mg/g VSS,respectively.In the end,under the long-term inhibition of high-dose AMP?300 mg/L?,the nitrogen removal performance of the bioreactor was significantly broken and could not recover by itself.The total nitrogen removal rate?NRR?and specific anammox activity?SAA?were reduced to 0.17 kg N m^-3·d^-1 and 101.86 mg N g^-1VSS·d^-1,respectively,and reduced the total nitrogen removal rate to 55%.In addition,the modified Boltzmann model was suitable to analyze long-term inhibitory effect on the reactor with high-dose AMP addition.The long-term inhibition of AMP also led to the variation of the microbial community structure in the reactor.The relative abundance of Pseudoalteromona rose to 38.13%,replacing Candidatus Scalindua?MAB?which has a relative abundance of 23.81%,occupied the dominant position in the reactor,while the abundance of the universal bacteria involved in the nitrogen cycle,such as Caldithrix and Marinericella,was greatly reduced.In addition,in order to detect changes of antibiotic resistance genes?ARGs?,13?-lactam ARGs were selected for qPCR analysis,and the results indicated that the total relative abundance of detected ARGs increased from 0.16‰to 0.24‰,and the dominant?-lactam gene was TEM,which accounted for more than 70%.Under continuous AMP stress,the relative abundance of AmpC and CTX-M?-lactam genes increased rapidly due to the characteristics of plasmid-to-species transmission.Furthermore,the recovery of nitrogen removal through MAB under AMP stress with Zn??? addition were studied by adding different amounts of ZnSO₄·7H₂O after cycle 200.When the concentration of Zn??? is 6 mg/L,the effect of promoting the recovery reaches the maximum peak,the NRR can be restored to 0.72 kg N m^-3·d^-1.While the higher dose of added Zn??? may cause joint toxicity with AMP,which can poison the bioreactor.Such as the Zn??? concentration was 12 mg/L,the NRR decreased rapidly to 0.14 kg N m^-3·d^-1.This experiment may provide new insights for the recovery strategy of MAB which are inhibited after dosing AMP.