Degradation Of Chloramphenicol Over The Interface Between Iron-containing Minerals And Shewanella

Along with the development of medicine,aquaculture and farming,the frequent use of chloramphenicol(CAP)has led to the presence of high concentrations of chloramphenicol residues in the natural environment,such as soil.This is not only causing pollution to the environment but also poses serious health risks to humans through the food chain.Microbial degradation is a greener and more economical meanthod for removing chloramphenicol.In the soil,most of the microorganisms are adherent and dependent with various minerals,which will definitely affect the biological degradation of antibiotics.In this study,Chloramphenicol was chosen as the research subject,Shewanella oneidensis MR-1 was selected as the degrading model strain,and needle iron ore and chlorite were used as the experimental materials.Various analytical methods were employed to investigate the influence and mechanisms of Shewanella oneidensis in conjunction with the two minerals on chloramphenicol degradation from physical,biological and chemical perspectives,providing reference and basis for the future treatment of antibiotic pollution.The following main results were obtained:(1)After reacting with chloramphenicol,the morphology of Shewanella appeared dried(shriveled)and crumpled.Since Shewanella was combined with goethite and nontronite espectively,it increased the positive charge on the bacterial surface while and improving the survival rate of the bacteria,thus weaking the toxic effect of chloramphenicol on Shewanella.(2)Adsorption experiments showed that the inactive Shewanella,goethite,nontronite and their complexes had almost no adsorption effect on chloramphenicol,and the degradation of chloramphenicol mainly depended on Shewanella.Kinetic experiments revealed that after 36 hours,the degradation rate of chloramphenicol by Shewanella was 80%,while the addition of goethite and nontronite accelerated the biodegradation rates to 97% and 95%,respectively.(3)An increase in Fe(II)content was detected on the solid phase surface of both of the reacted goethite and nontronite mineral complexes,reaching 43.8% and 19.17%respectively.Combined with the potential analysis experiments(ORP,CV),the results indicated a strong redox reaction occurs between Shewanella and goethite as well as nontronite,converting Fe(III)in the minerals into adsorbed Fe(II)with reduction activity,thereby promoting the chloramphenicol.(4)The degradation solution was identified by HPLC-MS analysis,and the possible pathways of chloramphenicol degradation by Shewanella were speculated to be divided into acetylation and hydrolysis pathways: chloramphenicol was acetylated to produce chloramphenicol 3-acetate,and the amide bond of chloramphenicol in the hydrolysis pathway was broken to produce dichloroacetate and p-nitrophenyl serine,which was in turn reduced to p-aminobenzoic acid by the action of nitroreductase.The post-hydrolytic carboxylation reduction pathway of chloramphenicol was detected after the addition of nontronite and goethite to the degradation solution of chloramphenicol.(5)In the toxicity assessment experiment,the growth inhibition rate of E.coli K12 in chloramphenicol stock solution reached 49.13%,while the growth inhibition rate of this bacterium in the other three treatments(Shewanella,Shewanella-goethite,Shewanella-nontronite)were 8.09%,2.96% and 5.92%,respectively.It showed that the toxicity of the degraded solution after chloramphenicol was degraded was reduced compared with the pristine chloramphenicol solution.