Study On The Characteristics Of Manganese Oxide Produced By Manganese Oxidizing Bacteria And Its Removal From Typical Antibiotics

Antibiotics are secondary metabolites or synthetic and semi-synthetic analogues produced by bacteria,mold or other microorganisms.They are mainly used in antiviral,anti-tumor,anti-parasite,and are widely used in clinical medicine and animal husbandry.Antibiotics are frequently detected in soil,water and other environments,and the residual antibiotics can affect the normal life activities of microorganisms,animals and plants,and ultimately affect human health.Microbial remediation technology has the advantages of low consumption,high efficiency and environmental safety,and has become a research hotspot in the field of environmental science.A large number of manganese oxidizing bacteria exist in nature,and the biological manganese oxides produced by them have excellent adsorption and catalytic oxidation properties,which can effectively remove antibiotics in the environment and solve the environmental harm caused by antibiotic pollution.In this study,a strain H38 capable of producing manganese oxides was obtained.Morphological observation and identification of the strain were carried out,and the conditions for its production of manganese oxides were optimized and characterized.The removal effect of manganese oxides produced by this bacterium on antibiotics oxytetracycline（OTC）,ciprofloxacin（CIP）,sulfamethoxazole（SMX）and tylomycin（TYL）was studied,and relevant removal mechanism was explored.Specific research conclusions are as follows:（1）A strain H38 capable of producing manganese oxides was obtained.A strain H38,which can produce manganese oxide efficiently,was screened by the detection of leucoberbelin blue I（LBB）color reagent.Bacillus Thuringiensis was identified by morphological observation and 16S rRNA sequence analysis.The growth curve of strain H38 was preliminarily obtained,and the optimal culture time was determined to be 10 h.（2）The optimum culture conditions for the production of manganese oxides by strain H38were determined.The production of manganese oxides by strain H38 was affected by four factors,such as culture time,initial Mn（Ⅱ）concentration,pH and temperature.Manganese oxides could be produced under the conditions of culture temperature 15～45℃,pH 5.0～8.0 and initial Mn（Ⅱ）concentration 1～40 mmol/L,and increased with the increase of culture time.The optimum conditions for the production of biological manganese oxides were as follows:the optimum temperature was 35℃,the optimum culture medium pH was 7.5,the optimum initial Mn（Ⅱ）concentration was 10 mmol/L,and the shaking speed was 150 r/min.（3）The manganese oxide produced by strain H38 was characterized and its internal structure and properties were analyzed.The biological manganese oxides were characterized by scanning electron microscopy-energy dispersive spectrometer（SEM-EDS）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy（XPS）,fourier infrared spectroscopy（FTIR）,specific surface area（BET）and particle size distribution（BJH）.The results showed that the biological manganese oxides were irregular particles or massive.Attached to the surface or around the thallus,with holes;Its composition is complex,mainly containing MnCO₃,Mn₂O₃,MnO₂;Most manganese elements exist in the form of high-valence manganese,in which Mn（Ⅲ）is the main element,and has rich functional groups and Mn-O bonds.It has the characteristics of small particle size,large specific surface area and large pore volume,so it has excellent adsorption and strong catalytic oxidation capacity.（4）It was found that the manganese oxide produced by strain H38 had the removal effect on a variety of antibiotics.Studies have found that it has the best effect on OTC removal,up to90%;The removal effect of CIP,SMX and TYL was poor,about 5.83%～23.76%.Biological manganese oxides contain bacteria,which have little effect on the removal of antibiotics,mainly the adsorption and catalytic oxidation of biological manganese oxides.（5）The conditions for the removal of OTC by manganese oxide produced by strain H38were optimized.It was found that the effect of biological manganese oxides on OTC removal was affected by four factors:culture time,dosage of biological manganese oxides,initial concentration of OTC and pH.OTC can be removed at dosages of 25-250μmol/L,initial concentration of 2.5-20 mg/L and pH of 4.0-8.0,and the removal rate increases with the increase of culture time.When the dosage of biological manganese oxide was 75μmol/L and pH 5.0,2.5 mg/L OTC was removed.After 12 h incubation at 35℃and 150 r/min,the removal rate was close to 100%.（6）The mechanism of OTC removal by biological manganese oxides was elaborated.Firstly,OTC was adsorbed by biological manganese oxides to form precursor complex.Then,OTC lost electrons to form free radicals,biological manganese oxides obtained electrons to change into Mn（Ⅲ）,and the active substances in the system formed superoxide anion radical（·O₂^-）,hydroxyl radical（·OH）,singlet oxygen（¹O₂）and other free radicals through various ways.Then Mn（Ⅲ）is produced by REDOX reaction with OTC or free radical.OTC reacts with free radicals,demethylates,amino,hydroxyl and other functional groups under the catalytic oxidation of biological manganese oxides,and undergoes bond breaking,substitution,elimination,and isomerization of enol-ketone,and finally transforms into carbon dioxide（CO₂）and water（H₂O）.