Hydrogen Iron Oxide Produced By Acinetobacter Strain Exhibiting Intrinsic Enzyme-like Activity And Their Analytical Applications

In recent years,magnetic nanoparticles have attracted extensive attention due to their unique magnetic properties and enzyme-like catalytic activity.However,artificially synthesized magnetic nanoparticles are easy to collect,have poor biocompatibility,and entail high environmental costs during the synthesis process,which limits their development and application.The method of microbial synthesis of nanoparticles has attracted increasing attention as it can eliminate or reduce the toxicity of raw materials and by-products in the synthesis process.Microbial synthesis of magnetic nanoparticles is a green and environmentally friendly synthesis strategy for new magnetic nanomaterials particles.In this study,Fe_0.96O_0.88（OH）_1.12 nanomagnetic particles produced by Acinetobacter strains were identified for the first time.A bacterial strain containing biomagnetic nanoparticles（MNPs）grown under microaerobic conditions was isolated from the sediment and identified as an Acinetobacter strain by physiology,biochemistry,and 16S r DNA.This is the first report on the production of Fe_0.96O_0.88（OH）_1.12 by Acinetobacter strains.The effects of pH,oxygen concentration,carbon,nitrogen,iron source,temperature and incubation time on the growth of Acinetobacter strains and synthesis intracellular magnetic nanoparticles were investigated.Separation and purification of magnetic nanoparticles from bacterial cells by sonication,ultracentrifugation,and magnetic adsorption.The properties of the prepared magnetic nanoparticles were verified by transmission electron microscopy（TEM）,X-ray diffraction（XRD）,X-ray photoelectron spectroscopy,and magnetization hysteresis loops at room temperature.Experiments were performed on a vibrating sample magnetometer.Fe_0.96O_0.88（OH）_1.12 has hysteresis parameters such as high coercivity（147.61 OE）and low Mrs/Ms ratio,indicating that Fe_0.96O_0.88（OH）_1.12 has crystalline behavior.Furthermore,these extracted Fe_0.96O_0.88（OH）_1.12 NPs were shown to exhibit biomagnetic behavior and peroxidase-like activity.These extracted Fe_0.96O_0.88（OH）_1.12 NPs can catalyze the oxidation of the peroxidase substrate 3,3’,5,5’-tetramethylbenzidine（TMB）in hydrogen peroxide（H₂O₂）to produce blue（typical color reaction）.Catalysis was studied according to Michaelis-Menton kinetics and showed good affinity for TMB and H₂O₂.The Km values of BMNPs using TMB and H₂O₂ as substrates were 0.412 mm and 2.14 mm,respectively,which were close to and almost identical to those of the natural enzyme（HRP）.Electron spin resonance spectroscopy analysis shows that Fe_0.96O_0.88（OH）_1.12 can catalyze H₂O₂ to generate hydroxyl radicals（·OH）in the presence of 5,5-dimethyl-1-pyrrole n-oxide DMPO.H₂O₂ does not react alone in the presence of DMPO,but the addition of Fe_0.96O_0.88（OH）_1.12 catalyzes the formation of·OH.As a novel peroxidase mimetic,BMNPs provide a simple,selective and sensitive colorimetric method for the detection of H₂O₂ and glucose,which can be applied to the detection of glucose in diluted serum.Research on the catalytic degradation of various toxic substances using nano-magnetic particles to decompose toxic organic compounds has received extensive attention.In this study,biological magnetite Fe_0.96O_0.88（OH）_1.12 nanoparticles were extracted from Acinetobacter strains as peroxidase mimics,and the efficient removal action of azo dyes was studied by a photocatalytic degradation process.Under these conditions(100μg m L^-1 Fe_0.96O_0.88（OH）_1.12,50m L^-1 H₂O₂,470 m L 100 mg/m L Congo red dye at pH 4.6,reacted at 60℃ for 200 min),Azo will completely remove dyes.The degradation effect of nano-Fe_0.96O_0.88（OH）_1.12 on azo dyes can reach about 70%within 200 min.After repeating the treatment 7 times,the degradation rate of Congo red dye was reduced by about 30%compared to the first treatment.Here,the catalytic activity of BMNPs as catalase mimics was investigated for the first time.BMNPs extracted from Acinetobacter strains showed catalase-like activity when the pH was above 7.The effects of catalysts such as catalase activity,catalytic kinetics and stability have been studied.The results showed that BMNPs as catalase mimics depend on BMNP concentration,pH and temperature,and their catalytic ability gradually increases with the increase of BMNP concentration,pH and temperature.Compared to natural enzymes,BMNPs have higher stability under high pH and high temperature conditions and are not easily attacked by the antibacterial agent sodium azide.The Michaels constant of BMNPs was almost the same as that of natural enzymes,indicating that a higher H₂O₂ concentration was required to reach the maximum activity of BMNPs.For the first time,Fe_0.96O_0.88（OH）_1.12 was found to have another important antioxidant enzyme,superoxide dismutase（SOD）,derived from its intrinsic POD and CAT-like activities.The SOD activity of BMNPs was determined by the modified nitrotetrazolium blue ammonium chloride（NBT）method.The cycle test showed that BMNPs could still maintain high SOD activity after the 4th cycle test.