| With the rapid development of industrialization and urbanization,the problem of arsenic pollution in my country has become increasingly serious.After being absorbed by crops,arsenic will be transmitted to humans through the food chain,posing a threat to people’s health.Therefore,how to effectively solve the arsenic pollution in the environment is the difficulty of current research.Compared with traditional chemical and physical treatment methods,microbial methods have attracted widespread attention due to their low cost and remarkable treatment effect.Microorganisms such as bacteria can not only adsorb and absorb arsenic in the environment,but also convert arsenic from a highly toxic form to a low-toxic or non-toxic form through biotransformation,which provides the possibility to fundamentally solve the problem of arsenic pollution.Obtaining strains with special arsenic resistance and transformation ability is the key to carry out arsenic-contaminated microbial remediation.In this paper,aerobic arsenic-tolerant bacteria were isolated from typical arseniccontaminated soil by designing separation experiments,and the species and arsenic transformation ability of the strains were identified.The functional As(Ⅲ)oxidizing bacteria were screened,and the oxidation characteristics and adsorption and absorption experiments were carried out to reveal the oxidation mechanism of As(Ⅲ)by the strain from the gene level,and the removal mechanism of arsenic by the strain from the cellular level.The main research contents and related results are as follows:(1)Isolation and identification of aerobic arsenic-resistant bacteriaBacteria with arsenic resistance,oxidation and reduction ability were screened from the arsenic-contaminated soil in the realgar mining area of Hunan by means of enrichment,separation and purification.A total of 88 strains of arsenic-resistant bacteria were isolated,and 7 strains with arsenic oxidation function were preliminarily isolated.Bacteria,3 strains with arsenic reduction function,the strain species was finally determined by physiological and biochemical identification and 16 S r RNA phylogenetic analysis.They belong to Agrobacterium,Achromobacter sp,Pseudomonas,Acinetobacter sp,Klebsiella pneumonia,Leclercia adecarboxylata.It provides a good strain resource for heavy metal arsenic remediation.(2)Oxidation characteristics and mechanism of As(Ⅲ)oxidizing bacteriaThe optimal growth conditions of the strains and the tolerance to arsenic were studied,and the oxidation curves of the two strains were determined to study the oxidation efficiency of arsenic.Design specific primers to amplify functional genes to study the oxidation mechanism of bacteria and build a phylogenetic tree.The optimal growth conditions for SMS06 and SMS11 were a temperature of 37 °C and a phosphate concentration of 40 mg/L.The optimum p H was 6 and 9,respectively.The tolerance of strains SMS06 and SMS11 to As(Ⅲ)was 600 mg/L.The oxidation efficiency of As(Ⅲ)at 450 mg/L and 600 mg/L was 100%.Amplification of putative genes including arr A,aio A,ars B,ars C and ars M resulted in successful amplification of the ars C and aio A genes,and the successful amplification of the aio A gene indicated the As(Ⅲ)resistance and detoxification of strains SMS06 and SMS11 The effect is mainly dominated by the oxidation process.The results show that the two As(Ⅲ)oxidizing bacteria have potential application value for the bioremediation of As(Ⅲ)in the environment.(3)Study on Adsorption Mechanism of Arsenic by As(Ⅲ)Oxidizing BacteriaThe strain SMS11 was selected to study the adsorption mechanism of arsenic,and the strain was characterized by means of SEM and FT-IR.The adsorption kinetics,adsorption isotherm,and intracellular and extracellular adsorption of arsenic were investigated by static adsorption experiments.The adsorption kinetics experiments showed that the adsorption of As(Ⅲ)and As(Ⅴ)by strain SMS11 conformed to the pseudo-second-order kinetic adsorption model.The adsorption isotherm experiments showed that the two isotherm models fit well in the adsorption of As(Ⅲ)by strain SMS11,but the fitting results for the adsorption of As(Ⅴ)were general.The maximum adsorption capacity of As(Ⅲ)by SMS11 was 131.5789 mg/g.The adsorption and transformation of arsenic by strain SMS11 were studied by studying the extracellular adsorption and intracellular accumulation of arsenic by strain SMS11 in aqueous solutions with different concentrations of arsenic and CDM medium with different concentrations of arsenic.The results showed that bacteria could adsorb,absorb and transform arsenic in both arsenic aqueous solution and CDM culture medium.SEM analysis showed that the non-As-adsorbed strain SMS11 had a smooth surface,regular shape and relatively slender shape.After the adsorption of arsenic,the surface of the strain SMS11 was wrinkled,the cells were invaginated,part of the strain was deformed,the volume increased,and it became more spherical.It shows that As has a toxic effect on bacteria,which makes bacteria change to resist the toxicity of As.Through the analysis of FT-IR spectroscopy,in the adsorption process of strain SMS11 to As(Ⅲ),the functional groups that play a major role are hydroxyl,amino and polysaccharides.The research results show that the strain provides a theoretical basis for screening microbial adsorption materials,and can be used as an adsorption material to remove heavy metal arsenic in aqueous solution,which has a good application prospect. |
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