Removal Of Tetracycline In Soil By Biochar@ Azotobacter Sp. MS1

Tetracycline is a commonly used broad-spectrum antibiotic that is also widely used as a feed additive in animal husbandry.Tetracycline cannot be completely metabolized in animals;it is mostly excreted with animal feces as antibiotic prototypes or secondary metabolites.Therefore,breeding wastewater and animal manure often contain a large amount of tetracycline and its residues.Improper treatment of breeding wastewater discharge or use of animal manure as fertilizer can cause a large amount of tetracycline to accumulate in the environment;causing ecological harm to soil environments.Tetracyclines in the environment often migrate into the human body through food chains and other pathways,posing a potential threat to human health.Currently,there are few studies on the physiological effects of tetracyclines on plants and their mechanisms of action,most of which are focused on aquatic plants,with few reports on terrestrial plants.This study took the common northern crop Pakchoi（Brassica campestris L.ssp.chinensis Makino var.communis Tsen et Lee）and the microbial community of planting soil as research objects,Corn straw biochar（hereinafter referred to as Biochar）loaded with nitrogen-fixing bacteria Azotobacter sp.MS1（hereinafter referred to as Biochar@Azotobacter sp.MS1）was used as detoxification materials to study the protective effect of Biochar@Azotobacter sp.MS1 on Pakchoi and soil microbial communities in tetracycline-contaminated soil.This article draws the following conclusions:（1）A strain of bacteria Azotobacter sp.MS1 with nitrogenase gene was isolated and identified as Proteobacteria,Pseudomonadales,Pseudomonadaceae,Azotobacter.The specific surface area analyzer,scanning electron microscope and Fourier infrared spectrometer were used to analyze the specific surface area,morphological structure and surface functional groups of Biochar and Biochar@Azotobacter sp.MS1 loaded with Azotobacter sp.MS1.The results showed that Azotobacter sp.MS1 could be loaded onto Biochar,and the binding mode between Azotobacter sp.MS1 and Biochar was physical adsorption.The pore structure of Biochar@Azotobacter sp.MS1was more abundant than that that of Biochar,and Biochar@Azotobacter sp.MS1 could increase the binding sites of tetracycline.（2）Tetracycline adsorption kinetics experiments showed that Biochar@Azotobacter sp.MS1had a stronger adsorption effect on tetracycline（adsorption capacity:Biochar@Azotobacter sp.MS1>Biochar>control）.The adsorption kinetics of tetracycline by Biochar and Biochar@Azotobacter sp.MS1 conformed to pseudo-first-order kinetics description.The thermodynamic test results showed that the adsorption thermodynamics of Biochar@Azotobacter sp.MS1 on tetracycline conformed to Langmuir model description.The maximum adsorption amount was 382.19 mg·g^-1 at 40℃,and the adsorption process belonged to spontaneous endothermic process.（3）Tetracycline inhibits Pakchoi growth mainly by inhibiting germination rate,reducing biomass and chlorophyll content,and producing oxidative stress.After adding Biochar@Azotobacter sp.MS1 to tetracycline-contaminated soil,basic phenotype,antioxidant system and rhizosphere soil microbial community of Pakchoi were altered.The biomass and chlorophyll content of Pakchoi increased,while root length,volume and root tip number also increased.Peroxidase（POD）,superoxide dismutase（SOD）,catalase（CAT）activity and malondialdehyde（MDA）content decreased.In addition,Biochar@Azotobacter sp.MS1 has an improvement effect on the diversity of rhizosphere soil microbial communities in tetracycline-contaminated soil.It shows that Biochar@Azotobacter sp.MS1 can effectively alleviate the inhibitory effect of tetracycline on Pakchoi growth and development,improve soil microbial community diversity,weaken tetracycline toxicity.