Effects Of Biogas Fertilizers Containing Tetracycline On Vegetables Quality And Resistance Genes

Antibiotics are widely used in modern livestock and poultry breeding industry.Most antibiotics were excreted through faeces. Anaerobic fermentation is the important way to process livestock and poultry faeces, biogas fertilizers the product of anaerobic fermentation of animal faeces are often used as organic fertilizer. Residual antibiotics in biogas fertilizers were introduced into the soil environment through the application of biogas fertilizers, and it had a certain influence on crop quality and resistance genes. Tetracycline is common antibiotic in animal faeces, so tetracycline was selected as the research object in this study. Through a pot experiment, we investigated the effects of biogas fertilizer containing different concentration levels of tetracycline on pakchoi quality, soil enzyme activity, functional diversity of soil microbial community, antibiotic residue and tetracycline resistance genes. The main results were as follows:1. Effects of biogas fertilizers containing tetracycline on pakchoi qualityThe biogas fertilizer containing low concentration(5 mg/kg) of tetracycline increased the fresh weight of pakchoi by 15.5% whereas reduced the nitrate content by 13.1%. The biogas fertilizer containing high concentration(15 mg/kg) of tetracycline reduced the fresh weight and vitamin C content of pakchoi by 5.7% and16.7% respectively whereas increased the nitrate content by 34.3%. Tetracycline did not significantly affect the plant height of pakchoi.There are tetracycline residues in soil and vegetables after fertilization. As the extension of time, the tetracycline content of every treatment in soil were gradually decreased, and the biogas fertilizer containing high concentration(15 mg/kg) of tetracycline significantly increased the tetracycline residue in the vegetables.2. Effects of biogas fertilizers containing tetracycline on soil enzyme activity and functional diversity of soil microbial communityThe biogas fertilizer containing low concentration(5 mg/kg) of tetracycline increased the activity of soil urease and alkaline phosphatase. The biogas fertilizercontaining high concentration(15 mg/kg) of tetracycline reduced the activity of soil urease and alkaline phosphatase. The biogas fertilizer containing tetracycline could promote the activity of soil catalase, and as the extension of time, the effect gradually disappeared. The biogas fertilizer containing low concentration of tetracycline significantly reduced the diversity and richness of soil microbe, and improved the ability of microflora to use carboxylic acids and polyphenols. The biogas fertilizer containing high concentration(15 mg/kg) of tetracycline significantly increased the diversity and richness of soil microbe, and improved the ability of microflora to use polymer and polyamino.3. Effects of biogas fertilizers containing tetracycline on tetracycline resistance genes in soil and pakchoi endophytesThe relative abundance of enzymatic modification gene(tetX) was 1~2 orders of magnitude higher than efflux pump genes(tetC) and ribosomal protection proteins genes(tetM tetQ tetW) in the soil. In seedling stage, the biogas fertilizer containing high concentration(15 mg/kg) of tetracycline significantly increased the relative abundance of tetracycline resistance genes in soil, it was 0.69~4.03 times higher than control treatment, and with the growth of pakchoi, the relative abundances of 5tetracycline resistance genes were gradually reduced. We detected 5 tetracycline resistance genes in pakchoi endophytes,and the relative abundance of the 5 genes of control treatment are the highest, it was 0.55~325.72 times higher than other treatments.