Effects of veterinary medicines in manure on the abundance and transfer of bacterial antibiotic resistance genes in soils in dependence of varying soil moisture conditions

对B3的研究表明，在两种不同土壤中，重复施含磺胺嘧啶(SDZ)的有机肥后，抗性基因(sul1、sul2)的拷贝数较不施抗生素或对照的处理显著增加，并随着重复施药而积累。田间条件下，施药猪粪便显著提高了田间小区对SDZ抗性的转移性。根际土壤的迁移频率高于非根际土壤。含有SDZ的肥料对玉米和牧草根际中sul基因丰度的影响因取样时间不同而不同，可能是由于气候因素。我们假设，干燥和复湿会导致养分有效性、植物分泌物和生物可达孔隙空间的变化，并且这些变化会影响SDZ对土壤微生物群落中抗性基因丰度和转移的影响。为了阐明干燥-复湿和温度的影响，并弄清这一缺失的环节，我们将从中央田间采集的草根圈和根面样本中，研究sul基因的丰度及其可转移性，并进行室内模拟干湿循环实验。对经过粪便处理的土壤中的可转移耐药组进行焦解测序，将为了解SDZ共同选择的质粒多样性和其他抗生素耐药基因提供独特的见解。

Research of B3 revealed that in two different soils repeatedly treated with sulfadiazine (SDZ)-containing manure, resistance gene (sul1, sul2) copies significantly increased compared to treatments with antibiotic-free manure or control, and accumulated with repeated applications. Under field conditions, the transferability of SDZ resistance was significantly increased in plots treated with manure originating from pigs medicated with SDZ. Transfer frequencies were higher in the rhizosphere compared to bulk soil. The effects of SDZ-containing manure on the abundance of sul genes in the rhizosphere of maize and grass varied between different sampling times supposedly due to climatic factors. We hypothesize that drying and re-wetting cause shifts of nutrient availability, plant exudation and bio accessible pore space, and that these shifts influence the effects of SDZ on abundance and transfer of resistance genes in soil microbial communities. In order to elucidate the effects of drying-rewetting and temperature and to clarify this missing link, the abundance of sul genes and their transferability will be investigated in samples taken from rhizosphere and rhizoplane of grass from the central field and laboratory experiments with manipulated drying and wetting cycles. Pyrosequencing of the transferable resistome in manure-treated soils will provide unique insights into plasmid diversity and other antibiotic resistance genes co-selected by SDZ.