城市污水生物处理过程中结合型和游离型胞外抗生素抗性基因的产生特征

Generation of Absorbed and Free Extracellular Antibiotic Resistance Genes during Biological Treatment Processes of Municipal Wastewater

胞外抗生素抗性基因是抗性基因的重要存在形式,可能通过转化重新进入细胞表达抗药性。因此其具有严峻却隐蔽的健康风险,且不同形态胞外抗生素抗性基因的风险存在显著差异,然而当前针对胞外抗性基因风险的研究极为稀少。本研究以序批式活性污泥反应器(SBR)为例,考察了污水生物处理过程中结合型和游离型胞外抗性基因产生的时空特征,以及曝气强度和污泥负荷的影响。结果表明,SBR启动期2种胞外抗性基因均大量产生,且游离型胞外抗性基因的增加倍数和持续时间高于结合型;稳定运行后2种胞外抗性基因的丰度显著下降。从胞内外抗性基因的比重来看,好氧阶段以胞外抗性基因为主,且游离型胞外抗性基因比例达60%以上;厌氧阶段以胞内抗性基因为主,且结合型胞外抗性基因比例升高(7.5%~31.9%);出水中游离型胞外抗性基因占据绝对优势,比例达66.5%~86.9%。曝气强度提高使2种胞外抗性基因丰度显著提高,但游离型胞外抗性基因提高程度(2.2倍~12.2倍)高于结合型(2.1倍~6.2倍)。污泥负荷提高同样导致2种胞外抗性基因丰度提高,但游离型胞外抗性基因提高程度(1.3倍~7.8倍)低于结合型(1.9倍~13.3倍)。研究表明,大量胞外抗性基因将在污水生物处理过程中产生,并随污水排放至环境中,是水环境中抗生素抗性基因(ARGs)的重要来源之一。

Extracellular antibiotic resistance genes(eARGs)are an important form of antibiotic resistance genes.eARGs may re-enter cells and express antibiotic resistance through transformation,thus imposing great but concealed health risks.Further,the risks of different forms of eARGs are significantly different.However,current studies on the risks of eARGs are extremely rare.This study investigated the spatiotemporal characteristics of absorbed eARGs(a-eARGs)and free eARGs(f-eARGs)during biological wastewater treatment processes by taking sequencing batch reactor(SBR)activated sludge process as an example,then the influence of aeration intensity and sludge loading rate were explored.Results showed that both types of eARGS were abundant during the start-up stage of SBR process,and the increase of f-eARGs were higher than a-eARGs in terms of content and period.The abundance of two forms of eARGs decreased significantly among steady operation stage.Concerning the proportion of eARGs and intracellular ARGs(iARGs),eARGs are dominant during the aeration stage and the proportion of f-eARGs was more than 60%.iARGs was dominant during the anaerobic stage,with the proportion of a-eARGs being increased to 7.5%~31.9%.f-eARGs occupied in the effluent,with the proportion at 66.5%~86.9%.The increase of aeration intensity significantly increased the abundance of two forms of eARGs,but the increase of f-eARGs(2.2~12.2 times)was higher than that of a-eARGs(2.1~6.2 times).The increase of sludge loading rate also resulted in the increase of two eARGs,but the increase in f-eARGs(1.3~7.8 times)was lower than that of the a-eARGs(1.9~13.3 times).This study indicates that abundant extracellular antibiotic resistance genes will be generated during the biological treatment processes of municipal wastewater and then discharged,which is an important ARGs sources of the aquatic environment.