污泥蚯蚓堆肥对染色体和质粒上耐药基因归趋的影响

Fate of antibiotic resistance genes on chromosomes and plasmids affected by earthworms during vermicomposting of dewatered sludge.

染色体和质粒分别介导污泥中的抗生素抗性基因(Antibiotic resistance genes,ARGs)进行垂直和水平转移,使ARGs在亲代或不同菌种之间传播,导致污泥蚯蚓堆肥对ARGs的削减有限.为了解决这个问题,本实验通过研究蚯蚓堆肥过程中染色体与质粒上ARGs和移动遗传元件(Mobile genetic elements,MGEs)的丰度变化,以无添加蚯蚓为对照,进行20d的蚯蚓堆肥,探究蚯蚓堆肥对污泥中ARGs的垂直和水平转移的影响.结果显示:前10d是污泥蚯蚓堆肥中ARGs转移的高峰期.除了tetM,蚯蚓组其余ARGs丰度在质粒和染色体上均发生了显著的增加(P<0.05).与对照组相比,质粒上的ermF、ermB、tetX、sul1的丰度在蚯蚓组显著增加了1.02倍、1.97倍、2.43倍、0.75倍(P<0.05),而染色体上仅ermB在蚯蚓组显著增加(P<0.05).对于MGEs,质粒上的intI1丰度在蚯蚓组中比对照组显著增加了1.63倍(P<0.05),而染色体上的却截然相反,是对照组大于蚯蚓组.堆肥的后10d,两组染色体和质粒中的MGEs和总ARGs的丰度均降低,且蚯蚓堆肥组降低速度更快.蚯蚓堆肥中,在质粒上MGEs与ermF、ermB、sul2有显著的正相关性(P<0.05),而在染色体上MGEs与所有ARGs均无显著相关性.冗余分析发现,ARGs的变化与MGEs、蚯蚓堆肥引起的环境变化有关,而且环境因素如电导率、有机质、氨氮和硝酸盐氮,对质粒上ARGs和MGEs的影响比对染色体的更为强烈.综上所述,携带MGEs的质粒介导的水平转移是蚯蚓堆肥中ARGs难以削减的的主要原因.

Chromosomes and plasmids mediate the vertical and horizontal transfer of antibiotic resistance genes(ARGs)in sludge,respectively,which allows ARGs to spread between parents or different bacteria strains,resulting in limited reduction of ARGs during vermicomposting.To address this issue,the effects of vermicomposting on vertical and horizontal transfer of ARGs in sludge were investigated by detecting the abundance changes of ARGs and mobile genetic elements(MGEs)on chromosomes and plasmids during vermicomposting for 20 days,with no addition of earthworms as the control.The results showed that the first 10d was the peak of ARGs transfer in sludge vermicomposting.Except for tetM gene,a significant increase in the abundance of the remaining ARGs in the vermicomposting occurred on both plasmids and chromosomes(P<0.05).Compared with the control,the gene abundances of ermF,ermB,tetX,and sul1on plasmids significantly increased by 1.02-fold,1.97-fold,2.43-fold,and 0.75-fold in the vermicomposting(P<0.05),while only ermB on chromosomes significantly increased(P<0.05).Compared with the control,the MGEs abundance of intI1 on plasmids significantly enriched by 1.63-fold in the vermicomposting(P<0.05),while its abundance on chromosomes was diametrically opposite,its abundance in the control was larger than vermicomposting.In the 10~20 d of composting,the abundance of MGEs and total ARGs on chromosomes and plasmids decreased in both treatments,with a faster decrease in the vermicomposting.In addition,the MGEs had a significant positive correlation(P<0.05)with ermF,ermB,and sul2 on plasmids,while no significant correlation among MGEs and all ARGs on chromosomes was recorded during vermicomposting.The redundancy analysis revealed that the changes of ARGs were related to the MGEs and environmental changes during vermicomposting,and the environmental factors such as conductivity,organic matter,ammonia and nitrate had a stronger effect on ARGs and MGEs on plasmids than those on chromosomes.This study suggests that the plasmids carrying MGEs mediated horizontal transfer is a major reason for hardly reducing ARGs in sludge vermicompost.