摘要
为了探讨翻堆次数对异位发酵床连续堆肥过程中抗生素抗性基因(ARGs)和可移动基因元件(MGEs)的影响,设置1 d翻堆1次(F1组)和2 d翻堆1次(F2组)2种条件,采用PCR技术检测堆肥过程中15种基因,包括2种四环素类(tetG、tetW)、3种磺胺类(sul1、sul2、dfrA1)、2种β-内酰胺类(blaTEM-1、fexA)、2种MLSB类(ermX、ermQ)、2种FCA类(optrA、IsaE)、1种氨基糖苷类(aac(6ʼ)-Ib-cr)、1种整合子(intI1)及2种转座子(Tn916/1545、ISCRI)基因。PCR结果显示,2组样品中均检出11种ARGs(tetG、tetW、sul1、sul2、blaTEM-1、fexA、ermX、ermQ、optrA、IsaE、aac(6ʼ)-Ib-cr)和3种MGEs(intI1、Tn916/1545、ISCR1),其中7种基因(tetG、tetW、sul1、sul2、blaTEM-1、ermQ、intI1)的检出率较高;F1和F2组0~5 d均检出12种,33 d和40 d分别检出1种,40 d后明显增加,表明ARGs和MGEs种类随温度的变化而改变。采用qPCR技术对检出率较高的7种基因进行检测,结果显示,F1和F2组7种目标基因的总相对丰度呈先降低后升高再降低的趋势,试验结束时较0 d分别降低82.33%和78.89%,其中tetG、tetW、sul1、blaTEM-1、ermQ、intI1的相对丰度分别降低16.51%、87.89%、54.58%、99.99%、97.80%、59.29%和64.32%、99.46%、50.91%、99.29%、82.22%、99.92%。结果表明,异位发酵床降解粪污高温期可减少ARGs种类和丰度,且2 d翻堆1次对大部分ARGs的去除效果更好。
抗生素类药物在畜禽疾病防治及促生长方面发挥了积极作用,但进入体内的抗生素类药物仅少量被吸收利用,绝大部分抗生素类药物及产生的抗性基因(antibiotic resistance genes,ARGs)随粪尿排出体外,粪尿中残留抗生素类药物的选择压力可能诱导微生物再次产生ARGs
异位发酵床技术是以微生物好氧发酵为基础,结合原位发酵床和好氧堆肥形成的新型粪污处理技术,以锯末、谷壳、砻糠等为垫料,通过接种复合微生物菌剂和连续添加粪污方式,实现粪便和污水异地的动态堆肥。翻堆是异位发酵床动态堆肥的保障,通过翻堆可补充粪污,增加通气量,为微生物增殖提供养分和氧气,调节温度变化,调整微生物群落结构,促进物料的分解,提高ARGs等污染物的消减或去除效果。近年来,对粪污异位发酵床中ARGs的变化也进行了一些研究,如李可心
粪污(包括粪便、尿液及生产污水,含水量约90%)和异位发酵床垫料(锯末、谷壳、砻糠)来自湖北省某奶牛场。微生物菌剂(含芽孢杆菌、粪球菌、乳酸菌和酵母菌等,总菌量≥1×1
土壤DNA提取试剂盒购自TIANGEN公司,TaqDNA聚合酶购自大连宝生物公司(TaKaRa),Agarose 琼脂糖(100 g/瓶)购自北京索莱宝科技有限公司,iTaq Universal SYBR Green Supermix购自上海根生生物科技有限公司,抗生素抗性基因引物由北京擎科生物科技有限公司合成。
根据奶牛场异位发酵床生产方式,于2020年7月29日至9月27日采用无盖塑料盒在雨棚内开展试验。塑料盒总容积0.7
按翻堆频次分为2组, F1组:1 d翻堆1次;F2组:2 d翻堆1次。
用实时数显温度仪垂直插入物料中心20~30 cm处监测温度,每天09:00记录实时数显温度仪温度及空气温湿度测定器的温度和湿度。
试验期间含水量控制在60%左右。采用微波炉加热法监测含水量,并根据含水量变化调整粪污添加量,粪污添加量=。
分别于堆肥0、5、12、26、33、40、47、61 d按上、中、下3层(分别距表面 10、30、50 cm)采用五点采样法取样,混合均匀,再用四分法收集样品约 500 g,密封于5号自封袋,置于-20 ℃保存。
PCR和qPCR引物设计参照文献 [
对PCR检出率较高的7种基因(tetG、tetW、sul1、sul2、blaTEM-1、ermQ、intI1)进一步在ABI ViiA 7 Real Time PCR System荧光定量PCR仪上进行荧光定量PCR检测。反应体系为基因组DNA 1 μL,iTaq Universal SYBR Green Supermix(2×) 10 μL,10 μmol/L的上下游引物各0.25 μL,双蒸水8.5 μL,总体积20 μL。反应条件:95 ℃ 3 min,95 ℃ 5 s、60 ℃ 30 s、72 ℃ 30 s,共40个循环,65 ℃延伸5 s。每个样品3个重复。
粪污降解过程中温度变化见
采用PCR方法检测了12种ARGs和3种MGEs。结果显示,2组样品中,除磺胺类dfrA1基因外,其余11种ARGs和3种MGEs均检出,其中sul1、sul2、tetG、tetW、blaTEM-1、ermQ、intI1的检出率较高。粪污降解过程中,目标基因种类整体上随温度的升高而减少或降低而增加(
1) 目标基因总相对丰度变化。采用qPCR检测了6种ARGs(sul1、sul2、tetG、tetW、blaTEM-1、ermQ)及1种MGEs(intI1)的相对丰度,F1和F2组目标基因总相对丰度整体上呈先降低后升高再降低的变化趋势(

图1 粪污降解过程中F1(A)、F2(B)组ARGs和MGEs的变化
Fig.1 Changes of ARGs and MGEs in group F1 (A) and F2 (B) during degradation of manure and sewage
2) tetG和tetW的相对丰度变化。粪污降解过程中tetG和tetW的相对丰度变化见

图2 粪污降解过程中tetG(A)和tetW(B)的变化
Fig.2 Changes of tetG (A) and tetW (B) during degradation of manure and sewage
同组中不含相同小写字母表示差异显著(P<0.05),不含相同大写字母表示差异极显著(P<0.01),下同。Note: Not containing the same lowercase letters in same group indicate significant differences (P<0.05), and not containing the same uppercase letters indicate extremely significant differences(P<0.01), the same as below.
F1、F2组中tetW整体呈降低变化趋势(
整体上,F1和F2组均可不同程度降低tetG(16.51%和64.32%)、tetW(87.89%和99.46%)的相对丰度,且F2组可较好地去除tetG、tetW,尤其是高温期。
3) sul1和sul2的相对丰度变化。磺胺类抗性基因sul1、sul2相对丰度变化如

图3 粪污降解过程中sul1(A)和sul2(B)的变化
Fig.3 Changes of sul1 (A) and sul2 (B) during degradation of manure and sewage
F1组初始样品中sul2的相对丰度较低,F2组较高(
试验结束时,F1和F2组中sul1的相对丰度均降低(54.58%和50.91%),但sul2的丰度变化有较大差别(-327.33%和30.87%),说明F1和F2组均可较好地去除sul1,但去除sul2的效果不理想。相比较来看,F2组可较好地降低sul1、sul2的丰度。
4) blaTEM-1和ermQ的相对丰度变化。粪污降解过程中blaTEM-1相对丰度整体上降低(

图4 粪污降解过程中blaTEM-1(A)和ermQ(B)的变化
Fig.4 Changes of blaTEM-1 (A) and ermQ (B) during degradation of manure and sewage
ermQ的相对丰度变化如
F1和F2组均可显著降低blaTEM-1、ermQ的相对丰度,且两组间无明显差别,说明2种翻堆方式均可有效去除blaTEM-1、ermQ,尤其是高温期。
5)整合子基因intI1的相对丰度变化。粪污降解过程中intI1的相对丰度变化见

图5 粪污降解过程中intI1的变化
Fig.5 Changes of intI1 during degradation of manure and sewage
研究表明,畜禽粪便堆肥过程中添加功能性菌
武中
堆肥过程中产生的高温可杀灭/去除不耐热的ARGs宿主菌及破坏耐药质
研究表明,堆肥过程中微生物群落结构变化是ARGs丰度变化的关键因
Qian
研究表明,堆肥可降低大部分四环素类抗性基因如tetG、tetX的丰
有研
Jang
intI1是ARGs水平转移的一个重要MGEs,降低intI1相对丰度可抑制ARGs的扩散和传
综上,奶牛粪污异位发酵床中添加复合菌剂、2 d翻堆1次更有利于提高堆肥温度并延长高温持续时间,有利于去除粪污中大部分ARGs,降低ARGs传播扩散风险。
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