Abstract
Antibiotics are widely added to swine forage and are the main reason for the environmental accumulation of antibiotic resistance genes (ARGs) in swine manure-dwelling microorganisms. Aerobic composting (AC) and anaerobic digestion (AD) are efficient methods for converting swine manure to bio-fertilizer while degrading residual antibiotics. However, the influence of these methods on ARG accumulation and the difference in their efficiency have rarely been investigated. In this study, we explored the variations in four tetracycline antibiotics (TCs) and their associated ARGs and in microbial communities after AC and AD treatment. After full-scale manure AC and AD, the four TCs were removed effectively. AD had a higher TC removal efficiency than AC and a slower rate of TC-associated ARG accumulation. In addition, the community structure was more stable in the AC and AD manures than in untreated manure, and the relationship among microbial species also evolved into competition from mutualism after both AC and AD treatment. It was also speculated that the genera Acholeplasma and Arthrobacter were the possible hosts of tetO, tetW, and tetQ; the shift in the prokaryotic community composition and the alleviation of selective pressure by TC degradation led to decreased relative abundance of ARGs in AD- and AC-treated manure.
Highlights
Antibiotics have been heavily used for disease treatment in livestock and aquaculture, and in swine farming as feed additives (Zhang et al, 2015; Henriksson et al, 2018)
There was no significant difference in the level of OTC antibiotics between the Aerobic composting (AC) and anaerobic digestion (AD) treatment samples
Previous studies have shown that AC and AD treatment can effectively degrade tetracycline antibiotics (TCs) residues and reduce TC-associated antibiotic resistance genes (ARGs) in swine manure (Ward et al, 2008; Diehl and Lapara, 2010; Selvam et al, 2012; Sun et al, 2016)
Summary
Antibiotics have been heavily used for disease treatment in livestock and aquaculture, and in swine farming as feed additives (Zhang et al, 2015; Henriksson et al, 2018). The AC process often leads to a significant increase in ARGs because ARGs are highly mobile among the genomes of drug-resistant strains, and the accumulation of specific ARGs in certain bacterial genomes causes the accumulation of ARGs for specific antibiotics (Ghosh and Lapara, 2007; Looft et al, 2012; Zhu et al, 2013; Su et al, 2015) These drug-resistant strains harboring specific ARGs are important sources of ARGs in the environment (Enne et al, 2001) when distributed into the environment (Li et al, 2015a). There is no corroborating evidence suggesting that AD should or should not be promoted in manure treatment with respect to the risk of environmental ARG contamination Since both AC and AD are readily available approaches for animal manure management on an industrial scale, knowledge regarding their comparative performance in terms of antibiotic degradation and ARG accumulation is necessary to find a suitable method for manure management
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