Jie Gu

Variable effects of oxytetracycline on antibiotic resistance gene abundance and the bacterial community during aerobic composting of cow manure

Livestock manure is often subjected to aerobic composting but little is known about the variation in antibiotic resistance genes (ARGs) during the composting process under different concentrations of antibiotics. This study compared the effects of three concentrations of oxytetracycline (OTC; 10, 60, and 200mg/kg) on ARGs and the succession of the bacterial community during composting. Very similar trends were observed in the relative abundances (RAs) of each ARG among the OTC treatments and the control during composting. After composting, the RAs of tetC, tetX, sul1, sul2, and intI1 increased 2-43 times, whereas those of tetQ, tetM, and tetW declined by 44-99%. OTC addition significantly increased the absolute abundances and RAs of tetC and intI1, while 200mg/kg OTC also enhanced those of tetM, tetQ, and drfA7. The bacterial community could be grouped according to the composting time under different treatments. The highest concentration of OTC had a more persistent effect on the bacterial community. In the present study, the succession of the bacterial community appeared to have a greater influence on the variation of ARGs during composting than the presence of antibiotics. Aerobic composting was not effective in reducing most of the ARGs, and thus the compost product should be considered as an important reservoir for ARGs.

Effects of Cu on metabolisms and enzyme activities of microbial communities in the process of composting.

With the compost matrix of pig manure, wheat straw, and spent mushroom substrate, and then inoculated with the Compound Microbe Preparation, the study investigated the effects of the heavy metal Cu on the process of composting. Biolog EcoPlate™ test revealed that at a low content, Cu could improve the capacities of microbial communities to transform and exploit carbon sources in the form of polymer, thus speeding up the decomposition of agricultural wastes, and at a high content, Cu presented inhibiting effect on microbial communities to exploit complex macromolecular carbon sources, thus extending the decomposition of agricultural wastes. Enzyme activity testing showed that at a low content, Cu presented enzyme activity-activating effect at the early period of composting and inhibiting effect in the late period of composting, and at a high content, Cu presented enzyme activity-inhibiting effects through the process of composting.

Reducing antibiotic resistance genes, integrons, and pathogens in dairy manure by continuous thermophilic composting

This study explored the effects of composting using three temperature regimes, namely, insufficient thermophilic composting (ITC), normal thermophilic composting (NTC), and continuous thermophilic composting (CTC), on antibiotic resistance genes (ARGs), integrons, and human pathogenic bacteria (HPB), as well as the mechanisms involved. The NTC and CTC treatments led to greater decreases in 5/10 ARGs and two integrons than ITC, and the abundances of ARGs (tetC, tetG, and tetQ) and int1 only declined in the NTC and CTC treatments. The abundances of HPB decreased by 82.8%, 76.9%, and 96.9% under ITC, NTC, CTC, respectively. Redundancy analysis showed that both bacterial succession and horizontal gene transfer play important roles in the variation of ARGs, and the changes in different ARGs were due to diverse mechanisms. CTC performed significantly better at reducing ARGs, integrons, and HPB, thus it may be used to manage the public health risks of ARGs in animal manure.

Effects of Copper Addition on Copper Resistance, Antibiotic Resistance Genes, and intl1 during Swine Manure Composting

Copper is one of the most abundant heavy metals present in swine manure. In this study, a laboratory-scale aerobic composting system was amended with Cu at three levels (0, 200, and 2000 mg kg-1, i.e., control, Cu200, and Cu2000 treatments, respectively) to determine its effect on the fate of copper resistance genes [copper resistance genes (CRGs): pcoA, cusA, copA, and tcrB], antibiotic resistance genes [antibiotic resistance genes (ARGs): erm(A) and erm(B)], and intl1. The results showed that the absolute abundances of pcoA, tcrB, erm(A), erm(B), and intl1 were reduced, whereas those of copA and cusA increased after swine manure composting. Redundancy analysis showed that temperature significantly affected the variations in CRGs, ARGs, and intl1. The decreases in CRGs, ARGs, and intI1 were positively correlated with the exchangeable Cu levels. The bacterial community could be grouped according to the composting time under different treatments, where the high concentration of copper had a more persistent effect on the bacterial community. Network analysis determined that the co-occurrence of CRGs, ARGs, and intI1, and the bacterial community were the main contributors to the changes in CRGs, ARG, and intl1. Thus, temperature, copper, and changes in the bacterial community composition had important effects on the variations in CRGs, ARGs, and intl1 during manure composting in the presence of added copper.

Effects of different swine manure to wheat straw ratios on antibiotic resistance genes and the microbial community structure during anaerobic digestion

This study explored the effects of different mass ratios of swine manure relative to wheat straw (3:7, 5:5, and 7:3, i.e., control reactors C1, C2, and C3, respectively) on variations in antibiotic resistance genes (ARGs) and the microbial community during anaerobic digestion (AD). The cumulative biogas production volumes were 1711, 3857, and 3226mL in C1, C2, and C3, respectively. After AD, the total relative abundance of ARGs decreased by 4.23 logs in C3, whereas the reductions were only 1.03 and 1.37 logs in C1 and C2, respectively. Network analysis showed that the genera Solibacillus, Enterococcus, Facklamia, Corynebacterium_1, and Acinetobacter were potential hosts of ermB, sul1, and dfrA7. Redundancy analysis showed that the bacterial communities and environmental factors played important roles in the variation in ARGs. Thus, reductions in ARGs should be considered before reusing animal manure treated by AD.

Mechanisms and effects of arsanilic acid on antibiotic resistance genes and microbial communities during pig manure digestion

High concentrations of residual arsanilic acid occur in pig manure due to its use in feed to promote growth and control diseases. This study compared the effects of arsanilic acid at three concentrations (0, 325, and 650mg/kg dry pig manure) on the abundance of antibiotic resistance genes (ARGs) and the microbial community during anaerobic digestion. Addition of 650mg/kg arsanilic acid enhanced the absolute abundances of tetC, sul2, ermB, and gyrA more than twofold in the digestion product. Redundancy analysis indicated that the change in the microbial community structure was the main driver of variation in the ARGs profile. The As resistance gene arsC co-occurred with four ARGs and intI1, possibly causing the increase in ARGs under pressure by arsanilic acid. High arsanilic acid concentrations can increase the risk of ARGs occurring in anaerobic digestion products. The amount of arsanilic acid used as a feed additive should be controlled.

Diversity, abundance, and persistence of antibiotic resistance genes in various types of animal manure following industrial composting

Aerobic composting is used widely for animal manure recycling, and it may reduce the amount of antibiotic resistance genes (ARGs) that enter the environment. We sampled three types of animal (bovine, chicken, and pig) manure and the corresponding composts from 12 large-scale farms, and tested multiple ARGs and mobile genetic elements (MGEs) by high-throughput qPCR. A total of 109 ARGs were detected in the manure and compost samples, thereby demonstrating that both are important ARG reservoirs. The diversity and abundance of ARGs were significantly higher in chicken and pig manure than bovine manure, but industrial composting was more efficient at reducing the ARGs in chicken manure than pig and bovine manure. Composting universally reduced some ARGs, but inconsistently influenced other ARGs from different types of animal manures. Network analysis detected the widespread co-occurrence of ARGs and MGEs. floR, ermF, catB3, aac(6)-lb(akaaacA4), and aadA were identified as suitable indicator genes for estimating the total abundance of ARGs. Our results suggest that different animal species had significant effects on the diversity, abundance, and persistence of ARGs, where the abundance of transposons, heavy metal concentration, total nitrogen level, and the dosage and duration of exposure to antibiotics may explain these differences.

Behavior of antibiotic resistance genes during co-composting of swine manure with Chinese medicinal herbal residues

Swine manure is considered to be a reservoir for antibiotic resistance genes (ARGs) but little is known about the variations in ARGs during the co-composting of swine manure with Chinese medicinal herbal residues (CMHRs). Thus, this study explored the effects of CMHRs on the variations in ARGs during co-composting with swine manure. The results showed that CMHRs could reduce effectively most of the targeted ARGs (0.18-2.82logs) and mobile genetic elements (MGEs) (0.47-3.34logs). The correlations indicated that CMHRs might decrease the spread of ARGs via horizontal gene transfer. Redundancy analysis showed that the bacterial communities had more important effects on the variations in ARGs compared with environmental factors and MGEs. The results of this study demonstrate that CMHRs can decrease the abundances of ARGs and MGEs, as well as reducing the risk of ARGs spreading during the application of compost products to farmland.

Effects of superabsorbent polymers on the abundances of antibiotic resistance genes, mobile genetic elements, and the bacterial community during swine manure composting

Superabsorbent polymers (SAPs) are considered suitable amendments for reducing the selection pressure due to heavy metals and the abundances of antibiotic resistance genes (ARGs) during composting. In this study, three SAP (sodium polyacrylate) levels (0, 5, and 15mgkg-1 of compost) were applied and their effects on the abundances of ARGs, mobile genetic elements (MGEs), and the bacterial community were investigated. After composting, the abundances of ARGs and MGEs decreased to different extent, where the removal efficiencies for tetW, dfrA7, ermX, aac(6)-ib-cr and MGEs exceeded 90%. The high SAP concentration significantly reduced the abundances of ARGs and MGEs, and changed the microbial community. Redundancy analysis indicated that the moisture content mainly explained the changes in ARGs and MGEs. Network analysis determined the potential hosts of ARGs and MGEs, and their co-occurrence. The results suggested that applying 15mgkg-1 SAP is appropriate for reducing ARGs in compost.

Effects of copper on the abundance and diversity of ammonia oxidizers during dairy cattle manure composting.

This study investigated the effects of adding Cu(II) at two exposure levels (50 and 500mgkg-1, i.e., Cu50 and Cu500 treatments, respectively) on the activity of ammonia-oxidizing microorganisms during dairy cattle manure composting. The results showed that the pH, NH4+-N, NO3--N, and potential ammonia oxidation values were inhibited significantly by the addition of Cu(II). Furthermore, the abundances of the ammonia-oxidizing archaea (AOA) amoA gene and ammonia-oxidizing bacteria (AOB) amoA gene were determined by quantitative PCR, and their compositions were evaluated by denaturing gradient gel electrophoresis (DGGE). AOA was the dominant ammonia oxidizing microorganism, of which the abundance was much higher than AOB during composting. Cu50 and Cu500 had significant inhibitory effects on the abundance of the amoA gene. The DGGE profile and statistical analysis showed that Cu(II) changed the AOA and AOB community structure and diversity, where Nitrosomonas and Crenarchaeota dominated throughout the composting process.