Elucidating the microbiological characteristics of cyromazine affecting the nitrogen cycle during aerobic composting of pig manure.

Cyromazine as insect growth inhibitor have been frequently detected in the environment, which show a potential threat to environment and soil health. Nitrogen is an essential component of all living organisms and the main nutrient limiting life on our planet. In this study, quantitative polymerase chain reaction (qPCR) and sequencing of nitrifying and denitrifying bacteria were conducted to investigate the dynamic effects of cyromazine on nitrogen conversion during laboratory-based composting. Results showed that the presence of cyromazine significantly reduced the abundance of amoA gene during the thermophilic phase of composting (p < 0.01), resulting in lower oxidation of NH4+-N. The archaea amoA gene was more resistant to cyromazine. The nirK gene was more abundant than the nirS gene during composting and was significantly reduced only under high concentrations of cyromazine (p < 0.01). The high dose of cyromazine (15 mg/kg) severely damaged the nitrogen fixation capacity of compost products. Cyromazine exhibited an inhibition effect on richness (ACE, Chao) of nitrifying and denitrifying microorganisms during the thermophilic period, while increased the diversity (shannon) at all stages of composting. Pseudomonas_formosensis was the core denitrifiers that harbored nosZ gene, Nitrosomonas_eutropha and Nitrosospira_sp_Nl5 were the dominant nitrifier that harbored amoA gene, and these species have a negative response to cyromazine. Network analysis indicated that the dominant bacteria harboring amoA and nosZ genes were hubs of nitrogen oxidation and reduction processes. Structural equation modeling revealed that NO2--N conversion played a crucial role in driving denitrification, and increase of NH4+-N content was attributed to the inhibition of nitrification and denitrification during composting caused by cyromazine.

Key role of cyromazine in the distribution of antibiotic resistance genes and bacterial community variation in aerobic composting.

The risks that have not been noted so far have come from the use of non-antibiotics. In this study, non-antibiotic drug (cyromazine) was used in composting to investigate its possible effects on the distribution of ARGs and changes of bacterial community. Results showed that cyromazine increased the abundances of highly-risky ARGs (blaCTX-M and blaVIM), and heavy metal resistance genes (MRGs). Low and high concentrations of cyromazine increased the abundance of Tn916/1545 by 18.27% and 64.26%, respectively, compared with the control treatment. Mobile genetic elements (MGEs) and MRGs were not the major cause of the dynamic changes in ARGs, but instead the bacterial community succession changed according to the moisture content, pH, and bio-Cu. Network analysis showed that Proteobacteria and Actinobacteria were the major hosts for ARGs, and there was a significant correlation between tcrB, sul1 and Tn916/1545.

Fate of antibiotic resistance genes and mobile genetic elements during anaerobic co-digestion of Chinese medicinal herbal residues and swine manure.

Swine manure is an important reservoir for antibiotic resistance genes (ARGs) but anaerobic co-digestion (AcoD) can potentially reduce the abundance of these ARGs. However, few studies have considered the effects of Chinese medicinal herbal residues (CMHRs) on the variations in ARGs and mobile genetic elements (MGEs) during AcoD. Thus, this study explored the fate of ARGs and MGEs during the AcoD of CMHRs and swine manure. The results showed that CMHRs effectively reduced the abundances of the main ARGs (excluding ermF, qnrA, and tetW) and four MGEs (by 36.7-96.5%) after AcoD. Redundancy analysis showed that changes in the bacterial community mainly affected the fate of ARGs rather than horizontal gene transfer by MGEs. Network analysis indicated that 17 bacterial genera were possible hosts of ARGs. The results of this study suggest that AcoD with CMHRs could be employed to remove some ARGs and MGEs from swine manure.

Influence of combined sulfachloropyridazine sodium and zinc on enzyme activities and biogas production during anaerobic digestion of swine manure.

In order to study the influence of different concentrations of zinc and sulfachloropyridazine sodium (SCPS) on anaerobic digestion (AD) during biogas production, we determined the levels of urease, dehydrogenase activity, and volatile fatty acids (VFAs) in batch tests. The experiments were conducted in small AD devices at a temperature of 37 °C using swine manure and wheat straw as raw materials. Four digestion trials were performed using different zinc and SCPS contents: control digestion with no additives (CK), SCPS at 630 mg kg-1 dry weight (S), SCPS at 630 mg kg-1 with zinc at 500 mg kg-1 dry weight (SL), and SCPS at 630 mg kg-1 with zinc at 5,000 mg kg-1 dry weight (SH). The biogas accumulation under S was 1.7 times that with CK, while SL and SH produced 78% and 35% of that under S, respectively. Correlation analysis showed that the accumulated biogas was significantly negatively correlated (p < 0.05) with VFAs, and the urease activity was significantly negatively correlated (p < 0.01) with zinc and significantly positively correlated with VFAs (p < 0.05). The dehydrogenase activity was strongly correlated (p < 0.01) with the biogas accumulated during the AD of swine manure.

Variations in the denitrifying microbial community and functional genes during mesophilic and thermophilic anaerobic digestion of cattle manure.

In this study, the anaerobic digestion (AD) of cattle manure was conducted at two temperatures (mesophilic: 35 °C; thermophilic: 55 °C) to analyze the dynamics of the denitrifying functional microbial community and functional genes. The cumulative N2O production under thermophilic conditions was 130.3% higher than that under mesophilic conditions. Thermophilic AD decreased the abundance of nosZ, which was more functional than other denitrifying genes. Firmicutes, Proteobacteria, and Bacteroidetes were the main phyla, and they were also related to denitrification during AD. Redundancy analysis indicated that pH, temperature, and NH4+-N mainly affected the functional bacterial community. Temperature altered the co-occurrence patterns of the bacterial community and the keystone genera in AD. Desulfovibrio in mesophilic AD and Thiobacillus in thermophilic AD were closely related to nitrogen transformation among the keystone genera. The variations in the abundances of members of the denitrifying microbial community and functional genes during AD suggest that thermophilic AD may have caused greater nitrogen losses.

Effects of copper on the composition and diversity of microbial communities in laboratory-scale swine manure composting.

This study investigated the effects of adding copper at 3 treatment levels (0 (control: CK), 200 (low: L), and 2000 (high: H) mg·kg-1 treatments) on the bacterial communities during swine manure composting. The abundances of the bacteria were determined by quantitative PCR and their compositions were evaluated by high-throughput sequencing. The results showed that the abundance of bacteria was inhibited by the H treatment during days 7-35, and principal component analysis clearly separated the H treatment from the CK and L treatments. Actinobacteria, Firmicutes, and Proteobacteria were the dominant bacterial taxa, and a high copper concentration decreased the abundances of bacteria that degrade cellulose and lignin (e.g., class Bacilli and genus Truepera), especially in the mesophilic and thermophilic phases. Moreover, network analysis showed that copper might alter the co-occurrence patterns of bacterial communities by changing the properties of the networks and the keystone taxa, and increase the competition by increasing negative associations between bacteria during composting. Temperature, water-soluble carbohydrates, and copper significantly affected the variations in the bacterial community according to redundancy analysis. The copper content mainly contributed to the bacterial community in the thermophilic and cooling phases, where it had positive relationships with potentially pathogenic bacteria (e.g., Corynebacterium_1 and Acinetobacter).

Prevalence of quinolone resistance genes, copper resistance genes, and the bacterial communities in a soil-ryegrass system co-polluted with copper and ciprofloxacin.

The presence of high concentrations of residual antibiotics and antibiotic resistance genes (ARGs) in soil may pose potential health and environmental risks. This study investigated the prevalence of plasmid-mediated quinolone resistance (PMQR) genes, copper resistance genes (CRGs), and the bacterial communities in a soil-ryegrass pot system co-polluted with copper and ciprofloxacin (CIP; 0, 20, or 80 mg kg-1 dry soil). Compared with the samples on day 0, the total relative abundances of the PMQR genes and mobile genetic elements (MGEs) were reduced significantly by 80-89% in the ryegrass and soil by the cutting stage (after 75 days). The abundances of PMQR genes and MGEs were reduced by 63-81% in soil treated with 20 mg kg-1 CIP compared with the other treatments, but the abundances of CRGs increased by 18-42%. The presence of 80 mg kg-1 CIP affected the microbial community structure in the soil by increasing the abundances of Acidobacteria and Thaumarchaeota, but decreasing those of Firmicutes. Redundancy analysis indicated that the pH and microbial composition were the main factors that affected the variations in PMQR genes, MGEs, and CRGs, where they could explain 42.2% and 33.3% of the variation, respectively. Furthermore, intI2 may play an important role in the transfer of ARGs. We found that 80 mg kg-1 CIP could increase the abundances of ARGs and CRGs in a soil-ryegrass pot system.

Impacts of biochar on the environmental risk of antibiotic resistance genes and mobile genetic elements during anaerobic digestion of cattle farm wastewater.

Biochar has positive effects on nitrogen conservation during anaerobic digestion, but its impacts on antibiotic resistance genes (ARGs) are unclear. Therefore, the effect of biochar (0, 5, 20, and 50 g/L) on the environmental risk of ARGs during cattle manure wastewater anaerobic digestion were investigated. The results showed that 5 g/L biochar reduced the relative abundances (RAs) of 5/13 ARGs while 20 g/L biochar significantly reduced the total RAs of ARGs in the digestion products, where the RA of ISCR1 was 0.89 log lower than the control. Biochar mainly affected the distribution of ARGs by influencing the RAs of Firmicutes and Proteobacteria, and the influence of 20 g/L biochar was greater than that of 5 g/L. Mobile genetic elements also influenced the ARG profiles, especially intI2 and ISCR1. The addition of 20 g/L biochar to cattle farm wastewater anaerobic digestion systems could reduce the environmental risk of ARGs.

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 biochar on reducing the abundance of oxytetracycline, antibiotic resistance genes, and human pathogenic bacteria in soil and lettuce.

Antibiotics and antibiotic resistance genes (ARGs) in soil can affect human health via the food chain. Biochar is a soil amendment but its impacts on ARGs and the microbial communities associated with soil and vegetables are unclear. Therefore, we established three lettuce pot culture experiments, i.e., O300: 300 mg/kg oxytetracycline (OTC), BO300: 300 mg/kg OTC + 2% biochar, and a control without OTC or biochar. We found that under BO300, the relative abundances of ARGs were reduced by 51.8%, 43.4%, and 44.1% in lettuce leaves, roots, and soil, respectively, compared with O300. intI1 was highly abundant in soil and lettuce, and it co-occurred with some ARGs (tetW, ermF, and sul1). Redundancy analysis and network analysis indicated that the bacterial community succession was the main mechanism that affected the variations in ARGs and intI1. The reduction of Firmicutes due to the biochar treatment of soil and lettuce was the main factor responsible for the removal of tetracycline resistance genes in leaves. Biochar application led to the disappearance of human pathogenic bacteria (HPB), which was significantly correlated with the abundances of ermF and ermX. In summary, biochar is an effective farmland amendment for reducing the abundances of antibiotics, ARGs, and HPB in order to ensure the safety of vegetables and protect human health.