Xiaojuan Wang

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.

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.

Effects of oxytetracycline on the abundance and community structure of nitrogen-fixing bacteria during cattle manure composting

The effects of oxytetracycline (OTC) on nitrogen-fixing bacterial communities were investigated during cattle manure composting. The abundance and community structure of nitrogen-fixing bacteria were determined by qPCR and denaturing gradient gel electrophoresis (DGGE), respectively. The matrix was spiked with OTC at four levels: no OTC, 10mg/kg dry weight (DW) OTC (L), 60mg/kg DW OTC (M), and 200mg/kg DW OTC (H). The high temperature period of composting was shorter with M and H, and the decline in temperature during the cooling stage was accelerated by OTC. OTC had a concentration-dependent inhibitory effect on the nitrogenase activity during early composting, and the nifH gene abundance declined significantly during the later composting stage. The DGGE profile and statistical analysis showed that OTC changed the nitrogen-fixing bacterial community succession and reduced the community richness and dominance. The nitrogen-fixing bacterial community structure was affected greatly by the high level of OTC.

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).

Impact of copper on the diazotroph abundance and community composition during swine manure composting

Biological nitrogen fixation is a major pathway in ecosystems. This study investigated the effects of adding Cu at different levels (0, 200, and 2000 mg kg-1) on the diazotroph community during swine manure composting. Quantitative PCR and high-throughput sequencing were used to analyze the abundances of diazotrophs and the community composition based on the nifH gene. The nifH gene copy number was relatively high in the early stage of composting and Cu had a significant inhibitory effect on the nifH copy number. Furthermore, Cu decreased the diversity of nifH and changed the microbial community structure in the early stage. The nifH genes from members of Firmicutes and Clostridium were most abundant. Co-occurrence ecological network analysis showed that the Cu treatments affected the co-occurrence patterns of diazotroph communities and reduced the associations between different diazotrophs. Interestingly, Cu may weaken symbiotic diazotrophic interactions and enhance the roles of free-living diazotrophs.

Effects of inoculation with organic-phosphorus-mineralizing bacteria on soybean (Glycine max) growth and indigenous bacterial community diversity

Three different organic-phosphorus-mineralizing bacteria (OPMB) strains were inoculated to soil planted with soybean (Glycine max), and their effects on soybean growth and indigenous bacterial community diversity were investigated. Inoculation with Pseudomonas fluorescens Z4-1 and Brevibacillus agri L7-1 increased organic phosphorus degradation by 22% and 30%, respectively, compared with the control at the mature stage. Strains P. fluorescens Z4-1 and B. agri L7-1 significantly improved the soil alkaline phosphatase activity, average well color development, and the soybean root activity. Terminal restriction fragment length polymorphism analysis demonstrated that P. fluorescens Z4-1 and B. agri L7-1 could persist in the soil at relative abundances of 2.0%-6.4% throughout soybean growth. Thus, P. fluorescens Z4-1 and B. agri L7-1 could potentially be used in organic-phosphorus-mineralizing biofertilizers. OPMB inoculation altered the genetic structure of the soil bacterial communities but had no apparent influence on the carbon source utilization profiles of the soil bacterial communities. Principal components analysis showed that the changes in the carbon source utilization profiles of bacterial community depended mainly on the plant growth stages rather than inoculation with OPMB. The results help to understand the evolution of the soil bacterial community after OPMB inoculation.

Effects of chromium(III) on enzyme activities and bacterial communities during swine manure composting

The present study investigated the effects of different concentrations of chromium (i.e., 200 and 700mgkg-1 Cr corresponding to Cr200 and Cr700, respectively) on the microorganisms in swine manure compost. The results demonstrated that a high concentration of Cr(III) could inhibit the activity of key microbial enzymes (i.e., dehydrogenase, cellulase, and urease) in the early composting stages, with maximal inhibition rates of 54.9%, 32.8%, and 46.7% for cellulase, urease, and dehydrogenase, respectively. Furthermore, the bacterial abundances were determined by quantitative PCR and their compositions were evaluated by denaturing gradient gel electrophoresis. Cr200 and Cr700 had significant inhibitory effects on the abundances of bacteria. The DGGE results showed that Cr200 and Cr700 changed the bacterial community structure and diversity, where Cr(III) might enhance the abundance of pathogenic bacteria (e.g., Saccharomonospora) and decrease the abundances of bacteria that degrade cellulose and lignin (e.g., Paenibacillus) during composting.