Oxytetracycline and copper are the common residues in animal manures. Meanwhile, anaerobic digestion is considered as a clean biotechnology for the disposal of animal manures. In this paper, the performance of anaerobic digesters and the dynamics of bacterial communities under the different treatments of oxytetracycline and copper were discussed. The parameters of methane production and pH values were studied to reflect the performance of anaerobic digester. Results showed that the changes of methane production and pH values were not obvious compared with the control. This means that the treatments of oxytetracycline and copper almost have no effects on the performance of anaerobic digesters. This phenomenon might be due to the chelation reaction between oxytetracycline and copper. This chelation reaction might reduce the toxicity of oxytetracycline. The study on the dynamics of bacterial communities was based on the polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) method. Results indicated that the bacterial communities had significant differences under the different treatments of oxytetracycline and copper. Uncultured
With the development of livestock, the residual antibiotics and heavy metals in animal manure have attracted more and more world-wide attention. This residual phenomenon is due to the low bioavailability of antibiotics and heavy metals which are widely added to the feeds in order to control diseases and enhance the growth of livestock animals [
Animal manures belong to the organic wastes. The common methods of the disposal of manure include aerobic composting and anaerobic digestion [
The performance of anaerobic digester can be reflected by methane production and pH values [
The objectives of this study were to evaluate the performance of anaerobic digesters and discuss the dynamics of bacterial communities under the treatments of oxytetracycline and copper during the anaerobic digestion of cow manure. Methane production and pH values were measured and analyzed to reflect the performance of anaerobic digestion. Furthermore, the PCR-DGGE method was used to discuss the dynamics of bacterial communities.
Cow manure samples were taken from the surrounding countryside Shenyang City, China. Then the samples were stored in a refrigerator at 4°C before used. The physical and chemical properties of samples were as follows: total solids, 25.67%; pH value, 8.26; volatile organic acids, 878.4 mg l−1; and organic carbon, 42.75%. Laboratory-scale anaerobic digesters (1 L) were prepared. Then each digester was added with 200 g cow manure. Different amounts of oxytetracycline and copper (dose as CuSO4) were added to each digester (Table
Different treatments of oxytetracycline and copper in the laboratory-scale anaerobic digesters.
Treatments | Oxytetracycline | Copper (dose as CuSO4) |
---|---|---|
A1 | 20 | 100 |
A2 | 20 | 200 |
A3 | 20 | 300 |
B1 | 50 | 100 |
B2 | 50 | 200 |
B3 | 50 | 300 |
C1 | 100 | 100 |
C2 | 100 | 200 |
C3 | 100 | 300 |
Control | 0 | 0 |
Total genomic DNA of manure samples was extracted on days 1, 15, and 50, respectively. In this experiment, the primers 341F with 40 bp GC-clamps and 907R were used for the polymerase chain reaction amplification [
The selected DGGE bands were reamplified and electrophoresed to confirm the mobility and then transported to Beijing Huada Gene Company (Beijing, China) for sequencing. Through the CLUSTAL X and MEGA 4.0, the phylogenetic tree was built via the neighbor-joining method [
Nucleotide sequences were deposited in the NCBI nucleotide sequence databases to get the accession numbers: KM491540-KM491545.
Methane production under the different treatments of oxytetracycline and copper is present in Figure
Variations of methane production with time under different oxytetracycline and copper treatments.
The changes of pH values during the anaerobic digestion are shown in Figure
Variations of pH value with time under different oxytetracycline and copper treatments.
Dynamics of bacterial communities under the different treatments of oxytetracycline and copper are present via the DGGE fingerprints in Figure
Denaturing gradient gel electrophoresis (DGGE) fingerprints of bacterial 16S-rRNA gene fragments of cow manure samples under different oxytetracycline and copper treatments at day 1, day 10, and day 50.
Although band H5 was not shown at the control DGGE bands of day 1, it appeared at the control DGGE bands of day 10 and day 50. In contrast, band H6 was shown at all DGGE bands. This indicated that band H6 seemed to play as the functional bacteria. Through the sequence similarity analysis by the BLAST program, these six bacterial sequences were conducted by homology comparison (Table
Closest relatives of the bacterial 16S-rRNA gene sequences.
DGGE band | Closest GenBank Relative (accession number) | Sequence homology (%) | Accession |
---|---|---|---|
H1 | | 95% | KM491540 |
H2 | Uncultured bacterium (KJ853330.1) | 98% | KM491541 |
H3 | Uncultured | 90% | KM491542 |
H4 | | 99% | KM491543 |
H5 | Uncultured | 99% | KM491544 |
H6 | Uncultured | 98% | KM491545 |
Phylogenetic tree of the bacterial 16S-rRNA gene sequences compared with known sequences from Genbank.
In this experiment, it could be concluded that uncultured
This study discussed the performance of anaerobic digesters and the dynamics of bacterial communities under different treatments of oxytetracycline and copper. Results indicated that methane production and pH values were hardly affected compared with the control. This might be due to the chelation reaction between oxytetracycline and copper. The reaction might reduce the toxicity of oxytetracycline. Meanwhile, uncultured
The authors declare that there are no conflicts of interest.
This study was supported by Agro-Scientific Research in the Public Interest (201503118-10), National Natural Science Foundation of China (41601230), and Postdoctoral Science Foundation (2017M611265).