Oxytetracycline (OTC) residues have been found in soil and water, and they may pose potential risks to agricultural ecological environments.  One of the most impactful ways for OTC to enter the soil and water environments is through excrement used as organic fertilizer.  Therefore, it is important to remove OTC during manure composting and to understand the transformation of the organic materials during composting in the presence of OTC.  In the present paper, chicken manure and wheat sawdust spiked with OTC were composted under different initial moisture contents (MC) to evaluate the degradation of OTC and  changes of organic matter during the composting process.  The MC has a significant effect on OTC degradation during composting.  A higher MC of 65% was more conducive to OTC degradation (77.4%) and compost maturity compared to the lower MC.  However, the higher MC of 65% could increase the ammonia volatilization by promoting nitrification compared to the lower MC.  An increase in the initial MC could improve the composting temperature.  NMR results illustrated that the presence of OTC could affect the internal transformation of aliphatics, and OTC inhibited compost humification.  Thus, an initial MC of 55–65% can alleviate the impacts of OTC on humification during manure composting.

The dynamic changes in microbial diversity during the aerobic composting of agricultural crop straw with additives were evaluated using high-throughput sequencing at four phases of composting (mesophilic, thermophilic, cooling and maturation phases).  In addition, the physicochemical parameters of the composting system were determined in this study.  The fermentation time of the thermophilic period was prolonged with the addition of urea or urea combined with a microbial agent.  The ratio of C/N and germination index variation indicated that the additives were favorable for composting, because the additives directly changed the physicochemical properties of the compost and had effects on the diversity and abundance of bacteria and fungi.  The abundance of operational taxonomic units (OTUs), diversity index (Shannon) and richness index (Chao1) of fungi and bacteria were found to significantly increase when urea+microbial agents  were added to straw in the thermophilic phase.  The relative abundance of the predominant bacteria and fungi at the phylum and genus levels differed during different composting phases.  The abundance of the phyla Firmicutes and Proteobacteria declined in the order of treatments SNW>SN>S (S is straw only compost; SN is straw+5 kg t^–1 urea compost; and SNW is straw+5 kg t^–1 urea+1 kg t^–1 microbial agent compost) in the thermophilic phase.  The abundance of the genera Staphylococcus, Bacillus and Thermobifida followed the same order in the mesophilic phase.  Ascomycota accounted for more than 92% of the total fungal sequences.  With the progression of the composting process, the abundance of Ascomycota decreased gradually.  The abundance of Ascomycota followed the order of S>SN>SNW during the thermophilic phase.  The abundance of Aspergillus accounted for 4–59% of the total abundance of fungi and increased during the first two sampling periods.  Aspergillus abundance followed the order of SNW>SN>S.  Additionally, principal component analysis (PCA) revealed that the community compositions in the straw and straw+urea treatments were similar, and that the bacterial communities in treatments S, SN and SNW in the mesophilic phase (at day 1) were different from those observed in three other phases (at days 5, 11, and 19, respectively), while the fungal communities showed only slight variations in their structure in response to changes in the composting process.  Canonical correlation analysis (CCA) and redundancy analysis (RDA) showed that total carbon (TC), NO₃^–-N (NN), electrical conductivity (EC) and pH were highly correlated with community composition.  Therefore, this study highlights that the additives are beneficial to straw composting and result in good quality compost.

 

Antibiotics residues have been accumulating in the environment day by day due to overuse of antibiotics.  Recalcitrant antibiotic residues, such as tylosin (TYL), can cause serious environmental problems, which makes it important to eliminate TYL from the environment.  It is important to eliminate TYL from the environment.  In this study, a strain was isolated and purified from fermentation by-product that came from a TYL production factory.  The TYL degrading strain was identified by its morphology, physiological and biochemical reactions and sequencing the PCR-amplified fragments of its 16S rDNA-coding genes.  The temperature, shaking speed, initial TYL concentration, pH and inoculum sizes were investigated under simulated conditions by using single factor tests.  The results showed that TYL2, a high efficient strain was isolated and was identified as Brevibacillus borstelensis.  The degradation rate of TYL by this strain could reach to 75% with an initial concentration of 25 mg L^–1 within 7 days under conditions of 7% B. borstelensis (v/v, 2×10⁸ CFU mL^–1) at pH 7.0 and at 35°C.  It is interesting that this strain has a very strong ability to degrade the TYL in natural sewage with the degradation rate of 65% within 7 days.  This result could be helpful for the degradation of TYL and provide guidance for the degradation of other antibiotics.

Over the past few decades, the usage of oxytetracycline (OTC), a kind of antibiotic, has increased with the development of aquaculture and livestock breeding.  However, about 30–90% of the applied antibiotics are excreted as the parent compounds into the environment, especially with the application of animal manure to agricultural fields.  This large influx of antibiotics may lead to the destruction of the natural microbial ecological community and pose great threats to human beings through the food chain.  Therefore, the fate and toxicity of OTC in the environment are issues of great concern.  Degradation of OTC, including the non-biodegradation and biodegradation, and the biological toxicity of its degradation products or metabolites, are reviewed in this paper.  The non-biodegradation pathways include hydroxylation, quinonization, demethylation, decarbonylation, dehydration and secondary alcohol oxidation.  Light (particularly UV light), pH and oxidizing substances play important roles in non-biodegradation.  Biodegradation products include 4-epi-OTC (EOTC), 2-acetyl-2-decarboxy-amido-OTC (ADOTC), α-apo-OTC and β-apo-OTC.  EOTC is an epimer and identied except for the configuration of the C4 dimethylamino group of OTC.  Temperature and pH are the main factors affecting biodegradation pathways of OTC.  In addition, this review discusses concerns over the biological toxicity of OTC degradation products.