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

Triclosan disturbs nitrogen removal in constructed wetlands: Responses of microbial structure and functions

This study investigated the influence of wetland types (vertical and tidal flow constructed wetlands [CWs] [VFCW and TFCW, respectively]) and concentrations of triclosan (TCS) on the removal of pollutants (TCS and nitrogen) and microbial characteristics. The efficiency of TCS removal was significantly higher with 5 μg/L TCS (Phase B) than with 30 μg/L (Phase C) in the two CWs. The efficiencies of removal of NH4+-N and NO3--N were significantly inhibited in Phase C. Compared with the VFCW, the TFCW removed more NH4+-N at the same concentration of TCS, whereas less NO3--N was removed, and it even accumulated. Saccharimondales, an important functional genus with the highest abundance and more node connections with other genera, had a sharp decrease in relative abundance as the increasing concentrations of TCS of the two CWs conformed with its relative abundance and significantly negatively correlated with the concentration of TCS. Differentiated Roseobacter_Clade_CHAB-I-5_Lineage and Sphaerotilus were enriched in the VFCW and TFCW, respectively. The abundance of enzymes that catalyzed nitritation was significantly inhibited by TCS, whereas nitrate reductase (EC 1.7.99.4) catalyzed both denitrification and dissimilatory nitrate reduction to ammonium (DNRA), and nitrite reductase (NADH) (EC 1.7.1.15) that catalyzed DNRA comprised a larger proportion in the two CWs. Simultaneously, the abundances of two enzymes were higher in the TFCW than in the VFCW. The network analysis indicated that the main genera were promoted more by TCS in the VFCW, while inhibited in the TFCW. Moreover, the concentrations of nitrogen (NH4+-N, NO3--N, and TN) significantly positively correlated with TCS-resistant bacteria, and negatively correlated with most nitrogen-transforming bacteria with species that varied between the VFCW and TFCW. The results of this study provide a reference for the molecular biological mechanism of the simultaneous removal of nitrogen and TCS in the CWs.

Effects of magnesite on nitrogen conversion and bacterial community during pig manure composting

The objective of this research was to elucidate the effect of varying proportions of magnesite (MS) addition - 0% (T1), 2.5% (T2), 5% (T3), 7.5% (T4), and 10% (T5) - on nitrogen transformation and bacterial community dynamics during pig manure composting. In comparison to T1 (control), MS treatments amplified the abundance of Firmicutes, Actinobacteriota, and Halanaerobiaeota, bolstered the metabolic functionality of associated microorganisms, and enhanced the nitrogenous substance metabolic pathway. A complementary effect in core bacillus species played a key role in nitrogen preservation. Compared to T1, 10% MS demonstrated the most substantial influence on composting because Total Kjeldahl Nitrogen increased by 58.31% and NH₃ emission decreased by 41.52%. In conclusion, 10% MS appears to be optimal for pig manure composting, as it can augment microbial abundance and mitigate nitrogen loss. This study offers a more ecologically sound and economically viable method for curtailing nitrogen loss during composting.

Di-n-butyl phthalate stress induces changes in the core bacterial community associated with nitrogen conversion during agricultural waste composting

Nitrogen (N) loss during composting reduces the quality of compost products and causes secondary environmental pollution. Phthalate esters (PAEs) are common pollutants in agricultural wastes. However, little information is currently available on how PAEs affect N conversion during agricultural waste composting. This research systematically analyzed the impact of di-n-butyl phthalate (DBP) pollution on the N conversion and its related microbial community during composting. Our results indicated that DBP stress results in a shorter thermophilic phase, and then slower compost maturation during composting. Notably, DBP stress inhibited the conversion of ammonia to nitrate, but increased the release of NH₃ and N₂O leading to an increased N loss and an elevated greenhouse effect. Furthermore, DBP exposure led to a reduction of bacteria related to NH₄⁺ and NO₃^- conversion and altered the network complexity of the bacterial community involved in N conversion. It also reduced the abundance of a major nitrification gene (amoA) (P < 0.01) and increased the abundance of denitrification genes (nirK and norB) (P < 0.05). Moreover, DBP affected the overall microbial community composition at all tested concentrations. These findings provide theoretical and methodological basis for improving the quality of PAE-contaminated agricultural waste compost products and reducing secondary environmental pollution.

The nitrogen cycle and mitigation strategies for nitrogen loss during organic waste composting: A review

Composting is a promising technology to decompose organic waste into humus-like high-quality compost, which can be used as organic fertilizer. However, greenhouse gases (N₂O, CO₂, CH₄) and odorous emissions (H₂S, NH₃) are major concerns as secondary pollutants, which may pose adverse environmental and health effects. During the composting process, nitrogen cycle plays an important role to the compost quality. This review aimed to (1) summarizes the nitrogen cycle of the composting, (2) examine the operational parameters, microbial activities, functions of enzymes and genes affecting the nitrogen cycle, and (3) discuss mitigation strategies for nitrogen loss. Operational parameters such as moisture, oxygen content, temperature, C/N ratio and pH play an essential role in the nitrogen cycle, and adjusting them is the most straightforward method to reduce nitrogen loss. Also, nitrification and denitrification are the most crucial processes of the nitrogen cycle, which strongly affect microbial community dynamics. The ammonia-oxidizing bacteria or archaea (AOB/AOA) and the nitrite-oxidizing bacteria (NOB), and heterotrophic and autotrophic denitrifiers play a vital role in nitrification and denitrification with the involvement of ammonia monooxygenase (amoA) gene, nitrate reductase genes (narG), and nitrous oxide reductase (nosZ). Furthermore, adding additives such as struvite salts (MgNH₄PO₄·6H₂O), biochar, and zeolites (clinoptilolite), and microbial inoculation, namely Bacillus cereus (ammonium strain), Pseudomonas donghuensis (nitrite strain), and Bacillus licheniformis (nitrogen fixer) can help control nitrogen loss. This review summarized critical issues of the nitrogen cycle and nitrogen loss in order to help future composting research with regard to compost quality and air pollution/odor control.

Red mud conserved compost nitrogen by enhancing nitrogen fixation and inhibiting denitrification revealed via metagenomic analysis

The objective of this study was to investigate the effects of adding red mud (RM) on denitrification and nitrogen fixation in composting. The results revealed that the retentions of NH₄⁺-N and NO₃^--N in experimental group (T) with RM were 16.20% and 7.27% higher than that in control group (CK) at the mature stage, respectively. The composition and structure of RM can effectively inhibit denitrification and enhance nitrogen fixation. Moreover, metagenomic analysis revealed that Actinobacteria and Proteobacteria were the main microorganisms in denitrification process, while Firmicutes were the main microorganisms in nitrogen fixation process. In T, denitrifying genes nirK and nosZ were 11% and 18% lower than those in CK, respectively, while nitrogen-fixing genes nifK and nifD were 18% and 34% higher than those in control group, respectively. Therefore, adding RM could reduce nitrogen loss and improve the quality of compost via enhancing nitrogen fixation and inhibiting denitrification process.

Evaluation of humic acid conversion during composting under amoxicillin stress: Emphasizes the driving role of core microbial communities

This study aimed to investigate the effects of various amoxicillin (AMX) concentrations on humic acid (HA) formation and the bacterial community structure (BCS) during chicken manure aerobic composting. The findings showed that AMX caused a rise in pH and a shortening of the thermophilic cycle during the thermophilic period. Moreover, a high concentration of AMX (150 mg/kg) inhibited community succession and humification at maturity. In addition to influencing environmental factors, AMX increased the relative abundance (RA) of the dominant bacteria in the thermophilic phase (Firmicutes) and decreased the RA of the dominant bacteria in the mature phase (Proteobacteria). From carbon conversion, AMX promoted fulvic acid (FA) anabolism in the early period and inhibited HA accumulation in the later period. As a result, the primary impact of AMX on HA transformation was the alteration of the BCS, ultimately affecting the quality of compost.

Succession of diazotroph community and functional gene response to inoculating swine manure compost with a lignocellulose-degrading consortium

Diazotroph community contributes to the nitrogen mass and improves the agronomic quality of composting product, but their responses to microbial inoculation during composting are unclear. In this study, the lignocellulose-degrading consortium was inoculated at different levels (0%: CK (control) and 10%: T) to investigate their effects on the variations in the diazotroph community and functional gene during composting. In the later composting phase, the nifH gene copy number was 17.50-25.28% higher in T than CK. The nitrogenase abundance in CK and T were 0.042% and 0.046% in composting product, respectively. Network analysis indicated that inoculation affected the co-occurrence patterns of the diazotroph community and changed the keystone species composition. Partial least-squares path modeling showed that available carbon sources and the succession of the diazotroph community mainly determined the increased abundance of nifH gene. Microbial inoculation stimulated the diazotrophs activities, and was conducive to the nitrogen production in composting product.

Elimination and analysis of mcr-1 and blaNDM-1 in different composting pile layers under semipermeable membrane composting with copper-contaminated poultry manure

The mcr-1 and bla_NDM-1 elimination in copper contamination poultry manure was evaluated by semi-permeable membrane composting. The results showed the mcr-1 in control and high copper groups could not be removed, but mcr-1 decreased superlatively 80.1% in low copper treatment group. Bla_NDM-1 was increased after composting, especially the copper addition groups, the results indicated that the relative abundance of mcr-1 and bla_NDM-1 was obviously different in the different pile layers of copper treatment groups. Three mobile gene elements (MEGs) correlated both mcr-1 and bla_NDM-1,copB correlated mcr-1, czcA and copA correlated both mcr-1 and bla_NDM-1. The major phyla were Firmicutes, Bacteroidota, Actinobacteriota and Proteobacteria in all layers. The correlation analysis showed that the antibiotic resistance genes (ARGs) potential hosts could be influenced by copper form and physicochemical parameters. Semi-permeable membrane composting could decrease the abundance of major potential pathogens. Furthermore, the composting pile was not homogeneous by semi-permeable membrane composting.

Pathways and mechanisms of nitrogen transformation during co-composting of pig manure and diatomite

The aim of this study was to investigate the pathways and mechanisms of nitrogen transformation during the composting process, by adding diatomite (0%, 2.5%, 5%, 10%, 15% and 20%) into initial mixtures of pig manure and sawdust. The results revealed that diatomite facilitated the conversion from NH₄⁺-N to amino acid nitrogen and hydrolysis undefined nitrogen, then reduced NH₃ and N₂O emission by 8.63-35.29% and 14.34-73.21%, respectively. Moreover, the structure and abundance of nitrogen functional genes provided evidence for nitrogen loss. Furthermore, compared with the control (0.03), the treatment blended with 10% diatomite (T3) had the highest value in composting score (-1.27). Additionally, the ratio of carbon and nitrogen (57.30%) was vital for reducing nitrogen loss among all physio-chemical parameters in this study. In conclusion, adding diatomite was a practical way to enhance nitrogen conservation and increase quality of end products, and the optimum added dosage was at 10%.

Garbage enzymes effectively regulated the succession of enzymatic activities and the bacterial community during sewage sludge composting

This study evaluated nitrogen transformation, enzymatic activities and bacterial succession during sewage sludge composting with and without garbage enzymes (GE and CK, respectively). The results showed that GE addition significantly increased fluorescein diacetate hydrolase (FDA), cellulase, and nitrogenase activities during the composting process. GE addition reduced the cumulative NH₃ emissions by 66.5%, increased the peak NH₄-N content by 26.3% and increased the total nitrogen (TN) content of the end compost by 39.2% compared to CK. Microbiological analysis revealed that GE addition significantly increased the relative abundance of Firmicutes during the thermophilic and cooling phases relative to CK. The selected factors affected the bacterial community composition in the following order: NH₄-N > TOC > FDA > TN > C/N. Network analysis also showed that the enzymes were secreted mainly by Bacillus and norank_f_Caldilineaceae in GE, while they were secreted primarily by norank_f_Methylococcaceae in CK during the composting process.

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.

Evaluation of nitrogen conversion pathway during composting under amoxicillin stress: Mainly driven by core microbial community

The aim of this study was to explore the effects of different concentrations of amoxicillin (AMX) on nitrogen (N) conversion and bacterial community structure during aerobic composting. The results revealed that AMX led to a lower temperature and increased pH during the thermophilic phase of composting. AMX inhibited the relative abundance (RA) of Firmicutes at the initial phase but increased the RA of Actinobacteria and Bacteroidetes compared with the control treatment. The core bacterial community linked to N conversion was determined by network analysis. AMX decreased the RA of amoA, a gene related to nitrification, and increased the RAs of nirK and nosZ, which are related to denitrification. Meanwhile, AMX inhibited the activity of ammonia-oxidizing bacteria but promoted the activity of denitrifying bacteria. Therefore, the main adverse effect of AMX on compost quality is to change the microbial community structure and affect the physical and chemical properties of composting.

Dynamics of denitrification performance and denitrifying community under high-dose acute oxytetracycline exposure and various biorecovery strategies in polycaprolactone-supported solid-phase denitrification

Solid-phase denitrification (SPD) is a promising technology for nitrate-rich water purification. This study aimed to examine the variation in denitrification performance and denitrifying community under high-dose acute oxytetracycline (OTC) exposure and various biorecovery strategies. The denitrification performance was impaired significantly after one-day OTC shock at 50 mg L^-1 in a continuous-flow SPD system supported by a polycaprolactone (PCL) carrier but could rapidly recover without the addition of OTC. When 50 mg L^-1 OTC stress was applied for a longer time in the batch tests, a natural recovery period of more than 20 days was required to reach more than 95% nitrate reduction. Under the same conditions, the addition of both mature biofilm-attached PCL carrier and fresh biofilm-free PCL carrier significantly shortened the recovery time for efficient nitrate reduction, mainly due to the increase in organic availability from the PCL carriers. However, the composition of the microbial community notably changed due to the effects of OTC according to high-throughput sequencing and metagenomic analysis. Genes encoding NAR and NIR were much more sensitive than those encoding NOR and NOS to OTC shock. Tetracycline resistance gene (TRG) enrichment was 15.86% higher in the biofilm that experienced short-term OTC shock than in the control biofilm in the continuous-flow SPD system.

Effects of phosphogypsum and medical stone on nitrogen transformation, nitrogen functional genes, and bacterial community during aerobic composting

This study explored the effects of adding phosphogypsum (PPG), medical stone (MS), and both (PPM) during composting on nitrogen transformation, nitrogen functional genes, the bacterial community, and their relationships with NH₃ and N₂O emissions. Adding MS and PPM reduced NH₃ emissions by 25.78-68.37% and N₂O emissions by 19.00-42.86%. PPG reduced NH₃ emissions by 59.74% but slightly increased N₂O emissions by 8.15%. MS was strongly correlated with the amoA-dominated nitrification process. PPG and PPM had strong correlations with nirS- and nirK-dominated, and nosZ-dominated denitrification processes, respectively. PPM promoted nitrification and denitrification processes more than PPG and MS. Different functional bacteria had key roles in nitrification and denitrification during different composting stages. Firmicutes probably contributed to the conversion and release of nitrogen in the thermophilic period, whereas Proteobacteria, Chloroflexi, Bacteroidetes, and other phyla might have played important roles in the cooling and maturation periods. PPM obtained the greatest reductions in NH₃ and N₂O release via the regulation of environmental variables, nitrogen functional genes, and the bacterial community. Overall, these results provide insights at a molecular level into the effects of PPG and MS on nitrogen transformation and NH₃ and N₂O emissions during composting.

Effects of lime amendment on the organic substances changes, antibiotics removal, and heavy metals speciation transformation during swine manure composting

Aerobic composting has been used for a long time for bioconversion of manure wastes, however, its application has been limited due to slow transition of organic matters and influence of heavy metals and antibiotics residues. Compost with lime addition can speed up the composting process, while its effects on the evolution of organic matters, heavy metals and antibiotics need to be further investigated. In this research, the effects of lime amendment on organic substances changes was assessed by the spectroscopic characteristics. Besides, chlortetracycline (CTC) removal and Cu, Zn chemical speciation transformation were also evaluated. Results showed that the humic acid-like substances region of fluorescence regional integration (FRI-EEM) increased from 20.5% to 40.9% and 20.6%-32.6%, respectively, in lime addition treatment and control after 15 days of composting, indicating that the addition of lime remarkably improved the transition of organic matter and accelerated the maturity process. Besides, 94.04% of CTC in the manure was removed when lime was added, higher than 86.10% in the control group. The transformation of zinc from exchangeable and reducible into oxidizable and residual fractions was improved while the transformation of copper was affected slightly. Therefore, lime is a suitable amendment material for manure composting, which can accelerate the transition of organic matters due to the regulation of composting pH, as well as eliminate harmful CTC and bioavailable heavy metal, thus promoting the further utilizing of organic substance.

Oxytetracycline stress reconstruct the core microbial community related to nitrogen transformation during composting

This study investigated oxytetracycline (OTC) effects on nitrogen (N) transformation and bacterial community diversity during chicken manure composting. The addition of OTC inhibited nitrifying bacteria, resulted in a decrease in the transformation of NH₄⁺-N to NO₃^--N during composting, and affected in the order T3 (32.76%) > T2 (28.76%) > T1 (17.02%) > CK. The OTC could act as an inhibitor against core microbial growth, leading to a delay effect during composting. 16S rRNA sequencing was employed for the functional prediction, and results indicated the bacterial community related to N transformation reconstructed under OTC stress. The core microorganisms were changed after OTC addition, with the emergence of Bacillus and Thermobifida, which could inhibit the N transformation by network analysis. Therefore, core microorganisms could be regulated to reduce the negative of OTC impacts on N transformation and thus reduce N loss during composting.

Comparative analysis of denitrification performance, denitrifying community and functional genes to oxytetracycline exposure between single and hybrid biodegradable polymers supported solid-phase denitrification systems

Biodegradable carrier are vital for the solid-phase denitrification (SPD) systems for treating nitrate-rich water. Two solid-phase denitrification reactors were developed with both 200 g L^-1 of single (polycaprolactone, PCL) (R1) and hybrid solid carbon sources (PCL/polylactic acid (PLA) /polyhydroxyalkanoates (PHA)) (R2) to examine the denitrification performance, denitrifying community and functional genes to various oxytetracycline (OTC) exposure in this study, respectively. Complete denitrification performance was achieved in the both SPD systems at low stress of OTC (1 mg L^-1), but then dramatically reduced to less than 20% of nitrate reduction efficiency after one-month high OTC stress (10 mg L^-1), and rapidly recovered to stable nitrate removal rates of 76.77 ± 5.48% (R1) and 40.68 ± 4.40% (R2) after the next day of no OTC stress. However, the reactor R1 with single PCL carriers acquired more efficient nitrate removal rate than that of reactor R2 at the high OTC stress and recovery phase with OTC stress, mainly due to the more organics availability from the single PCL carriers. The richness and diversity of nirK and nirS deintrifiers significantly declined at high OTC stress, and much more of those occurred in biofilm R1 with more organics availability. Besides, biofilm R1 achieved much more abundant periplasmic nitrate reductase, nitrite reductase genes and tetracycline resistance genes after high OTC stress, which explained the potential resistance to OTC and rapid recovery efficiency after no stress of OTC. Thus, the organics availability played an important role in assuring SPD system to be efficient under high OTC stress.

Response of denitrifying community, denitrification genes and antibiotic resistance genes to oxytetracycline stress in polycaprolactone supported solid-phase denitrification reactor

The coexistence of nitrate and antibiotics in wastewater is a common problem. The study aimed to explore the response of denitrifying community, denitrification genes and antibiotic resistance genes (ARGs) to oxytetracycline (OTC) stress in polycaprolactone (PCL) supported solid-phase denitrification (SPD) reactors. Complete nitrate reduction (greater than99%) was achieved in SPD system with OTC stress of 0, 0.05, 0.25 and 1 mg L^-1 during three-month operation, while it significantly declined by about 5% at a further increased OTC level of 5 mg L^-1. The efficient denitrification strongly related with a rich diversity of denitrifiers, while the abundances of which dramatically reduced as the OTC concentration reached ≥0.25 mg L^-1, which caused significant decline of denitrification genes, especially for narH, narJ, narI nirD, nosZ, and norB. Tetracycline resistance genes were a major type of promoted ARGs by different OTC stress, mainly related with the increase of tet36, tetG, tetA, tetM and tetC.

Dynamic change of bacterial community during dairy manure composting process revealed by high-throughput sequencing and advanced bioinformatics tools

The aim of this work was to study the dynamic change in structure and potential function of bacterial community during dairy manure composting process using high-throughput sequencing and advanced bioinformatics tools. Alpha diversity of microbial community significantly decreased during the thermophilic phase and then recovered gradually. Beta diversity analysis showed unique community structures in different composting phases. Keystone microbes such as genus Corynebacterium, Bacillus, Luteimonas and Nonomuraea were identified for different composting phases. Six functional modules were identified for bacterial community during the composting process using co-occurrence analysis. These modules were significantly associated with temperature, pH, degradation of organic matter and maturation of compost. Predicted metagenomics analysis showed that the relative abundance of amino acid, lipid, energy and xenobiotics metabolism increased during the composting process. These results provide valuable insights into the microbiota during dairy manure composting and how the structures and metabolic functions changed in response to composting phases.

Insight to key diazotrophic community during composting of dairy manure with biochar and its role in nitrogen transformation

Analyzing diazotrophic community may help to understand nitrogen transformation in composting and improves the final compost quality. In this study, diazotrophic community dynamics were investigated in terms of nifH gene during dairy manure and corn straw composting with biochar addition using high-throughput sequencing. Biochar decreased the diversity of diazotrophic community and altered diazotroph community structure during composting. At phylum level, Proteobacteria, Actinobacteria and Firmicutes were dominant diazotrophic communities throughout composting process. Biochar addition registered higher correlation coefficient (R) between physicochemical factors (temperature, ammonium (NH₄⁺-N) and nitrate (NO₃^--N)) and diazotroph community composition. Rhodopseudomonas and Pseudoxanthomonas was the key diazotrophic communities influencing NH₄⁺-N transformation in control (CK) and biochar compost (BC), respectively, while for NO₃^--N transformation Clostridium and Bradyrhizobium in CK, Azospira and Methylocystis in BC served as predominant factors. These results indicated that addition of biochar altered the key diazotroph communities influencing nitrogen transformation. Furthermore, some diazotrophs (e.g. Rhodopseudomonas, Bradyrhizobium and Azospira) affecting NH₄⁺-N and NO₃^--N transformation were also observed to be mediating total nitrogen (TN). Interestingly, interactions between diazotrophic communities were observed and these interactions could also influence nitrogen transformation.

Inoculation of cattle manure with microbial agents increases efficiency and promotes maturity in composting

In this study, fresh cattle manure was mixed with rice straw at a ratio of 10:1 in fresh weight and then composted in a self-built, aerated static composting box, whose dimension was 1 m × 0.8 m × 0.8 m with a volume of approximately 0.6 m³. To deal with the inconvenient and time-consuming problem of multiple stage inoculation, a single, one-time inoculation agent containing diverse microorganisms that are active at both the initial heating and thermophilic phases was developed. A total of 12 from 42 strains isolated from the none-inoculated Experiment 1 composting system were selected as microorganismal agents in Experiment 2 according to their species, prevalence and cultural temperature. 200 mL of each microorganism enrichment broth was mixed to the inoculation group at the beginning of composting. A total of 2400 mL of sterilize distilled water was added to the control group. The parameters of temperature, moisture, pH, C/N ratio, organic matter degradation, and germination index were investigated for both inoculation and control composting groups. Results showed that inoculation did not significantly shorten composting time. However, the pile temperature was increased with the maximum temperatures of 64.6 °C and 60.3 °C for the inoculation and control groups, respectively. The degradation of organic matter was accelerated (P < 0.05), and significantly higher GI value (P < 0.05) indicated that the maturity was promoted by the inoculation microorganism. This suggests that the final composting product would provide value as alternative source of nutrients for plants. Conclusively, we suggested a multiple microorganism inoculation method to increase the efficiency and promote maturity in cattle manure composting.

Insight into the effects of sulfamethoxazole and norfloxacin on nitrogen transformation functional genes during swine manure composting

The effects of sulfamethoxazole and norfloxacin on nitrogen functional genes were investigated in four composting treatments of swine manure: CK (no antibiotics), SMZ (spiked with 5 mg kg^-1 dry weight (DW) sulfamethoxazole), NOR (spiked with 5 mg kg^-1DW norfloxacin), and SN (spiked with 5 mg kg^-1DW sulfamethoxazole and 5 mg kg^-1DW norfloxacin). Antibiotics decreased relative abundance of bacterial amoA and nxrA, while increased nosZ/nirK. The decline in amoA/16S rRNA increased the total NH₃ emission in SMZ and NOR from 1027.05 to 1144.39 and 1278.22 mg kg^-1DW. The decrease of nxrA/16S rRNA enhanced the NO₂^--N content and N₂O emission in SMZ in the initial composting. Additionally, the increase in nosZ/nirK probably was the main reason for the lower N₂O emission in SN than other treatments in the cooling phase. The inhibition on nitrification process and increase in NH₃ emission resulted from antibiotics is worthy of attention in the future.

Effects of clay on nitrogen cycle related functional genes abundance during chicken manure composting

The objective of this study was to identify the effect of clay additive to explore the nitrogen cycling related ammonification, denitrifying genes and their relation N₂O and ammonia emission during the chicken manure (CM) composting. The consequences indicated that the additive clay could optimize the environment and improve the NH₄⁺-N into NO₃^--N transformation. Meanwhile, the results observed that 8% clay amendment was significant correlated the abundance of nifH and nosZ genes. Compared with the other treatments, the 6% and 10% clay treatments observed low abundance of nifH. The heat map indicated that clay amendment could enhance the function genes abundance. The redundancy analysis showed that N₂O and ammonia emission among all physiochemical parameters had great relationship with functional genes. Therefore, the addition of 10% clay into CM composting system could efficiently enhance the abundance of nirK and narG genes, and improve the composting with its application.

Symbiotic Nitrogen Fixation in Soil Contaminated with the Veterinary Antibiotics Oxytetracycline and Sulfamethazine

Veterinary and growth-promoting antibiotics are widely used in animal husbandry and accumulate in manure-fertilized soils. However, the impact of these antibiotics on symbiotic nitrogen fixation is poorly understood. We investigated the effect of the veterinary antibiotics oxytetracycline and sulfamethazine, and a combination of both, on nitrogen fixation in alfalfa ( L.) inoculated with . In a pot experiment, was grown in soils fertilized with fresh manure that contained environmentally relevant antibiotic concentrations (0.2, 2, and 200 mg kg). Nodulation, nitrogen fixation, and nutrient concentrations were determined in the alfalfa plants and soils after 12 wk. Compared with the antibiotic-free control, symbiotic nitrogen fixation increased significantly in soils mixed with manure containing 2 and 200 mg kg oxytetracycline (20.1 and 20.8% increase, respectively) and a mixture of 200 mg kg oxytetracycline and sulfamethazine (12.4% increase). The measured plant- and soil-related parameters failed to explain the observed increase in nitrogen fixation. However, using concentration levels that accurately reflect common agricultural practices, we obtained results that directly contradict other experiments conducted under unrealistically high antibiotic concentrations.

Effects of amoxicillin on nitrogen transformation and bacterial community succession during aerobic composting

This study systematically analyzed the effects of amoxicillin (AMX) on the nitrogen transformation and its corresponding functional bacterial communities by conducting two aerobic composting experiments, and AMX impact on bacterial community succession was also evaluated. It provides theoretical and methodological support for harmless composting treatment of large quantities of manure containing AMX in China and for the high-quality compost products. The results showed that AMX exerted several effects on basic physicochemical and biological compost parameters. Notably, temperature changes typically accompanying compost maturation were delayed in AMX compost, reflecting altered compost maturation kinetics and bacterial community structure. Moreover, relative to control, AMX inhibited growth and reproduction of dominant bacterial phyla Firmicutes and Bacteroidetes, with respective reductions of 17.8-26.1% and 0-7.76% in relative abundance (RA) and significantly increased Proteobacteria RA by 1.9-24.8%. Thus, AMX altered both compost bacterial community structure and succession. From the perspective of various nitrogen content changes, AMX has a significant effect on nitrogen conversion and release. Simultaneously, AMX may inhibit ammoniated and ammonia-oxidizing bacterial activity, while significantly increasing the RA of denitrifying bacteria. Indeed, during early composting with AMX, the RA of denitrifying bacteria was 1361.9-1435.0% of control, highlighting differences in nitrogen transformation and release between groups.

Effects of Elevated Tetracycline Concentrations on Aerobic Composting of Human Feces: Composting Behavior and Microbial Community Succession

The effects of antibiotics on aerobic composting are investigated by dosing of tetracycline (TC) in fresh human feces with sawdust as biomass carrier. Variability in process parameters such as temperature, pH, water-soluble carbon, germination index (GI) and dehydrogenase activity (DHA) are evaluated at TC dosages of 0, 100, 250 and 500 mg/kg in a 21-day composting. Moreover, microbial community succession is examined by high-throughput 16S rRNA gene sequencing. Findings indicate significant impacts to the process parameters with the increase of TC concentration such as inhibition of temperature increases during aerobic composting, lowering of pH, increasing of water-soluble carbon residue, a decrease of GI, and hindering of DHA. Furthermore, elevated TC concentrations significantly alter the microbial community succession and reduce the community diversity and abundance. Therefore, interference in microbial community structures and a hindrance to biological activity are believed to be the main adverse effects of TC on the composting process and maturity of the composting products.

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.

The effects of bio-available copper on macrolide antibiotic resistance genes and mobile elements during tylosin fermentation dregs co-composting

In this study, aerobic co-composting of tylosin fermentation dregs (TFDs) and sewage sludge with different adding concentrations of copper (Cu) was investigated to inspect the fate of antibiotic resistance genes (ARGs), metal resistance genes (MRGs) and mobile genetic elements (MGEs). Results showed that two concentrations of Cu did affect not only the abiotic factors but the relative abundances of resistance genes. High concentration of Cu inhibited the metabolic capacity of microbial community and the nitrogen-fixing process while had little effect on the degradation of TYL and TOC. The abundance of ermT, mefA, mphA increased partly attributed to the toxic effects and co-selective pressure from heavy metal reflected by MRGs. There was significant correlation among some environmental factors like pH, bio-Cu, organic matters and ARGs.

Metagenomic mining pectinolytic microbes and enzymes from an apple pomace-adapted compost microbial community

BACKGROUND

Degradation of pectin in lignocellulosic materials is one of the key steps for biofuel production. Biological hydrolysis of pectin, i.e., degradation by pectinolytic microbes and enzymes, is an attractive paradigm because of its obvious advantages, such as environmentally friendly procedures, low in energy demand for lignin removal, and the possibility to be integrated in consolidated process. In this study, a metagenomics sequence-guided strategy coupled with enrichment culture technique was used to facilitate targeted discovery of pectinolytic microbes and enzymes. An apple pomace-adapted compost (APAC) habitat was constructed to boost the enrichment of pectinolytic microorganisms.

RESULTS

Analyses of 16S rDNA high-throughput sequencing revealed that microbial communities changed dramatically during composting with some bacterial populations being greatly enriched. Metagenomics data showed that apple pomace-adapted compost microbial community (APACMC) was dominated by Proteobacteria and Bacteroidetes. Functional analysis and carbohydrate-active enzyme profiles confirmed that APACMC had been successfully enriched for the targeted functions. Among the 1756 putative genes encoding pectinolytic enzymes, 129 were predicted as novel (with an identity <30% to any CAZy database entry) and only 1.92% were more than 75% identical with proteins in NCBI environmental database, demonstrating that they have not been observed in previous metagenome projects. Phylogenetic analysis showed that APACMC harbored a broad range of pectinolytic bacteria and many of them were previously unrecognized.

CONCLUSIONS

The immensely diverse pectinolytic microbes and enzymes found in our study will expand the arsenal of proficient degraders and enzymes for lignocellulosic biofuel production. Our study provides a powerful approach for targeted mining microbes and enzymes in numerous industries.

Bacterial and fungal communities and contribution of physicochemical factors during cattle farm waste composting

During composting, the composition of microbial communities is subject to constant change owing to interactions with fluctuating physicochemical parameters. This study explored the changes in bacterial and fungal communities during cattle farm waste composting and aimed to identify and prioritize the contributing physicochemical factors. Microbial community compositions were determined by high‐throughput sequencing. While the predominant phyla in the bacterial and fungal communities were largely consistent during the composting, differences in relative abundances were observed. Bacterial and fungal community diversity and relative abundance varied significantly, and inversely, over time. Relationships between physicochemical factors and microbial community compositions were evaluated by redundancy analysis. The variation in bacterial community composition was significantly related to water‐soluble organic carbon (WSOC), and pile temperature and moisture (p < .05), while the largest portions of variation in fungal community composition were explained by pile temperature, WSOC, and C/N (p < .05). These findings indicated that those parameters are the most likely ones to influence, or be influenced by the bacterial and fungal communities. Variation partitioning analyses indicated that WSOC and pile temperature had predominant effects on bacterial and fungal community composition, respectively. Our findings will be useful for improving the quality of cattle farm waste composts.