Effects of heavy metals stress on chicken manures composting via the perspective of microbial community feedback

Effects of hydrothermal treatment on the reduction of antibiotic-resistant Escherichia coli and antibiotic resistance genes and the fertilizer potential of liquid product from cattle manure

In this study, the reduction in the abundance of antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs) and the fertilizer potential of liquid products from hydrothermally treated cattle manure were investigated. Hydrothermal treatment (HTT) was conducted under different reaction temperatures (125, 150, 175 and 200 °C) and retention times (60, 90 and 120 min). The total organic carbon (TOC) and total nitrogen (TN) of the liquid product increased with increasing reaction temperature. The germination index (GI), a measure of the percentage of germination, exceeded 90 % at 125, 150, and 175 °C in diluted samples, while it decreased to 18 % at 200 °C. Although a longer retention time contributed to an increase in TOC of liquid products, it did not increase the GI values. The liquid product should be diluted or adjusted before use as fertilizer to prevent phytotoxicity. In our analysis of ARB and ARGs, E. coli and antibiotic-resistant E. coli were completely reduced after HTT, except for the operating conditions of 125 °C and 60 min. Although both a higher reaction temperature and longer retention time tended to be better for the reduction of ARGs and intI1, it was found that the longer retention time is much more effective than the higher reaction temperature. The reduction of target ARGs and intI1 was 2.9-log under175 °C and 120 min. Comprehensively considering the fertilizer potential of liquid product and the reduction of ARB and ARGs, 175 °C of reaction temperature and 120 min of retention time of operating conditions for HTT were recommended.

Microbial mechanisms involved in negative effects of amoxicillin and copper on humification during composting of dairy cattle manure

Livestock manure often contains various pollutants. The aim of this study was to investigate how adding amoxicillin (AMX), Cu, and both AMX and Cu (ACu) affected humification during composting and the microbial mechanisms involved. The cellulose degradation rates were 16.96%, 10.86%, and 9.01% lower, the humic acid contents were 18.71%, 12.89%, and 16.78% lower, and the humification degrees were 24.72%, 24.16%, and 15.73% lower for the AMX, Cu, and ACu treatments, respectively, than the control. Adding AMX and Cu separately or together inhibited humic acid formation and decreased the degree of humification, but the degree of humification was decreased less by ACu than by AMX or Cu separately. The ACu treatment decreased the number of core bacteria involved in humic acid formation and decreased carbohydrate and amino acid metabolism during the maturing period, and thereby delayed humic acid formation and humification. The results support composting manure containing AMX and Cu.

Relationships between arsenic biotransformation genes, antibiotic resistance genes, and microbial function under different arsenic stresses during composting

Although the arsenic contamination and antibiotic resistance genes (ARGs) during composting have been studied separately, there is limited information on their interactions, particularly, the relationship between arsenic biotransformation genes (ABGs) and ARGs. Therefore, the present study used different forms of arsenic stress (organic and inorganic arsenic at 10 and 50 mg/kg) in pig manure and straw co-composting, to evaluate the effects of arsenic stress on microbial community structures, metabolic function, ABGs, and ARGs. The results showed that arsenic stress had different effects on different parameters and promoted the microbial formation of humic acid and the biodegradation of fulvic acid. Inorganic arsenic showed more rapid effects on microbial community structure, visible within about 20 days, while the effects of organic arsenic were later (about 45 days) due to the necessity of transformation. Moreover, the addition of organic roxarsone and inorganic arsenic resulted in higher expression of ABGs and ARGs, respectively. Arsenic addition also caused increased expression of genes associated with replication and repair. A significant relationship was observed between ABG and ARG expression, for instance, genes involved in arsenic reduction and oxidation were influenced by genes involved in aminoglycoside and chloramphenicol resistance genes (p < 0.05). These complex interactions among microorganisms, functional genes, and external parameters contribute to the understanding of the mechanisms underlying cross-contamination.

Klebsiella pneumoniae in the intestines of Musca domestica larvae can assist the host in antagonizing the poisoning of the heavy metal copper

BACKGROUND

Musca domestica larvae are common saprophytes in nature, promoting the material-energy cycle in the environment. However, heavy metal pollution in the environment negatively affects their function in material circulation. Our previous research found that some intestinal bacteria play an important role in the development of housefly, but the responses of microbial community to heavy metal stresses in Musca domestica is less studied.

RESULTS

In this study, CuSO4, CuSO4-Klebsiella pneumoniae mixture and CuSO4-K. pneumoniae phage mixture were added to the larval diet to analyze whether K. pneumoniae can protect housefly larvae against Cu2+ injury. Our results showed that larval development was inhibited when were fed with CuSO4, the bacterial abundance of Providencia in the intestine of larvae increased. However, the inhibition effects of CuSO4 was relieved when K. pneumoniae mixed and added in larval diets, the abundance of Providencia decreased. Electron microscope results revealed that K. pneumoniae showed an obvious adsorption effect on copper ion in vitro.

CONCLUSIONS

Based on the results we assume that K. pneumoniae could adsorb Cu2+, reduce Cu2+ impact on gut community structure. Our study explains the role of K. pneumoniae antagonizing Cu2+, which could be applied as a probiotic to saprophytic bioantagonistic metal contamination.

Occurrence and transformation of heavy metals during swine waste treatment: A full scale study

This study tracked the fate of nine detected heavy metals in an industrial swine farm with integrated waste treatment, including anoxic stabilization, fixed-film anaerobic digestion, anoxic-oxic (A/O), and composting. Results show that heavy metals exhibited different transformation behaviors in the treatment streamline with Fe, Zn, Cu and Mn as the most abundant ones in raw swine waste. The overall removal of water-soluble heavy metals averaged at 30 %, 24 % and 42 % by anoxic stabilization, anaerobic digestion and A/O unit, respectively. In particular, anoxic stabilization could effectively remove Cu, Mn and Ni; while A/O unit was highly effective for Fe, Cr and Zn elimination from water-soluble states. As such, the environmental risk of liquid products for agricultural irrigation decreased gradually to the safe pollution level in swine waste treatment. Furthermore, heavy metals in the solid (slurry) phase of these bioprocesses could be immobilized with the passivation rate in the range of 42-70 %. Nevertheless, heavy metals preferably transformed from liquid to biosolids to remain their environmental risks when biosolids were used as organic fertilizer in agriculture, thereby requiring effective strategies to advance their passivation in all bioprocesses, particularly composting as the last treatment unit.

Regulatory effects of different anionic surfactants on the transformation of heavy metal fractions and reduction of heavy metal resistance genes in chicken manure compost

Surfactants are widely used as a passivating agent in heavy metal passivation process, but their effect on transformation of heavy metal fraction and reduction of heavy metal resistance genes (MRGs) in composting process is still unknown. The aim of this study was to compare the effects of two anionic surfactants (rhamnolipid and sodium dodecyl sulfate) on heavy metal passivation and resistance gene reduction in chicken manure composting. The results showed that the addition of surfactant can effectively enhance degradation of organic matter (OM). Both surfactants could effectively reduce the bioavailability of heavy metals (HMs) and the relative abundance of resistance genes, especially rhamnolipids. The potential functional bacteria affecting heavy metal passivation were identified by the changes of microbial community. Redundancy analysis (RDA) showed that protease (PRT) activity was the key factor affecting the fractions of the second group of HMs including ZnF1, CuF1, CuF2, PbF1 and PbF3. These findings indicate that addition of anionic surfactants can reduce the bioavailability of HMs and the abundance of resistance genes in compost products, which is of guiding significance for the reduction of health risks in the harmless utilization of livestock and poultry manure.

A potential heavy metals detoxification system in composting: Biotic and abiotic synergy mediated by shell powder

Regulating heavy metal resistance genes (HMRGs) was an effective method for heavy metal resistant bacteria (HMRB) to cope with heavy metal stress during dairy manure composting. This research aimed to investigate heavy metal detoxification mediated by shell powder (SP) in composting and the response of HMRB and HMRGs to changes in heavy metal bioavailability during composting. Research showed that SP additive reduced the bioavailability of Zu, Cu, and Mn by 10.64%, 13.90% and 14.14%, respectively. SP increased the composition percentage of humic acid (HA) in humus (HS) by 8%. SP enhanced the resistance of Actinobacteria to heavy metals and improved the regulation of HMRGs. Correlation analysis demonstrated that the bioavailability of heavy metals was positively correlated with most HMRGs. HA was significantly negatively correlated with the bioavailability of Zn, Cu and Mn. Therefore, SP additive could be a novel strategy for heavy metals detoxification during composting.

Independent and combined effects of sepiolite and palygorskite on humus spectral properties and heavy metal bioavailability during chicken manure composting

The effects of the independent and combined addition strategies of sepiolite and palygorskite on humification and heavy metals (HMs) during chicken manure composting were evaluated. Results showed that clay mineral addition showed a favorable effect on composting, prolonged the duration of the thermophilic phase (5-9 d) and improved the TN content (14%-38%) compared to CK. Independent strategy enhanced the humification degree in equal measures with the combined strategy. Carbon nuclear magnetic resonance spectroscopy (¹³C NMR) and fourier transform infrared spectroscopy (FTIR) confirmed that aromatic carbon species increased by 31%-33% during composting process. Excitation-emission matrix (EEM) fluorescence spectroscopy showed that humic acid-like compounds increased by 12%-15%. In addition, the maximum passivation rate of Cr, Mn, Cu, Zn, As, Cd, Pb and Ni were 51.35%, 35.98%, 30.39%, 32.46%, -87.02%, 36.61% and 27.62%, respectively. The independent addition of palygorskite exhibits the most potent effects for most HMs. Pearson correlation analysis indicated that pH and aromatic carbon were the key determinants of the HMs passivation. This study provided preliminary evidence and perspective of the application of clay minerals on the humification and safety of composting.

Amended compost alleviated the stress of heavy metals to pakchoi plants and affected the distribution of heavy metals in soil-plant system

With the development of the social economy, soil heavy metal pollution has become a common worldwide issue. Therefore, the remediation of soil heavy metal pollution is imminent. This study aimed to investigate the effect of amended compost on reducing heavy metal bioavailability in soil and relieving heavy metals stress on plants under Cu and Zn stress in a pot experiment. To model the restoration of heavy metal-polluted farming soil, conventional compost (CKw), activated carbon compost (ACw), modified biochar compost (BCw) and rhamnolipid compost (RLw) were utilized. The results showed that the application of amended compost could promote the growth and quality of pakchoi and enhance the stress ability of malondialdehyde and antioxidant enzymes to heavy metals. The distribution of Cu and Zn in different subcellular parts of pakchoi was also affected. The application of amended compost significantly reduced the heavy metals content in the shoot of pakchoi, among which the content of Cu and Zn in the shoot of pakchoi in RLw was significantly decreased by 57.29% and 60.07%, respectively. Our results can provide a new understanding for efficient remediation of contaminated farmland soil by multiple heavy metals.

Biochar preparation and evaluation of its effect in composting mechanism: A review

This article provides an overview of biochar application for organic waste co-composting and its biochemical transformation mechanism. As a composting amendment, biochar work in the adsorption of nutrients, the retention of oxygen and water, and the promotion of electron transfer. These functions serve the micro-organisms (physical support of niche) and determine changes in community structure beyond the succession of composing primary microorganisms. Biochar mediates resistance genes, mobile gene elements, and biochemical metabolic activities of organic matter degrading. The participation of biochar enriched the α-diversity of microbial communities at all stages of composting, and ultimately reflects the high γ-diversity. Finally, easy and convincing biochar preparation methods and characteristic need to be explored, in turn, the mechanism of biochar on composting microbes at the microscopic level can be studied in depth.

Microbial metabolism and humic acid formation in response to enhanced copper and zinc passivation during composting of wine grape pomace and pig manure

Copper (Cu) and zinc (Zn) in piglet feed can lead to heavy metals (HMs) accumulation in pig manure (PM). Composting is crucial for recycling biowaste and decreasing HMs bioavailability. This study aimed to investigate the impact of adding wine grape pomace (WGP) on the bioavailability of HMs during PM composting. WGP facilitated the passivation of HMs through Cytophagales and Saccharibacteria_genera_incertae_sedis which promoted the formation of humic acid (HA). Polysaccharide and aliphatic groups in HA dominated the transformation of chemical forms of HMs. Moreover, adding 60% and 40% WGP enhanced the Cu and Zn passivation effects by 47.24% and 25.82%, respectively. Polyphenol conversion rate and core bacteria were identified as key factors in affecting HMs passivation. These results offered new insights into the fate of HMs during PM composting in response to the addition of WGP, which is helpful to practical application of WGP to inactivate HMs for improving compost quality.

Phosphorus functional microorganisms and genes: A novel perspective to ascertain phosphorus redistribution and bioavailability during copper and tetracycline-stressed composting

There is limited information on the phosphorus availability under copper and tetracycline-amended composting: Insights into microbial communities and genes. Thus, this work investigated the phosphorus redistribution and transformation, illustrated the variation in microbial communities and genes, and ascertained the multiple action-patterns among which within copper and tetracycline-amended composting. Phosphorus bioavailability reduced by 8.96 % ∼ 13.10 % due to the conservation of Ex-P to Ca-P. Copper and tetracycline showed a significant effect on fungal succession, but not to bacteria, as well as inhibited the phosphorus functional genes in fungal communities, while accelerated it in bacterial communities. Under the copper/tetracycline-stressed conditions, bacterial Firmicutes could promote the mineralization of organic phosphorus, and bacterial Proteobacteria might facilitate the dissolution of inorganic phosphorus. These findings could provide theoretical guidance for the further research on phosphorus bioavailability ascribed to microbial communities and genes.

Revisiting organic waste-source-dependent molecular-weight governing the characterization within humic acids liking to humic-reducing microorganisms in composting process

Humic acids (HAs) coupled with humic-reducing microorganisms (HRMs) can facilitate contaminants reduction. Molecular-weight (MW) of HA governs the chemical and HRMs behavior. However, MW of HAs with chemical characteristics linking to HRMs in different wastes composting have never been investigated. Results from the HPSEC-UV analysis showed that composting significantly increased weight-average molecular weight (M_w) of HA with a broad range from 675 Da to 27983 Da, and governing heterogeneous chemical characteristics. In proteinaceous composts, MW< 4000 Da of HAs were greatly related to alkyl and carbonyl, while MW> 20000 Da of HAs were presented by oxygen-nitrogenous functional groups, methyl, and alkyl groups. For cellulosic composts, MW< 1500 Da and 4000-10000 Da of HAs were characterized by aliphatic ethers and aromatic groups. MW> 20000 Da of HAs were constructed by phenols, methoxy and nitrogen functional groups. In lignocellulosic composts, MW> 20000 Da of HAs were only characterized by aromatic groups. Furthermore, seven groups of HRMs adapted to the heterogeneous chemical characteristics within HAs ranked by MW were recognized. Consequently, the possible routes that composting properties response to the connections of HRMs-chemical structures-MW of HAs in proteinaceous, cellulosic and lignocellulosic composts were constructed, respectively. Our results can help to develop the fine classification-oriented approach for recycling utilization of organic wastes.

Evolution and Emergence of Antibiotic Resistance in Given Ecosystems: Possible Strategies for Addressing the Challenge of Antibiotic Resistance

Antibiotics were once considered the magic bullet for all human infections. However, their success was short-lived, and today, microorganisms have become resistant to almost all known antimicrobials. The most recent decade of the 20th and the beginning of the 21st century have witnessed the emergence and spread of antibiotic resistance (ABR) in different pathogenic microorganisms worldwide. Therefore, this narrative review examined the history of antibiotics and the ecological roles of antibiotics, and their resistance. The evolution of bacterial antibiotic resistance in different environments, including aquatic and terrestrial ecosystems, and modern tools used for the identification were addressed. Finally, the review addressed the ecotoxicological impact of antibiotic-resistant bacteria and public health concerns and concluded with possible strategies for addressing the ABR challenge. The information provided in this review will enhance our understanding of ABR and its implications for human, animal, and environmental health. Understanding the environmental dimension will also strengthen the need to prevent pollution as the factors influencing ABR in this setting are more than just antibiotics but involve others like heavy metals and biocides, usually not considered when studying ABR.

Structural and functional characteristics of soil microbial communities in response to different ecological risk levels of heavy metals

Objective

The potential ecological risk index (RI) is the most commonly used method to assess heavy metals (HMs) contamination in soils. However, studies have focused on the response of soil microorganisms to different concentrations, whereas little is known about the responses of the microbial community structures and functions to HMs at different RI levels.

Methods

Here, we conducted soil microcosms with low (L), medium (M) and high (H) RI levels, depending on the Pb and Cd concentrations, were conducted. The original soil was used as the control (CK). High-throughput sequencing, qPCR, and Biolog plate approaches were applied to investigate the microbial community structures, abundance, diversity, metabolic capacity, functional genes, and community assembly processes.

Result

The abundance and alpha diversity indices for the bacteria at different RI levels were significantly lower than those of the CK. Meanwhile, the abundance and ACE index for the fungi increased significantly with RI levels. Acidobacteria, Basidiomycota and Planctomycetes were enriched as the RI level increased. Keystone taxa and co-occurrence pattern analysis showed that rare taxa play a vital role in the stability and function of the microbial community at different RI levels. Network analysis indicates that not only did the complexity and vulnerability of microbial community decrease as risk levels increased, but that the lowest number of keystone taxa was found at the H level. However, the microbial community showed enhanced intraspecific cooperation to adapt to the HMs stress. The Biolog plate data suggested that the average well color development (AWCD) reduced significantly with RI levels in bacteria, whereas the fungal AWCD was dramatically reduced only at the H level. The functional diversity indices and gene abundance for the microorganisms at the H level were significantly lower than those the CK. In addition, microbial community assembly tended to be more stochastic with an increase in RI levels.

Conclusion

Our results provide new insight into the ecological impacts of HMs on the soil microbiome at different risk levels, and will aid in future risk assessments for Pb and Cd contamination.

Evaluating differences in humic substances formation based on the shikimic acid pathway during different materials composting

This study aimed to evaluate differences in humic substance (HS) formation based on the shikimic acid pathway (SAP) during five different materials composting. The results showed that compared with other three materials, gallic acid, protocatechuic acid and shikimic acid of the SAP products in lawn waste (LW) and garden waste (GW) compost decreased significantly. Furthermore, as important indicators for evaluating humification, humic acid and degree of polymerization increased by 39.4%, 79.5% and 21.8%, 87.9% in LW and GW, respectively. Correlation analysis showed that SAP products were strongly correlated with HS fractions in LW and GW. Meanwhile, network analysis indicated that more core bacteria associated with both SAP products and HS were identified in LW and GW. Finally, the structural equation model proved that SAP had more significant contribution to humification improvement in LW and GW. These findings provided theoretical foundation and feasible actions to improve compost quality by the SAP.

Ecological risk assessment and sources identification of heavy metals in surface sediments of a river-reservoir system

Heavy metal contamination of river water and sediments is a global issue affecting ecological health. To reveal heavy metals' ecological risks and biological toxicity in the middle and lower Han River (MLHR), sediment samples collected in this area were analyzed based on a modified ecological risk assessment method (NIRI) and a biological toxicity assessment method. Also, Spearman correlation analysis and Positive Matrix Factorization (PMF) methods were applied to identify the potential sources of heavy metals. The results indicated that the heavy metal content significantly exceeded the background concentrations in Hubei Province. The average potential risk of heavy metals at sampling sites was: Cd > Hg > As > Pb > Cu > Zn. Consequently, high biological toxicity occurred along the MLHR due to the heavy metal enrichment. River damming and water diversion significantly enhanced the hydrologic regime variations and ecological risk in the MLHR. Moreover, two possible pollution sources of the MLHR were identified: one is a combined source of traffic pollution, agricultural pollution, and partial industrial pollution consisting of five heavy metals, Pb, Hg, Zn, Cu, and As, the other is an industrial pollution source dominated by Cd and As. This study provides insights into sediment heavy metal pollution management and ecological risk control in the MLHR and similar rivers worldwide.

Functional keystone drive nitrogen conversion during different animal manures composting

In this study, nitrogen transformation of chicken manure (CM) and cattle dung (CD) during composting was analyzed and its related functional keystones were identified. The results showed that chicken manure showed more severe nitrogen conversion during composting. The main N conversion factors in cattle dung were nitrite nitrogen (NO₂^--N) and ammonium nitrogen (NH₄⁺-N), while the main N conversion factors in chicken manure were NH₄⁺-N and nitrate nitrogen (NO₃^--N). The nitrogen-transforming bacterial community in chicken manure was more diverse. Variations in functional keystone abundances in cattle dung tended to be confined to the cooling and maturation periods, whereas changes in chicken manure persisted throughout the composting process. Environmental factors affected the functional keystones of nitrogen transformation. This study may provide directions for regulating nitrogen conversion in animal manure composting.

Slowed down nitrogen mineralization under bacterial community-driven conditions by adding inhibitors during rice straw composting

The aim of this paper was to confirm the role of inhibitors addition, namely adenosine triphosphate (ATP) and malonic acid (MA), on nitrogen availability during rice straw (RS) composting. The results showed that inhibitors addition slowed down the mineralization of ammonium nitrogen and nitrate nitrogen compared to CK. Meanwhile, amino sugar nitrogen and hydrolysable unknown nitrogen contents in ATP and MA treatments were higher, indicating that their addition improved the retention of organic nitrogen components. Furthermore, inhibitors additions attenuated the responsive relationship between bacterial communities and nitrogen components. The main reason was that the addition changed the bacterial community structure of RS compost. The final structural equation verified that inhibitors addition enhanced conversion between nitrogen components, that was, to complex nitrogen components to improve the quality of compost, and the remodeling of bacterial community played an important role. Therefore, adding inhibitors had a driving effect on promoting nitrogen sequestration.

Ammonium stress promotes the conversion to organic nitrogen and reduces nitrogen loss based on restructuring of bacterial communities during sludge composting

This study aimed to clarify the conversion relationship between organic and inorganic nitrogen. The NH₄Cl was used to enhance the inorganic nitrogen content. The key role of bacterial conversion of ammonium to organic nitrogen under ammonium stress was explored. Studies had shown that ammonium stress increased the amide nitrogen and bioavailable nitrogen content by 36.95% and 32.25%, respectively. Network and regression analyses showed that the microbial community structure was restructured by high ammonium and more bacteria were involved in the conversion of inorganic nitrogen to organic nitrogen(i.e., amide nitrogen, unknown nitrogen). Variation partition analysis and structural equation model showed that the bacterial community was the main contributor to organic nitrogen production(up to 67.4%), which reduced the nitrogen loss by 6.03%. These findings shed light on the poorly understood interaction between inorganic and organic nitrogen by clarifying the role of core bacterial communities in nitrogen conversion.

Microbial inoculants reshape structural distribution of complex components of humic acid based on spectroscopy during straw waste composting

This study aimed to explore the mechanism of actinomycetes inoculation to promote humification based on spectroscopy during straw waste composting. Results showed that inoculating actinomycetes could significantly increase the humification index and humification ratio, which were 2.53% and 21.79% respectively (P < 0.05). A spectroscopic analysis suggested that actinomycetes promoted the relative content of complex components of humic acid and reshaped the structural distribution of two sub fluorescence peaks in it. Furthermore, variance partitioning analysis demonstrated that compared with the intensity, the high-quality uniform distribution of fluorescence peaks had a greater contribution to the improvement of humification. In addition, structural equation model further verified that actinomycetes inoculation promoted the transformation of fulvic acid to humic acid, and then promoted the formation of humic acid. Therefore, actinomycetes inoculation can promote the humification of straw compost by reshaping the complex components of humic acid.

Effect of leaching time on phytotoxicity of dissolved organic matter derived from black carbon based on spectroscopy

Black carbon (BC) exports huge amounts of its derived DOM from terrestrial ecosystems annually through a variety of ways (i.e., erosion or runoff migration). The pyrolytic feedstock type and temperature resulted in DOM derived from highly condensed aromatic and non-aromatic BC. However, the behaviors of low aromatic BC-derived DOM at diverse leaching time are poorly understood. In this work, low aromatic BCs were prepared by pyrolysis corn straws at 250 °C, 350 °C and 450 °C. Extraction experiments for four leaching time (6 h, 10 h, 15 h and 21 h) were set up to simulate BC-derived DOM generative process in nature. The phytotoxicity of BC-derived DOM was evaluated via germination index (GI). Spectral characteristics were discussed to analyze the phytotoxicity variations of fluorescence components composition at different time, including the excitation-emission matrix-parallel factor, two-dimensional correlation spectra and Fourier transform infrared spectroscopy. The results suggested that low aromatic BC-derived DOM might contain aromatic phenolic compounds. A longer time contributed to accumulate the complex, hard-to-use organic matters, leading to lower GI. These results would supplement the dynamic spectral characteristics of low aromatic BC-derived DOM and its environmental risks during the leaching process.

Insights into phenol monomers in response to electron transfer capacity of humic acid during corn straw composting process

Quinone is the important redox functional group for electron transfer capacity (ETC) of humic acid (HA). Lignin, as major component in corn straw, can be decomposed into phenol monomers, then oxidation into quinones for synthesis of HA during composting process. However, it is still unclear that the effects of type and variation characteristics of phenol monomers on redox characteristics of HA during straw composting process. In this study, p-hydroxybenzoic acid (P1), vanillic acid (P2), syringic acid (P3), p-hydroxy benzaldehyde (P4), 4-coumaric acid (P5), 4-hydroxyacetophenone (P6), ferulic acid (P7) and 4-hydroxy-3-methylacetophenone (P8) were recognized and clustered into three groups. The concentration of polyphenol presented a significant downward trend during the straw composting process. Based on the relationships among phenol monomers to ETC, electron donating capacity (EDC), electron accepting capacity (EAC) and quinone, we found that P1, P2, P3, P5 and P7 were significantly related to ETC, EDC and EAC of HA (P < 0.05). Furthermore, NH₄⁺-N and NO₃^--N were the main micro-environmental factors linking to ETC-related phenol monomers and redox characteristics of HA in straw composts (P < 0.05). Finally, two groups of core microflora that promoting the ETC-related phenol monomers and NH₄⁺-N, and ETC-related phenol monomers and NO₃^--N were identified by Mantel test, respectively. This study contributes a new insight for polyphenol way for redox capacity of HA in traditional composting and utilization of straw compost in contaminated environments.

The important role of tricarboxylic acid cycle metabolism pathways and core bacterial communities in carbon sequestration during chicken manure composting

As a kind of livestock manure, chicken manure (CM) was rich in organic matter and microorganisms. However, a large amount of foul gas discharged by its random stacking not only threatened the environment, but also caused harm to human health. In view of the serious carbon loss and the unclear action mechanism of microbial community on carbon metabolism during CM composting, the effect of adding regulators on the sequestration of organic carbon was explored. Therefore, the purpose of this study was to explore the regulation mechanism of adding tricarboxylic acid cycle (TCA cycle) regulators on the core carbon metabolism pathway during CM composting. The results showed that the adenosine triphosphate (ATP) and malonic acid (MA) slowed down organic carbon degradation, resulting in lower carbon loss rate, which were 64.99% (CK), 62.35% (MA), and 61.26% (ATP) in each treatment. By comparing the abundance and structure of the carbon-related bacterial communities in different treatments, it was found that adding ATP and MA not only reduced the bacterial community abundance, but also tended to be similar in bacterial community composition. Moreover, the microbial specificity related to carbon metabolism pathway was enhanced, while the related gene expression and gene abundance were weakened. The regulation of TCA cycle metabolism pathway was confirmed to be the main way to improve organic carbon content. These findings revealed the positive effects of ATP and MA on carbon fixation from the perspective of gene metabolism.

Unraveling diverse survival strategies of microorganisms to vanadium stress in aquatic environments

Worldwide vanadium contamination is posing serious risks to ecosystems. Although abilities of microbial communities to cope with vanadium stress using specific survival strategies have been reported, little is known regarding their relative importance and the underlying detoxification/tolerance mechanisms. Herein, we investigated the potential survival strategies of microbial communities and associated pathways in aquatic environments based on geochemistry and molecular biology. High vanadium content was observed for both water (12.6 ± 1.15 mg/L) and sediment (1.18 × 10³ ± 10.4 mg/kg) in the investigated polluted stream. Co-occurrence network investigation implied that microbial communities showed cooperative interactions to adapt to the vanadium-polluted condition. Vanadium was also characterized as one of the vital factors shaping the community structure via redundancy analysis and structural equation models. Based on the metagenomic technology, three survival strategies including denitrification pathway, electron transfer, and metal resistance in innate microbes under the vanadium stress were revealed, with comprehensively summarized vanadium detoxification/tolerance genes. Remarkable role of electron transfer genes and the prevalent existence of resistance genes during detoxifying vanadium were highlighted. Overall, these findings provide novel insights into survival strategies under the vanadium contamination in aquatic environments, which can be of great significance for the identification, isolation, and application of vanadium reducing bacteria in vanadium bioremediation.

Predicting the humification degree of multiple organic solid waste during composting using a designated bacterial community

Microbes are the drivers for disposing of organic solid waste (OSW) during aerobic fermentation. Notwithstanding, the significance of microbes is underestimated in numerous studies on aerobic fermentation product assessments. Here, we investigated the humification degree (HD), and the humic acid content was assessed in terms of the bacterial community. The bacterial communities were useful indicators for making predictions and even correctly determined the categories of OSWs with 94% accuracy. The bacterial codes can also provide a better prediction of HD. Our results demonstrate that the bacteria code is a reliable biological method to assess HD effectively. Bacterial codes can be used as ecological and biological indicators to evaluate the quality of aerobic fermentation of different materials.

Activation effect of catechol on biotic and abiotic factors of humus formation during chicken manure composting

In this present study, catechol was added to promote humus formation in chicken manure composting using 12.5-L working volume lab-scale reactors. Chicken manure composting were carried out on two treatments, control (CK) and 0.5% (w/w) catechol treated group. Results showed that catechol addition reduced organic matter loss and improved the content of recalcitrant components. Humus and humic acid (HA) contents were, respectively, 69.2% and 82.3% higher in catechol treated-compost than in the control. With the addition of catechol, the bacterial community composition and richness was changed, e.g., the relative percentage of Bacillus and Sinibacillus were increased, which might contribute to humus and HA formation. Additionally, the activities of polyphenol oxidase and laccase (related to humus formation) were increased by the addition of catechol. Importantly, the catechol addition reduced the polyphenol content by 39.6% compared to control. Overall, the addition of catechol enhanced the biotic and abiotic factors to promote the humification process during composting, which might be a promising approach for accelerating the humification process and reducing contamination of phenolic compounds.

Resource utilization of mink manure: Functional microbial inoculation to elevate the bioavailability of organic nitrogen during composting

Mink manure is one of the high nitrogenous wastes, which can easily cause nitrogen mineralization during composting, resulting in low resource reutilization. However, there are few studies on the resource utilization of mink manure. Therefore, this study investigated the effects of functional microbial (bacterial and actinomycetes agents) inoculation on nitrogen mineralization during mink manure composting. Results suggested that the inoculum, especially actinomycetes agents, could increase organic nitrogen and bioavailable organic nitrogen (BON) content. Principal component analysis and Random Forest model demonstrated that the inoculants increase the abundance of microorganisms that positively correlated with BON, decrease the microorganisms that negatively correlated with BON. Consequently, the inoculation of functional microbial agents could effectively reduce nitrogen mineralization and improve composting quality. Therefore, this study provided theoretical and technical support for optimizing mink manure composting, promoting the resource utilization of high nitrogen wastes.

Identifying the role of fired clay minerals on reducing of nitrogen loss and immobilization of organic nitrogen during chicken manure composting

This study compared effects of clay minerals before and after firing in immobilization of organic nitrogen and reducing of nitrogen loss during chicken manure composting. The clay minerals and fired clay minerals treatments increased organic nitrogen contents and significantly reduced nitrogen loss, the loss was in order CK (52.61%) > M (47.15%) > I (45.90%) > M- (42.58%) > I- (40.59%). Meanwhile, network analysis indicated that core bacterial community associated with nitrogen transformation were more abundant, and conversion effect of single core bacteria on nitrogen components was enhanced in fired clay minerals treatments. In addition, fired clay minerals strengthened correlation between environmental factors, bacterial community and organic nitrogen, and enhanced interaction of abiotic and biotic pathways, which verified by variance partitioning analysis and structural equation model. Therefore, fired clay minerals play a remarkable driving role in formation and immobilization of organic nitrogen.