Mechanism analysis of humification coupling metabolic pathways based on cow dung composting with ionic liquids

The addition of vermiculite reduced antibiotic resistance genes during composting: Novel insights based on reducing host bacteria abundance and inhibiting plasmid-mediated conjugative transfer

Antibiotic resistance genes (ARGs) are prevalent in raw materials used for composting. The utilization of eco-friendly materials for the removal of ARGs is regarded as an economically effective method. Therefore, this study focused on the impact of incorporating different proportions of vermiculite (0% (CK), 5% (T1), and 10% (T2)) on the dynamics of ARGs during composting. In comparison to CK, the total absolute abundances of ARGs decreased by 14.17% and 31.52% in T1 and T2, respectively. Potential human pathogenic bacteria, including Acinetobacter, Corynebacterium, and Lactobacillus, were identified as core hosts of ARGs. The addition of vermiculite effectively inhibited proliferation of ARG hosts by extending the thermophilic phase of composting and reducing bioavailable copper concentrations. Incorporation of vermiculite decreased the absolute abundances of transposons and integrons, such as intI1 and Tn916/1545, which were significantly positively correlated with most ARGs. Adding vermiculite simultaneously enhanced the removal of common environmental plasmids (e.g., Inc.P, Inc.W), and downregulated expression of genes associated with bacterial conjugation and plasmid replication (e.g., trBbp, trfAp), thereby inhibiting the dissemination of ARGs. Taken together, this study provides novel insights that the incorporation of vermiculite can effectively enhance the reduction rate of ARGs during composting by reducing the host of ARGs and inhibiting their dissemination.

Potassium persulfate enhances humification of chicken manure and straw composting: The perspective of rare and abundant microbial community structure and ecological interactions

Improper disposal of organic solid waste results in serious environmental pollution. Aerobic composting provides an environmentally friendly treatment method, but improving humification of raw materials remains a challenge. This study revealed the effect of different concentrations of potassium persulfate (PP) on humification of chicken manure and straw aerobic composting and the underlying microbial mechanisms. The results showed that when 0.6 % PP was added (PPH group), humus and the degree of polymerization were 80.77 mg/g and 2.52, respectively, which were significantly higher than those in 0.3 % PP (PPL group). As the concentration of PP was increased, the composition of rare taxa (RT) changed and improved in evenness, while abundant taxa (AT) was unaffected. Additionally, the density (0.037), edges (3278), and average degree (15.21) in the co-occurrence network decreased compared to PPL, while the average path (4.021) and modularity increased in PPH. This resulted in facilitating the turnover of matter, information, and energy among the microbes. Interestingly, cooperative behavior between microorganisms during the maturation period (24-60 d) occurred in PPH, but competitive relationships dominated in PPL. Cooperative behavior was positively correlated with humus (p < 0.05). Because the indices, such as higher degree, betweenness centrality, eigenvector centrality, and closeness centrality of the AT, were located in the microbial network center compared to RT, they were unaffected by the concentration of PP. The abundance of carbohydrate and amino acid metabolic pathways, which play an important role in humification, were higher in PPH. These findings contribute to understanding the relative importance of composition, interactions, and metabolic functionality of RT and AT on humification during chicken manure and straw aerobic composting under different concentrations of PP, as well as provide a basic reference for use of various conditioning agents to promote humification of organic solid waste.

Investigating the inhibitory mechanism of methanogenesis during composting under the combined influence of amoxicillin and copper pollution

This study investigated the effects of different levels of combined amoxicillin and copper (Cu) pollution on the methanogenesis of microbial communities during aerobic composting of dairy manure. Three groups were established: the control group (CK), a low-level combined pollution group (L), and a high-level combined pollution group (H). As the level of pollution increased, carbohydrate metabolism decreased during the thermophilic phase of composting, while signal translation increased. Compared with the initial phase, functional genes related to the acetoclastic pathway decreased significantly in abundance during the thermophilic phase, and cdh had the lowest relative abundance among acetoclastic pathway with a decrease of 81.52%, 81.88%, and 84.73% in groups CK, L, and H, respectively. The cumulative methane emissions in group H decreased by 31.56% and 9.23%, respectively, compared with those from groups CK and L. These results contribute to understanding the effects of combined amoxicillin and Cu pollution on methane emissions during composting.

Preference and regulation mechanism mediated via mobile genetic elements for antibiotic and metal resistomes during composting amended with nano ZVI loaded on biochar

This study assessed the effectiveness of nano zero-valent iron loaded on biochar (BC-nZVI) during swine manure composting. BC-nZVI significantly reduced the abundance of antibiotic resistance genes (ARGs), metal resistance genes (MRGs), and mobile genetic elements (MGEs). BC-nZVI modified the preference of MGEs to carry ARGs and MRGs, and the corrosion products of BC-nZVI could destroy cell structure, hinder electron transfer between cells, and weaken the association between ARGs, MRGs, and host bacteria. Functional genes analysis revealed that BC-nZVI down-regulated the abundance of genes affecting the transmission and metabolism of ARGs and MRGs, including type IV secretion systems, transporter systems, two-component systems, and multidrug efflux pumps. Furthermore, the BC-nZVI decreased genes related to flagella and pili production and cell membrane permeability, thereby hindering the transfer of ARGs, MRGs, and MGEs in the environment. Redundancy analysis demonstrated that changes in the microbial community induced by BC-nZVI were pivotal factors impacting the abundance of ARGs, MRGs, and MGEs. Overall, this study confirmed the efficacy of BC-nZVI in reducing resistance genes during swine manure composting, offering a promising environmental strategy to mitigate the dissemination of these contaminants.

Effects of black soldier fly larvae on biotransformation and residues of spent mushroom substrate and wet distiller's grains

Black soldier fly larvae (BSFL) could convert a variety of organic wastes, including spent mushroom substrate (SMS) and wet distiller's grains (WDG). Nevertheless, little is known about the conversion of these wastes by BSFL. Thus, this study investigates the conversion of SMS and WDG in five different proportions by BSFL. This study demonstrates that BSFL can convert SMS, WDG, and their mixtures. It can also encourage the humification of the substrate, increasing the amount of element in the residues. It is evident that there were differences in the carbon and nitrogen element fractionation mode as well as the microbial community present in the residue. The microbial community of the substrate and the physiochemical parameters are intimately related to this. Although the mixture treated with BSFL helps to generate a residue with more humus, it might not be stable.

Enhanced organic degradation and microbial community cooperation by inoculating Bacillus licheniformis in low temperature composting

Microbial activity and interaction are the important driving factors in the start-up phase of food waste composting at low temperature. The aim of this study was to explore the effect of inoculating Bacillus licheniformis on the degradation of organic components and the potential microbe-driven mechanism from the aspects of organic matter degradation, enzyme activity, microbial community interaction, and microbial metabolic function. The results showed that after inoculating B. licheniformis, temperature increased to 47.8°C on day 2, and the degradation of readily degraded carbohydrates (RDC) increased by 31.2%, and the bioheat production increased by 16.5%. There was an obvious enhancement of extracellular enzymes activities after inoculation, especially amylase activity, which increased by 7.68 times on day 4. The inoculated B. licheniformis colonized in composting as key genus in the start-up phase. Modular network analysis and Mantel test indicated that inoculation drove the cooperation between microbial network modules who were responsible for various organic components (RDC, lipid, protein, and lignocellulose) degradation in the start-up phase. Metabolic function prediction suggested that carbohydrate metabolisms including starch and sucrose metabolism, glycolysis / gluconeogenesis, pyruvate metabolism, etc., were improved by increasing the abundance of related functional genes after inoculation. In conclusion, inoculating B. licheniformis accelerated organic degradation by driving the cooperation between microbial network modules and enhancing microbial metabolism in the start-up phase of composting.

Characteristics of humification, functional enzymes and bacterial community metabolism during manganese dioxide-added composting of municipal sludge

The aim of this study was to assess effects of MnO2 addition (CK-0%, T1-2% and T2-5%) on humification and bacterial community during municipal sludge (MS) composting. The results suggested that MnO2 addition inhibited the growth of Nitrospira but stimulated Nonomuraea, Actinomadura, Streptomyces and Thermopolyspora, facilitating the lignocellulose degradation and humification with the increase in organic matter degradation by 13.8%-19.2% and humic acid content by 10.9%-20.6%. Compared to CK, the abundances of exoglucanase (EC:3.2.1.91), endo-1,4-beta-xylanase (EC:3.2.1.136) and endomannanase (EC:3.2.1.78) increased by 88-99, 52-66 and 4-15 folds, respectively. However, 5%-MnO2 induced the enrichment of Mizugakiibacter that harms the environment of agricultural production. The addition of 2%-MnO2 was recommended for MS composting. Furthermore, metabolic function analysis indicated that MnO2 addition altered amino acid and carbohydrate metabolism, especially enhancing propanoate metabolism and butanoate metabolism but inhibiting citrate cycle. Structural equation modeling revealed that Nonomuraea and Actinomadura were the main drivers for lignocellulose degradation. This study provided theoretical guidance in regulating humification via MnO2 for MS composting.

The bioaugmentation effect of microbial inoculants on humic acid formation during co-composting of bagasse and cow manure

The effective degradation of recalcitrant lignocellulose has emerged as a bottleneck for the humification of compost, and strategies are required to improve the efficiency of bagasse composting. Bioaugmentation is a promising method for promoting compost maturation and improving the quality of final compost. In this study, the bioaugmentation effects of microbial inoculants on humic acid (HA) formation during lignocellulosic composting were explored. In the inoculated group, the maximum temperature was increased to 72.5 °C, and the phenol-protein condensation and Maillard humification pathways were enhanced, thus increasing the HA content by 43.85%. After inoculation, the intensity of the microbial community interactions increased, particularly for fungi (1.4-fold). Macrogenomic analysis revealed that inoculation enriched thermophilic bacteria and lignocellulose-degrading fungi and increased the activity of carbohydrate-active enzymes and related metabolic functions, which effectively disrupted the recalcitrant structure of lignocellulose to achieve a high humification degree. Spearman correlation analysis indicated that Stappia of the Proteobacteria phylum, Ilumatobacter of the Actinomycetes phylum, and eleven genera of Ascomycota were the main HA producers. This study provides new ideas for bagasse treatment and recycling and realizing the comprehensive use of resources.

Low-intensity alternating ventilation achieves effective humification during food waste composting by enhancing the intensity of microbial interaction and carbon metabolism

Vertical static composting is an efficient and convenient technology for the treatment of food waste. Exploring the impact of oxygen concentration levels on microbial community structure and functional stability is crucial for optimizing ventilation technology. This study set three experimental groups with varying ventilation intensities based on self-made alternating ventilation composting reactor (AL2: 0.2 L kg-1 DM·min-1; AL4: 0.4 L kg-1 DM·min-1; AL6: 0.6 L kg-1 DM·min-1) to explore the optimal alternating ventilation rate. The results showed that the cumulative ammonia emission of AL2 group reduced by 25.13% and 12.59% compared to the AL4 and AL6 groups. The humification degree of the product was 1.18 times and 1.25 times higher than the other two groups. AL2 increased the relative abundance of the core species Saccharomonospora, thereby strengthening microbial interaction. Low-intensity alternating ventilation increased the carbon metabolism levels, especially aerobic_chemoheterotrophy, carbohydrate and lipid metabolism. However, it simultaneously reduced nitrogen metabolism. Structural equation model analysis demonstrated that alternating low-intensity ventilation effectively regulated both microbial diversity (0.81, p < 0.001) and metabolism (0.81, p < 0.001) by shaping the composting environment. This study optimized the intensity of alternating ventilation and revealed the regulatory mechanism of community structure and metabolism. This study provides guidance for achieving efficient and low-consumption composting.

Exogenous additive ferric sulfate regulates sulfur-oxidizing bacteria in cow manure composting to promote carbon fixation

Enhancing carbon fixation in the composting process was of great significance in the era of massive generation of organic solid waste. In this study, the experimental results showed that the contents of dissolved organic matter (DOM) in the experimental group (CT) were 37.58% higher than those in the control group (CK). The CO2 emission peaked on day 5, and the value of CK was 1.34 times that of CT. Significant differences were observed between the contents of sulfur fractions in CT and CK. This phenomenon may be due to the suppression of sulfur-reducing gene expression in CT. On day 51 of composting, the abundance of sulfur-oxidizing bacteria (SOB) Rhodobacter (5.33%), Rhodovulum (14.76%), and Thioclava (23.83%) in CT was higher than that in CK. In summary, the composting fermentation regulated by Fe2(SO4)3 increased the sulfate content, enhanced the expression of sulfur-oxidizing genes and SOB, and ultimately promoted carbon sequestration during composting.

Effect of the addition of biochar and wood vinegar on the morphology of heavy metals in composts

In the experiment, the morphology of heavy metals (Pb, Cr, Cd, and Ni, HMs) was characterized using flame atomic absorption spectroscopy. In addition, Fourier transform infrared spectroscopy (FTIR) and three-dimensional excitation-emission matrix fluorescence spectroscopy (3D-EEM) were used to characterize the correlation between environmental factors and metal morphology in the rotting compost from several angles. The results showed that the humus treated with wood vinegar solution had a high degree of humification and rich aromatic structure. FTIR spectroscopy confirmed that the degree of humus aromatization gradually increased during the composting process, which enhanced the complexation of humus (HS) with HMs but had less effect on Ni. In addition, the optimum concentration of wood vinegar (WV) was determined to be 1.75%. The results of the study showed that in the Pb passivation treatment group, the proportion of soluble (Red) and exchangeable states (Exc) converted to oxidized (Oxi) and residual states (Res) was 8%, 14%, 6%, 1%, and 12% in the CK, T1, T2, T3, and T4 treatment groups, respectively; in the Cr passivation treatment group, the proportion of Cr-Red and Cr-Exc converted to oxidized and residual states was 31%, 33%, 25%, 29%, and 25%; in the Cd passivation treatment group, the proportions of Cd-Red and Cd-Exc converted to oxidized and residual states were 5%, 15%, 4%, 9%, and 11%, respectively; whereas the Ni treatment group did not show any significant passivation effect. The proportion of Pb-Oxi was relatively stable, Cr-Oxi was converted to Cr-Res, whereas Cd showed the conversion of Cd-Oxi to Cd-Exc. SUVA254 and SUVA280 showed significant positive correlations with Pb-Res, Cr-Res and Ni-Res, and significant positive correlations with moisture content (MC); whereas MC was significantly negatively correlated with each form of HMs. Total potassium (TK), total nitrogen (TN), and both carbon (TOC) were negatively correlated with Pb-Res and Pb-Exc. Structural equation modeling verified the relationship between environmental factors and HMs, and the composting results showed that the addition of biochar (BC) and a higher percentage of WV could increase compost decomposition and passivate HMs to improve its agronomic function.

Bacillus licheniformis inoculation promoted humification process for kitchen waste composting: Organic components transformation and bacterial metabolic mechanism

Kitchen waste (KW) composting always has trouble with slow humification process and low humification degree. The objective of this study was to develop potentially efficient solutions to improve the humification of KW composting, accelerate the humus synthesis and produce HS with a high polymerization degree. The impact of Bacillus licheniformis inoculation on the transformation of organic components, humus synthesis, and bacterial metabolic pathways in kitchen waste composting, was investigated. Results revealed that microbial inoculation promoted the degradation of organic constituents, especially readily degradable carbohydrates during the heating phase and lignocellulose fractions during the cooling phase. Inoculation facilitated the production and conversion of polyphenol, reducing sugar, and amino acids, leading to an increase of 20% in the content of humic acid compared to the control. High-throughput sequencing and network analysis indicated inoculation enriched the presence of Bacillus, Lactobacillus, and Streptomyces during the heating phase, while suppressing the abundance of Pseudomonas and Oceanobacillus, enhancing positive microbial interactions. PICRUSt2 analysis suggested inoculation enhanced the metabolism of carbohydrates and amino acids, promoting the polyphenol humification pathway and facilitating the formation of humus. These findings provide insights for optimizing the humification process of kitchen waste composting by microbial inoculation.

Insights into antibiotic resistance gene abundances and regulatory mechanisms induced by ionic liquids during composting

This study investigated the regulatory mechanism of the evolution of antibiotic resistance genes (ARGs) during the composting process with sawdust and cow manure as raw materials using ionic liquids (ILs) pretreatment. The results showed that genes of MLS, chloramphenicol, tetracycline, beta - lactam as composting gradually decreased. From day0 to day3, MLS in control group (CK) and experimental group (T) decreased by 25.62% and 26.66%, respectively. Tetracycline decreased by 7.21% in CK and by 7.86% in T. Chloramphenicol decreased by 2.85% in CK and 3.34% in T. Beta-lactam decreased by 1.95% in Ck and by 3.69% in T. Mechanism studies have shown that ILs can effectively decompose extracellular polymeric substances (EPS) and enhance lactose dehydrogenase (LDH) release, resulting in ARGs release and elimination. Meanwhile, ILs pretreatment can inhibit growth of some ARGs hosts, especially Firmicutes, resulting in decreased ARGs. Moreover, metabolic pathways and related genes take part in ARGs transmission were down regulated, leading to decreased ARGs.

Evaluation of fungal dynamics during sheep manure composting employing peach shell biochar

In this study, explored the influence of different proportion (0%, 2.5%, 5%, 7.5%, and 10%) peach shell biochar (PSB) with microbial agents (EM) on the carbon transformation, humification process and fungal community dynamics during sheep manure (SM) composting. And no additives were used as control. The results manifested that the CO2 and CH4 emissions were effectively reduced 8.23%∼13.10% and 17.92%∼33.71%. The degradation rate of fulvic acid increased by 17.12%∼23.08% and the humic acid contents were enhanced by 27.27%∼33.97% so that accelerated the composting. Besides, the dominant fungal phylum was Ascomycota (31.43%∼52.54%), Basidiomycota (3.12%∼13.85%), Mucoromycota (0.40%∼7.61%) and Mortierellomycota (0.97%∼2.39%). Pearson correlation analysis and network indicated that there were different correlations between physicochemical indexes and fungal community under different additive concentrations. In brief, the two modifiers application promoted the SM degradation and affected the fungal community structure.

Comparing bacterial dynamics for the conversion of organics and humus components during manure composting from different sources

The study aimed to compare the differences in organic fractions transformation, humus components and bacterial community dynamics during manure composting from different sources, and to identify the key biotic and abiotic factors driving the humification process. Five types of manure [pig manure (PM), cow dung (CD), sheep manure (SM), chicken manure (CM), and duck manure (DM)] were used as raw materials for 30 days composting. The results showed the obvious difference of organic fractions decomposition with more cellulose degradation in CD and SM composting and more hemicellulose degradation in PM and CM composting. Composting of PM and CD contained significantly higher humus fractions than the other composts. Fluorescence spectra indicated that SM composting tended to form structurally stable humic acid fractions, while CM and DM tended to form structurally complex fulvic acid fractions. Pearson correlation analysis showed that humification process of composts in category A (PM, CD) with higher humification degree than category B (SM, CM, and DM) was positively correlated with lignin and hemicellulose degradation. Bioinformatics analysis found that Lysinibacillus promoted the degradation of hemicellulose and the conversion of fulvic to humic acid in the composts of category A, and in category B, Thermobifida, Lactobacillus, and Ureibacillus were key genera for humic acid formation. Network analysis indicated that bacterial interaction patterns had obvious differences in composting with different humus and humification levels.