The microbial mechanisms of enhanced humification by inoculation with Phanerochaete chrysosporium and Trichoderma longibrachiatum during biogas residues composting

Response of humification process to fungal inoculant in corn straw composting with two different kinds of nitrogen sources

Inoculation is widely used in composting to improve the mineralization process, however, the link of fungal inoculant to humification is rarely proposed. The objective of this study was to investigate the effect of compound fungal inoculation on humification process and fungal community dynamics in corn straw composting with two different kinds of nitrogen sources [pig manure (PM) and urea (UR)]. Structural equation modeling and random forest analysis were conducted to identify key fungi and explore the fungi-mediated humification mechanism. Results showed that fungal inoculation increased the content of humic acids in PM and UR by 71.76 % and 53.01 % compared to control, respectively. High-throughput sequencing indicated that there were more key fungal genera for lignin degradation in PM especially in the later stage of composting, but a more complex fungal (genera) connections with lower humification degree was found in UR. Network analysis and random forest suggested that inoculation promoted dominant genus such as Coprinus, affecting lignocellulose degradation. Structural equation modeling indicated that fungal inoculation could promote humification by direct pathway based on lignin degradation and indirect pathway based on stimulating the indigenous microbes such as Scedosporiu and Coprinus for the accumulation of carboxyl and polyphenol hydroxyl groups. In summary, fungal inoculation is suitable to be used combining with complex nitrogen source such as pig manure in straw composting.

Application of oil-degrading agents consisted of thermophilic Bacillus subtilis and Bacillus glycinifermentans in food waste

This work aims to investigate the effective removal of oil in food waste (FW). Two bacteria, Bacillus subtilis and Bacillus glycinifermentans, were obtained under high temperature conditions and named YZQ-2 and YZQ-5, respectively. The oil degradation rate of two bacteria was explored under different pH value, temperature, and NaCl concentration. In addition, the lipase and emulsifying activity were evaluated. The maximum oil degradation rate was 83.41 ± 0.86% and the maximum lipase activity reached 89.73 ± 20.89 U L-1 with YZQ-2. The fermentation broth of YZQ-2 displayed exceptional emulsification activity. Subsequently, YZQ-2 and YZQ-5 were added to aerobic FW composting. The moisture content of the compost treated with inoculated strains decreased at a faster rate during the first three days of composting. The microbial quantity increased rapidly in the first three days, and the oil degradation rate reached 39.96% after five days. Due to the excellent adaptability to high temperature and ability to degrade oil, strains YZQ-2 and YZQ-5 exhibit superior potential for various applications.

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.

Metabolomics analysis of advancing humification mechanism in secondary fermentation of composting by fungal bioaugmentation

The aim of this study was to investigate the differential metabolites and core metabolic pathways caused by fungal bioaugmentation (pH regulation and Phanerochaete chrysosporium inoculation) in secondary fermentation of composting, as well as their roles in advancing humification mechanism. Metabolomics analyses showed that inoculation strengthened the expression of carbohydrate, amino acid, and aromatic metabolites, and pH regulation resulted in the up-regulation of the phosphotransferase system and its downstream carbohydrate metabolic pathways, inhibiting Toluene degradation and driving biosynthesis of aromatic amino acids via the Shikimate pathway. Partial least squares path model suggested that lignocellulose degradation, precursors especially amino acids and their metabolism process enhanced by the regulation of pH and Phanerochaete were the main direct factors for humic acid formation in composting. This finding helps to understand the regulating mechanism of fungal bioaugmentation to improve the maturity of agricultural waste 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.

Effect of initial moisture content, resulting from different ratios of vegetable waste to maize straw, on compost was mediated by composting temperatures and microbial communities at low temperatures

Owing to the huge amounts and perishable character of vegetable wastes, composting is one of the best options for recycling vegetable wastes post-harvest. The initial moisture content (MC) is critical for optimizing composting process, but the effect of high MC in undehydrated vegetable wastes on composting was rarely reported. For this, the plant-scale windrows were prepared by mixing cauliflower waste and maize straw at different ratios to control initial MC of 70 % (T1-70) and 80 % (T2-80), respectively, and composted in winter. As composting progressed, substantial organic matter degradation, progressive humification, decreases in electrical conductivity and increases of pH and germination index (GI) were observed in both treatments. Nonetheless, T1-70 accelerated heating rate early during composting, prolonged high temperature period (>50 °C) by 30 d, thus increased the harmless level of composting, and significantly improved the humification of end-products compared to T2-80. Results also revealed that T1-70 activated more indigenous microbes and enhanced microbial interactions early during composting, with the fungi enriched in T1-70 playing an important role in accelerating the composting process. Remarkably, the difference in composting temperatures, humification degree, and microbial communities between the two treatments was most significant during the maturation phase. In this phase, MWH_CFBk5, Planktosalinus, Pseudopedobacter, and Luteimonas enriched in T1-70 were positively correlated with humification indices. It is suggested that the effect of initial MC, resulting from different ratios of vegetable waste to maize straw, on their composting was mediated by the composting temperature and microbial communities at low temperatures.

Simulated nitrogen load promoted mineralization of N2P1 compounds and accumulation of N4S2 compounds in soil dissolved organic matter in a typical subtropical estuarine marsh

Soil dissolved organic matter (DOM) is the most reactive pool in estuarine marshes, playing an important role in the biogeochemical processes of biogenetic elements. To investigate the impacts of enhanced nitrogen (N) load on DOM molecular composition and its interactions with microbes in typical Cyperus malaccensis mashes of the Min River estuary, a field N load experiment with four N levels (0, 37.50, 50 and 100 g exogenous N m-2 yr-1, respectively; applied monthly for a total of seven months) was performed. DOM molecular composition was characterized by Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS), the microbial community compositions (MCC, including fungi and bacteria) were determined by high-throughput sequencing technique, and their relationships were presented by co-occurrence network analysis. The results indicated that enhanced N load had significant impacts on soil DOM molecular composition, with N/C and P/C of DOM decreasing but S/C increasing markedly. Meanwhile, enhanced N load decreased the percentages of N2P1 compounds (primarily lipids) but increased those of N4S2 compounds (mainly lignins and lipids). The relative abundances of lignins significantly increased with increasing N load levels, whereas the proportions of lipids decreased. The abundance of N2P1 and N4S2 compounds was primarily positively correlated with eutrophic and oligotrophic microorganisms, respectively. Therefore, mineralization of N2P1 compounds might act as a source to replenish inorganic P, while enrichment of N4S2 compounds may make great contribution to organic S accumulation. Overall, enhanced N load promoted P depletion and S enrichment via altering plant growth, litter decomposition and MCC.

The positive effect of the enzyme inducer (MnSO4) on the formation of humic substance in rice straw composting by stimulating key microorganisms

This study investigated the impact of adding enzyme inducer (MnSO4) on humic substance (HS) formation during straw composting. The results demonstrated that both enzyme inducer treatment group (Mn) and functional microorganism treatment group (F) led to an increase in the content of HS compared to the treatment group without enzyme inducer and functional microorganism (CK). Interestingly, the enzyme inducer exhibited a higher promoting effect on HS (57.80 % ~ 58.58 %) than functional microbial (46.54 %). This was because enzyme inducer stimulated the growth of key microorganisms and changed the interaction relationship between microorganisms. The structural equation model suggested that the enzyme inducer promoted the utilization of amino acids by the fungus and facilitated the conversion of precursors to humic substance components. These findings provided a direction for improving the quality of composting products from agricultural straw waste. It also provided theoretical support for adding MnSO4 to compost.

Co-composting of green waste and biogas waste: physical, chemical parameters and quality of ripe compound

The impact of adding biogas waste (BW) to green waste (GW) composting to increase nitrogen supplementation and improve mature compost quality was investigated. Conducted over 90 days using static windrows, the experiment compared treatments with GW alone (T1) and GW supplemented with BW (T2 and T3). The results showed that the addition of BW increased temperatures, improved the C/N ratio, and expedited the stabilization process compared to T1. Furthermore, the addition of BW led to significant degradation of hemicellulose (up to 39.98%) and cellulose (up to 27.63%) compared to GW alone. Analysis of Fourier-transform infrared (FTIR) spectra revealed the presence of aromatic, phenolic, aliphatic, and polysaccharide structures in the compost, with BW supplementation enhancing these characteristics. Importantly, the germination index (GI) assessment indicated that the compounds produced were not toxic and instead exhibited stimulatory effects on seed germination. Overall, the findings suggest that supplementing GW composting with BW can enhance the quality and efficacy of the composting process, resulting in compost with desirable properties for agricultural use.

Enhanced humification via lignocellulosic pretreatment in remediation of agricultural solid waste

Stover and manure are the main solid waste in agricultural industry. The generation of stover and manure could lead to serious environmental pollution if not handled properly. Composting is the potential greener solution to remediate and reduce agricultural solid waste, through which stover and manure could be remediated and converted into organic fertilizer, but the long composting period and low efficiency of humic substance production are the key constraints in such remediation approach. In this study, we explore the effect of lignocellulose selective removal on composting by performing chemical pretreatment on agricultural waste followed by utilization of biochar to assist in the remediation by co-composting treatment and reveal the impacts of different lignocellulose component on organic fertilizer production. Aiming to discover the key factors that influence humification during composting process and improve the composting quality as well as comprehensive utilization of agricultural solid waste. The results demonstrated that the removal of selective lignin or hemicellulose led to the shift of abundances lignocellulose-degrading bacteria, which in turn accelerated the degradation of lignocellulose by almost 51.2%. The process also facilitated the remediation of organic waste via humification and increased the humic acid level and HA/FA ratio in just 22 days. The richness of media relies on their lignocellulose content, which is negatively correlated with total nitrogen content, humic acid (HA) content, germination index (GI), and pH, but positively correlated with fulvic acid (FA) and total organic carbon (TOC). The work provides a potential cost effective and efficient framework for agricultural solid waste remediation and reduction.

Preparation of high-temperature and low-temperature-resistant solid microbial agent for cattle manure fermentation and effect on composting

We used microbiology and molecular biology techniques to screen out high-temperature and low-temperature-resistant saprobiotics for compost and prepared a compound fermentation bacteria agent to rapidly ferment cattle manure into high-quality organic fertilizer in low-temperature season. Conventional composting and high-throughput techniques were used to analyze the changes of physical and chemical indexes and biodiversity in the process of composting, from which high and low-temperature-resistant strains were obtained, and high-temperature and low-temperature-resistant solid composite bactericides were prepared and added to composting to verify the effects of composite bactericides on composting. The conventional composting cycle took 22 days, and the diversity of microflora increased first and then decreased. Composting temperature and microbial population were the key factors for the success or failure of composting. Two strains of high-temperature-resistant bacteria and six strains of low-temperature-resistant bacteria were screened out, and they were efficient in degrading starch, cellulose, and protein. The high-temperature and low-temperature-resistant solid bacterial agent was successfully prepared with adjuvant. The preparation could make the compost temperature rise quickly at low temperature, the high temperature lasted for a long time, the water content, C/N, and organic matter fell quickly, the contents of total phosphorus and total potassium were increased, and the seed germination index was significantly improved. Improve the composting effect. The solid composite bacterial agent can shorten the composting time at low temperature and improve the composting efficiency and quality.

Enhancing aerobic composting performance of high-salt oily food waste with Bacillus safensis YM1

To alleviate the inhibitory effects of salt and oil on food waste compost, the compost was inoculated with salt-tolerant and oil-degrading Bacillus safensis YM1. The YM1 inoculation could effectively improve compost maturation index. Compared with uninoculated group, the oil content and Cl- concentration in the 0.5% YM1-inoculated compost decreased significantly by 19.7% and 8.1%, respectively. The addition of the YM1 inoculant substantially altered the richness and composition of the microbial community during composting, as evidenced by the identification of 47 bacterial and 42 fungal biomarker taxa. The enrichment of some oil-degrading salt-tolerant microbes (Bacillus, Haloplasma, etc.) enhanced nutrient conversion, which is crucial for the improved maturity of the YM1 compost. This study demonstrated that YM1 could regulate both abiotic and biotic processes to improve high-salt and oily food waste composting, which may be an effective inoculant in the industrial-scale composting.

Effect of microbial inoculum on composting efficiency in the composting process of spent mushroom substrate and chicken manure

This work aimed to investigate the microbial mechanisms for the improvement of composting efficiency driven by the compound microbial inoculum (MI) (Bacillus subtilis SL-44, Enterobacter hormaechei Rs-189 and Trichoderma reesei) during co-composting of spent mushroom substrate (SMS) and chicken manure (CM). The treatments used in the study were as follows: 1) MI (inoculation with microbial inoculum), 2) CI (inoculation with commercial microbial inoculum), and 3) CK (without inoculation). The results demonstrated that MI increased the seed germination index (GI) by 25.11%, and contents of humus, humic acid (HA) and available phosphorus (AP) were correspondingly promoted by 12.47%, 25.93% and 37.16%, respectively. The inoculation of MI increased the temperature of the thermophilic stage by 3-7 °C and achieved a cellulose degradation rate of 52.87%. 16S rRNA gene analysis indicated that Actinobacteria (11.73-61.61%), Firmicutes (9.46-65.07%), Proteobacteria (2.86-32.17%) and Chloroflexi (0.51-10.92%) were the four major phyla during the inoculation composting. Bacterial metabolic functional analysis revealed that pathways involved in amino acid and glycan biosynthesis and metabolism were boosted in the thermophilic phase. There was a positive correlation between bacterial communities and temperature, humification and phosphorus fractions. The average dry weight, fresh weight and seedling root length in the seedling substrates adding MI compost were 1.13, 1.23 and 1.06 times higher than those of the CK, respectively. This study revealed that biological inoculation could improve the composting quality and efficiency, potentially benefiting the resource utilization of agricultural waste resources.

Composting municipal solid waste and animal manure in response to the current fertilizer crisis - a recent review

The dynamic price increases of fertilizers and the generation of organic waste are currently global issues. The growth of the population has led to increased production of solid municipal waste and a higher demand for food. Food production is inherently related to agriculture and, to achieve higher yields, it is necessary to replenish the soil with essential minerals. A synergistic approach that addresses both problems is the implementation of the composting process, which aligns with the principles of a circular economy. Food waste, green waste, paper waste, cardboard waste, and animal manure are promising feedstock materials for the extraction of valuable compounds. This review discusses key factors that influence the composting process and compares them with the input materials' parameters. It also considers methods for optimizing the process, such as the use of biochar and inoculation, which result in the production of the final product in a significantly shorter time and at lower financial costs. The applications of composts produced from various materials are described along with associated risks. In addition, innovative composting technologies are presented.

Inoculating functional bacteria improved the humification process by regulating microbial networks and key genera in straw composting by adding different nitrogen sources

The aim of this study was to compare the effect of functional inoculant and different nitrogen sources on the relationship among lignocellulose, precursors, and humus as well as their interactions with bacterial genera in straw composting. Results showed that inoculation improved the heating process and retained more nitrate compared to control. Inoculation increased the degradation of lignocellulosic components by 26.9%-81.6% and the formation of humus by 15.7%-23.0%. Bioinformatics analysis showed that inoculation enriched key genera Chryseolinea in complex nitrogen source (pig manure) compost and Pusillimas, Luteimonas, and Flavobacteria in single nitrogen source (urea) compost, which were related to humus formation. Network analysis found that inoculation and urea addition improved the microbial synergistic effect and inoculation combined with pig manure had more complex modularity and interactions. Combining the functional bacterial inoculant with urea helped to enhance the degradation of lignocellulose and humification process during straw composting especially with single nitrogen source.

Urea addition as an enhanced strategy for degradation of petroleum contaminants during co-composting of straw and pig manure: Evidences from microbial community and enzyme activity evaluation

Alterations in microbial community succession patterns and enzyme activities by petroleum pollutants during co-composting of straw and swine manure with the supplementary nitrogen source are unclear. In this study, urea was added into co-composting systems, and the removal performance of petroleum, microbial enzyme activity and community changes were investigated. Results showed that the polyphenol oxidase and catalase activities which were both related to the degradation of petroleum contaminants were accordingly increased from 20.65 to 30.31 U/g and from 171.87 to 231.86 U/g due to urea addition. The removal efficiency of petroleum contaminants in composting with urea increased from 45.06% to 82.29%. The addition of urea increased the diversity and abundance of petroleum-degrading microorganisms, and enhanced microbial linkages. This study provides a novel strategy for the degradation of petroleum hydrocarbon as well as a new insight into the effect of urea on both microbial processes and composting phases.

The co-inoculation of Trichoderma viridis and Bacillus subtilis improved the aerobic composting efficiency and degradation of lignocellulose

The aim of this study was to reveal the mechanism by which co-inoculation with both Trichoderma viridis and Bacillus subtilis improved the efficiency of composting and degradation of lignocellulose in agricultural waste. The results showed that co-inoculation with Trichoderma and Bacillus increased abundance of Bacteroidota to promote the maturation 7 days in advance. Galbibacter may be a potential marker of co-inoculation composting efficiency compost. The compost became dark brown, odorless, and had a carbon to nitrogen ratio of 16.40 and a pH of 8.2. Moreover, Actinobacteriota and Firmicutes still dominated the degradation of lignocellulose following inoculation with Trichoderma or Bacillus 35 days after composting. Bacterial function prediction analysis showed that carbohydrate metabolism was the primary metabolic pathway. In conclusion, co-inoculation with Trichoderma and Bacillus shortened the composting cycle and accelerated the degradation of lignocellulose. These findings provide new strategies for the efficient use of agricultural waste to produce organic fertilizers.

Effect of heterogeneous fenton-like pretreatment on semi-permeable membrane-covered co-composting: Humification and microbial community succession

This study focused on the impacts of heterogeneous Fenton-like pretreatment on the humification and bacterial community during co-composting of wheat straw with cattle dung covered with a semi-permeable membrane. In this study, FeOCl and low concentration of H2O2 were used for pretreatment and composting, which lasted for 39 days. The results showed that the pretreatment promoted the humification process, with degree of polymerization and percentage of humic acid increasing by 53.2 % and 7.3 %, respectively. Furthermore, the diversity and structure of bacterial communities were altered by pretreatment. During the thermophilic phase, pretreatment considerably promoted the metabolism of carbohydrate. According to redundancy analysis, C/N, moisture and organic matter were the key environmental factors that dominated the microbial community. In summary, heterogeneous Fenton-like pretreatment provided a novel idea for improving the humic acid content and maturity of the compost pile.

Effects of biochar and volcanic rock addition on humification and microbial community during aerobic composting of cow manure

Additives are important for accelerating humification during aerobic composting. The impacts of porous additives biochar and volcanic rock on the physicochemical parameters, maturity indicators, microbial communities, and bacterial functional metabolism during the aerobic composting of cow manure were investigated in this study. The results showed that the biochar addition decreased the E4/E6 value by 10.42% and increased the abundance of Geobacillus (1.69 times), and volcanic rock addition decreased the E4/E6 value by 11.31% and increased the abundance of Thermobacillus (1.29 times) and Paenibacillus (1.72 times). The network analysis demonstrated that biochar promoted maturity by reducing the abundance of Pseudomonas and increasing the abundance of genes related to the metabolism of other amino acids, while volcanic rock promoted maturity by reducing the abundance of genes related to nucleotide metabolism. These results provided data and theoretical justification for the selection of porous additives for composting.

Regulation of fungal communities during pig manure composting

The role of protein shell (PS) amendment in altering the fungal community during pig manure (PM) composting was investigated. Six different dosages of PS based on the dry weight of PM (0 %, 2.5 %, 5 %, 7.5 %, 10 %, and 12 %; T1-T6, respectively) were mixed with wheat straw to make the initial feedstock and composted for 42 days. The results showed that Ascomycota, Basidiomycota, and Giomeromycota were the most abundant phyla in all treatments. However, the relative abundance of Giomeromycota was the highest in the control treatment, although a substantially greater population was observed in all treatments. Genus abundance declined steadily from T1 to T6; however, T4 and T6 had smaller populations. Correlation analysis also suggested that T6 amendment increased the overall fungal dynamics and organic matter degradation. Thus, T6 was more efficient to enhance the overall fungal population and dynamics with considerable network connections among all the analyzed parameters.

Microbial dynamics and nitrogen retention during sheep manure composting employing peach shell biochar

In this study, the effects of peach shell biochar (PSB) and microbial agent (EM) amendment on nitrogen conservation and bacterial dynamics during sheep manure (SM) composting were examined. Six treatments were performed including T1 (control with no addition), T2 (EM), T3 (EM + 2.5 %PSB), T4 (EM + 5 %PSB), T5 (EM + 7.5 %PSB), and T6 (EM + 10 %PSB). The results showed that the additives amendment reduced NH3 emissions by 6.12%∼32.88% and N2O emissions by 10.96%∼19.76%, while increased total Kjeldahl nitrogen (TKN) content by 8.15-9.13 g/kg. Meanwhile, Firmicutes were the dominant flora in the thermophilic stages, while Proteobacteria, Actinobacteriota, and Bacteroidota were the dominant flora in the maturation stages. The abundance of Bacteroidota and Actinobacteriota were increased by 17.49%∼32.51% and 2.31%∼12.60%, respectively, which can accelerate the degradable organic materials decomposition. Additionally, redundancy analysis showed that Proteobacteria, Actinobacteriota, and Bacteroidota were positively correlated with NO3--N, TKN, and N2O, but a negative correlation with NH3 and NH4+-N. Finally, results confirmed that (EM + 10 %PSB) additives were more effective to reduce nitrogen loss and improve bacterial dynamics.

The effect of manure-borne doxycycline combined with different types of oversized microplastic contamination layers on carbon and nitrogen metabolism in sandy loam

The different forms and properties of microplastics (MPs) have different effects on the elemental cycles in soil ecosystems, and this is further complicated when the soil contains antibiotics; meanwhile, oversized microplastic (OMP) in soil is always ignored in studies of environmental behavior. In the context of antibiotic action, the effects of OMP on soil carbon (C) and nitrogen (N) cycling have rarely been explored. In this study, we created four types of oversized microplastic (thick fibers, thin fibers, large debris, and small debris) composite doxycycline (DOX) contamination layers (5-10 cm) in sandy loam, hoping to reveal the effects on soil C and N cycling and potential microbial mechanisms when exposed to the combination of manure-borne DOX and different types of OMP from the perspective of metagenomics in the longitudinal soil layer (0-30 cm). The results showed that all different forms of OMP, when combined with DOX, reduced the soil C content in each layer, but only reduced the soil N content in the upper layer of the OMP contamination layer. The microbial structure of the surface soil (0-10 cm) was more noteworthy than that of the deeper soil (10-30 cm). The genera Chryseolinea and Ohtaekwangia were key microbes involved in C and N cycling in the surface layer and regulated carbon fixation in photosynthetic organisms (K00134), carbon fixation pathways in prokaryotes (K00031), methane metabolism (K11212 and K14941), assimilatory nitrate reduction (K00367), and denitrification (K00376 and K04561). The present study is the first to reveal the potential microbial mechanism of C and N cycling under OMP combined with DOX in different layers, mainly the OMP contamination layer and its upper layer, and the OMP shape plays an important role in this process.

Straw mulch improves soil carbon and nitrogen cycle by mediating microbial community structure and function in the maize field

This study was conducted to investigate the capability of the microbial community characteristics and soil variables to promote carbon and nitrogen cycles in maize fields under straw mulch. We covered the surface soil of the maize field with different amounts of wheat straw (0 kg/ha, 2,250 kg/ha, and 4,500 kg/ha) and used 16S rRNA and ITS sequencing, Biology ECO-plate, traditional enzymology, TOC analyzer, and HPLC to measure bacterial and fungal community composition and functions, characteristics of microbial carbon source metabolism, carbon and nitrogen fraction, enzyme activity, and organic acid content in the maize rhizosphere and non-rhizosphere. The results indicated that short-term straw mulch insignificantly affected the alpha diversity of bacterial and fungal communities whereas significantly influenced their beta diversity. The results of functional prediction revealed that straw mulch considerably boosted the relative abundances of bacteria belonging to chemoheterotrophy, aerobic chemoheterotrophy, ureolysis, and nitrogen fixation and inhibited fermentation and nitrate reduction in maize rhizosphere soil. These processes primarily drove the C and N cycles in soil. Straw mulch also improved fungal saprotrophs by raising the proportion of Chaetomiaceae and Chaetosphaeriaceae. The Biology ECO-plate results illustrated that straw mulch weakened the metabolism capacity of microbial labile carbon resources. As a result, the labile C and N fractions were raised under straw mulch. Our results also showed that straw mulch primarily regulated the microbial community structure in rhizosphere soil by significantly decreasing Firmicutes and Ascomycota relative abundance while increasing Basidiomycota. The fungal community structure is more than bacterial for affecting soil microbial biomass carbon, readily oxidizable organic carbon, dissolved organic carbon, available nitrogen, ammonium, and nitrate directly and indirectly through malic acid content and cellulase, protease, and amylase activity. Overall, our findings imply that straw mulch might influence the bacterial and fungal community structures, thereby boosting the production of labile C and N components and accelerating the C and N cycle in maize fields.

From waste to wealth: Innovations in organic solid waste composting

Organic solid waste (OSW) is not only a major source of environmental contamination, but also a vast store of useful materials due to its high concentration of biodegradable components that can be recycled. Composting has been proposed as an effective strategy for recycling OSW back into the soil in light of the necessity of a sustainable and circular economy. In addition, unconventional composting methods such as membrane-covered aerobic composting and vermicomposting have been reported more effective than traditional composting in improving soil biodiversity and promoting plant growth. This review investigates the current advancements and potential trends of using widely available OSW to produce fertilizers. At the same time, this review highlights the crucial role of additives such as microbial agents and biochar in the control of harmful substances in composting. Composting of OSW should include a complete strategy and a methodical way of thinking that can allow product development and decision optimization through interdisciplinary integration and data-driven methodologies. Future research will likely concentrate on the potential in controlling emerging pollutants, evolution of microbial communities, biochemical composition conversion, and the micro properties of different gases and membranes. Additionally, screening of functional bacteria with stable performance and exploration of advanced analytical methods for compost products are important for understanding the intrinsic mechanisms of pollutant degradation.

Exploration of potential driving mechanisms of Comamonas testosteroni in polycyclic aromatic hydrocarbons degradation and remodelled bacterial community during co-composting

Polycyclic aromatic hydrocarbons (PAHs) are a cluster of highly hazardous organic pollutants that are widespread in ecosystems and threaten human health. Composting has been shown to be an effective strategy for PAHs degredation. Here, we used Comamonas testosteroni as an inoculant in composting and investigated the potential mechanisms of PAHs degradation by co-occurrence network and structural equation modelling analysis. The results showed that more than 60% of PAHs were removed and the bacterial community responded to the negative effects of PAHs by upgrading the network. Inoculation with C. testosteroni altered bacterial community succession, intensified bacterial response to PAHs, improved metabolic activity, and promoted the degradation of PAHs during co-composting. The increased in the positive cohesion index of the community suggested that agents increased the cooperative behaviour between bacteria and led to changes in keystones of the bacterial network. However, the topological values of C. testosteroni in the network were not elevated, which confirmed that C. testosteroni altered communities by affecting other bacterial growth rather than its own colonisation. This study strengthens our comprehension of the potential mechanisms for the degradation of PAHs in inoculated composting.

Revealing ecotype influences on Cistanche sinensis: from the perspective of endophytes to metabolites characteristics

Introduction

Plant microorganism is critical to plant health, adaptability, and productive forces. Intriguingly, the metabolites and microorganisms can act upon each other in a plant. The union of metabolomics and microbiome may uncover the crucial connections of the plant to its microbiome. It has important benefits for the agricultural industry and human being health, particularly for Chinese medical science investigation.

Methods

In this last 2 years study, on the strength of the UPLC-MS/MS detection platform, we accurately qualitatively, and quantitatively measured the Cistanche sinensis fleshy stems of two ecotypes. Thereafter, through high-throughput amplicon sequencing 16S/ITS sequences were procured.

Results

PhGs metabolites including echinacoside, isoacteoside, and cistanoside A were significantly downregulated at two ecotypes of C. sinensis. Add up to 876 metabolites were monitored and 231 differential metabolites were analyzed. Further analysis of 34 core differential metabolites showed that 15 compounds with up-regulated belonged to phenolic acids, flavonoids, and organic acids, while 19 compounds with down-regulated belonged to phenolic acids, flavonoids, alkaloids, amino acids, lipids, and nucleotides. There was no noteworthy discrepancy in the endophytic bacteria's α and β diversity between sandy and loam ecotypes. By comparison, the α and β diversity of endophytic fungi was notably distinct. The fungal community of the loam ecotype is more abundant than the sandy ecotype. However, there were few such differences in bacteria. Most abundant genera included typical endophytes such as Phyllobacterium, Mycobacterium, Cistanche, Geosmithia, and Fusarium. LEfSe results revealed there were 11 and 20 biomarkers of endophytic bacteria and fungi in C. sinensis at two ecotypes, respectively. The combination parsing of microflora and metabolites indicated noteworthy relativity between the endophytic fungal communities and metabolite output. Key correlation results that Anseongella was positive relation with Syringin, Arsenicitalea is negative relation with 7-methylxanthine and Pseudogymnoascus is completely positively correlated with nepetin-7-O-alloside.

Discussion

The aim of this research is: (1) to explore firstly the influence of ecotype on C. sinensis from the perspective of endophytes and metabolites; (2) to investigate the relationship between endophytes and metabolites. This discovery advances our understanding of the interaction between endophytes and plants and provides a theoretical basis for cultivation of C. sinensis in future.

Effect of biodrying of lignocellulosic biomass on humification and microbial diversity

By optimizing the carbon to nitrogen (C/N) ratio, this study accomplished an improved level of humification and microbial diversity in the biodrying process of lignocellulosic biomass. The results demonstrated that C/N ratio of 20 accelerated the decomposition of refractory lignocellulose, resulting in lower greenhouse gas emissions and the production of highly mature fertilizer with a germination index of 119.0% and a humic index of 3.2. Moreover, C/N ratio of 20 was found to diversify microbial communities, including Pseudogracilibacillus, Sinibacillus, and Georgenia, which contributed to the decomposition of lignocellulosic biomass and the production of humic acid. Hence, it is recommended to regulate the C/N ratio to 20:1 during the biodrying of biogas residue and wood chips to promote the economic feasibility and bioresource recycling.

Regulating pH and Phanerochaete chrysosporium inoculation improved the humification and succession of fungal community at the cooling stage of composting

This study aimed to explore the effect of regulating pH and Phanerochaete chrysosporium inoculation at the cooling stage of composting on the lignocellulose degradation, humification process and related precursors as well as fungal community for secondary fermentation. Results showed that composting with P. chrysosporium inoculation and pH regulation (T4) had 58% cellulose decomposition, 73% lignin degradation and improved enzyme activities for lignin decomposition. There was 81.98% increase of humic substance content and more transformation of polyphenols and amino acids in T4 compared to control. Inoculating P. chrysosporium affected the fungal community diversity, and regulating pH helped to increase the colonization of P. chrysosporium. Network analysis showed that the network complexity and synergy between microorganisms was improved in T4. Correlation and Random Forest analysis suggested that enriched Phanerochaete and Thermomyces in the mature stage of T4 were key taxa for lignocellulose degradation, and humic acid formation by accumulating precursors.

Transmission and retention of antibiotic resistance genes (ARGs) in chicken and sheep manure composting

Transmission of ARGs during composting with different feedstocks (i.e., sheep manure (SM), chicken manure (CM) and mixed manure (MM, SM:CM= 3:1 ratio) was studied by metagenomic sequencing. 53 subtypes of ARGs for 22 types of antibiotics were identified as commonly present in these compost mixes; among them, CM had higher abundance of ARGs, 1.69 times than that in SM, while the whole elimination rate of CM, MM and SM were 55.2%, 54.7% and 42.9%, respectively. More than 50 subtypes of ARGs (with 8.6%, 11.4% and 20.9% abundance in the initial stage in CM, MM and SM composting) were "diehard" ARGs, and their abundance grew significantly to 56.5%, 63.2% and 69.9% at the mature stage. These "diehard" ARGs were transferred from initial hosts of pathogenic and/or probiotic bacteria to final hosts of thermophilic bacteria, by horizontal gene transfer (HGT) via mobile gene elements (MGEs), and became rooted in composting products.

Enhanced degradation of microplastics during sludge composting via microbially-driven Fenton reaction

It has been increasingly documented that the hydroxyl radical (•OH) can promote the transformation of organic contaminants such as microplastics (MPs) in various environments. However, few studies have sought to identify an ideal strategy for accelerating in situ MPs degradation through boosting the process of •OH production in practical applications. In this work, iron-mineral-supplemented thermophilic composting (imTC) is proposed and demonstrated for enhancing in situ degradation of sludge-based MPs through strengthening •OH generation. The results show that the reduction efficiency of sludge-based MPs abundance was about 35.93% in imTC after treatment for 36 days, which was 38.99% higher than that of ordinary thermophilic composting (oTC). Further investigation on polyethylene-microplastics (PE-MPs) suggested that higher abundance of •OH (the maximum value was 408.1 μmol·kg^-1) could be detected on the MPs isolated from imTC through microbially-mediated redox transformation of iron oxides, as compared to oTC. Analyses of the physicochemical properties of the composted PE-MPs indicated that increased •OH generation could largely accelerate the oxidative degradation of MPs. This work, for the first time, proposes a feasible strategy to enhance the reduction efficiency of MPs abundance during composting through the regulation of •OH production.

Sustainable management and recycling of anaerobic digestate solid fraction by composting: A review

The aim of the study was to review and discuss the management and recycling of anaerobic digestate solid fraction by composting process in the context of circular bioeconomy and sustainable development. The conversion of the solid fraction into compost can be recognized as novel process-enhancing supplements for land reclamation. Moreover, the solid fraction of the digestate is a valuable substrate for compost production, both as a monosubstrate and as a valuable additive for other raw materials to enrich in organic matter. These results should serve as reference point to target adjusting screws for anaerobic digestate solid fraction by composting process improvement, its implementation in modern bioeconomy perspective as well as provide a guideline for effective waste management.

High oil content inhibits humification in food waste composting by affecting microbial community succession and organic matter degradation

Composting is an effective technology to realize resource utilization of food waste in rural China. However, high oil content in food waste limits composting humification. This study investigated the effects of blended plant oil addition at different proportions (0, 10, 20, and 30%) on the humification of food waste composting. Oil addition at 10%-20% enhanced lignocellulose degradation by 16.6%-20.8% and promoted humus formation. In contrast, the high proportion of oil (30%) decreased the pH, increased the electrical conductivity, and reduced the seed germination index to 64.9%. High-throughput sequencing showed that high oil inhibited the growth and reproduction of bacteria (Bacillus, Fodinicurvataceae, and Methylococcaceae) and fungi (Aspergillus), attenuated their interaction, thus, reducing the conversion of organic matter, such as lignocellulose, fat, and total sugar, to humus, consequently leading to negative impacts on composting humification. The results can guide composting parameter optimization and improve effective management of rural food waste.

Exogenous microbial antagonism affects the bioaugmentation of humus formation under different inoculation using Trichoderma reesei and Phanerochaete chrysosporium

This study was aimed at exploring the effect of antagonism of Trichoderma reesei (T.r) and Phanerochaete chrysosporium (P.c) on humification during fermentation of rice (RS) and canola straw (CS). Results showed that exogeneous fungi accelerated straw degradation and enzyme activities of CMCase, xylanase and LiP. P.c inhibited the activity of LiP when co-existing with T.r beginning, it promoted the degradation of lignin and further increased the production of humus-like substances (HLS) and humic-like acid (HLA) in later fermentation when nutrients were insufficient. The HLS of RTP was 54.9 g/kg RS, higher than the other treatments, and displayed more complex structure and higher thermostability. Brucella and Bacillus were the main HLA bacterial producers. P.c was the HLA fungal producer, while T.r assisted FLA and polyphenol transformation. Therefore, RTP was recommended to advance technologies converting crop straw into humus resources.

Synergistic PAH biodegradation by a mixed bacterial consortium: based on a multi-substrate enrichment approach

Polycyclic aromatic hydrocarbon (PAH) contamination in the environment involves multiple PAHs and various intermediates produced during the microbial metabolic process. A multi-substrate enrichment approach was proposed to develop a mixed bacterial community (MBC) from the activated sludge of a coking wastewater plant. The degradation performance of MBC was evaluated under different initial concentrations of PAHs (25-200 mg/L), temperature (20-35 °C), pH (5.0-9.0), salinity (0-10 g/L NaCl), and coexisting substrates (catechol, salicylic acid, and phthalic acid). The results showed that the degradation rates of phenanthrene and pyrene in all treatments were up to (99 ± 0.71)% and (99 ± 0.90)% after incubation of 5 days, respectively, indicating excellent biodegradation ability of PAHs by MBC. Furthermore, 16S rRNA gene amplicon sequencing analysis revealed that Pseudomonas was dominant, while Burkholderia had the largest proportion in acidic (pH = 5.0) and saline (10 g/L NaCl) environments. However, the proportion of dominant bacteria in MBC was markedly affected by intermediate metabolites. It was shown that MBC had a higher degradation rate of PAHs in the coexisting matrix due to the timely clearance of intermediates reducing the metabolic burden. Overall, our study provided valuable information to help design an effective strategy for the bioremediation of PAHs in complex environments.

Combined use of biochar and microbial agent can promote lignocellulose degradation and humic acid formation during sewage sludge-reed straw composting

This study investigated the effects of corn straw biochar (CSB) and effective microorganisms (EM) added individually or combinedly on lignocellulose degradation, compost humification, and microbial communities during sewage sludge-reed straw composting process. All the additive practices were found to significantly elevate the humification degree of compost products. The degradation rates of cellulose, hemicellulose, and lignin in different additive treatments were 20.8-31.2 %, 36.2-44.8 %, and 19.9-25.7 %, respectively, which were greatly higher than those of the control. Compared with the single uses of CSB or EM, the combined use of CSB and EM generated greater promotions in lignin and hemicellulose degradations and increase in humic acid content. By comparing the differences in microbial communities among different treatments, the CSB-EM demonstrated greater increases in activity and diversity of lignocellulose degradation-related microbes, especially for fungus. Lastly, the combined use of CSB and EM was highly recommended as a high-efficient improvement strategy for organic compost production.

Effect of Phanerochaete chrysosporium inoculation on manganese passivation and microbial community succession during electrical manganese residue composting

Electrolytic manganese residue poses potentially threats to the environment and therefore needs eco-friendly treatment. Composting has been reported to effectively passivate heavy metals and alleviate their ecotoxicity. Observation of the Mn concentration during composting indicated that the mobility of Mn was significantly reduced, with the easily extraction fraction (acid extractable and easily reduction fraction) of Mn in the control pile (pile 1 without Phanerochaete chrysosporium inoculation) and treat pile (pile 2 with Phanerochaete chrysosporium inoculation) decreasing by 17% and 29%, respectively. The inoculation of Phanerochaete chrysosporium prompted the passivation of manganese, prolonged the thermophilic period, and enriched the microbial community structure, which was attributed to the rapid growth and reproduction of thermophilic bacteria. Moreover, Phanerochaete chrysosporium inoculation promoted the effect of pH on the stabilization of Mn, but the opposite contribution of organic matter. This study would provide a new perspective for remediating EMR contaminated soil via composting.

Effects of 3D-printed bulking agent on microbial community succession and carbohydrate-active enzymes genes during swine manure composting

The bulking agent plays an important role in aerobic composting, but their shape, porosity, and homogeneity need to be optimized. In the present work, a bulking agent with a uniform shape was prepared by 3D printing to explore its influence on physicochemical parameters, microbial community succession, and gene abundance of carbohydrate-active enzymes (CAZymes) in swine manure aerobic composting. The results showed that adding 3D-printed bulking agents can increase maximum temperature, prolong the thermophilic period, and improve the degradation rate of volatile solids, which was attributed to ameliorative air permeability by the porous 3D-printed bulking agent. The abundances of some pathogenic bacteria decreased and CAZymes genes increased respectively in response to the addition of the 3D-printed bulking agent, implying it has a certain positive effect on improving the safety of compost products and promoting the degradation of organic matter. In summary, the 3D-printed bulking agent has good application potential in laboratory-scale aerobic composting.

Insight into the fraction variations of selenium and their effects on humification during composting

This study investigated the variation of selenium fractions and their effects on humification during composting. Selenite and selenate were added to a mixture of goat manure and wheat straw for composting. The results demonstrated that the bioavailable Se in the selenite added treatment (9.3-13.8%) was lower than in the selenate added treatment (18.1-47.3%). Meanwhile, the HA/FA of selenite and selenate added treatments were higher than in control, indicating that the selenium addition (especially selenite) promoted the humification of composting. Importantly, selenite enriched the abundance of Tepidimicrobium and Virgibacillus which were responsible to improve humification performance. Selenate increased the abundance of Thermobifida and Cellvibrio which facilitated the composting humification. The genes encoding CAZymes involved in the degradation of organic materials were also analyzed, and selenium could contribute to the synthesis of humus. KEGG pathway analysis revealed that the selenite addition promoted amino acids and carbohydrate metabolism compared to the control.

Role of multistage inoculation on the co-composting of food waste and biogas residue

Effect of diverse Lactobacillus amylophilus, Geobacillus thermoleovorans, and Bacillus subtilis inoculation patterns on the co-composting performance of food waste and biogas residue was explored. Experimental results revealed that, compared to the single-stage inoculation and non-inoculation groups, the multistage inoculation pattern prolonged the thermophilic period during composting, consequently improving organic matter decomposition and humification [with a high germination index (120.9%)]. In addition, it could promote the development of humic substances [with a high humus index (4.3) and biological index (1.4)] and lower emissions of carbon dioxide (CO₂), methane (CH₄), and ammonia (NH₃). Additionally, it could improve the microbial variety and the amounts of functional bacteria (i.e., Chloroflexi) in compost, which might be advantageous for the decomposition of refractory organic materials and plant growth. Therefore, the multistage inoculation pattern is recommended for organic waste composting in terms of its gas emissions, compost quality and efficacy benefits.

Deciphering the internal driving mechanism of microbial community for carbon conversion and nitrogen fixation during food waste composting with multifunctional microbial inoculation

In this study, the effects of multifunctional microbial inoculation on food waste composting based on the synergistic property between organic matter degradation and nitrogen fixation were investigated. The results showed that inoculation simultaneously strengthened organic matter degradation by 9.9% and improved the nitrogen content by 20.6% compared with that of the control group. Additionally, spectral analysis demonstrated that inoculation was conducive to the enhanced humification, which was supported by the improvement in polyphenol oxidase activity. Microbial analysis showed that most of the introduced microorganisms (Bacillus, Streptomyces, Saccharomonospora) successfully colonized, and stimulated the growth of other indigenous microorganisms (Enterobacter, Paenibacillus). Meanwhile, the change in microbial community structure was accompanied by the enhanced tricarboxylic acid cycle and amino acid metabolism. Furthermore, network analysis and structural equation model revealed that the enhanced cooperation of microorganisms, in which more carbon sources could be provided by cellulose decomposition for nitrogen fixation.