Relationship between bacterial diversity and environmental parameters during composting of different raw materials

Succession of fungal dynamics and their influence on physicochemical parameters during pig manure composting employing with pine leaf biochar

The effects of pine leaf biochar (PLB) on fungal community during pig manure composting were investigated. Five different doses of PLB [0% (T1), 2.5% (T2), 5% (T3), 10% (T4) and 15% (T5)] were mixed with mixture of pig manure and sawdust (2:1) for 50 days of composting. The present results indicated that fungal diversity increased more obvious in biochar amendment treatments than control (T1) and that the highest was recorded in T4 treatment. Basidiomycota, Ascomycota and Mucoromycota were the most three abundant phyla in all the treatments, while Heterobasidion, Pezoloma, Mucor, Geastrum, Talaromyces and Cystofilobasidium were the richness genera. In addition, network analysis indicated that fungal community abundance was significantly (p < 0.05) associated with temperature, pH, CO₂ and CH₄ emission and the seed germination index. In summary, the 10% PLB amendment (T4) was a potential option to strengthen fungal diversity and improve the composting efficiency as well as compost quality.

New insight into the impact of biochar during vermi-stabilization of divergent biowastes: Literature synthesis and research pursuits

Biochar amendment for compost stabilization of divergent biowastes is gaining considerable attention due to environmental, agronomic and economic benefits. Research to date exhibits its favorable physico-chemical characteristics, viz. greater porosity, surface area, amount of functional groups, and cation exchange capacity (CEC), which allow interface with main nutrient cycles, favor microbial activities during composting, and improve the reproduction of earthworms during vermicomposting. Biochar amendment during composting and vermicomposting of biowastes boosts physico-chemical properties of compost mixture, microbial activities and organic matter degradation; and reduces nitrogen loss and emission of greenhouse gases (GHGs). It also improves the quality of final compost by increasing concentration of plant available nutrients, enhancing maturity, decreasing composting duration and reducing the toxicity of compost. Due to these characteristics, biochar could be considered a beneficial additive for the stabilization of different biowastes during composting and vermicomposting processes. Hence, good quality vermicompost, efficient recycling and management of biowastes could be achieved by addition of biochar through composting and vermicomposting.

Role of NH3 recycling on nitrogen fractions during sludge composting

The aim of this study is to reduce nitrogen (N) loss and investigate the role of ammonia (NH₃) recycling on N fractions, environmental factors and bacterial communities. In this study, collected NH₃ from composting and recycled in it. The results showed that NH₃ recycling affected N-cycling processes such as nitrification. Redundancy Analyses (RDA) showed that NH₄⁺-N had significantly negative correlation with denitrifying bacteria in treatment group (p < 0.05), demonstrating that NH₃ recycling have influenced on the bacterial community structure. Furthermore, Structural Equation Model (SEM) revealed causal relationships between visual variables. Based on these results, we concluded that NH₃ recycling is a novel method to reduce N loss.

Driving effects of minerals on humic acid formation during chicken manure composting: Emphasis on the carrier role of bacterial community

This work was aimed to determine the effects of different minerals on humic acid (HA) formation. Minerals can stimulate the formation of complex compounds, however, whether they can promote the conversion of complex compounds to HA has not been verified. Four treatments were setup from chicken manure mixed with rice hull and then added biochar (BC), montmorillonite (MMT) and biochar combined with montmorillonite (BC-MMT) for composting, while the control check (CK) was composted without minerals. The results showed that HA concentration was increased by 28.09%, 40.79%, 45.39% and 38.96% during CK, BC, BC-MMT and MMT composting. However, the bacterial community was the main reason for affecting HA concentration. Network analysis showed that obligate and facultative core microbes drove HA formation, and these driving effects were affected by minerals. Therefore, the core bacterial community promoted HA formation, which provided an insightful method to improve HA production.

Impact of pine leaf biochar amendment on bacterial dynamics and correlation of environmental factors during pig manure composting

The influence of pine leaf biochar (PLB) amendment on bacterial community succession and its correlation with physic-chemical parameters during pig manure (PM) composting was evaluated. The five different dosages of PLB [at 0% (T1), 2.5% (T2), 5% (T3), 10% (T4) and 15% (T5)] mixed with initial composting mass were conducted to composting for 50 days. The present study indicated that bacterial diversity was significantly (p < 0.05) higher in PLB amended treatments than the control, but T4 treatment showed the highest among the all PLB applied treatment. Firmicutes, Actinobacteria, Proteobacteria and Bacteroidete were four most abundant phyla of all the treatments. Furthermore, redundancy analysis showed that the bacterial community were significantly (p < 0.05) positively correlated with temperature, pH, TOC, CO₂ and NH₃ emissions, while they were negatively correlated with the N₂O and CH₄ emission. Overall, the results suggested that the addition of 10% PLB (T4 treatment) was a potential option to enhance the composting efficiency with significantly greater abundance of bacterial community and finally improved the compost quality.

A novel method for removing heavy metals from composting system: The combination of functional bacteria and adsorbent materials

The aim of this study was to remove heavy metals from composting system using a novel method combined functional bacteria with adsorbent materials. Four types of adsorbent materials were selected in this study. Results showed that Cr had significant removal efficiency, especially in sponge treatment (19.09%) and cotton treatment (26.36%). In addition, a significant movement of heavy metals from the outside to adsorbent column was also observed. RDA results indicated that bands 1, 2, 10, 18, 19 and 20 had negative correlations with six types of heavy metals, which contributed to the removal of heavy metals. Structural equation models further confirmed functional bacteria can directly affect the removal of Cu, Cd and Cr. In addition, it can also indirectly remove Pb and Cr by changing native bacteria. In summary, this study suggested the combination of functional bacteria and adsorbent materials was effective to remove heavy metals from composting system.

Recognition of the neutral sugars conversion induced by bacterial community during lignocellulose wastes composting

The aim of this study was to explore the conversion characteristics of neutral sugars during different lignocellulose wastes composting from rice straw (RS), leaf (L) and mushroom dreg (MD). The results showed that the changes of neutral sugars were different during different wastes composting, but the changes of various hexose or pentose were similar during composting of the same material. The diversity of bacterial community led to different conversion characteristics of neutral sugars. During RS composting, each neutral sugar was transformed by a specific group of bacteria. However, a group of bacteria could transform multiple neutral sugars during MD and L composting. Furthermore, GM/AX value was first applied to composting, which could be used to characterize the conversion of neutral sugars during composting. This will help to provide more efficient recommendations for lignocellulose wastes treatment and accelerating humic substances synthesis during composting.

Improved lignocellulose degradation efficiency based on Fenton pretreatment during rice straw composting

This study aims to explore the effect of Fenton pretreatment on organic fractions, enzymes activities and microbial communities during composting. In this study, rice straw was chosen to be composted after pretreatment. The results indicated that Fenton pretreatment significantly increased the degradation of organic matter and coarse fiber contents, which might be the reason that Fenton pretreatment enhanced lignocellulose-degrading enzymes activities during composting, including CMCase, FPase, xylanase, manganese peroxidase, lignin peroxidase and laccase. Additionally, Fenton pretreatment reshaped bacteria community. The key enzymes and environmental factors, which affected organic fractions degradation were identified by redundancy analysis. Furthermore, structural equation modeling and variation partitioning analysis further revealed possible mechanisms of organic fractions degradation in different treatments during composting. In summary, the combined application Fenton pretreatment and composting improved lignocellulose degradation efficiency, which provided for an effective and environment-friendly way to manage lignocellulose wastes.

Effect of tricarboxylic acid cycle regulators on the formation of humic substance during composting: The performance in labile and refractory materials

The aims of this study are to reveal the roles of tricarboxylic acid (TCA) cycle regulators in reducing CO₂ emission and promoting humic substance (HS) formation during composting with different materials. The results showed that the addition of adenosine tri-phosphate (ATP) or malonic acid (MA) reduced CO₂ emission during chicken manure composting. However, only the addition of MA reduced CO₂ emission during lawn waste and garden waste composting. In addition, both of the two inhibitors promoted HS formation, especially for ATP. Structural equation models further confirmed that ATP and MA reduced CO₂ emission by inhibiting the decomposition of amino acid by microorganisms. Meanwhile, ATP promoted the conversion of amino acid and soluble sugars to HS, while MA only promoted the conversion of soluble sugars to HS. In summary, this study provides a theoretical basis for the application of inhibitors to reduce CO₂ emission and promote HS formation during composting.

Effects of exogenous protein-like precursors on humification process during lignocellulose-like biomass composting: Amino acids as the key linker to promote humification process

The aim of this study is to assess the effectiveness of protein-like precursors addition on promoting humification process during lignocellulose-like biomass composting through adding amino acids to compost. The humification indexes of R1 and R2 was significantly higher than that of CK (P < 0.05). The decreasing ratio of Maillard precursor concentration of R2 and R1 was higher than CK. Amino acids addition affected the bacteria community and environmental factors during composting. Variance partitioning analysis showed that humification process was strengthened with environmental factors, bacteria community, Maillard precursors. Structural equation model (SEM) analysis showed that amino acids had substantial impact on promoting humic acid (HA) formation. The combined application of protein-like wastes and lignocellulose-like wastes was suggested to improve carbon sequestration. This study lays a foundation for economically and effectively managing different types of straws by composting.

Effect of microbial inoculation on physicochemical properties and bacterial community structure of citrus peel composting

In this study, microorganisms were inoculated during citrus peel composting for citrus waste recycling and valorisation. The physicochemical properties and the bacterial community structure of citrus peel composting inoculated microorganism were studied. The thermophilic stage of pilot-scale composting (T2) was 20 days longer than lab-scale composting (T1). C/N, organic matter, moisture, pectin and cellulose content decreased along with composing process, but the pH, soluble protein and total nutrient showed an opposite trend. The inoculation improved the richness and diversity of the bacterial community and the diversity index reached maximum on 21 days. As composting progress, Bacillus, Sphingobacterium and Saccharomonospora in inoculum became the dominant genus. Redundancy analysis showed that C/N, pectin degradation rate and temperature could explain 30.1%, 24.9% and 15.6% of the variation in bacterial genera, respectively.

Reducing ammonia and greenhouse gas emission with adding high levels of superphosphate fertilizer during composting

Previous studies revealed that superphosphate fertilizer (SSP) as an additive in compost can reduce the nitrogen loss and improve the effectiveness of phosphorus during composting. However, few studies have explored the influence of adding SSP with high levels on ammonia and greenhouse gas emission and the suitable amount for SSP addition according to a combined assessment of the composting process and product. The present study aimed to evaluate the impact of SSP with high additive amounts on NH₃, CO₂, CH₄, and N₂O emission and organic carbon loss. All piles were mixtures of pig manure and cornstalks with different levels of SSP addition including 10%, 14%, 18%, 22%, 26%, and 30% dry weight basis of raw materials. Compared with the control without SSP, the amount of NH₃ cumulative emissions was decreased by 23.8-48.1% for the treatments with 10-30% SSP addition, and the emission of greenhouse gas including CO₂, CH₄, and N₂O by 20.9-35.5% (CO₂ equivalent) was reduced by 20.9-35.5%. Adding SSP with the amount exceeding 14% to compost could reduce CO₂ emissions by 32.0-38.4% and more than 30% carbon loss at the end of composting but exceeding 26% had an adverse impact on maturity of the composts. Therefore, considering the maturity and safety of compost and gas emission reduction, 14-26% SSP was the optimum amount for composting addition, which is an effective and economical way to increase the nutrient level of carbon, nitrogen, and phosphorus in compost and reduce environmental risks.

Assessment contributions of physicochemical properties and bacterial community to mitigate the bioavailability of heavy metals during composting based on structural equation models

The aim of this study was to explore the pathways to mitigate the bioavailability of heavy metals (HM) during chicken and beef cattle manures composting. For raw materials, HM contents in animal manures from breeding farm were 1.5-3 times as much as that of domestic animal manures. Structural equation models (SEMs) based on denaturing gradient gel electrophoresis (DGGE) showed that mitigating bioavailability of HM was mainly attributed to physicochemical properties (organic matters content and temperature) during beef cattle manures composting. However, both physicochemical properties (organic matters content, temperature, pH and moisture) and bacterial community were critical factors during chicken manures composting. Furthermore, the statistical analysis from high-throughput sequencing verified the results of SEMs. Therefore, the bioavailability of HM will be mitigated by different deactivation pathways according to diverse raw materials composting.

Microbiology of municipal solid waste landfills: a review of microbial dynamics and ecological influences in waste bioprocessing

Municipal solid waste landfills are widely used as a waste management tool and landfill microbiology is at the core of waste degradation in these ecosystems. This review investigates the microbiology of municipal solid waste landfills, focusing on the current state of knowledge pertaining to microbial diversity and functions facilitating in situ waste bioprocessing, as well as ecological factors influencing microbial dynamics in landfills. Bioprocessing of waste in municipal landfills emanates from substrate metabolism and co-metabolism by several syntrophic microorganisms, resulting in partial transformation of complex substrates into simpler polymeric compounds and complete mineralisation into inorganic salts, water and gases including the biofuel gas methane. The substrate decomposition is characterised by evolution and interactions of different bacterial, archaeal and fungal groups due to prevailing biotic and abiotic conditions in the landfills, allowing for hydrolytic, fermentative, acetogenic and methanogenic processes to occur. Application of metagenomics studies based on high throughput Next Generation Sequencing technique has advanced research on profiling of the microbial communities in municipal solid waste landfills. However, functional diversity and bioprocess dynamics, as well as key factors influencing the in situ bioprocesses involved in landfill waste degradation; the very elements that are key in determining the efficiency of municipal landfills as tools of waste management, remain ambiguous. Such gaps also hinder progressive understanding of fundamentals that underlie technology development based on waste biodegradation, and exploration of municipal waste as a bioresource.

Key extracellular enzymes triggered high-efficiency composting associated with bacterial community succession

A consortium of key bacterial taxa plays critical roles in the composting process. In order to elucidate the identity and mechanisms by which specific bacterial species drive high-efficiency composting, the succession of key bacterial consortia and extracellular enzymes produced during the composting process were monitored in composting piles with varying initial C/N ratios. Results showed that C/N ratios of 25 and 35 enhanced composting efficiency through elevated temperatures, higher germination indices, enhanced cellulose and hemicellulose degradation, and higher cellulase and dehydrogenase activities. The activities of cellulase and β-glucosidase, cellulase and protease, and cellulase and β-glucosidase exhibited significant relationships with bacterial community composition within the mesophilic, thermophilic, and mature phases, respectively. Putative key taxa, linked to a higher composting efficiency, such as Nonomuraea, Desemzia, Cellulosimicrobium, Virgibacillus, Clostridium, and Achromobacter, exhibited significantly positive relationships with extracellular enzyme activities, suggesting a significant contribution to these taxa to the development of composting maturity.

Crop-based composting of lignocellulosic digestates: Focus on bacterial and fungal diversity

In this study, organic matter degradation and microbial diversity were assessed during the composting of lignocellulose-rich digestates. Digestates were collected based on each crop type during anaerobic co-digestion of cow manure and barley, triticale, wheat and rye. Bacterial and fungal diversity in digestate composting systems were determined by 16S and 18S rRNA gene amplicon sequencing, respectively. Crop-based composting of anaerobic digestates showed similar process trends in terms of pH, temperature, moisture content (MC) and C:N ratio. The properties of final compost products were in accordance with the national legislations regarding soil applications, except MC, which were therefore air-dried before being amended to soil. Most abundant bacterial genera were represented by Luteimonas, Bacillus, Ochrobactrum and Thermobifida. Meanwhile, Thermomyces, Aspergillus, Galactomyces and Neurospora were detected as the predominant fungal genera in all compost samples.

A compost-derived thermophilic microbial consortium enhances the humification process and alters the microbial diversity during composting

This work was conducted to assess the influence of a compost-born multifunctional thermophilic microbial consortium (CTMC) on the physico-chemical parameters, organic matter (OM) transformation and dynamic succession of microbial communities in dairy manure-sugarcane leaves co-composting. The results revealed that CTMC inoculation not only improved the bio-degradation of OM and lignocellulose but also distinctly enhanced the aromaticity and stability degrees of dissolved organic matter and humic substance (HS). Additionally, the complexity and diversity of bacterial and fungal community increased after inoculation. Redundancy analysis indicated that the microbial communities compositions and the physico-chemical parameters interacted with each other in humification process. The dominated bacterial and fungal species related to lignocellulose degradation and humification process were also detected. Accordingly, this research could put forward a possible optimized inoculation strategy to enhance the mineralization of organic carbon, accelerate the lignocellulose degradation and promote the humification process in solid organic waste composting.

Exploring the mechanisms of organic matter degradation and methane emission during sewage sludge composting with added vesuvianite: Insights into the prediction of microbial metabolic function and enzymatic activity

Effect mechanisms of organic matter (OM) degradation and methane (CH₄) emission during sewage sludge (SS) composting with added vesuvianite (V) were studied by high-throughput sequencing (HTS) and phylogenetic investigation of communities by reconstruction of unobserved states (PICRUSt). Results show that the addition of V accelerated the OM degradation and decreased the cumulative CH₄ emissions by 33.6% relative to the control. In addition, V significantly decreased the mcrA gene abundance and the methanogen community richness at the genus level. PICRUSt also indicated that V strengthens the microbial metabolic function and enzymatic activity related to OM degradation, and reduced the enzymatic activity related to CH₄ production. Methanogens community variation analysis proved the ratio of carbon and nitrogen and moisture content are the significant variables affecting CH₄ emissions. Thus, optimizing the ratio of carbon and nitrogen and moisture content will decrease CH₄ emission during SS composting.

Roles of bacterial community in the transformation of organic nitrogen toward enhanced bioavailability during composting with different wastes

This study aimed to explore the roles of bacterial community in the transformation of bioavailable organic-N (BON) during different wastes composting. BON fractions with different forms and molecular weights were identified in this study. Results indicated that core bacterial communities improved the availability of BON by degrading high molecular weights BON into low molecular weights BON during different wastes composting. A total of fifty-two core bacterial genera involved in BON transformation were identified by network analysis. Three types of high molecular weights BON fractions (amino acid-N, amine-N and amino sugar-N) were degraded by bacteria during chicken manure and garden waste composting, while only amine-N was degraded during municipal solid waste composting. Finally, moisture, C/N and pH were identified as the key operational parameters affecting BON transformation mediated by microorganisms, which can be used to improve bioavailability of organic-N and reduce N loss during composting.

The impacts of metal ions on phytotoxicity mediate by microbial community during municipal solid waste composting

Metal ions (MIs) are the main sources of phytotoxicity of compost product, which can be absorbed by plants, thereby reducing the germination rate. The aim of this study was to analyze the interactional mechanism among MIs, microbial community, the structure of water soluble organic matter and phytotoxicity during composting. The results indicated that phytotoxicity was positively correlated with MIs (II) (As, Cd, Hg, Cr, Fe, Mn and Pb), and negatively correlated with MIs (I) (Mg, Zn, Ni and Cu). Furthermore, SO₄^2-, organic matter (OM), pH and four bacterial species significantly influenced the association of MIs to phytotoxicity. Additionally, molecular weight, protein-like substance and oxygen-containing functional groups relating to MIs (II) were significantly influenced by the nine bacterial species. Based on the response of physicochemical parameters on these key bacterial species, three possible mutual mechanisms were proposed using the structural equation model. Accordingly, a regulating method was proposed to reduce the phytotoxicity during composting.

Assessing key microbial communities determining nitrogen transformation in composting of cow manure using illumina high-throughput sequencing

Insight to nitrogen transformation and cycling during composting is vital in developing management strategies that improve nitrogen content and quality of the end product. In this study, a positive ventilation device was constructed and used to elucidate nitrogen transformation and microbial community structures during the composting of cow manure and rice straw. Bacterial community successions were analyzed during the composting process by examining the change in their structural dynamics using high-throughput sequencing technique. The results revealed that dominant phyla, included Acidobacter, Proteobacteria, Firmicutes, Bacteroidetes, Chloroflexi, and Actinobacteria. Furthermore, a positive strong correlation was observed between the key bacterial communities and nitrogen transformation. Analyses of functional genera, Spearman correlation and Path showed that Thermomonospora_curvata_DSM_43183 followed by Luteimonas and Simiduia, Brevundimonas and Tamlana, Pseudomonas followed by Brevundimonas and Flavobacterium were the key bacterial communities affecting NH₄⁺-N, NO₃^--N, and NO₂^--N transformation, respectively. Thauera followed by Pseudomonas_putida_NBRC_14164 played a dominant role in N₂O transformation.

Hyperthermophilic pretreatment composting significantly accelerates humic substances formation by regulating precursors production and microbial communities

Hyperthermophilic pretreatment composting (HPC) is superior to traditional composting (TC) with enhanced compost maturity and accelerated humic substances (HS) formation. However, the regulators affecting HS formation, which is of great importance in evaluating the compost maturity, are still unclear. This study aimed to examine and compare the effects of HPC and TC on (i) HS formations under varying precursors, (ii) bacterial and fungal dynamics, and (iii) factors affecting HS formations. Results revealed that HS formation was accelerated in the heating, thermophilic and maturity phases for HPC, whereas the synthesis of HS was observed in the maturity phase for TC. Particularly, concentrations of humic acid, polyphenols, amino acids, polysaccharides and reducing sugar were increased in compost by 50, 60, 52, 44 and 92%, respectively after the hyperthermophilic pretreatment. These increased precursors could stimulate the activity of Planococcaceae that possessed a high degradation capacity on D-mannitol in the heating stage. Additionally, the thermophilic microbes Solibacillus and Aspergillus with high degradation capacity on lignocelluloses and lignin, respectively dominated in the thermophilic stage. These microorganisms may promote the formation of precursors and thus accelerated synthesis of HS in HPC. Finally, structural equation model (SEM) showed polyphenol and reducing sugar were the key precursors to directly or indirectly promote HS formation in HPC and the higher temperature rise as well as the higher N content provided advantages over TC in improving HS formation. This study provides the stability to the accelerated humification process in HPC and reveals its potential applicability in improving HS formation.

Humic substances developed during organic waste composting: Formation mechanisms, structural properties, and agronomic functions

Aerobic composting is a typical biochemical process of stabilization and harmlessness of organic wastes during which organic matter degrades, and then aggregates, to produce humic substances (HSs). HSs are a core product of-and a crucial indicator of-the maturation of compost that can be used in soil amendments. The formation of HSs is affected by the characteristics of the raw materials involved, the presence of compost additives, microbial activity, temperature, pH, the C/N ratio, moisture content, oxygen content and particle size, all of which can interact with each other. The formation of HSs is therefore complex. Moreover, it is difficult to identify definitive structures of humic acids (HAs) and fulvic acids (FAs), which are the two major components of HSs. However, HSs represent the same functional groups and structural arrangements, which helps to predict their structures. Functional groups represented by phenol and carboxylic acid groups of HAs and FAs can provide various agronomic functions, such as plant growth enhancement, water and nutrient retention, and disease suppression capacity. Overall, HSs can act as a soil amendment, fertilizer, and plant growth regulator. These functions of HSs enhance the reuse potential of organic waste compost products; however, this requires scientific control of various composting parameters and appropriate application of final products.

Microbial Community Succession and Response to Environmental Variables During Cow Manure and Corn Straw Composting

In composting system, the composition of microbial communities is determined by the constant change in the physicochemical parameters. This study explored the dynamics of bacterial and fungal communities during cow manure and corn straw composting using high throughput sequencing technology. The relationships between physicochemical parameters and microbial community composition and abundance were also evaluated. The sequencing results revealed the major phyla included Proteobacteria, Bacteroidetes, Firmicutes, Chloroflexi and Actinobacteria, Ascomycota, and Basidiomycota. Linear discriminant analysis effect size (LEfSe) illustrated that Actinomycetales and Sordariomycetes were the indicators of bacteria and fungi in the maturation phase, respectively. Mantel test showed that NO3 --N, NH4 +-N, TN, C/N, temperature and moisture content significantly influenced bacterial community composition while only TN and moisture content had a significant effect on fungal community structure. Structural equation model (SEM) indicated that TN, NH4 +-N, NO3 --N and pH had a significant effect on fungal abundance while TN and temperature significantly affected bacterial abundance. Our finding increases the understanding of microbial community succession in cow manure and corn straw composting under natural conditions.

Effect of MnO2 on biotic and abiotic pathways of humic-like substance formation during composting of different raw materials

The humic-like substances (HLS) are proposed to be formed by biotic and abiotic pathways. The abiotic pathways were neglected in existed composting studies. The present study aims to accelerate the abiotic pathways, and to investigate how MnO₂ drives the HLS transformation via changing the contribution of abiotic and biotic pathways during composting with different materials. Parallel factor analysis model (PARAFAC), hetero two-dimensional correlation spectra (hetero-2DCOS) and variance partitioning were used to identify the effects of MnO₂ on the formation of humic acid (HA) and fluvic acid (FA) during composting of chicken manure (CM) and corn straw (CS). The addition of MnO₂ could change the structures of HLS during CS and CM composting, mainly promoting the formation of complex components in HA and FA during CS composting, as well as the complex components of FA during CM composting. Meanwhile, the addition of MnO₂ could reshape the microbial ecology, which enhanced the correlation between microbes and complex components formation during composting, especially in CM composting. Variance partitioning showed that both abiotic and biotic pathways were stimulated in conversion of HLS components after adding MnO₂ during CS composting, especially for the abiotic pathways. During CM composting, the MnO₂ promoted biotic effects on the conversion of HLS components. Above all, the addition of MnO₂ could stimulate pathways of biotic, abiotic or both of them to improve the humification degree of HLS by changing microbial ecology, which could be a promising way for promoting the application value of composting products.

Dynamics of fungal diversity and interactions with environmental elements in response to wheat straw biochar amended poultry manure composting

The fungal dynamics and its correlation with physicochemical and gaseous emission were investigated using metagenomics and Heat map illustrator (HEMI). Five different concentrations of wheat straw biochar (WSB) were applied to poultry manure (PM) and composted for 50 days; those without the WSB treatment were used as a control. The results revealed the dominant phyla to be Chytridiomycota, Mucoromycota, Ascomycota and Basidiomycota, while Batrachochytrium, Rhizophagus, Mucor, and Puccinia were the superior genera. In particular, the diversity of Chytridiomycota and Ascomycota was more abundant among all of the treatments. Overall, the diversity of the fungal species was correspondent, but relative abundance varied significantly among all of the composts. Principle Coordinate Analysis (PCoA) and Non-Metric Multi- Dimensional Scaling (NMDS) indicated that different concentrations of WSB applied treatments have significantly distinct fungal communities. In addition, correlation analyses of fungal interactions with environmental elements via HEMI also indicate a clear difference among the treatments. Ultimately, the relative abundance of fungal composition significantly influenced the PM compost treated by the WSB.

How do fungal communities and their interaction with bacterial communities influence dissolved organic matter on the stability and safety of sludge compost?

This study was conducted to assess the effect of fungal communities and their interaction with bacterial communities on the dissolved organic matter (DOM) transformation for the stability and safety of sludge composting. The results showed that fungal community had strong shifts in diverse stages of sludge composting along with the changes of temperature. Correlation analysis demonstrated that fungal communities had significant connections with bacterial communities during composting but were not directly related to the indicators of phytotoxicity and maturity. Variance partitioning analysis suggested that the interactions of fungal and bacterial communities had the biggest contribution (49.75%) to composting stability and safety. Based on structural equation modeling, the possible way of fungal community participated in the transformation of DOM components and the formation of humic-like substances of DOM by interacting with bacterial community was proposed, which will provide important information for understanding the biotic interaction in composting and improving composting fermentation process.

Improved lignocellulose-degrading performance during straw composting from diverse sources with actinomycetes inoculation by regulating the key enzyme activities

This study was conducted to assess the effect of thermophilic actinomycetes inoculation on the lignocellulose degradation, enzyme activities and microbial community during different types of straw composting from wheat, rice, corn and soybean. The results showed that actinomycetes inoculation not only changed the structure of actinomycetic and bacterial community but also accelerated the degradation of cellulose, hemicellulose and lignin and increased the key enzymes activities including CMCase, Xylanase, manganese peroxidase, lignin peroxidase and laccase during composting particularly from wheat straw and rice straw. The key enzyme and physiochemical parameters which affected organic fractions degradation have been identified by redundancy analysis. The combined application of actinomycete inoculation and urea addition as a source of nitrogen was suggested to regulate the key enzyme activities and lignocellulose degradation, which lays a foundation for effectively managing organic wastes from different types of crop straws by composting.

Effects of exogenous microbial inoculum on the structure and dynamics of bacterial communities in swine carcass composting

Composting is a widely accepted method for the disposal of deceased livestock. It is a biological self-heating process during which animal carcasses are converted to fertilizer products. Additional inoculants can facilitate the composting progress. This study investigated how the addition of microbial inoculants could improve the composting effectiveness and could change the structure and dynamics of bacterial communities in the carcass composting process. Four strains of Bacillus were inoculated into the swine carcass composting piles. The groups with the additional inoculants showed a higher temperature in the thermophilic phase and higher germination indices in the composted products. The sequencing results showed that the dominant phyla were Proteobacteria, Firmicutes, and Actinobacteria, and the dominant classified genera were Brevibacterium and Bacillus. Canonical correlation analysis showed that temperature and moisture exerted a stronger influence on the bacterial community diversity. The interaction network of dominant genera and the abundance variation of the bacterial community demonstrated that the inoculated bacterial agent changed the structure of bacterial communities and enriched the diversity of the species due to antagonism and symbiosis among the dominant bacterial communities.

How does manganese dioxide affect humus formation during bio-composting of chicken manure and corn straw?

The aim of this study is to reveal the roles of MnO₂ in Maillard reaction of biotic composting, and to identify its effectiveness in promoting humus formation. Corn straw (CS) and chicken manure (CM) have been chosen to be composted. During CS composting, addition of MnO₂ rapidly reduced reducing sugars concentration (decreased by 84.0%) in 5 days and significantly improved humus production by 38.7% compared with treatment without MnO₂. Whereas in CM composting, the promoting effect of MnO₂ on humus formation was relatively weak by comparing with the treatment group of CS. Additionally, the presence of MnO₂ has reshaped bacteria community, which might be the reason of MnO₂ stimulated bacteria to utilize organic matter during CM composting. Therefore, the structural equation modeling has confirmed that MnO₂ mainly performed as chemical catalyst to promote humus formation during CS composting. Besides catalyst, MnO₂ also played as a bioactive activator in CM composting.

Roles of bacterial community in the transformation of dissolved organic matter for the stability and safety of material during sludge composting

This study was conducted to assess the roles of bacterial community in the dissolved organic matters (DOM) transformation during sludge composting. The relationship among the bacterial community, organic acids, diverse components of DOM as well as the indexes of the phytotoxin level and stability of materials was analyzed by regression and redundancy analysis. The results showed that there were significant correlations between the parameters for evaluating compost phytotoxicity and maturity including GI, C/N, SUVA₂₅₄, SUVA₂₈₀, E_253/203, and A_240-400, which led to a new index (PC1) by principal component analysis. PC1 was significantly affected by four components of DOM, acetic and tartaric acids that were correlated with the bacteria community shift, especially seven key bacteria. Based on structural equation modeling, the key bacteria with the ability to degrade tartaric acid exerted more important roles in regulating the transformation of DOM components, which was helpful for the stability and safety of compost.

Succession of bacteria diversity in the poultry manure composted mixed with clay: Studies upon its dynamics and associations with physicochemical and gaseous parameters

In this study, the bacterial community succession and variations were investigated in poultry manure (PM) compost by the using high-throughput sequencing in six different concentration of clay [at 0% (T1), 2% (T2), 4% (T3), 6% (T4), 8% (T5) and 10% (T6) on PM dry weight basis] applied compost. The results indicated that dominant phylum were Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes, while Bacillus, Paenibacillus, Virgibacillus, Oceanobacillus and Clostridium were the dominant genera in all the treatments. Correlation analyses provided useful tools for insight into the bacterial interactions with environmental factors and also extension of the compost maturation and resistance of bacteria. During the course of study, the diversity of bacteria similar but relative abundance variable in each treatments. However, the average and the normalized (to bacterial RAs or copies of sequences) both remained greater in higher dosage of clay applied treatments. Finally, the RAs of various bacterial community composition was affected in PM compost by the clay application.

Succession of organics metabolic function of bacterial community in swine manure composting

Organics metabolic function of bacterial communities was evaluated in 60 days composting of swine manure and pumice by using MiSeq sequencing, PICRUSt and Biolog tools. The diversity of bacterial communities significantly decreased during the first 10 days, and gradually increased in the cooling and curing phase. The PICRUSt and Biolog analysis indicated that carbohydrate, lipid and amino acids metabolisms were relatively higher in the thermophilic phases. Xenobiotics biodegradation and metabolism, lipid metabolism, terpenoids and polyketides and biosynthesis of other secondary metabolites were mainly detected in the curing phases. Canonical correspondence analysis (CCA) indicated that the succession of bacterial community and organics utilization characteristics were highly affected by the temperature, moisture and oxidation reduction potential (ORP) in the swine composting system.

Effect of the addition of exogenous precursors on humic substance formation during composting

The aim of this work was to explore the effect of the addition of exogenous precursors on humic substance (HS) formation during composting. HS formation is a complex biochemical process that occurs during composting. In addition, HS precursors and bacterial communities were recognized as the key factors that affect HS formation. The addition of exogenous precursors can promote the humification process during composting, but few studies have explored the potential relationships between the proportion of additional exogenous precursors, the bacterial community and HS formation. Jointly adding benzoic acid (BA) and soybean residue after extracted oil (SR) treatment can promote HS formation, especially humic acid formation. In addition, the increase in the proportion of exogenous precursors added could strengthen the relationship among different precursors, thereby changing the bacterial community composition and further promoting the humification process during composting. In addition, a structural equation model (SEM) showed that precursors were the key factors to regulate HS formation and certain bacteria as the direct drivers to affect HS formation. This model provides more possibilities to regulate HS formation during composting and enhances its potential applicability under real conditions.

Characterization of bacterial community structure during in-vessel composting of agricultural waste by 16S rRNA sequencing

Bacterial diversity during in-vessel (rotary drum) composting of agricultural waste was characterized using NGS-based 16S rRNA sequencing for microbial identification. The activity of the bacteria was observed to vary with the composting materials and degradation pattern. Taxonomic hits distribution at domain level revealed that 89.5% sequences belonged to bacteria, 9% to eukaryota followed by 1.4% archaea during drum composting. The lowest common ancestor (LCA) classification plot showed the high abundance of the phylum proteobacteria followed by actinobacteria in compost sample. Taxonomic hit distribution at family level showed that compost sample was enriched with Thermomonosporaceae. Thermomonospora curvata is an aerobic, cellulolytic, thermophilic Gram-positive bacterium which produces a number of industrially important compounds, i.e., cellulase, alpha-amylase, and polygalacturonate lyase. Thermomonospora family of bacteria play a major role in organic matter degradation during composting. Hence, in the present study species such as Actinomadura vinacea, Thermomonospora curvata, Actinoallomurus spadix, Actinomadura rubrobrunea. T. curvata were identified from the compost mixture, which can utilize many organic compounds such as cellulose starch, xylose or pectin. The other biggest group in compost sample was Actinobacteria with Thermoleophilum album as the most abundant species followed by Collinsella aerofaciens. The compost was stabilized with higher volatile solids reduction, lower OUR (4.49 mg/g VS/day) and CO₂ (2.28 mg/g VS/day) values at the end of 20 days. The final compost was observed with 2.31% of TKN and 4.3% of phosphorus. Finally the results indicate that degradation of agricultural waste using drum composter was dominated by Bacilli, γ, β-proteobacteria, and actinobacteria.

Bacterial community succession during pig manure and wheat straw aerobic composting covered with a semi-permeable membrane under slight positive pressure

Bacteria play an important role in organic matter degradation and maturity during aerobic composting. This study analyzed composting with or without a membrane cover in laboratory-scale aerobic composting reactor systems. 16S rRNA gene analysis was used to study the bacterial community succession during composting. The richness of the bacterial community decreased and the diversity increased after covering with a semi-permeable membrane and applying a slight positive pressure. Principal components analysis based on operational taxonomic units could distinguish the main composting phases. Linear Discriminant Analysis Effect Size analysis indicated that covering with a semi-permeable membrane reduced the relative abundance of anaerobic Clostridiales and pathogenic Pseudomonas and increased the abundance of Cellvibrionales. In membrane-covered aerobic composting systems, the relative abundance of some bacteria could be affected, especially anaerobic bacteria. Covering could effectively promote fermentation, reduce emissions and ensure organic fertilizer quality.

Response of humic acid formation to elevated nitrate during chicken manure composting

Nitrate can stimulate microbes to degrade aromatic compounds, whereas humic acid (HA) as a high molecular weight aromatic compound, its formation may be affected by elevated nitrate during composting. Therefore, this study is conducted to determine the effect of elevated nitrate on HA formation. Five tests were executed by adding different nitrate concentrations to chicken manure composting. Results demonstrate that the concentration of HA in treatment group is significantly decreased compared with control group (p < 0.05), especially in the highest nitrate concentration group. RDA indicates that the microbes associated with HA and environmental parameters are influenced by elevated nitrate. Furthermore, structural equation model reveals that elevated nitrate reduces HA formation by mediating microbes directly, or by affecting ammonia and pH as the indirect drivers to regulate microbial community structure.

Effects of copper on the composition and diversity of microbial communities in laboratory-scale swine manure composting

This study investigated the effects of adding copper at 3 treatment levels (0 (control: CK), 200 (low: L), and 2000 (high: H) mg·kg−1 treatments) on the bacterial communities during swine manure composting. The abundances of the bacteria were determined by quantitative PCR and their compositions were evaluated by high-throughput sequencing. The results showed that the abundance of bacteria was inhibited by the H treatment during days 7–35, and principal component analysis clearly separated the H treatment from the CK and L treatments. Actinobacteria, Firmicutes, and Proteobacteria were the dominant bacterial taxa, and a high copper concentration decreased the abundances of bacteria that degrade cellulose and lignin (e.g., class Bacilli and genus Truepera), especially in the mesophilic and thermophilic phases. Moreover, network analysis showed that copper might alter the co-occurrence patterns of bacterial communities by changing the properties of the networks and the keystone taxa, and increase the competition by increasing negative associations between bacteria during composting. Temperature, water-soluble carbohydrates, and copper significantly affected the variations in the bacterial community according to redundancy analysis. The copper content mainly contributed to the bacterial community in the thermophilic and cooling phases, where it had positive relationships with potentially pathogenic bacteria (e.g., Corynebacterium_1 and Acinetobacter).

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

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

Changes in structure and function of fungal community in cow manure composting

In this study, dynamic changes in fungal communities, trophic modes and effect factors in 60 days composting of cow manure were analyzed by using high throughput sequencing, FUNGuild and Biolog FF MicroPlate, respectively. Orpinomyces (relative abundance >10.85%) predominated in feedstock, and Mycothermus became the dominating genus (relative abundance >75%) during the active phase. Aerobic composting treatment had a significant effect on fungal trophic modes with pathogenic fungi fading away and wood saprotrophs increasing over composting time. Fungal communities had the higher carbon sources utilization capabilities at the thermophilic phase and mature phase than those in the other periods. Oxidation reduction potential (ORP) significantly increased from -180 to 180 mV during the treatment. Redundancy analysis showed that the succession of fungal community during composting had a significant association with ORP (p < .05). This indicated that aerobic composting treatment not only influenced fungal community structure, but also changed fungal trophic modes and metabolic characteristics.

Biostimulation of nutrient additions on indigenous microbial community at the stage of nitrogen limitations during composting

Microorganisms can play a crucial role in the efficiency for composting, which are essential for converting the organic wastes into a well-stabilized, value added product. However, the activity of most of the key functional microorganisms were inhibited due to the limited special nutrient substances or other physiochemical factors during composting, which further affected the quality of compost. The study was conducted to investigate the effects of enriched ammonium (NH₄⁺-N) and organic nitrogen (Org-N) on indigenous microbial community and whether nitrogen (N) nutrient additions could modify the special species during composting. The results showed that the abundance and structure of bacterial community had distinctly diverse responses to different N nutritional treatments (no nutrient addition, NH₄⁺-N addition, and Org-N addition). The addition of N sources enhanced the abundance of corresponding uncultured indigenous species negatively related to the factor of NH₄⁺ and Org-N in redundancy analysis (RDA) during composting but the effect of NH₄⁺ was more significant than Org-N. Nonmetric multidimensional scaling ordination (NMDS) demonstrated that both the two N additions changed bacterial community but had different duration for affecting bacterial composition. Conclusively, an optimized method for regulating the key stains with special biological capacity is proposed by controlling the single limiting-nutrient factor sharply decreasing at one of composting stages and negatively related to the key species in RDA.

Succession and diversity of microorganisms and their association with physicochemical properties during green waste thermophilic composting

A comprehensive characterization of the bacterial diversity associated to thermophilic stages of green waste composting was achieved. In this study, eight different treatments (T1-T8) and three replicated lab-scale green waste composting were carried out to compare the effect of the cellulase (i.e. 0, 2%), microbial inoculum (i.e. 0, 2 and 4%) and particle size (i.e. 2 and 5 mm) on bacterial community structure. Physicochemical properties and bacterial communities of T1-T8 composts were observed, and the bacterial structure and diversity were examined by high-throughput sequencing via a MiSeq platform. The results showed that the most abundant phyla among the treatments were the Firmicutes, Chloroflexi and Proteobacteria. The shannon index and non-metric multidimensional scaling (NMDS) showed higher bacterial abundance and diversity at the metaphase of composting. Comparing with 5-mm treatments, particle size of 2-mm had a richer diversity of bacterial communities. The addition of cellulase and a microbial inoculum could promote the fermentation temperature, reduce the compost pH and C/N ratio and result in higher GI index. The humic substance (HS) and humic acid (HA) contents for 2-mm particle size treatments were higher than those of 5-mm treatments. Canonical correspondence analysis suggested that differences in bacterial abundance and diversity significantly correlated with HA, E₄/E₆ and temperature, and the relationship between bacterial diversity and environmental parameters was affected by composting stages. Based on these results, the application of cellulase to promote green waste composting was feasible, and particle size was identified as a potential control of composting physicochemical properties and bacterial diversity.

Functional characteristics and influence factors of microbial community in sewage sludge composting with inorganic bulking agent

The metabolic function of microbial community dominated organics and nutrients transformation in aerobic composting process. In this study, the metabolic characteristics of bacterial and fungal communities were evaluated in 60 days composting of sludge and pumice by using FUNGuild and PICRUSt, respectively. The results showed that microbial community structure and metabolic characteristics were distinctively different at four composting periods. Bacterial genes related to carbohydrate metabolisms decreased during the first 30 days, but bacterial sequences associated with oxidative phosphorylation and fatty acids synthesis were enhanced in curing phase. Most of fungal animal pathogen and plant pathogen disappeared after treatment, and the abundance of saprotroph fungi increased from 44.3% to 97.8%. Oxidation reduction potential (ORP) significantly increased from -28 to 175 mV through incubation. RDA analysis showed that ORP was a crucial factor on the succession of both bacterial and fungal communities in sludge composting system.

Available forms of nutrients and heavy metals control the distribution of microbial phospholipid fatty acids in sediments of the Three Gorges Reservoir, China

The construction of the Three Gorges Reservoir (TGR) as well as the development of local industry and agriculture not only had tremendous impacts on the environment but also affected human health. Although water, soil, and air in the TGR have been well studied for environmental risk assessment, very little information is available on benthic sediments and microorganisms. In this study, sedimentary samples were collected along the main stream of the TGR to examine microbial phospholipid fatty acids (PLFA) and relevant variables (e.g., nutrients and heavy metals) after the full operation of the TGR. The results showed that there were prominent trends (increase or decrease) of sedimentary PLFAs and properties from downstream to upstream. Bacteria-specific PLFA decreased toward the dam, while fungi-specific PLFA did not show any significant trend. The PLFA ratio of fungi to bacteria (F/B) increased along the mainstream. The total PLFA concentration, which represents the microbial biomass, decreased significantly toward the dam. Upstream and downstream sampling points were clearly distinguished by PLFA ordination in the redundancy analysis (RDA). That finding showed microbial PLFAs to have an obvious distribution pattern (increase or decrease) in the TGR. The PLFA distribution was markedly controlled by nutrients and heavy metals, but nutrients were more important. Moreover, among nutrients, Bio-P, NH₄⁺-N, NO₃^--N, and DOC were more important than TP, TN, TOC, and pH in controlling PLFA distribution. For heavy metals, Tl, V, Mo, and Ni were more important than Zn, Cu, Cd, and Pb. These findings suggested that Tl, V, Mo, and Ni should not be ignored to guard against their pollution in the TGR, and we should pay attention to them and make them our first priority. This study highlighted that the construction of the TGR changed riverine environments and altered microbial communities in sediments by affecting sedimentary properties. It is a reminder that the microbial ecology of sediment as an indicator should be considered in assessing the eco-risk of the TGR.

Role of biochar as an additive in organic waste composting

The use of biochar in organic waste composting has attracted interest in the last decade due to the environmental and agronomical benefits obtained during the process. Biochar presents favourable physicochemical properties, such as large porosity, surface area and high cation exchange capacity, enabling interaction with major nutrient cycles and favouring microbial growth in the composting pile. The enhanced environmental conditions can promote a change in the microbial communities that can affect important microbially mediated biogeochemical cycles: organic matter degradation and humification, nitrification, denitrification and methanogenesis. The main benefits of the use of biochar in composting are reviewed in this article, with special attention to those related to the process performance, compost microbiology, organic matter degradation and humification, reduction of N losses and greenhouse gas emissions and fate of heavy metals.

Response of humic-reducing microorganisms to the redox properties of humic substance during composting

Humic substance (HS) could be utilized by humus-reducing microorganisms (HRMs) as the terminal acceptors. Meanwhile, the reduction of HS can support the microbial growth. This process would greatly affect the redox conversion of inorganic and organic pollutants. However, whether the redox properties of HS lined with HRMs community during composting still remain unclear. This study aimed to assess the relationships between the redox capability of HS [i.e. humic acids (HA) and fulvic acids (FA)] and HRMs during composting. The results showed that the changing patterns of electron accepting capacity and electron donating capacity of HS were diverse during seven composting. Electron transfer capacities (ETC) of HA was significantly correlated with the functional groups (i.e. alkyl C, O-alkyl C, aryl C, carboxylic C, aromatic C), aromaticity and molecular weight of HA. Aromatic C, phenols, aryl C, carboxylic C, aromaticity and molecular weight of HS were the main structuralfeatures associated with the ETC of FA. Ten key genera of HRMs were found significantly determine these redox-active functional groups of HS during composting, thus influencing the ETC of HS in composts. In addition, a regulating method was suggested to enhance the ETC of HS during composting based on the relationships between the key HRMs and redox-active functional groups as well as environmental variables.

Effects of biochar amendment on bacterial and fungal diversity for co-composting of gelatin industry sludge mixed with organic fraction of municipal solid waste

The aim of the study was to evaluate the bacterial and fungal diversities of 18contrastivecomposts applied with 17 different sources mad biochars applied treatments using 16S rRNA and 18S rDNA technology, while T-1 used as a control. The results showed that bacterial species of the phyla Actinobacteria, Proteobacteria and Chloroflexi, and fungi of the phylum Ascomycota and Basidiomycota were pre-dominant among the all treatments. The bacterial genus Subgroup_6_norank, Nocardioides, Pseudonocardia, Sphingomonas, Solirubrobacter and RB41_norank are first time identified in composting ecosystem. In addition, the fungal genus Ascomycota_unclassified, Aspergillus, Penicillium, Pleosporales_unclassified and Herpotrichlellacease_unclassified ubiquitous among the all compost. The Shannon and refraction-curve biodiversity indices showed a clear heterogeneity among all the treatments, which could be due to isolation of new genera in this system. Finally, the principal component analysis of the relative number of sequences also confirmed that bacterial and fungal population indiscriminate in different sources mad biochar applied treatments.

Bio-Heat Is a Key Environmental Driver Shaping the Microbial Community of Medium-Temperature Daqu

"Daqu" is a saccharifying and fermenting agent commonly used in the traditional solid-state fermentation industry (e.g., baijiu and vinegar). The patterns of microbial community succession and flavor formation are highly similar among batches, yet the mechanisms promoting temporal succession in the Daqu microbial ecology remain unclear. Here, we first correlated temporal profiles of microbial community succession with environmental variables (temperature, moisture, and titratable acidity) in medium temperature Daqu (MT-Daqu) throughout fermentation. Temperature dynamics significantly correlated (P < 0.05) with the quick succession of MT-Daqu microbiota in the first 12 d of fermentation, while the community structure was relatively stable after 12 d. Then, we explored the effect of temperature on the MT-Daqu community assembly. In the first 4 d of fermentation, the rapid propagation of most bacterial taxa and several fungal taxa, including Candida, Wickerhamomyces, and unclassified Dipodascaceae and Saccharomycetales species, significantly increased MT-Daqu temperature to 55°C. Subsequently, sustained bio-heat generated by microbial metabolism (53 to 56°C) within MT-Daqu inhibited the growth of most microbes from day 4 to day 12, while thermotolerant taxa, including Bacillus, unclassified Streptophyta, Weissella, Thermoactinomyces, Thermoascus, and Thermomyces survived or kept on growing. Furthermore, temperature as a major driving force on the shaping of MT-Daqu microbiota was validated. Lowering the fermentation temperature by placing the MT-Daqu in a 37°C incubator resulted in decreased relative abundances of thermotolerant taxa, including Bacillus, Thermoactinomyces, and Thermoascus, in the MT-Daqu microbiota. This study revealed that bio-heat functioned as a primary endogenous driver promoting the formation of functional MT-Daqu microbiota.IMPORTANCE Humans have mastered the Daqu preparation technique of cultivating functional microbiota on starchy grains over thousands of years, and it is well known that the metabolic activity of these microbes is key to the flavor production of Chinese baijiu. The pattern of microbial community succession and flavor formation remains highly similar between batches, yet mechanistic insight into these patterns and into microbial population fidelity to specific environmental conditions remains unclear. Our study revealed that bio-heat was generated within Daqu bricks in the first 4 d of fermentation, concomitant with rapid microbial propagation and metabolism. The sustained bio-heat may then function as a major endogenous driving force promoting the formation of the MT-Daqu microbiota from day 4 to day 12. The bio-heat-driven growth of thermotolerant microorganisms might contribute to the formation of flavor metabolites. This study provides useful information for the temperature-based modulation of microbiota function during the fermentation of Daqu.

Effect of Phanerochaete chrysosporium inoculation on bacterial community and metal stabilization in lead-contaminated agricultural waste composting

The effects of Phanerochaete chrysosporium inoculation on bacterial community and lead (Pb) stabilization in composting of Pb-contaminated agricultural waste were studied. It was found that the bioavailable Pb was transformed to stable Pb after composting with inoculum of P. chrysosporium. Pearson correlation analysis revealed that total organic carbon (TOC) and carbon/nitrogen (C/N) ratio significantly (P<0.05) influenced the distribution of Pb fractions. The richness and diversity of bacterial community were reduced under Pb stress and increased after inoculation with P. chrysosporium. Redundancy analysis indicated that C/N ratio, total organic matter, temperature and soluble-exchangeable Pb were the significant parameters to affect the bacterial community structure, solely explained 14.7%, 11.1%, 10.4% and 8.3% of the variation in bacterial community composition, respectively. In addition, the main bacterial species, being related to organic matter degradation and Pb stabilization, were found. These findings will provide useful information for composting of heavy metal-contaminated organic wastes.