Responses of microbial carbon metabolism and function diversity induced by complex fungal enzymes in lignocellulosic waste composting

Control of nitrogen and odor emissions during chicken manure composting with a carbon-based microbial inoculant and a biotrickling filter

Although aerobic composting is usually utilized in livestock manure disposal, the emission of odorous gases from compost not only induces harm to the human body and the environment, but also causes loss of nitrogen, sulfur, and other essential elements, resulting in a decline in product quality. The impact of biotrickling filter (BTF) and insertion of carbon-based microbial agent (CBMA) on compost maturation, odor emissions, and microbial population during the chicken manure composting were assessed in the current experiment. Compared with the CK group, CBMA addition accelerated the increase in pile temperature (EG group reached maximum temperature 10 days earlier than CK group), increased compost maturation (GI showed the highest increase of 41.3% on day 14 in EG group), resulted in 36.59% and 14.60% increase in NO3--N content and the total nitrogen retention preservation rate after composting. The deodorization effect of biotrickling filter was stable, and the removal rates of NH3, H2S, and TVOCs reached more than 90%, 96%, and 56%, respectively. Furthermore, microbial sequencing showed that CBMA effectively changed the microbial community in compost, protected the ammonia-oxidizing microorganisms, and strengthened the nitrification of the compost. In addition, the nitrifying and denitrifying bacteria were more active in the cooling period than they were in the thermophilic period. Moreover, the abundance of denitrification genes containing nirS, nirK, and nosZ in EG group was lower than that in CK group. Thus, a large amount of nitrogen was retained under the combined drive of BTF and CBMA during composting. This study made significant contributions to our understanding of how to compost livestock manure while reducing releases of odors and raising compost quality.

Behind the plant-bacteria system: The role of zucchini and its secondary metabolite in shaping functional microbial diversity in MCPA-contaminated soil

MCPA (2-methyl-4-chlorophenoxyacetic acid) contamination is an emerging problem, especially in water reservoirs. The early removal of MCPA residues from soil can prevent its spread to untreated areas. It has been found that the growth of cucurbits and the addition of selected plant secondary metabolites (PSMs) can stimulate MCPA removal from soil. However, the effect of these treatments on soil microbial activity remains poorly studied. Hence, the aim of this research was to evaluate the influence of zucchini (C. pepo cv Atena Polka) and its characteristic PSM: syringic acid (SA) on the functional diversity of soil microorganisms in MCPA-contaminated soil using Biolog® EcoPlates™. It also examines soil physicochemical properties and the growth parameters of zucchini. Microbial activity was enhanced by both zucchini cultivation and SA. All unplanted variants showed significantly lower microbial activity (average well color development, AWCD, ranging from 0.35 to 0.51) than the planted ones (AWCD ranging from 0.77 to 1.16). SA also stimulated microbial activity in the soil: a positive effect was observed from the beginning of the experiment in the unplanted variants, but over a longer time span in the planted variants. SA ameliorated the toxic effect of MCPA on the studied plants, especially in terms of photosynthetic pigment production: the MCPA+SA group demonstrated significantly increased chlorophyll content (401 ± 4.83 μg/g), compared to the MCPA group without SA (338 ± 50.1 μg/g). Our findings demonstrated that zucchini and the amendment of soils with SA, the characteristic PSM of cucurbits, can shape functional diversity in MCPA-contaminated soil. The changes of soil properties caused by the application of both compounds can trigger changes in functional diversity. Hence, both SA and MCPA exert indirect and direct effects on soil microbial activity.

Bacterial Community Drives the Carbon Source Degradation during the Composting of Cinnamomum camphora Leaf Industrial Extracted Residues

The increasing production of industrial aromatic plant residues (IAPRs) are potentially environmental risky, and composting is a promising solution to resolve the coming IAPR problems. Carbon source degradation is a basic but important field in compost research; however, we still lack a clear understanding of carbon source degradation and the corresponding relationship to microbial community variation during IAPR composting, which hampers the improvement of IAPR composting efficiency and the promotion of this technology. In this study, samples were chosen on the first day, the 10th day, the 20th day, and the last day during the composting of Cinnamomum camphora leaf IAPRs, and the microbial community composition, main carbon source composition, and several enzyme activities were measured accordingly. The results showed that during composting, the hemicellulose had the highest reduction (200 g kg−1), followed by cellulose (143 g kg−1), lignin (15.5 g kg−1), starch (5.48 g kg−1), and soluble sugar (0.56 g kg−1), which supported that hemicellulose and cellulose were the main carbon source to microbes during composting. The relative abundance of the main bacterial phylum Firmicute decreased from 85.1% to 40.3% while Actinobactreia increased from 14.4% to 36.7%, and the relative abundance of main fungal class Eurotiomycetes decreased from 60.9% to 19.6% while Sordariomycetes increased from 16.9% to 69.7%. Though principal coordinates analysis found that both bacterial and fungal community composition significantly varied during composting (p < 0.05), structure equation modeling (SEM) supported that bacterial composition rather than fungal counterpart was more responsible for the change in carbon source composition, as the standard total effects offered by bacterial composition (−0.768) was about five times the fungal composition (−0.144). Enzyme2 (comprised of xylanase, laccase, cellulase and manganese peroxidase) provided −0.801 standard total effects to carbon source composition, while Enzyme1 (comprised of lignin peroxidase and polyphenol oxidase) had only 0.172. Furthermore, xylanase and laccase were the only two enzymes appeared in co-occurrence network, clustered with nearly all the carbon sources concerned (except starch) in module-II. Xylanase, hemicellulose, and cellulose were linked to higher numbers of OTUs, more than laccase and other carbon sources. In addition, there were 11 BOTUs but only 1 FOTUs directly interacted to xylanase, hemicellulose, and cellulose simultaneously, three of them were Limnochordaceae and two were Savagea, which highlighted the potential core function in lignocellulose degradation provided by bacterial members, especially Limnochordaceae and Savagea. Thus, the results supported that during composting of Cinnamomum camphora leaf IAPRs, the degradation of dominate carbon sources, hemicellulose and cellulose, was mainly driven by bacterial community rather than fungal community. In addition, the bacterial originated xylanase and laccase played potentially core roles in the functional modules. This research clearly investigated the microbial dynamics of carbon source degradation during the composting of Cinnamomum camphora leaf IAPRs, and offers valuable information about and new insight into future IAPRs waste treatment.

Construction and carbon source optimization of a microbial-plant coupled reactor for treating acid mine drainage

Acid mine drainage (AMD) is recognized as one of the most serious contamination sources in the nonferrous metal mining industry. In this study, aerobic strains VCZ02 and VCZ09, which were identified as Leclercia adecarboxylata and Klebsiella aerogenes, were screened from 11 strains of copper-zinc-resistant bacteria in the soil of the Dexing copper mine with Cu²⁺/Zn²⁺ removal rates of 46.32%/41.03% and 57.96%/67.05%, respectively. The composition of extracellular polymers plays an important role in the removal of heavy metals by these two strains. A mixed community consisting of VCZ02 and VCZ09 was coupled with Sagittaria trifolia L.var.sinensis (Sims) Mak to construct a microbial-plant coupled reactor to remediate AMD. Under the optimal condition of sodium acetate as carbon source, the pH of AMD increased from less than 5 to above 6.5, showing Cu²⁺/Zn²⁺ removal rates of 70-80% and above 30%, respectively. SEM-EDS results showed that VZC02 and VZC09 in the coupled reactor also helped with resisting the toxicity of heavy metals to plants by forming biofilms on the root surface and increasing the content of heavy metals on the surface of roots, thus improving the treatment effect of plants. This study provides a theoretical basis for the bioremediation of AMD and its application.

The microbial metabolic activity on carbohydrates and polymers impact the biodegradability of landfilled solid waste

Biological waste degradation is the main driving factor for landfill emissions. In a 2-year laboratory experiment simulating different landfill in-situ aeration scenarios, the microbial degradation of solid waste under different oxygen conditions (treatments) was investigated. Nine landfill simulation reactors were operated in triplicates under three distinct treatments. Three were kept anaerobic, three were aerated for 706 days after an initial anaerobic phase and three were aerated for 244 days in between two anaerobic phases. In total, 36 solid and 36 leachate samples were taken. Biolog® EcoPlates™ were used to assess the functional diversity of the microbial community. It was possible to directly relate the functional diversity to the biodegradability of MSW (municipal solid waste), measured as RI₄ (respiration index after 4 days). The differences between the treatments in RI₄ as well as in carbon and polymer degradation potential were small. Initially, a RI₄ of about 6.5 to 8 mg O₂ kg^-1 DW was reduced to less than 1 mg O₂ kg^-1 DW within 114 days of treatment. After the termination of aeration, an increase 3 mg O₂ kg^-1 DW was observed. By calculating the integral of the Gompertz equation based on spline interpolation of the Biolog® EcoPlates™ results after 96 h two substrate groups mainly contributing to the biodegradability were identified: carbohydrates and polymers. The microbial activity of the respective microbial consortium could thus be related to the biodegradability with a multilinear regression model.

Bamboo charcoal enhances cellulase and urease activities during chicken manure composting: Roles of the bacterial community and metabolic functions

Microbial enzymes are crucial for material biotransformation during the composting process. In this study, we investigated the effects of adding bamboo charcoal (BC) (i.e., at 5%, 10%, and 20% corresponding to BC5, BC10, and BC20, respectively) on the enzyme activity levels during chicken manure composting. The results showed that BC10 could increase the cellulose and urease activities by 56% and 96%, respectively. The bacterial community structure in BC10 differed from those in the other treatments, and Luteivirga, Lactobacillus, Paenalcaligenes, Ulvibacter, Bacillus, Facklamia, Pelagibacterium, Sporosarcina, Cellvibrio, and Corynebacterium had the most important roles in composting. Compared with other treatments, BC10 significantly enhanced the average rates of degradation of carbohydrates (D-xylose (40%) and α-D-lactose (44%)) and amino acids (L-arginine (16%), L-asparagine (14%), and L-threonine (52%)). We also explored the associations among the bacterial community and their metabolic functions with the changes in the activities of enzymes. Network analysis demonstrated that BC10 altered the co-occurrence patterns of the bacterial communities, where Ulvibacter and class Bacilli were the keystone bacterial taxa with high capacities for degrading carbon source, and they were related to increases in the activities of cellulase and urease, respectively. The results obtained in this study may help to further enhance the efficiency of composting.

Effects of multi-phase inoculation on the fungal community related with the improvement of medicinal herbal residues composting

Composting has become the most important way to recycle medicinal herbal residues (MHRs). The traditional composting method, adding a microbial agent at one time, has been greatly limited due to its low composting efficiency, mutual influence of microbial agents, and unstable compost products. This study was conducted to assess the effect of multi-phase inoculation on the lignocellulose degradation, enzyme activities, and fungal community during MHRs composting. The results showed that multi-phase inoculation treatment had the highest thermophilic temperature (68.2 °C) and germination index (102.68%), significantly improved available phosphorus content, humic acid, and humic substances concentration, accelerated the degradation of cellulose and lignin, and increased the activities of cellulase in the mature phase, xylanase, manganese peroxidase, and utilization of phenolic compounds. Furthermore, the non-metric multi-dimensional scaling showed that the composting process and inoculation significantly influenced fungal community composition. In multi-phase inoculation treatment, Thermomyces in mesophilic, thermophilic, and mature phase, unclassified_Sordariales, and Coprinopsis in mature phase were the dominant genus that might be the main functional groups to degrade lignocellulose and improve the MHRs composting process.

Quality and yield of Pseudostellaria heterophylla treated with GGBS as pH adjuster against the toxicity of Cd and Cu

The contamination of Cd and Cu in soil is a great threat to medicinal plant. Ground granulated blast furnace slag (GGBS) is a potential soil pH adjuster to reduce metal toxicity. However, how GGBS affects the quality and yield of herbal plants under the stress of Cd and Cu is not clear. This study aims to investigate the quality and yield of a medicinal plant (Pseudostellaria heterophylla) responding to GGBS treatment in Cd and Cu contaminated soil. GGBS with three mass percentages (0%, 3%, 5%) was added into contaminated lateritic soils for planting. Each condition had 21 replicated seedlings. The concentrations of Cd and Cu in plant, amounts of active ingredients (polysaccarides and saponins) in medicinal organ, and tuber properties were measured after harvest. The results showed that under 3% and 5% GGBS treatments, Cd and Cu accumulations in all plant organs (leaf, stem, root and tuber) were reduced by 69.4-86.0% and 10.3-30.1%, respectively. They were below the permissible limits (World Health Organization, WHO). Even though the concentrations of active ingredients in P. heterophylla tuber decreased by up to 35.8%, they still met Hong Kong Chinese Materia Medica standard. Besides, the biomass of root tuber increased by 9.8% and 46%, due to 3% and 5% GGBS treatments, respectively. The recommended 5% GGBS treatment in practice can balance the reduction of active ingredients and the increase of plant yield when minimizing Cd and Cu accumulation in tuber.

Effects of urease inhibitors on enzymatic activities and fungal communities during the biosolids composting

This study evaluated the influences of urease inhibitors (UIs) on nitrogen conversion, enzyme activities, and fungal communities during aerobic composting. Results showed that UI addition reduced NH₃ emissions by 22.2% and 21.5% and increased the total nitrogen (TN) content by 9.7% and 14.3% for the U1 (0.5% UI of the dry weight of the mixture) and U2 (1% UI of the dry weight of the mixture) treatments, respectively. The addition of UI inhibited the enzyme activity during thermophilic stage while increased enzyme activity during the cool and maturity stages. Ascomycota, Basidiomycota and unclassified fungi were the main phyla, and Ascomycota increased significantly during the maturity period. Network analysis showed that Aspergillus, Penicillium, Trichoderma, Talaromyces, Peseudeurotium, and Exophiala were the main “connecting” genera. The redundancy analysis (RDA) showed that the fungal community was mainly influenced by temperature, DOC, pH, and urease. The results suggested that UI was an effective additive for nitrogen conservation and the increase of enzyme activity reduce nitrogen loss and promote enzyme activity during biosolids composting.

Adding UI was effective for nitrogen conservation and the increase of enzyme activity during biosolid composting.

Assessing the Microbial Communities in Four Different Daqus by Using PCR-DGGE, PLFA, and Biolog Analyses

Daqu made from raw wheat, barley or pea is used as an inoculum for the fermentation of Chinese Baijiu. In this study, the microbial communities of four different types of Daqus (sauce-flavor Wuling Daqu, sauce and strong-flavor Baisha Daqu, strong-flavor Deshan Daqu, and light-flavor Niulanshan Daqu) were analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE), phospholipid fatty acid (PLFA) analysis, and Biolog EcoPlates analysis (Biolog). Clear differences were seen between the microbial communities of the four Daqus. PCR-DGGE showed differences in the number and brightness of bands between the Daqus, indicating the presence of unique bacterial species in Deshan Daqu, Wuling Daqu, and Niulanshan Daqu. Lactobacillus sanfranciscensis, Bacillus thermoamylovorans, and some unclassified bacteria were unique to Wuling Daqu, Deshan Daqu, and Niulanshan Daqu, respectively. Moreover, some bacterial species were observed in all four Daqus. A total of 26 PLFAs between C12 to C20 were detected from the four Daqus by PLFA analysis. Wuling Daqu had the highest total and fungal biomasses, Baisha Daqu had the highest bacterial biomass, and Niulanshan Daqu had the highest ratio of fungal biomass to bacterial biomass. The Biolog results indicated differences in the carbon source use and mode of the four Daqus, and also demonstrated that each Daqu had varying abilities to utilize different types of carbon sources. The cluster analysis of the three methods showed that the microbial communities of the four Daqus were different. This study also demonstrates the applicability of the three analytical methods in the evaluating of the microbial communities of Daqus.

Nonlinear response of methane release to increased trophic state levels coupled with microbial processes in shallow lakes

Shallow lakes are a crucial source of methane (CH₄), a potent greenhouse gas, to the atmosphere. However, large uncertainties still exist regarding the response of CH₄ emissions to the increasing trophic levels of lakes as well as the underlying mechanisms. Here, we investigate the CH₄ emission flux from lakes with different trophic states in the middle and lower reaches of the Yangtze River basin, China to evaluate the effect of the trophic lake index (TLI) on CH₄ emissions. The mean CH₄ emission fluxes from mesotrophic, eutrophic, middle-eutrophic, and hyper-eutrophic lakes were 0.1, 4.4, 12.0, and 130.4 mg m^-2 h^-1, respectively. Thus, the CH₄ emission flux ranged widely and was positively correlated with the degree of eutrophication. The relative abundance of methanogens with respect to the total population for the mesotrophic, eutrophic, mid-eutrophic, and hyper-eutrophic states was 0.03%, 0.35%, 0.94%, and 1.17%, respectively. The biogeographic-scale pattern of lakes classified as each of these four trophic states indicated that CH₄ emissions could be well-predicted by the NH₄⁺-N concentration in the water column, as both NH₄⁺-N and CH₄ were produced during mineralisation of labile organic matter in lake sediment. In addition, the shift from clear to turbid water, which is an unhealthy evolution for lakes, was associated with a nonlinear increase in the CH₄ emissions from the studied lakes. In particular, the hypereutrophic lakes functioned as CH₄ emission hotspots. Our findings highlight that nutrient levels, as a potential facilitator of CH₄ emissions, should be considered in future research to accurately evaluate the greenhouse gas emissions from shallow lakes.

Degradation of rice straw at low temperature using a novel microbial consortium LTF-27 with efficient ability

In this study, a novel psychrotrophic lignocelluloses degrading microbial consortium LTF-27 was successfully obtained from cold perennial forest soil by successive enrichment culture under facultative anaerobic static conditions. The microbial consortium showed efficient degradation of rice straw, which cellulose, hemicelluloses and lignin lost 71.7%, 65.6% and 12.5% of its weigh, respectively, in 20 days at 15 °C. The predominant liquid products were acetic acid and butyric acid during degrading lignocellulose in anaerobic digestion (AD) process inoculated with the LTF-27. The consortium mainly composed of Parabacteroides, Alcaligenes, Lysinibacillus, Sphingobacterium, and Clostridium, along with some unclassified uncultured bacteria, indicating powerful synergistic interaction in AD process. A multi-species lignocellulolytic enzyme system working cooperatingly on lignocelluolse degradation was revealed by proteomics analysis of cellulose bound fraction of the crude extracellular enzyme, which provides key theoretical base for further exploration and application of LTF-27.

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.

Mycoremediation of petroleum contaminated soils: progress, prospects and perspectives

Mycoremediation, an aspect of bioremediation, has been investigated for some decades. However, there seems to be little progress on its commercial application to petroleum-contaminated soils despite some promising outcomes. In this review, mycoremediation is examined to identify development, limitations and perspectives for its optimal utilization on petroleum-contaminated soils. Mycoremediation agents and substrates that have been used for the treatment of petroleum contaminated soils have been identified, application methods discussed, recent advances highlighted and limitations for its applications accentuated. Possible solutions to the challenges in applying mycoremediation to petroleum-contaminated soils have also been discussed. From this review, we conclude that for optimal utilization of mycoremediation of petroleum-contaminated soils, ideal environmental, edaphic and climatic factors of a typical contaminated site must be incorporated into the approach from first principles. Development of application procedures that can easily translate laboratory results to field applications is also required.

Pilot-scale composting of typical multiple agricultural wastes: Parameter optimization and mechanisms

In this work, pilot-scale (100 kg of mixed wastes each time) composting of typical agricultural wastes, including chicken manure, vegetable leaves and rice husks with a mass ratio of 6:3:1, was studied. Effects of thermal phases and transformation time on performance, including moisture, nutrient, and carbon contents and C/N ratios of compost, were investigated. The optimal parameters were 75 ± 5 °C and 18 h; the compost met the requirements of Chinese National Agricultural Organic Fertilizer Standard (NY525-2012). Mechanisms investigations demonstrated that, Bacillus and Sinibacillus played key roles in degrading high-molecular-weighted organic substances into small-molecular-weighted humic- and fulvic-acid-like matters, resulting in smaller particle size and loose structure of the product; rice husk particles acted as a conditioning agent and remained their originally morphology. The mechanism provided informative guidance for optimizing the process in practical application.

An effective method of utilizing vegetable waste in the form of carriers for Trichoderma strains with phytosanitary properties

It has been assumed that compost from savoy cabbage and rapeseed straw is a good substrate for discrimination of the reproduction potential of Trichoderma strains. This hypothesis was verified based on a two-stage incubation experiment. The prepared mixture was fermented in a bio-reactor for 11 weeks. In the second experiment, the mature compost was inoculated with four strains of Trichoderma and a spore concentration of 10⁴ and 10⁶, and then incubated for four weeks. The biomass of autogenic fungi reached a maximum of 12.5 mg∙g^-1 DM in the cooling phase. The variability in temperature during composting significantly affected NH₃ emission. The pH of mature compost from cabbage wastes, as a result of the elevated NH₃ emission reached the alkaline range. The survival of the Trichoderma fungi introduced into the alkali substrate was a result of strain sensitivity to the high pH of the compost and to the initial inoculum density. The adaptation potential of Trichoderma harzianum to the alkali milieu depended on the pH stabilization of the substrate by this fungi, provided the spore inoculum density was 10⁶. The strains of Trichoderma atroviride responded negatively, regardless of the inoculum density, to the alkaline pH of the substrate and to self-induced changes in the compost pH.