Lignocellulosic crop residue composting by cellulolytic nitrogen-fixing bacteria: A novel tool for environmental sustainability

Maximizing microbial activity and synergistic interaction to boost biofuel production from lignocellulosic biomass

Addressing global environmental challenges and meeting the escalating energy demands stand as two pivotal issues in the current landscape. Lignocellulosic biomass emerges as a promising renewable bio-energy source capable of fulfilling the world's energy requirements on a large scale. One of the most important steps in lowering reliance on fossil fuel and lessening environmental effect is turning lignocellulosic biomass into biofuel. As carbon-neutral substitutes for traditional fuel, biofuel offer a solution to environmental concerns compared to conventional fuel. Effective utilization of lignocellulosic biomass is imperative for sustainable development. Ongoing research focuses on exploring the potential of various microorganisms and their co-interactions to synthesize diverse biofuels from different starting materials, including lignocellulosic biomass. Co-culture techniques demonstrate resilience to nutrient scarcity and environmental fluctuations. By utilising a variety of carbon sources, microbes can enhance their adaptability to environmental stressors and potentially increase productivity through their symbiotic interactions. Furthermore, compared to single organism involvement, co-interactions allow faster execution of multistep processes. Lignocellulosic biomass serves as a primary substrate for pre-treatment, fermentation, and enzymatic hydrolysis processes. This review primarily delves into the pretreatment, enzymatic hydrolysis process and the biochemical pathways involved in converting lignocellulosic biomass into bioenergy.

Upgrade from aerated static pile to agitated bed systems promotes lignocellulose degradation in large-scale composting through enhanced microbial functional diversity

Composting presents a viable management solution for lignocellulose-rich municipal solid waste. However, our understanding about the microbial metabolic mechanisms involved in the biodegradation of lignocellulose, particularly in industrial-scale composting plants, remains limited. This study employed metaproteomics to compare the impact of upgrading from aerated static pile (ASP) to agitated bed (AB) systems on physicochemical parameters, lignocellulose biodegradation, and microbial metabolic pathways during large-scale biowaste composting process, marking the first investigation of its kind. The degradation rates of lignocellulose including cellulose, hemicellulose, and lignin were significantly higher in AB (8.21%-32.54%, 10.21%-39.41%, and 6.21%-26.78%) than those (5.72%-23.15%, 7.01%-33.26%, and 4.79%-19.76%) in ASP at three thermal stages, respectively. The AB system in comparison to ASP increased the carbohydrate-active enzymes (CAZymes) abundance and production of the three essential enzymes required for lignocellulose decomposition involving a mixture of bacteria and fungi (i.e., Actinobacteria, Bacilli, Sordariomycetes and Eurotiomycetes). Conversely, ASP primarily produced exoglucanase and β-glucosidase via fungi (i.e., Ascomycota). Moreover, AB effectively mitigated microbial stress caused by acetic acid accumulation by regulating the key enzymes involved in acetate conversion, including acetyl-coenzyme A synthetase and acetate kinase. Overall, the AB upgraded from ASP facilitated the lignocellulose degradation and fostered more diverse functional microbial communities in large-scale composting. Our findings offer a valuable scientific basis to guide the engineering feasibility and environmental sustainability for large-scale industrial composting plants for treating lignocellulose-rich waste. These findings have important implications for establishing green sustainable development models (e.g., a circular economy based on material recovery) and for achieving sustainable development goals.

Effective microorganism combinations improve the quality of compost-bedded pack products in heifer barns: exploring pack bacteria-fungi interaction mechanisms

BACKGROUND

Compost-bedded pack barns (CBP) are getting huge attention as an alternative housing system for dairy cows due to their beneficial impact on animal welfare. Effective microorganisms (EM) inoculums are believed to enhance compost quality, improve soil structure and benefit the environment. However, little information is available on the impact of incubation with external EM combinations on the barn environment, compost quality and microbial diversity in CBP. This experiment was carried out to investigate the effect of inoculating different combinations of EM [Lactobacillus plantarum (L), Compound Bacillus (B) and Saccharomyces cerevisiae (S)] on compost quality and microbial communities of CBP products, as well as the relationship with the heifers' barn environment. CBP barns were subjected to the following four treatments: CON with no EM inoculum, LB/LS/LBS were Incubated with weight ratios of 1:2 (L: B), 1:2 (L: S), 1:1:1 (L: B: S), respectively.

RESULTS

The EM inoculation (LB, LS, LBS) reduced the concentration of respirable particulate matter (PM10 and PM2.5) in the CBP, and decreased the serum total protein and total cholesterol levels in heifers. Notably, LBS achieved the highest content of high-density lipoprotein compared to other treatments. Microbiome results revealed that EM inoculation reduced the bacterial abundance (Chao1 index) and fungal diversity (Shannon & Simpson indexes), while increasing the relative abundance of various bacterial genera (Pseudomonas, Paracoccus, Aequorivita) and fungi (Pestalotiopsis), which are associated with cellulose decomposition that ultimately resulted in accelerating organic matter degradation and humification. Furthermore, high nutrient elements (TK&TP) and low mycotoxin content were obtained with EM inoculation, with LBS showing a particularly pronounced effect. Meanwhile, LBS contributed to a decline in the proportion of fungal pathogen categories but also led to an increase in fungal saprotroph categories.

CONCLUSION

Generally, EM inoculation positively impacted compost product quality as organic fertilizer and barn environment by modifying the abundance of cellulolytic bacteria and fungi, while inhibiting the reproduction of pathogenic microbes, especially co-supplementing with L, B and S achieved an amplifying effect.

Optimizing biochar addition strategies in combined processes: Comprehensive assessment of earthworm growth, lignocellulose degradation and vermicompost quality

The sustainable management of agricultural waste is essential for curtailing environmental contamination. To address the shortcomings of single treatment methods, this study evaluated the feasibility of combining membrane-covered composting (MC) with vermicomposting. Based on this, the integrated effects of different biochar addition strategies on the combined process were investigated. The aim was to improve the efficiency of vermicomposting while eliminating the negative effects of biochar on earthworms. Addition of biochar before membrane-covered composting increased total earthworm biomass by 25.6 - 31.4 % and reproduction rate by 13.4 - 23.9 %. Specifically, the electrical conductivity (EC) (1061.0 - 1112.0 uS/cm) of the vermicompost was significantly reduced, while the total nutrient content (42.3 - 42.6 mg/g) and germination index (GI) (103.9 - 108.4 %) were maximized. Additionally, reductions in the carbon-to-nitrogen ratio and volatile content were observed. Overall, combination process is a promising approach to improve the quality of vermicomposting. The study's results offer a novel perspective on the value-added treatment of agricultural waste.

A comparative evaluation of biochar and Paenarthrobacter sp. AT5 for reducing atrazine risks to soybeans and bacterial communities in black soil

Application of biochar and inoculation with specific microbial strains offer promising approaches for addressing atrazine contamination in agricultural soils. However, determining the optimal method necessitates a comprehensive understanding of their effects under similar conditions. This study aimed to evaluate the effectiveness of biochar and Paenarthrobacter sp. AT5, a bacterial strain known for its ability to degrade atrazine, in reducing atrazine-related risks to soybean crops and influencing bacterial communities. Both biochar and strain AT5 significantly improved atrazine degradation in both planted and unplanted soils, with the most substantial reduction observed in soils treated with strain AT5. Furthermore, bioaugmentation with strain AT5 outperformed biochar in enhancing soybean growth, photosynthetic pigments, and antioxidant defenses. While biochar promoted higher soil bacterial diversity compared to strain AT5, the latter selectively enriched specific bacterial populations. Additionally, soil inoculated with strain AT5 displayed a notable increase in the abundance of key genes associated with atrazine degradation (trzN, atzB, and atzC), surpassing the effects observed with biochar addition, thus highlighting its effectiveness in mitigating atrazine risks in soil.

Study on the quality of soybean proteins fermented by Bacillus subtilis BSNK-5: Insights into nutritional, functional, safety, and flavor properties

Microbial fermentation emerges as a promising strategy to elevate the quality of soybean proteins in food industry. This study conducted a comprehensive assessment of the biotransformation of four types of soybean proteins by Bacillus subtilis BSNK-5, a proteinase-rich bacterium. BSNK-5 had good adaptability to each protein. Soluble protein, peptides and free amino acids increased in fermented soybean proteins (FSPs) and dominant after 48-84 h fermentation, enhancing nutritional value. Extensive proteolysis of BSNK-5 also improved antioxidant and antihypertensive activities, reaching peak level after 48 h fermentation. Furthermore, excessive proteolysis effectively enhanced the generation of beneficial spermidine without producing toxic histamine after fermentation, and formed the flavor profile with 56 volatiles in 48 h FSPs. Further degradation of amino acids showed a positive correlation with off-flavors, particularly the enrichment of 3-methylbutanoic acid. These findings establish a theoretical foundation for regulating moderate fermentation by BSNK-5 to enabling the high-value utilization of soybean protein.

Effects of two strains of thermophilic nitrogen-fixing bacteria on nitrogen loss mitigation in cow dung compost

Excavating nitrogen-fixing bacteria with high-temperature tolerance is essential for the efficient composting of animal dung. In this study, two strains of thermophilic nitrogen-fixing bacteria, NF1 (Bacillus subtilis) and NF2 (Azotobacter chroococcum), were added to cow dung compost both individually (NF1, NF2) and mixed together (NF3; mixing NF1 and NF2 at a ratio of 1:1). The results showed that NF1, NF2, and NF3 inoculants increased the total Kjeldahl nitrogen level by 38.43%-55.35%, prolonged the thermophilic period by 1-13 d, increased the seed germination index by 17.81%, and the emissions of NH3 and N2O were reduced by 25.11% and 42.75%, respectively. Microbial analysis showed that Firmicutes were the predominant bacteria at the thermophilic stage, whereas Chloroflexi, Proteobacteria, and Bacteroidetes were the predominant bacteria at the mature stage. These results confirmed that the addition of the isolated strains to cow dung composting improved the bacterial community structure and benefited nitrogen retention.

Enhancing C and N turnover, functional bacteria abundance, and the efficiency of biowaste conversion using Streptomyces-Bacillus inoculation

Microbial inoculation plays a significant role in promoting the efficiency of biowaste conversion. This study investigates the function of Streptomyces-Bacillus Inoculants (SBI) on carbon (C) and nitrogen (N) conversion, and microbial dynamics, during cow manure (10% and 20% addition) and corn straw co-composting. Compared to inoculant-free controls, inoculant application accelerated the compost's thermophilic stage (8 vs 15 days), and significantly increased compost total N contents (+47%) and N-reductase activities (nitrate reductase: +60%; nitrite reductase: +219%). Both bacterial and fungal community succession were significantly affected by DOC, urease, and NH4+-N, while the fungal community was also significantly affected by cellulase. The contribution rate of Cupriavidus to the physicochemical factors of compost was as high as 83.40%, but by contrast there were no significantly different contributions (∼60%) among the top 20 fungal genera. Application of SBI induced significant correlations between bacteria, compost C/N ratio, and catalase enzymes, indicative of compost maturation. We recommend SBI as a promising bio-composting additive to accelerate C and N turnover and high-quality biowaste maturation. SBI boosts organic cycling by transforming biowastes into bio-fertilizers efficiently. This highlights the potential for SBI application to improve plant growth and soil quality in multiple contexts.

A natural consortium of thermophilic bacteria from Huancarhuaz hot spring (Ancash-Peru) for promising lignocellulose bioconversion

The lignocellulose bioconversion process is an eco-friendly and green-economy alternative technology that allows the reduction of pollution and global warming, so it is necessary for thermophilic and thermostable hydrolytic enzymes from natural sources. This research aimed to isolate cellulolytic and xylanolytic microbial consortia from Huancarhuaz hot spring (Peru) from sludge or in situ baiting cultured with or without sugarcane bagasse. According to the hydrolytic activities consortium T4 from in situ baiting was selected. It was cultivated in submerged fermentation at 65 °C, pH 6.5 for eight days using LB supplemented with sugar cane bagasse (SCB), pine wood sawdust (PWS), CMC, xylan of birchwood, or micro granular cellulose. Crude extract of culture supplemented with SCB (T4B) showed better endoglucanase and xylanase activities with higher activities at 75 °C and pH 6. In these conditions, cellulase activity was kept up to 57% after 1 h of incubation, while xylanase activity was up to 63% after 72 h. Furthermore, this crude extract released reduced sugars from pretreated SCB and PWS. According to metagenomic analysis of 16S rDNA, Geobacillus was the predominant genus. It was found thermostable genes: a type of endoglucanase (GH5), an endo-xylanase (GH10), and alkali xylanase (GH10) previously reported in Geobacillus sp. strains. Finally, Huancarhuaz hot spring harbors a genetic microbial diversity for lignocellulosic waste bioconversion in high temperatures, and the T4B consortium will be a promising source of novel extreme condition stable enzymes for the saccharification process.

The Role of Soil Microbial Consortia in Sustainable Cereal Crop Residue Management

The global escalation in cereal production, essential to meet growing population demands, simultaneously augments the generation of cereal crop residues, estimated annually at approximately 3107 × 106 Mg/year. Among different crop residue management approaches, returning them to the soil can be essential for various ecological benefits, including nutrient recycling and soil carbon sequestration. However, the recalcitrant characteristics of cereal crop residues pose significant challenges in their management, particularly in the decomposition rate. Therefore, in this review, we aim to summarize the influence of different agricultural practices on enhancing soil microbial decomposer communities, thereby effectively managing cereal crop residues. Moreover, this manuscript provides indirect estimates of cereal crop residue production in Northern Europe and Lithuania, and highlights the diverse roles of lignocellulolytic microorganisms in the decomposition process, with a particular focus on enzymatic activities. This review bridges the knowledge gap and indicates future research directions concerning the influence of agricultural practices on cereal crop residue-associated microbial consortia.

Greenhouse gas emission characteristics and influencing factors of agricultural waste composting process: A review

China, being a major agricultural nation, employs aerobic composting as an efficient approach to handle agricultural solid waste. Nevertheless, the composting process is often accompanied by greenhouse gas emissions, which are known contributors to global warming. Therefore, it is urgent to control the formation and emission of greenhouse gases from composting. This study provides a comprehensive analysis of the mechanisms underlying the production of nitrous oxide, methane, and carbon dioxide during the composting process of agricultural wastes. Additionally, it proposes an overview of the variables that affect greenhouse gas emissions, including the types of agricultural wastes (straw, livestock manure), the specifications for compost (pile size, aeration). The key factors of greenhouse gas emissions during composting process like physicochemical parameters, additives, and specific composting techniques (reuse of mature compost products, ultra-high-temperature composting, and electric-field-assisted composting) are summarized. Finally, it suggests directions and perspectives for future research. This study establishes a theoretical foundation for achieving carbon neutrality and promoting environmentally-friendly composting practices.

Impact of Aspergillus fumigatus inoculation on the composting of wood shaving bedding for horses

Equine farming generates a significant amount of waste, prompting the need for effective management. Composting enhanced by filamentous fungi holds promise for this purpose. This study focused on inoculating Aspergillus fumigatus isolates in composting horse bedding made with wood shavings (Pinus elliottii). The experiment lasted 90 days, with two treatment groups, control and inoculated, analyzing temperature, pH, electrical conductivity, total organic carbon and nitrogen content, and cellulose, hemicellulose, and lignin contents. Both treatments entered the thermophilic phase by the fourth day, reaching temperatures above 55°C and mesophilic maturation at 35 days (41 ± 0.2°C). The inoculated treatment exhibited higher electrical conductivity after 30 days and a more pronounced reduction in the total carbon content (42.85% vs. 38.29%) compared to the control. While there was no significant nitrogen difference, the inoculated treatment had a sharper reduction in carbon/nitrogen ratio, and cellulose and hemicellulose contents. Both treatments showed low coliform counts, no Salmonella sp., and reduced Strongyloides sp. larvae. Inoculating A. fumigatus in saturated horse bedding made from wood shavings improved compost quality, providing a possibility for sustainable equine farming waste treatment.

Trends and social aspects in the management and conversion of agricultural residues into valuable resources: A comprehensive approach to counter environmental degradation, food security, and climate change

The circular economy is essential as it encourages the reuse and recycling of resources while reducing waste, which ultimately helps to reduce environmental pollution and boosts economic efficiency. The current review highlights the management of agricultural and livestock residues and their conversion into valuable resources to combat environmental degradation and improve social well-being. The current trends in converting agricultural residues into useful resources emphasize the social benefits of waste management and conversion. It also emphasizes how waste conversion can reduce environmental degradation and enhance food security. Using agricultural residues can increase soil health and agricultural output while reducing pollution, greenhouse gas emissions, and resource depletion. Promoting sustainable waste-to-resource conversion processes requires a combination of strategies that address technical, economic, social, and environmental aspects. These multiple strategies are highlighted along with prospects and considerations.

The Isolation and Characterization of a Novel Psychrotolerant Cellulolytic Bacterium, Microbacterium sp. QXD-8T

Cellulolytic microorganisms play a crucial role in agricultural waste disposal. Strain QXD-8T was isolated from soil in northern China. Similarity analyses of the 16S rRNA gene, as well as the 120 conserved genes in the whole-genome sequence, indicate that it represents a novel species within the genus Microbacterium. The Microbacterium sp. QXD-8T was able to grow on the CAM plate with sodium carboxymethyl cellulose as a carbon source at 15 °C, forming a transparent hydrolysis circle after Congo red staining, even though the optimal temperature for the growth and cellulose degradation of strain QXD-8T was 28 °C. In the liquid medium, it effectively degraded cellulose and produced reducing sugars. Functional annotation revealed the presence of encoding genes for the GH5, GH6, and GH10 enzyme families with endoglucanase activity, as well as the GH1, GH3, GH39, and GH116 enzyme families with β-glucosidase activity. Additionally, two proteins in the GH6 family, one in the GH10, and two of nine proteins in the GH3 were predicted to contain a signal peptide and transmembrane region, suggesting their potential for extracellularly degrade cellulose. Based on the physiological features of the type strain QXD-8T, we propose the name Microbacterium psychrotolerans for this novel species. This study expands the diversity of psychrotolerant cellulolytic bacteria and provides a potential microbial resource for straw returning in high-latitude areas at low temperatures.

Humic acid biosynthesis and bacterial community evolution during aerobic composting of rice straw

In this study, the effects of inoculum ratio, substrate particle size and aeration rate on humic acid (HA) biosynthesis during aerobic composting of rice straw were investigated, respectively. The contents of total organic carbon, total nitrogen and HA, as well as lignocellulose degradation in the composting were evaluated, respectively. It is found that the maximal HA yield of 356.9 g kg-1 was obtained at an inoculum ratio of 20%, a substrate particle size of 0.83 mm and an aeration rate of 0.3 L·kg-1 DM min-1 in the process of composting. The changes of microbial communities and metabolic functions at different stages of the composting were also analyzed through high-throughput sequencing. The result demonstrates that Proteobacteria, Firmicutes, Bacteroidetes and Actinobacteria were the dominant phyla and their relative abundance significantly varied over time (p < 0.05), and Rhizobium, Phenylobacterium, Pseudoxanthomonas and Paenibacillus were positively related to HA content in the compost. Furthermore, the metabolic function profiles of bacterial community indicate that these functional genes in carbohydrate metabolism and amino acid metabolism were involved in lignocellulose biodegradation and HA biosynthesis. This work may be conducive to explore new regulation strategy to improve bioconversion efficiency of agricultural residues to applicable biofertilizers. KEY POINTS: • Temperature, pH, TOC, TN and C/N caused a great influence on humic acids synthesis • The succession of the microbial community during the composting were evaluated • The metabolisms of carbohydrate and amino acids were involved in HA synthesis.

Enhanced humus synthesis from Chinese medicine residues composting by lignocellulose-degrading bacteria stimulation: Upregulation of key enzyme activity and neglected indirect effects on humus formation

Chinese medicine residues (CMHRs) resource is attracting widespread attention, as it is expected to be produced into Humus-rich fertilizer for soil application. This study aimed to promote effective humus (HS) production through lignocellulose-degrading bacteria (LDB) addition and explore the biological regulation mechanism of LDB affecting lignocellulose-to-humus conversion. The results showed higher HS production was achieved, with 109.73 and 111.44 g·kg-1, and HA/FA was raised by 12.70-16.02 % in compost products by LDB addition stimulation. Significant upregulation of β-glucanase and xylanase activities catalyzed higher decomposition of lignocellulose toward more HS potential precursors supply. Furthermore, exogenous LDB intervention induced microbial community restructure and microbial network establishment via enriching synergism functional bacteria, i.e., Thermobifida, Paenibacillus, Nonomuraea, etc. Mantel test results showed that it was variation of cellulose, hemicellulose and HS that affected microbial community succession (p < 0.01, r > 0.6), which represented the positive action of LDB addition stimulation on HS synthesis upregulation. Further exploration suggested LDB had an indirect effect on HS formation by enhanced lignin and hemicellulose conversion based on the Random Forest model and Partial least-squares path modeling results. This research provides new insights into the trigger effects of LDB introduction on upregulating HS synthesis and is expected to propose new perspectives for HS efficient production in CMHRs composting.

Mitigation of soil N2O emissions by decomposed straw based on changes in dissolved organic matter and denitrifying bacteria

The return of decomposed straw represents a less explored potential option for reducing N2O emissions. However, the mechanisms underlying the effects of decomposed straw return on soil N2O mitigation are still not fully clear. Therefore, we used a helium atmosphere robotized continuous flow incubation system to compare the soil N2O and N2 emissions from four treatments: CK (control: no straw), WS (wheat straw), IWS (wheat straw decomposed with Irpex lacteus), and PWS (wheat straw decomposed with Phanerochaete chrysosporium). All the treatments have been fertilized with the same amount of KNO3. Furthermore, we also analyzed i) the chemodiversity of soil dissolved organic matter (DOM), ii) the nirS, nirK, and nosZ gene copies and relative abundances of denitrifying bacterial communities (DBCs), and iii) the specific linkages between N2O emissions and DOM and DBC. The results showed that the WS, IWS and PWS treatments increased N2O emissions compared to the CK treatment. However, applying decomposed straw to soil, especially straw treated with P. chrysosporium, effectively decreased the soil N2O and increased N2 emissions compared to WS and IWS. Moreover, the IWS and PWS treatments increased the CHO composition, but they decreased the CHON and CHOS compositions of heteroatomic compounds of DOM compared with the WS and CK treatments. Furthermore, the WS, IWS and PWS treatments all significantly increased the nirS and nosZ gene copies compared with the CK treatment. Additionally, compared with the other treatments, the PWS treatment significantly shaped the DBC and led to a higher relative abundance of Pseudomonas with nirS and nosZ genes. Meanwhile, Network analysis showed that the mitigation of N2O was closely related to particular DOM molecules, and specific DBC taxa. These results highlight the potential for decomposed straw amendments to mitigate of soil N2O emissions not only by changing soil DOM but also mediating the soil DBC.

Exploitation of lignocellulosic-based biomass biorefinery: A critical review of renewable bioresource, sustainability and economic views

Urbanization has driven the demand for fossil fuels, however, the overly exploited resource has caused severe damage on environmental pollution. Biorefining using abundant lignocellulosic biomass is an emerging strategy to replace traditional fossil fuels. Value-added lignin biomass reduces the waste pollution in the environment and provides a green path of conversion to obtain renewable resources. The technology is designed to produce biofuels, biomaterials and value-added products from lignocellulosic biomass. In the biorefinery process, the pretreatment step is required to reduce the recalcitrant structure of lignocellulose biomass and improve the enzymatic digestion. There is still a gap in the full and deep understanding of the biorefinery process including the pretreatment process, thus it is necessary to provide optimized and adapted biorefinery solutions to cope with the conversion process in different biorefineries to further provide efficiency in industrial applications. Current research progress on value-added applications of lignocellulosic biomass still stagnates at the biofuel phase, and there is a lack of comprehensive discussion of emerging potential applications. This review article explores the advantages, disadvantages and properties of pretreatment methods including physical, chemical, physico-chemical and biological pretreatment methods. Value-added bioproducts produced from lignocellulosic biomass were comprehensively evaluated in terms of encompassing biochemical products , cosmetics, pharmaceuticals, potent functional materials from cellulose and lignin, waste management alternatives, multifunctional carbon materials and eco-friendly products. This review article critically identifies research-related to sustainability of lignocellulosic biomass to promote the development of green chemistry and to facilitate the refinement of high-value, environmentally-friendly materials. In addition, to align commercialized practice of lignocellulosic biomass application towards the 21st century, this paper provides a comprehensive analysis of lignocellulosic biomass biorefining and the utilization of biorefinery green technologies is further analyzed as being considered sustainable, including having potential benefits in terms of environmental, economic and social impacts. This facilitates sustainability options for biorefinery processes by providing policy makers with intuitive evaluation and guidance.

Fertilization of Microbial Composts: A Technology for Improving Stress Resilience in Plants

Microbial compost plays a crucial role in improving soil health, soil fertility, and plant biomass. These biofertilizers, based on microorganisms, offer numerous benefits such as enhanced nutrient acquisition (N, P, and K), production of hydrogen cyanide (HCN), and control of pathogens through induced systematic resistance. Additionally, they promote the production of phytohormones, siderophore, vitamins, protective enzymes, and antibiotics, further contributing to soil sustainability and optimal agricultural productivity. The escalating generation of organic waste from farm operations poses significant threats to the environment and soil fertility. Simultaneously, the excessive utilization of chemical fertilizers to achieve high crop yields results in detrimental impacts on soil structure and fertility. To address these challenges, a sustainable agriculture system that ensures enhanced soil fertility and minimal ecological impact is imperative. Microbial composts, developed by incorporating characterized plant-growth-promoting bacteria or fungal strains into compost derived from agricultural waste, offer a promising solution. These biofertilizers, with selected microbial strains capable of thriving in compost, offer an eco-friendly, cost-effective, and sustainable alternative for agricultural practices. In this review article, we explore the potential of microbial composts as a viable strategy for improving plant growth and environmental safety. By harnessing the benefits of microorganisms in compost, we can pave the way for sustainable agriculture and foster a healthier relationship between soil, plants, and the environment.

Batch-fed composting of food waste: Microbial diversity characterization and removal of antibiotic resistance genes

The aim of this work was to study the impact of batch-fed strategies on bacterial communities and ARGs in compost. The findings demonstrate that batch-feeding helped maintain high temperatures in the compost pile for an extended period (above 50 °C for 18 days), which in turn facilitated water dissipation. High-throughput sequencing showed that Firmicutes played a significant role in batch-fed composting (BFC). They had a high relative abundance at the beginning (98.64%) and end (45.71%) of compost. Additionally, BFC showed promising results in removing ARGs, with reductions of 3.04-1.09 log copies/g for Aminoglycoside and 2.26-2.44 log copies/g for β_Lactamase. This study provides a comprehensive survey of BFC and demonstrates its potential for eliminating resistance contamination in compost.

Long-term microbial community succession and mechanisms of regulation of dissolved organic matter derivation in livestock manure fermentation system

Industrial-scale aerobic fermentation was conducted with livestock manures. Microbial inoculation promoted the growth of Bacillaceae and consolidated its position as the dominant microorganism. Microbial inoculation substantially influenced dissolved organic matter (DOM) derivation and variations of related components in the fermentation system. The relative abundance of humic acid-like substances of DOM increased from 52.19% to 78.27% in microbial inoculation system, resulting in a high humification level. Moreover, lignocellulose degradation and microbial utilization were the important factors influencing DOM content in fermentation systems. The fermentation system was regulated by microbial inoculation, thus achieving a high level of fermentation maturity.

The temporal profile of GH1 gene abundance and the shift in GH1 cellulase-producing microbial communities during vermicomposting of corn stover and cow dung

Vermicomposting is a promising method for corn stover management to achieve bioresource recovery and environmental protection. Most β-glucosidases, which limit the cellulose degradation rate during vermicomposting of corn stover, belong to glycoside hydrolase family 1 (GH1). This study was conducted with different earthworm densities to quantify the GH1 gene abundance and investigate the evolution of GH1 cellulase-producing microbial communities using qPCR and pyrosequencing. The results showed that β-glucosidase activity, GH1 gene abundance, TOC, and microbial communities carrying the GH1 gene were affected by processing time and earthworm density. After introducing earthworms, β-glucosidase activity increased to 1.90-2.13 U/g from 0.54 U/g. The GH1 gene abundance of treatments with earthworms (5.82E+09-6.70E+09 copies/g) was significantly higher than that of treatments without earthworms (2.48E+09 copies/g) on Day 45. Earthworms increased the richness of microbial communities. The relative abundances of Sphingobium and Dyadobacter, which are dominant genera harboring the GH1 gene, were increased by earthworms to peak values of 23.90% and 11.20%, respectively. Correlation analysis showed that Sphingobium, Dyadobacter, Trichoderma, and Starkeya were positively associated with β-glucosidases. This work sheds new light on the mechanism of cellulose degradation during vermicomposting at the molecular level.

Pretreatment and composting technology of agricultural organic waste for sustainable agricultural development

With the continuous development of agriculture, Agricultural organic waste (AOW) has become the most abundant renewable energy on earth, and it is a hot spot of research in recent years to realize the recycling of AOW to achieve sustainable development of agricultural production. However, lignocellulose, which is difficult to degrade in AOW, greenhouse gas emissions, and pile pathogenic fungi and insect eggs are the biggest obstacles to its return to land use. In response to the above problems researchers promote organic waste recycling by pretreating AOW, controlling composting conditions and adding other substances to achieve green return of AOW to the field and promote the development of agricultural production. This review summarizes the ways of organic waste treatment, factors affecting composting and problems in composting by researchers in recent years, with a view to providing research ideas for future related studies.

Environmental factors induced macrolide resistance genes in composts consisting of erythromycin fermentation residue, cattle manure, and maize straw

With the growing concerns about antibiotic resistance, it is more and more important to prevent the environmental pollution caused by antibiotic fermentation residues. In this study, composted erythromycin fermentation residue (EFR) with the mixture of cattle manure and maize straw at ratios of 0:10 (CK), 1:10 (T1), and 3:10 (T2) explores the effects on physicochemical characteristics, mobile genetic elements (MGEs), and antibiotic resistance genes (ARGs). Results reflected that the addition of EFR reduced the carbon/nitrogen ratio of each compost and improved the piles' temperature, which promoted the composting process. However, the contents of Na⁺, SO₄^2-, and erythromycin were also significantly increased. After 30 days of composting, the degradation rates of erythromycin in CK, T1, and T2 were 72.7%, 20.3%, and 37.1%, respectively. Meanwhile, the total positive rates for 26 detected ARGs in T1 and T2 were 65.4%, whereas that of CK was only 23.1%. Further analysis revealed that ARGs responsible for ribosomal protection, such as ermF, ermT, and erm(35), dominated the composts of T1 and T2, and most were correlated with IS613, electrical conductivity (EC), nitrogen, and Zn²⁺. Above all, adding EFR helps to improve the nutritional value of composts, but the risks in soil salinization and ARG enrichment caused by high EC and erythromycin content should be further investigated and eliminated.

Applications of agricultural residue biochars to removal of toxic gases emitted from chemical plants: A review

Crop residues are representative agricultural waste materials, massively generated in the world. However, a large fraction of them is currently being wasted, though they have a high potential to be used as a value-added carbon-rich material. Also, the applications of carbon-rich materials from agricultural waste to industries can have economic benefit because waste-derived carbon materials are considered inexpensive waste materials. In this review, valorization methods for crop residues as carbon-rich materials (i.e., biochars) and their applications to industrial toxic gas removals are discussed. Applications of crop residue biochars to toxic gas removal can have significant environmental benefits and economic feasibility. As such, this review discussed the technical advantages of the use of crop residue biochars as adsorbents for hazardous gaseous pollutants and greenhouse gases (GHGs) stemmed from combustion of fossil fuels and the different refinery processes. Also, the practical benefits from the activation methods in line with the biochar properties were comprehensively discussed. The relationships between the physico-chemical properties of biochars and the removal mechanisms of gaseous pollutants (H₂S, SO₂, Hg⁰, and CO₂) on biochars were also highlighted in this review study. Porosity controls using physical and chemical activations along with the addition of specific functional groups and metals on biochars have significantly contributed to the enhancement of flue gas adsorption. The adsorption capacity of biochar for each toxic chemical was in the range of 46-76 mg g^-1 for H₂S, 40-182 mg g^-1 for SO₂, 80-952 μg g^-1 for Hg⁰, and 82-308 mg g^-1 CO₂, respectively. This helps to find suitable activation methods for adsorption of the target pollutants. In the last part, the benefits from the use of biochars and the research directions were prospectively provided to make crop residue biochars more practical materials in adsorption of pollutant gases.

Development of genetic tools for heterologous protein expression in a pentose-utilizing environmental isolate of Pseudomonas putida

Pseudomonas putida has emerged as a promising host for the conversion of biomass-derived sugars and aromatic intermediates into commercially relevant biofuels and bioproducts. Most of the strain development studies previously published have focused on P. putida KT2440, which has been engineered to produce a variety of non-native bioproducts. However, P. putida is not capable of metabolizing pentose sugars, which can constitute up to 25% of biomass hydrolysates. Related P. putida isolates that metabolize a larger fraction of biomass-derived carbon may be attractive as complementary hosts to P. putida KT2440. Here we describe genetic tool development for P. putida M2, a soil isolate that can metabolize pentose sugars. The functionality of five inducible promoter systems and 12 ribosome binding sites was assessed to regulate gene expression. The utility of these expression systems was confirmed by the production of indigoidine from C6 and C5 sugars. Chromosomal integration and expression of non-native genes was achieved by using chassis-independent recombinase-assisted genome engineering (CRAGE) for single-step gene integration of biosynthetic pathways directly into the genome of P. putida M2. These genetic tools provide a foundation to develop hosts complementary to P. putida KT2440 and expand the ability of this versatile microbial group to convert biomass to bioproducts.

Kinetics of combined hydrothermal pretreatment and anaerobic digestion of lignocellulosic biomass (pepper plant and eggplant)

A large quantity of lignocellulosic biomass is generated annually across the world which leads to environmental pollution and requires valorization. This study investigated the effect of hydrothermal pretreatment on the anaerobic digestion and co-digestion of the residual pepper plant and eggplant with a focus on kinetics. Two thermal hydrolysis rates were observed, with the optimal conditions for the hydrothermal pretreatment of lignocellulosic biomass being 120°C for 40 min. Subsequently, single and combined biomethanization was successfully carried out in laboratory-scale completely stirred tank reactors at mesophilic temperature (35°C). A high increase in methane production was observed after the pretreatment of the pepper plant and eggplant. The pretreated and co-digested wastes led to an optimal methane yield of 79 ± 23 mL CH₄/g VS. The modified Gompertz model was used to fit the cumulative methane production of the pretreated lignocellulosic substrates. The kinetic model adequately reproduced the experimental results and might be considered a useful tool to simulate the biomethanization behaviour of complex organic substrates.

Emerging technologies of employing algae and microorganisms to promote the return-to-field of crop straws: A mini-review

As an agricultural waste, crop straw enriched with a variety of nutrients is regarded as an important fertilizer resource. In the past, crop straw return-to-field played a key role in the sustainability of agricultural environment, but some problems, such as ammonia loss in ammoniation, low rate of straw decomposition, and high carbon footprint, attracted researchers' attentions. In this paper, we propose three technical routes, including cyanobacteria-based ammonia assimilation, microorganisms-based crop straw pretreatment, and microalgae-based carbon capture, to address the aforementioned problems. Besides, challenges which may hinder the practical application of these technical routes as well as the potential solutions are discussed in detail. It is expected that this paper could provide new ideas to the practical application of crop straw return-to-field.

Independent and combined effects of biochar and microbial agents on physicochemical parameters and microbial community succession during food waste composting

This study evaluated the independent and combined effects of biochar and microbial agents on food waste composting. The results indicated that combined addition increased the peak temperature to 63.5 °C and extended the thermophilic periods to 8 days, resulting in the highest organic matter degradation rate (12.7%). Analysis of enzymatic activity indicated that combined addition increased urease and dehydrogenase activity by 22.9% and 26.5%. Furthermore, the degradation of volatile fatty acids also increased by 37.4% with combined addition. Microbial analysis demonstrated that combined addition effectively increased the relative abundances of Enterobacter, Sphingobacterium and Aspergillus, which could be attributed to the optimal environment provided by biochar and stimulation of microbial agents. Moreover, correlation analysis showed a strong interaction between the microbial community and environment with combined addition. In general, combined addition could be beneficial for composting based on the synergistic effects of biochar and inoculation on microorganism.

Microbial co-occurrence networks driven by low-abundance microbial taxa during composting dominate lignocellulose degradation

Lignocellulose, which contains cellulose, hemicellulose and lignin, is one of the most important factors determining the rate and quality of compost decomposition, and the microbial community composition affects the rate of lignocellulose decomposition. Interactions between microbial taxa contribute significantly to ecosystem energy flow and material cycling. However, it is not clear how interactions between microbial taxa affect the degradation of lignocellulose during the composting process. For this reason we carried out aerobic co-composting experiments with maize straw and cattle manure to explore the contribution of microbial community diversity and the interaction between taxa to lignocellulosic degradation. The results showed that moisture and temperature had the greatest effect on microbial communities during composting and that lignocellulose degradation was dominated by microbial co-occurrence networks rather than microbial community diversity. Overall co-occurrence network and bacterial-fungal interactions explained 23.9-84.1 % of lignocellulosic degradation, whereas microbial diversity only accounted for 24.6-31.5 %. Interestingly, keystone taxa analysis of the microbial co-occurrence networks revealed that low-abundance taxa influenced microbial interactions driving lignocellulose degradation. Our results provide a new perspective for understanding lignocellulose degradation during composting, offering insights into important microbial interaction mechanisms for improving compost quality and efficiency.

Potential of lignocellulose degrading microorganisms for agricultural residue decomposition in soil: A review

Lignocellulosic crop residues (LCCRs) hold a significant share of the terrestrial biomass, estimated at 5 billion Mg per annum globally. A massive amount of these LCCRs are burnt in many countries resulting in immense environmental pollution; hence, its proper disposal in a cost-effective and eco-friendly manner is a significant challenge. Among the different options for management of LCCRs, the use of lignocellulose degrading microorganisms (LCDMOs), like fungi and bacteria, has emerged as an eco-friendly and effective way for its on-site disposal. LCDMOs achieve degradation through various mechanisms, including multiple supportive enzymes, causing oxidative attacks by which recalcitrance of lignocellulose material is reduced, paving the way to further activity by depolymerizing enzymes. This improves the physical properties of soil, recycles plant nutrients, promotes plant growth and thus helps improve productivity. Rapid and proper microbial degradation may be achieved through the correct combination of the LCDMOs, supplementing nutrients and controlling different factors affecting microbial activity in the field. The review is a critical discussion of previous studies revealing the potential of individuals or a set of LCDMOs, factors controlling the rate of degradation and the key researchable areas for better understanding of the role of these decomposers for future use.

Production of biochar from crop residues and its application for biofuel production processes - An overview

A sustainable carbon-neutral society is imperative for future generations, and biochars and biofuels are inevitable choice to achieve this goal. Crop residues (CR) such as sugarcane bagasse, corn stover, and rice husk are promising sustainable resources as a feedstock for biochars and biofuels. Extensive research has been conducted on CR-based biochar production not only in environmental remediation areas but also in application for biofuel production. Here, the distribution and resource potential of major crop residues are presented. The production of CR-biochar and its applications in biofuel production processes, focusing on the latest research are discussed. Finally, the challenges and areas of opportunity for future research in terms of CR supply, CR-biochar production, and CR-biochar utilization for biofuel production are proposed. Compared with other literature reviews, this study can serve as a guide for the establishment of sustainable, economical, commercial CR-based biorefineries.

Role of psychrotrophic bacteria and cold-active enzymes in composting methods adopted in cold regions

Temperature-dependent composting is a challenging task but is worthy if it is done in the right manner. Cold composting has been known to be practiced since ancient times but there were not enough advancements to overcome the long mesophilic phase and bring the compost maturation to a short period. The composting processes that have been well practiced are discussed and the role of psychrotrophic bacteria that produce cold tolerant hydrolytic enzymes has been highlighted. In this chapter, the mechanism of substrate degradation has been elaborated to better understand the need of specific bacteria for a specific kind of substrate allowing fast and efficient decomposition. This chapter attempts to pave an appropriate way and suggest the best-suited method of composting for efficient production of compost by the conservation of heat in cold regions.

Straw waste promotes microbial functional diversity and lignocellulose degradation during the aerobic process of pig manure in an ectopic fermentation system via metagenomic analysis

This study compares the physicochemical properties, lignocellulose degradation, microbial community composition, and carbohydrate-active enzymes (CAZymes) in ectopic fermentation systems (EFS) of pig manure mixed with either conventional padding (C) or straw waste (A). The degradation rates of cellulose, hemicellulose, and lignin were found to be significantly higher in A (27.72%, 22.72%, and 18.80%, respectively) than in C (21.05%, 16.17%, and 11.69%, respectively) owing to the activities of lignocellulolytic enzymes. Metagenomics revealed that straw addition had a stronger effect on the bacterial community succession than fungi. The abundances of Sphingobacterium, Pseudomonas, and CAZymes were higher in A than in C, as well as the auxiliary activity enzymes, which are crucial for lignocellulose degradation. Redundancy analysis indicates a positive correlation between lignocellulose degradation and Sphingobacterium, Pseudomonas, Bacillus, and Actinobacteria contents. A structural equation model was applied to further verify that the increased microbial functional diversity was the primary driver of lignocellulosic degradation, which could be effectively regulated by the enhanced temperature with straw addition. Replacing traditional padding with straw can thus accelerate lignocellulosic degradation, promote microbial functional diversity, and improve the EFS efficiency.

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

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

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

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

In-situ generation of H2O2 by zero valent iron to control depolymerization of lignocellulose in composting niche

Lignocellulosic degradation is a bottleneck of bioconversion during the composting process. In-situ generation of H₂O₂ in the composting system was an ideal method for efficiently promoting lignocellulase degradation, and zero valent iron (ZVI) was concerned because it can generate H₂O₂ by reducing dissolved oxygen. This study focused on the effects of ZVI treatment on lignocellulose degradation, microbial communities, and carbohydrate-active enzymes (CAZymes) genes during composting. Its results indicated that ZVI increased H₂O₂ content during composting, accompanied by the formation of •OH. The degradation rates of lignin, cellulose and hemicellulose in ZVI group (20.77%, 30.35% and 44.7%) were significantly higher than in CK group (17.01%, 26.12% and 38.5%). Metagenomic analysis showed that ZVI induced microbial growth that favored lignocellulose degradation, which increased the abundance of Actinobacteria and Firmicutes but reduced Proteobacteria. At the genus level, the abundance of Thermomonospora, Streptomyces, and Bacillus significantly increased. In addition, glycoside hydrolases and auxiliary activities were important CAZymes families of lignocellulose degradation, and their abundance was higher in the ZVI group. Redundancy analysis showed that the increased H₂O₂ and •OH content was a critical factor in improving lignocellulose degradation. Overall, H₂O₂ as a co-substrate enhanced the enzymatic efficiency, •OH unspecifically attacked lignocellulose, and the increase in functional microbial abundance was the main reason for promoting lignocellulose degradation in composting.

The Addition of Biochar and Hyper-Thermal Inoculum Can Regulate the Fate of Heavy Metals Resistant Bacterial Communities during the Livestock Manure Composting

In the present investigation the effects of biochar and hyper-thermal inoculum on the heavy-metal-resistant bacteria (HMRB) during livestock manure composting were studied. An experiment was performed on composting livestock manure and wheat straw amended with biochar and hyper-thermal inoculum. Physicochemical properties, enzyme activity, heavy metals (HMs), and bacterial activities were monitored, and a comprehensive assessment was analyzed during the composting process. The results showed that the dominant phyla of Proteobacteria, Bacteroidota, Actinobacteriota, and Chloroflexi were enriched, but this was not the case with Firmicutes. The abundance of Galbibacter, Thermobifida, Sphaerobacter, and Actinomadura was significantly different in CT15 and BHCT15. In addition, this study showed that the selected factors are less correlated with HMRB compared with the CT group. Therefore, this study could provide new insights into the effect of biochar and hyper-thermal inoculum amendments on the fate of HMRB under HMs and high temperature stress during livestock manure composting.

Performance evaluation of a novel two-stage biodegradation technique through management of toxic lignocellulosic terrestrial weeds

The present study investigates the biodegradation of two potentially toxic terrestrial weeds Parthenium hysterophorus and Lantana camara, implementing a novel two-stage biodegradation technique; Rotary drum composting followed by vermicomposting (RV). The RV approach was refined for a 7-day thermophilic degradation in an in-vessel rotary drum composter, followed by a 20-day mesophilic degradation utilizing Eisenia fetida and Eudrilus eugeniae vermi-monocultures. However, rotary drum composting (RDC) was performed for both the weeds (for 27 days), facilitating only initial thermophilic degradation to compare the efficacy of the RV technique. Lignocelluloses analysis revealed that cellulose degradation doubled during RV technique, indicating efficient biodegradation in reactors administered with E. fetida vermiculture compared to RDC (19.60 to 42.80% and 26.80 to 66.50% in P. hysterophorus and L. camara feedstocks). Further, these results also correlated with the X-Ray diffractograms of all trials showing the degradation of crystalline cellulose at 2θ: 20-50° for RV. Moreover, to ensure product safety, the analyzed total heavy metals content also unveiled the advantage of RV over RDC as validated by the accumulation of higher concentrations of zinc (45% and 33% in P. hysterophorus and L. camara feedstocks) and lead (55% and 45% in P. hysterophorus and L. camara feedstocks) in reactors with E. fetida. The material's seed germination index increased to 80% in the final product of all trials in the RV technique, indicating the diminishing of the phytotoxic nature. Subsequently, pot studies also indicated that the RV technique was coherent in managing noxious weeds.

Co-composting of biochar and nitrogen-poor organic residues: Nitrogen losses and fate of polycyclic aromatic hydrocarbons

Composting recycles nutrients and biodegrades organic pollutants, but often results in N leaching. Biochar can enhance the composting process and reduce N losses. Research, however, has focused on composting N-rich residues; also, information on the fate of biochar polycyclic aromatic hydrocarbons (PAHs) during composting is scarce. We explored the composting of biochar with N-poor organic residues as a strategy to reduce N losses and biochar PAHs. A small-scale composting experiment was performed with three treatments: 100% yard residues and two mixtures of 85% yard residues and 15% gasification- or pyrolysis-derived biochar. Temperatures were recorded daily during composting and Nlosses and changes in PAHs loads were calculated. Results across all treatments showed overall low N losses, likely caused by low temperatures and N contents, circumneutral pH values, and absence of leachate, and simultaneous immobilization and mineralization of PAH contents. Treatments with biochar showed a slower release of inorganic N (NO₃--N and NH₄⁺-N), although they also had overall lower inorganic N contents. This slower release of inorganic N may relate to biochar's high surface area. We conclude that biochar provides valuable benefits for N-poor composting, and that composting should be further explored as a promising strategy to reduce the contents of PAHs in biochar.

Mechanism that allows manno-oligosaccharide to promote cellulose degradation by the bacterial community and the composting of cow manure with straw

The new sugar source manno-oligosaccharide can regulate the structure of the microbial community. This study investigated the effects of adding manno-oligosaccharide at four different levels (0, 0.1%, 0.5%, and 1% w/w compost) to composting cow manure and straw on lignocellulose degradation and the bacterial community. Adding 0.5% manno-oligosaccharide had the greatest effects on accelerating the composting process, reducing its toxicity, and improving the stability of the product. After composting for 25 days, adding 0.5% manno-oligosaccharide decreased the hemicellulose, cellulose, and lignin contents to 2.25%, 11.25%, and 7.07%, respectively, compared with those under CK. Manno-oligosaccharide promoted the degradation of lignocellulose by increasing the abundances of Thermobifida, Streptomyces, and Luteimonas. In addition, manno-oligosaccharide inhibited pathogenic bacteria and increased the abundances of functional genes related to metabolism. Finally, adding 0.5% manno-oligosaccharide mainly affected the degradation of lignocellulose by enhancing the C/N ratio and the abundances of Streptomyces and the secretion system during composting according to redundancy analysis.

Effects of Microbial Inoculation with Different Indigenous Bacillus Species on Physicochemical Characteristics and Bacterial Succession during Short-Term Composting

Bacillus accelerates lignocellulose degradation, promotes the stabilization and resource utilization of compost by secreting enzymes, and plays an important role in compost formation and quality control. This study evaluated enzyme activity, lignocellulosic degradation, and bacterial succession in composting inoculated with different microbial Bacillus agents. They were identified as B. licheniformis, B. subtilis, B. thermoamylovorans, B. thermoruber, and B. hisashii. Four treatments were established, including a CK (uninoculated microorganisms), A (B. licheniformis, B. subtilis, B. thermoamylovorans,and B. hisashii), B (B. subtilis, B. thermoamylovorans, B. thermoruber, and B. hisashii), and C (B. subtilis, B. thermoamylovorans, and B. hisashii), and the composting lasted 7–14 days. Lignin and cellulose degradation rates in B during composting were 17.1% and 36.7% at the cooling stage, respectively. Redundancy analysis showed that degradation of lignocellulose in the thermophilic stage was mainly related to the secretion of lignocellulose-degrading enzymes after microbial inoculation. 16S rRNA sequencing revealed that Bacillus (20.3%) and Thermobifida (20.2%) were the dominant genera. Inoculation with a combination including B. thermoruber was a feasible way to increase lignocellulose degradation and promote maturity in sewage sludge composting.

A paradigm shift towards production of sustainable bioenergy and advanced products from Cannabis/hemp biomass in Canada

The global cannabis (Cannabis sativa) market was 17.7 billion in 2019 and is expected to reach up to 40.6 billion by 2024. Canada is the 2nd nation to legalize cannabis with a massive sale of $246.9 million in the year 2021. Waste cannabis biomass is managed using disposal strategies (i.e., incineration, aerobic/anaerobic digestion, composting, and shredding) that are not good enough for long-term environmental sustainability. On the other hand, greenhouse gas emissions and the rising demand for petroleum-based fuels pose a severe threat to the environment and the circular economy. Cannabis biomass can be used as a feedstock to produce various biofuels and biochemicals. Various research groups have reported production of ethanol 9.2-20.2 g/L, hydrogen 13.5 mmol/L, lipids 53.3%, biogas 12%, and biochar 34.6% from cannabis biomass. This review summarizes its legal and market status (production and consumption), the recent advancements in the lignocellulosic biomass (LCB) pre-treatment (deep eutectic solvents (DES), and ionic liquids (ILs) known as "green solvents") followed by enzymatic hydrolysis using glycosyl hydrolases (GHs) for the efficient conversion efficiency of pre-treated biomass. Recent advances in the bioconversion of hemp into oleochemicals, their challenges, and future perspectives are outlined. A comprehensive insight is provided on the trends and developments of metabolic engineering strategies to improve product yield. The thermochemical processing of disposed-off hemp lignin into bio-oil, bio-char, synthesis gas, and phenol is also discussed. Despite some progress, barricades still need to be met to commercialize advanced biofuels and compete with traditional fuels.

Epichloë Fungal Endophytes Have More Host-Dependent Effects on the Soil Microenvironment than on the Initial Litter Quality

Fungal endophytes have been extensively found in most terrestrial plants. This type of plant-microorganism symbiosis generates many benefits for plant growth by promoting nutrient availability, uptake, and resistance to environmental disease or stress. Recent studies have reported that fungal endophytes have a potential impact on plant litter decomposition, but the mechanisms behind its effect are not well understood. We proposed a hypothesis that the impacts of fungal endophytes on litter decomposition are not only due to a shift in the symbiont-induced litter quality but a shift in soil microenvironment. To test this hypothesis, we set-up a field trial by planting three locally dominant grass species (wild barley, drunken horse grass, and perennial ryegrass) with Epichloë endophyte-infected (E+) and -free (E-) status, respectively. The aboveground litter and bulk soil from each plant species were collected. The litter quality and the soil biotic and abiotic parameters were analyzed to identify their changes across E+ and E- status and plant species. While Epichloë endophyte status mainly caused a significant shift in soil microenvironment, plant species had a dominant effect on litter quality. Available nitrogen (N) and phosphorus (P) as well as soil organic carbon and microbial biomass in most soils with planting E+ plants increased by 17.19%, 14.28%, 23.82%, and 11.54%, respectively, in comparison to soils with planting E- plants. Our results confirm that fungal endophytes have more of an influence on the soil microenvironment than the aboveground litter quality, providing a partial explanation of the home-field advantage of litter decomposition.

Cellulolytic bacteria joined with deproteinized whey decrease carbon to nitrogen ratio and improve stability of compost from wine production chain by-products

Composting residues from wine and dairy chains would contribute to increase the environmental sustainability of the production. The aim of this study was to evaluate the effects of deproteinized whey combined with bioactivators on the composting process. Bacillus velezensis and Kocuria rhizophila, bacteria with cellulolytic activity, were isolated from raw materials and inoculated in the organic mass to be composted. Piles moistened with deproteinized whey showed the highest reduction of total and dissolved organic carbon due to the stimulation of bacterial activity by nitrogen compounds held within deproteinized whey. Such findings were also confirmed by the speed up of the microbial carbon mineralization. Bioactivators and deproteinized whey speeded up the composting process and returned compost characterized by high stability and quality. The addition of available N is crucial to improve the composting process and can act even better if combined with cellulolytic bacteria.

Microbial Fuel Cell Based on Nitrogen-Fixing Rhizobium anhuiense Bacteria

In this study, the nitrogen-fixing, Gram-negative soil bacteria Rhizobium anhuiense was successfully utilized as the main biocatalyst in a bacteria-based microbial fuel cell (MFC) device. This research investigates the double-chambered, H-type R. anhuiense-based MFC that was operated in modified Norris medium (pH = 7) under ambient conditions using potassium ferricyanide as an electron acceptor in the cathodic compartment. The designed MFC exhibited an open-circuit voltage (OCV) of 635 mV and a power output of 1.07 mW m-2 with its maximum power registered at 245 mV. These values were further enhanced by re-feeding the anode bath with 25 mM glucose, which has been utilized herein as the main carbon source. This substrate addition led to better performance of the constructed MFC with a power output of 2.59 mW m-2 estimated at an operating voltage of 281 mV. The R. anhuiense-based MFC was further developed by improving the charge transfer through the bacterial cell membrane by applying 2-methyl-1,4-naphthoquinone (menadione, MD) as a soluble redox mediator. The MD-mediated MFC device showed better performance, resulting in a slightly higher OCV value of 683 mV and an almost five-fold increase in power density to 4.93 mW cm-2. The influence of different concentrations of MD on the viability of R. anhuiense bacteria was investigated by estimating the optical density at 600 nm (OD600) and comparing the obtained results with the control aliquot. The results show that lower concentrations of MD, ranging from 1 to 10 μM, can be successfully used in an anode compartment in which R. anhuiense bacteria cells remain viable and act as a main biocatalyst for MFC applications.

Response of bacterial community to iron oxide nanoparticles during agricultural waste composting and driving factors analysis

The succession of bacterial communities and their function, and the core microorganisms for water soluble organic carbon (WSC) and organic matter (OM) changes during agricultural waste composting with addition of iron oxide nanomaterials (FeONPs, Fe₂O₃ NPs and Fe₃O₄ NPs) were investigated. Moreover, driving factors for bacterial composition and metabolism were analyzed. Results showed that FeONPs treatments increased the relative abundance of thermophilic microorganisms for OM degradation. Most of the core genera were responsible for decomposition of OM and synthesis of WSC. Additionally, FeONPs promoted the metabolism of amino acids. The most significant factors for dominant genera in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were moisture (62.1%), moisture (62.0%) and OM (58.2%), respectively. For metabolism, the most significant factors in control, Fe₂O₃ NPs and Fe₃O₄ NPs group were temperature (57.2%), NO₃^--N (60.5%), NO₃^--N (62.6%), respectively. The relationships between compost properties, bacterial community and metabolism were changed by FeONPs.

Influence of microbial inoculants on co-composting of lignocellulosic crop residues with farm animal manure: A review

The rapidly developing agro-industry generates huge amounts of lignocellulosic crop residues and animal manure worldwide. Although co-composting represents a promising and cost-effective method to treat various agricultural wastes simultaneously, poor composting efficiency prolongs total completion time and deteriorates the quality of the final product. However, supplementation of the feedstock with beneficial microorganisms can mitigate these negative effects by facilitating the decomposition of recalcitrant materials, enhancing microbial enzyme activity, and promoting maturation and humus formation during the composting process. Nevertheless, the influence of microbial inoculation may vary greatly depending on certain factors, such as start-up parameters, structure of the feedstock, time of inoculation, and composition of the microbial cultures used. The purpose of this contribution is to review recent developments in co-composting procedures involving different lignocellulosic crop residues and farm animal manure combined with microbial inoculation strategies. To evaluate the effectiveness of microbial additives, the results reported in a large number of peer-reviewed articles were compared in terms of composting process parameters (i.e., temperature, microbial activity, total organic carbon and nitrogen contents, decomposition rate of lignocellulose fractions, etc.) and compost characteristics (humification, C/N ratio, macronutrient content, and germination index). Most studies confirmed that the use of microbial amendments in the co-composting process is an efficient way to facilitate biodegradation and improve the sustainable management of agricultural wastes. Overall, this review paper provides insights into various inoculation techniques, identifies the limitations and current challenges of co-composting, especially with microbial inoculation, and recommends areas for further research in this field.

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.