Enhanced lignin degradation by Irpex lacteus through expanded sterilization further improved the fermentation quality and microbial community during the silage preservation process.

Traditional autoclaving, slow degradation rate and preservation of biomass treated by fungi are the main factors restricting biological treatment. In our previous studies, strains with high efficiency and selective lignin degradation ability were obtained. To further solve the limiting factors of biological treatment, this paper proposed a composite treatment technology, which could replace autoclaves for fungal treatment and improve the preservation and utilization of fungal-pretreated straw. The autoclaved and expanded buckwheat straw were, respectively, degraded by Irpex lacteus for 14 days (CIL, EIL), followed by ensiling of raw materials (CK) and biodegraded straw of CIL and EIL samples with Lactobacillus plantarum for different days, respectively (CP, CIP, EIP). An expansion led to lactic acid bacteria, mold, and yeast of the samples below the detection line, and aerobic bacteria was significantly reduced, indicating a positive sterilization effect. Expansion before I. lacteus significantly enhanced lignin selective degradation by about 6%, and the absolute content of natural detergent solute was about 5% higher than that of the CIL. Moreover, EIL decreased pH by producing higher organic acids. The combination treatment created favorable conditions for ensiling. During ensiling, EIP silage produced high lactic acid about 26.83 g/kg DM and the highest acetic acid about 22.35 g/kg DM, and the pH value could be stable at 4.50. Expansion before I. lacteus optimized the microbial community for ensiling, resulting in EIP silage co-dominated by Lactobacillus, Pediococcus and Weissella, whereas only Lactobacillus was always dominant in CP and CIP silage. Clavispora gradually replaced Irpex in EIP silage, which potentially promoted lactic acid bacteria growth and acetic acid production. In vitro gas production (IVGP) in EIL was increased by 30% relative to CK and was higher than 24% in CIL. The role of expansion was more significant after ensiling, the IVGP in EIP was increased by 22% relative to CP, while that in CIP silage was only increased by 9%. Silage of fungal-treated samples reduced methane emissions by 28% to 31%. The study demonstrated that expansion provides advantages for fungal colonization and delignification, and further improves the microbial community and fermentation quality for silage, enhancing the nutrition and utilization value. This has practical application value for scaling up biological treatment and preserving the fungal-treated lignocellulose.

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.

Effects of turning frequency on fermentation efficiency and microbial community metabolic function of sheep manure composting on the Qinghai-Tibet Plateau.

This study explored the effects of turning frequency on fermentation efficiency and microbial metabolic function of sheep manure composting on the Qinghai-Tibet Plateau (QTP). Five treatments with different turning frequencies were set up in this study: turning every 1 day (T1), 2 days (T2), 4 days (T3), 6 days (T4), and 8 days (T5). Results showed that the high temperature period for T1 and T5 lasted only 4 days, while that for T2-T4 lasted more than 8 days. The germination index of T1 and T5 was lower than 80%, while that of T2-T4 was 100.6%, 97.8%, and 88.6%, respectively. This study further predicted the microbial metabolic function of T2-T4 using the bioinformatics tool PICRUSt2 (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) and determining the activities of various functional enzymes. The results showed that carbohydrate metabolism, protein metabolism, and nucleotide metabolism were the main metabolic pathways of microorganisms, and that T2 increased the abundance of functional genes of these metabolic pathways. The activities of protease, cellulase, and peroxidase in T2 and T3 were higher than those in T4, and the effect of T2 was more significant. In conclusion, turning once every 2 days can improve the quality of sheep manure compost on the QTP.

Expansion Improved the Physical and Chemical Properties and In Vitro Rumen Digestibility of Buckwheat Straw.

The hard texture and poor palatability of straw are important factors that hinder its application in feed. Expansion is a technology that can improve the utilization of biomass, but few studies have comprehensively revealed how to change physicochemical characteristics to improve nutritional value. In this study, mechanical and chemical methods were combined to study the texture properties, rheological properties, and physicochemical structures of straw, and its utilization value was evaluated by in vitro rumen digestion. Expansion caused hemicellulose degradation, cellulose separation, and lignin redistribution, resulting in a decrease in crystallinity. The hardness and chewiness of expanded straw were reduced by 55% to 66%, significantly improving palatability. The compressive stress could be reduced by 54-73%, and the relaxation elasticity was reduced by 5% when expanded straw was compressed. The compression deformation of expanded straw was doubled compared to feedstock, and the compacting degree was improved. Expanded straw significantly improved digestibility and gas production efficiency, which was due to the pore structure increasing the attachment of rumen microorganisms; besides that, the reduction of the internal structural force of the straw reduced energy consumption during digestion. The lignin content decreased by 10%, the hardness decreased further in secondary expansion, but the digestibility did not improve significantly.

Effects of white-rot fungal pretreatment of corn straw return on greenhouse gas emissions from the North China Plain soil.

Straw-return with fungal treatment is a potential method for reducing soil greenhouse gas emissions through carbon (C) sequestration and N2O mitigation. However, there is little information on the effects of different fungal treatments of crop straw return on soil CO2 and N2O emissions. To explore to what extent decomposed corn straw and its components controls soil CO2 and N2O emissions, we set up three sequential incubation experiments using soil collected from the North China Plain, an intensive agricultural area. Interactions between the different C contents of corn straw (CS), CS pretreated with Irpex lacteus (ICS), CS pretreated with Phanerochaete chrysosporium (PCS) and different NO3--N concentrations on the effect of soil CO2 and N2O emissions were conducted, and the kinetics of CO2 and N2O as influenced by changes in soil biochemical factors were analyzed. The effects of different lignocellulose components (lignin, cellulose, and xylan) on soil CO2 and N2O emissions were further studied. The results showed that straw pretreatment did not affect CO2 emissions. Both CO2 and N2O emissions increased when the C and N contents increased. However, applying PCS to 70% water-filled pore space soil effectively decreased the soil N2O emissions, by 41.8%-76.3% compared with adding the same level of CS. Moreover, extracellular enzyme activities related to C and N cycling were triggered, and the nosZI and nosZII abundances were significantly stimulated by the PCS application. These effects are closely related to the initial soluble C content of this treatment. Furthermore, adding xylan can significantly reduce N2O emissions. Overall, our data suggest that the environmentally beneficial effects of returning straw can be greatly enhanced by applying the straw-degrading white-rot fungi of P. chrysosporium in the North China Plain soil. Future studies are needed in the field to upscale this technology.

Effects of Ensiling Oxytropis glabra with Whole-Plant Corn at Different Proportions on Fermentation Quality, Alkaloid Swainsonine Content, and Lactic Acid Bacteria Populations.

Oxytropis glabra (OG) is a leguminous forage that is potentially valuable for solving the shortage of feed for livestock production, while, in large quantities, it may be toxic because of its swainsonine (SW) content. In this study, OG was ensiled with whole-plant corn (Zea mays L.) at 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, and 0:10 ratios on a fresh matter basis, and, after 60 d of ensiling, the chemical composition, fermentation characteristic, SW removal rate, lactic acid bacteria (LAB) populations, and their capabilities for SW removal were analyzed. As the proportion of corn in the silage increased, the pH, as well as the propionic acid, ammonia-N, dry matter, crude protein, and SW contents, decreased linearly, while the lactic acid, neutral detergent fiber, and residual water-soluble carbohydrate contents increased linearly. Lactobacillus plantarum was the most common microorganism present in all mixture silages. Lactobacillus amylovorus and Lactobacillusbrevis were prevalent at lower ratios of corn to OG. Meanwhile, the LAB strains belong to L. amylovorus and L. plantarum had a higher SW removal rate. Our results suggested that ensiling OG with whole-plant corn improves fermentation and decreases SW content, and that 5:5 is the optimal ratio, so this type of mixed silage could make OG useable for ruminant production.

Vitamin A and E in the total mixed ration as influenced by ensiling and the type of herbage.

The objective of this study was to evaluate the effects of ensiling on vitamin A (retinol) and vitamin E (α-tocopherol) contents in the total mixed ration (TMR) containing different types of herbage. Oat hay (O-TMR), alfalfa hay (A-TMR) and oat hay + alfalfa hay (OA-TMR) were separately mixed with soybean milk residue, corn meal, soybean meal, salt and a vitamin-mineral supplement to make the TMR. The TMR was sampled after 0, 7, 14, 28 and 56 days of ensiling. The fermentation quality, chemical composition and contents of vitamins A and E were determined. The vitamin A content was affected by the ensiling and herbage type (p < 0.05). After 56 days of ensiling, the three TMR silages had good fermentation quality, but the vitamin A content of O-TMR, OA-TMR and A-TMR decreased by 59.4%, 58.1% and 53.7%, respectively. Moreover, the content of vitamin A was positively correlated with the pH and negatively correlated with the lactic acid content during the 56 days of ensiling of the TMR silages. However, there were no effects of ensiling and herbage type on the vitamin E content. Thus, the preservation strategy for vitamin A in the TMR during ensiling requires further study.

Yeast population dynamics on air exposure in total mixed ration silage with sweet potato residue.

To investigate the yeast population dynamics during air exposure in total mixed ration (TMR) silage containing sweet potato residue. TMR were ensiled in laboratory silos (1 kg) with or without two lactic acid bacteria strains, Lactobacillus plantarum (LP), and Lactobacillus amylovorus (LA). Fermentation characteristics were measured and yeast population was investigated by ITS1 region gene sequencing using Illumina MiSeq platform. All treatments were well ensiled, and L. amylovorus improved aerobic stability. During aerobic exposure, Pichia kudriavzevii was detected with increased relative abundance in all treatments and more relative abundant in LP. Pichia fermentans was more relative abundant in control. Higher relative abundance of Pichia anomala was detected in deteriorating LP. The relative abundance of Pichia ohmeri increased during later aerobic exposure in the control and LA, with a significant increase in the count of yeast population. Despite Cryptococcus was detected more relative abundant during early stage of aerobic exposure, the yeast population was below the detection limit. Aerobic deterioration was characterized by an increase in operational taxonomic units of Pichia. High relative abundance of P. anomala and P. kudriavzevii made aerobic deterioration easier. Inhibition of P. fermentans might be an effective strategy for improving the aerobic stability to some instance.

A lower cost method of preparing corn stover for Irpex lacteus treatment by ensiling with lactic acid bacteria.

OBJECTIVE: This study investigated a method of preparing corn stover for Irpex lacteus (I. lacteus) treatment to improve its in vitro rumen degradability under non-sterile conditions. METHODS: Corn stover was inoculated with Lactobacillus plantarum (L. plantarum), Lactobacillus buchneri (L. buchneri), and an equal mixture of these strains, and ensiled for 0, 3, 7, 14, and 28 days. After each period, a portion of the silage was sampled to assess the silage quality, and another portion of the silage was further treated with I. lacteus at 28°C for 28 d. All the samples were analyzed for fermentation quality, chemical composition, and in vitro gas production (IVGP) as a measure of rumen fermentation capacity. RESULTS: Lactic acid bacteria (LAB) was found to improve the silage quality of the corn stover, and the corn stover silage inoculated with L. plantarum produced more lactic acid and higher IVGP than other silage groups. The I. lacteus colonies flourished in the early stage of corn stover silage, especially on the 3-d corn stover silage inoculated with both L. plantarum and L. buchneri. This led to an 18% decrease in the acid detergent lignin content, and a 49.6% increase in IVGP compared with the raw stover. CONCLUSION: The combination of ensiling with the mixed LAB inoculation and I. lacteus treatment provided a cost-effective method for the improvement of the IVGP of corn stover from 164.8 mL/g organic matter (OM) to 246.6 mL/g OM.

Novel strategy to improve the colonizing ability of Irpex lacteus in non-sterile wheat straw for enhanced rumen and enzymatic digestibility.

Pretreatment with white rot fungi is a promising method to enhance the digestibility of lignocelluloses; however, sterilization of feedstocks prior to inoculation is one of the costliest steps. To improve the colonizing ability of white rot fungi under non-sterile condition, Irpex lacteus, Pleurotus ostreatus, and Phanerochaete chrysosporium were inoculated in the wheat straw ensiled for 28 days and incubated for 56 days to determine the changes in microbe counts, organic acid content, chemical composition, and rumen and enzymatic digestibility. Results showed that ensiling produced abundant organic acids and suppressed most microbes in wheat straw. Significant growth of I. lacteus was observed after 3 days of incubation, and molds were only detectable at day 7 in the group. At the end of incubation, aerobic bacteria and lactic acid bacteria decreased by 18% and 38% in the wheat straw treated with I. lacteus, but molds, aerobic bacteria, and lactic acid bacteria thrived in those treated with P. ostreatus and P. chrysosporium. Even more, P. ostreatus and P. chrysosporium increased the lignin content of the ensiled wheat straw by 34% and 65%. However, I. lacteus selectively degraded lignin by 28% and improved the rumen and enzymatic digestibility by 18% and 34%. The finding indicates that ensiling prior to fermentation with I. lacteus is an effective method to control spoilage microbes and to enhance the rumen and enzymatic digestibility of wheat straw.

Effect of Irpex lacteus, Pleurotus ostreatus and Pleurotus cystidiosus pretreatment of corn stover on its improvement of the in vitro rumen fermentation.

BACKGROUND: The present work investigated changes in corn stover pretreated with different white rot fungi. Corn stover was inoculated with Irpex lacteus, Pleurotus ostreatus and Pleurotus cystidiosus prior to incubation under solid-state fermentation conditions at 28 °C for 42 days. Changes in the chemical composition, in vitro rumen degradability, lignocellulolytic enzyme activity and multi-scale structure of the corn stover were analysed. RESULTS: Content of all lignocellulose components decreased to a certain extent after fungal pretreatment. The total gas production of sterilized corn stover treated with I. lacteus for 42 days increased from 200 to 289 mL g-1 organic matter. Moreover, the cellulase activity was highest at the later stage of I. lacteus pretreatment. Multi-scale structural analysis indicated that white rot fungal pretreatment, and in particular that of I. lacteus, increased and enlarged substrate porosity and caused changes in the structure of corn stover. CONCLUSION: Irpex lacteus pretreatment improved the nutritional value of corn stover as a ruminant feed by degrading both cellulose and acid-insoluble lignin as well as changing the structure of the cell walls. © 2018 Society of Chemical Industry.

Effects of microbial enzymes on starch and hemicellulose degradation in total mixed ration silages.

OBJECTIVE: This study investigated the association of enzyme-producing microbes and their enzymes with starch and hemicellulose degradation during fermentation of total mixed ration (TMR) silage. METHODS: The TMRs were prepared with soybean curd residue, alfalfa hay (ATMR) or Leymus chinensis hay (LTMR), corn meal, soybean meal, vitamin-mineral supplements, and salt at a ratio of 25:40:30:4:0.5:0.5 on a dry matter basis. Laboratory-scale bag silos were randomly opened after 1, 3, 7, 14, 28, and 56 days of ensiling and subjected to analyses of fermentation quality, carbohydrates loss, microbial amylase and hemicellulase activities, succession of dominant amylolytic or hemicellulolytic microbes, and their microbial and enzymatic properties. RESULTS: Both ATMR and LTMR silages were well preserved, with low pH and high lactic acid concentrations. In addition to the substantial loss of water soluble carbohydrates, loss of starch and hemicellulose was also observed in both TMR silages with prolonged ensiling. The microbial amylase activity remained detectable throughout the ensiling in both TMR silages, whereas the microbial hemicellulase activity progressively decreased until it was inactive at day 14 post-ensiling in both TMR silages. During the early stage of fermentation, the main amylase-producing microbes were Bacillus amyloliquefaciens (B. amyloliquefaciens), B. cereus, B. licheniformis, and B. subtilis in ATMR silage and B. flexus, B. licheniformis, and Paenibacillus xylanexedens (P. xylanexedens) in LTMR silage, whereas Enterococcus faecium was closely associated with starch hydrolysis at the later stage of fermentation in both TMR silages. B. amyloliquefaciens, B. licheniformis, and B. subtilis and B. licheniformis, B. pumilus, and P. xylanexedens were the main source of microbial hemicellulase during the early stage of fermentation in ATMR and LTMR silages, respectively. CONCLUSION: The microbial amylase contributes to starch hydrolysis during the ensiling process in both TMR silages, whereas the microbial hemicellulase participates in the hemicellulose degradation only at the early stage of ensiling.