Lignin Transformation of One-Year-Old Plants During Anaerobic Digestion (AD)

Engineered reduction of S-adenosylmethionine alters lignin in sorghum

BACKGROUND

Lignin is an aromatic polymer deposited in secondary cell walls of higher plants to provide strength, rigidity, and hydrophobicity to vascular tissues. Due to its interconnections with cell wall polysaccharides, lignin plays important roles during plant growth and defense, but also has a negative impact on industrial processes aimed at obtaining monosaccharides from plant biomass. Engineering lignin offers a solution to this issue. For example, previous work showed that heterologous expression of a coliphage S-adenosylmethionine hydrolase (AdoMetase) was an effective approach to reduce lignin in the model plant Arabidopsis. The efficacy of this engineering strategy remains to be evaluated in bioenergy crops.

RESULTS

We studied the impact of expressing AdoMetase on lignin synthesis in sorghum (Sorghum bicolor L. Moench). Lignin content, monomer composition, and size, as well as biomass saccharification efficiency were determined in transgenic sorghum lines. The transcriptome and metabolome were analyzed in stems at three developmental stages. Plant growth and biomass composition was further evaluated under field conditions. Results evidenced that lignin was reduced by 18% in the best transgenic line, presumably due to reduced activity of the S-adenosylmethionine-dependent O-methyltransferases involved in lignin synthesis. The modified sorghum features altered lignin monomer composition and increased lignin molecular weights. The degree of methylation of glucuronic acid on xylan was reduced. These changes enabled a ~20% increase in glucose yield after biomass pretreatment and saccharification compared to wild type. RNA-seq and untargeted metabolomic analyses evidenced some pleiotropic effects associated with AdoMetase expression. The transgenic sorghum showed developmental delay and reduced biomass yields at harvest, especially under field growing conditions.

CONCLUSIONS

The expression of AdoMetase represents an effective lignin engineering approach in sorghum. However, considering that this strategy potentially impacts multiple S-adenosylmethionine-dependent methyltransferases, adequate promoters for fine-tuning AdoMetase expression will be needed to mitigate yield penalty.

Evaluation of Chemical Composition of Miscanthus × giganteus Raised in Different Climate Regions in Russia

Lignocellulosic biomass is of great interest as an alternative energy resource because it offers a range of merits. Miscanthus × giganteus is a lignocellulosic feedstock of special interest, as it combines a high biomass productivity with a low environmental impact, including CO₂ emission control. The chemical composition of lignocellulose determines the application potential for efficient industrial processing. Here, we compiled a sample collection of Miscanthus × giganteus that had been cultivated in different climate regions between 2019 and 2021. The chemical composition was quantified by the conventional wet methods. The findings were compared with each other and with the known data. Starting as soon as the first vegetation year, Miscanthus was shown to feature the following chemical composition: 43.2-55.5% cellulose content, 17.1-25.1% acid-insoluble lignin content, 17.9-22.9% pentosan content, 0.90-2.95% ash content, and 0.3-1.2% extractives. The habitat and the surrounding environment were discovered herein to affect the chemical composition of Miscanthus. The stem part of Miscanthus was found to be richer in cellulose than the leaf (48.4-54.9% vs. 47.2-48.9%, respectively), regardless of the planation age and habitat. The obtained findings broaden the investigative geography of the chemical composition of Miscanthus and corroborate the high value of Miscanthus for industrial conversion thereof into cellulosic products worldwide.

Conversion of Carbohydrates in Lignocellulosic Biomass after Chemical Pretreatment

The aim of the study was to determine the quantitative and qualitative changes taking place in biomass components actively participating in methane fermentation, i.e., in carbohydrates, as a result of chemical pretreatment. Analyses were conducted on agricultural waste (corn stover, also called corn straw, and corncobs) as materials most commonly used in methane fermentation, as well as poplar wood, a material relatively rarely used in biogas production. Pretreatment with the aim of increasing efficiency of methane fermentation was carried out with the use of acid and alkaline solutions of different concentrations. The effect of pretreatment on carbohydrates was analyzed based on the quantitative and qualitative changes in this component. Due to the structural heterogeneity of carbohydrates, their varied reactivity and fermentability were determined in terms of holocellulose, cellulose, and pentosans. The chemical structure of cellulose was also analyzed. It is shown in this study that chemical pretreatment causes transformations of carbohydrate components, which differ quantitatively and qualitatively in the compared raw materials. It was found that the alkaline treatment caused smaller changes in the percentage shares of the carbohydrate biomass components as compared to the acid treatment. Moreover, it was observed that the compared materials differ in terms of quantitative changes in their chemical composition depending on the composition of the raw material prior to pretreatment. In the case of corn waste subjected to the action of 1 and 3% NaOH, the share of pentosans in the biomass increased. It was established that this is a change with a positive effect on fermentation efficiency. The action of acids and alkalis on the biomass led to similar structural changes in cellulose, which are adverse for the fermentation process.

Anaerobic Digestion for Producing Renewable Energy-The Evolution of This Technology in a New Uncertain Scenario

Anaerobic digestion is a well-known technology with wide application in the treatment of high-strength organic wastes. The economic feasibility of this type of installation is usually attained thanks to the availability of fiscal incentives. In this review, an analysis of the different factors associated with this biological treatment and a description of alternatives available in literature for increasing performance of the process were provided. The possible integration of this process into a biorefinery as a way for producing energy and chemical products from the conversion of wastes and biomass also analyzed. The future outlook of anaerobic digestion will be closely linked to circular economy principles. Therefore, this technology should be properly integrated into any production system where energy can be recovered from organics. Digestion can play a major role in any transformation process where by-products need further stabilization or it can be the central core of any waste treatment process, modifying the current scheme by a concatenation of several activities with the aim of increasing the efficiency of the conversion. Thus, current plants dedicated to the treatment of wastewaters, animal manures, or food wastes can become specialized centers for producing bio-energy and green chemicals. However, high installation costs, feedstock dispersion and market distortions were recognized as the main parameters negatively affecting these alternatives.

The Influence of Corn Straw Extrusion Pretreatment Parameters on Methane Fermentation Performance

The aim of the study is to determine the energy consumption of the extrusion-cooking process of corn straw under various conditions (screw speed, moisture content), water absorption measurements and water solubility indices as well as biogas efficiency evaluation. The extrusion-cooking of corn straw was carried out using a single screw extruder with L/D = 16:1 at various rotational screw speeds (70, 90, and 110 rpm) and with various initial moisture content of raw material (25 and 40%). Prior to the process, the moisture content of the raw material was measured, and next, it was moistened to 25 and 40% of dry matter. For example, at 70 rpm extruder screw speed, the temperature range was 126–150 °C. Energy consumption of straw pretreatment through extrusion-cooking was assessed in order to evaluate the possibility of using the process in an agricultural biogas plant. Biogas and methane efficiency of substrates after extrusion was tested in a laboratory scale biogas plant and expressed as a volume of cumulative methane production for fresh matter, dry matter, and dry organic matter. Pretreated corn straw moistened to 25% and processed at 110 rpm during the extrusion-cooking processing produced the most advantageous effect for methane and biogas production (51.63%) efficiency as compared to corn straw without pretreatment (49.57%). Rotational speed of the extruder screw influenced biogas and methane production. With both dry matter and dry organic matter, the increase of rotational speed of the extruder screw improved the production of cumulated biogas and methane. Pretreatment of corn straw has a positive effect on the acquisition of cumulated methane (226.3 Nm³ Mg⁻¹ for fresh matter, 243.99 Nm³ Mg⁻¹ for dry matter, and 254.83 Nm³ Mg⁻¹ for dry organic matter). Preliminary analysis of infrared spectra revealed changes in the samples also at the molecular level, thus opening up the possibility of identifying marker bands that account for specific degradation changes.

Energy Efficiency of Comminution and Extrusion of Maize Substrates Subjected to Methane Fermentation

The production of methane in the anaerobic digestion process is a proven technology, but it is characterized by low cost-effectiveness. The pretreatment of substrates seems to be a promising technology, which may increase the cost-effectiveness of biogas installations. The aim of the study was to investigate the influence of the comminution and extrusion of maize silage and maize straw silage on the course and yield of anaerobic digestion. The use of a pretreatment (comminution, extrusion) is justified when its energy balance is positive. The greatest increase in the methane yield per dry matter (12.4%) was observed after the extrusion of maize straw silage at 175 °C. The change in the methane yield resulting from the extrusion of maize silage and maize straw silage at 150 °C was small and amounted to 6.4% and 9%, respectively. The comminution caused an increase in the methane yield and accelerated the fermentation of substrates. The methane yield from maize silage was 38.4%, whereas the yield from maize straw silage was only 8.3%.