Pre-treatment of Pinus radiata substrates by basidiomycetes fungi to enhance enzymatic hydrolysis

Fungal lignocellulolytic enzymes and lignocellulose: A critical review on their contribution to multiproduct biorefinery and global biofuel research

The continuous increase in the global energy demand has diminished fossil fuel reserves and elevated the risk of environmental deterioration and human health. Biorefinery processes involved in producing bio-based energy-enriched chemicals have paved way to meet the energy demands. Compared to the thermochemical processes, fungal system biorefinery processes seems to be a promising approach for lignocellulose conversion. It also offers an eco-friendly and energy-efficient route for biofuel generation. Essentially, ligninolytic white-rot fungi and their enzyme arsenals degrade the plant biomass into structural constituents with minimal by-products generation. Hemi- or cellulolytic enzymes from certain soft and brown-rot fungi are always favoured to hydrolyze complex polysaccharides into fermentable sugars and other value-added products. However, the cost of saccharifying enzymes remains the major limitation, which hinders their application in lignocellulosic biorefinery. In the past, research has been focused on the role of lignocellulolytic fungi in biofuel production; however, a cumulative study comprising the contribution of the lignocellulolytic enzymes in biorefinery technologies is still lagging. Therefore, the overarching goal of this review article is to discuss the major contribution of lignocellulolytic fungi and their enzyme arsenal in global biofuel research and multiproduct biorefinery.

Fiber degradation and carbohydrate production by combined biological and chemical/physicochemical pretreatment methods of lignocellulosic biomass - A review

Sustainable biorefinery concepts based on lignocellulosic biomass are gaining worldwide research interest because of their inexpensiveness and abundance. The recalcitrance of lignocellulosic biomass poses a major hindrance to enhance biofuel production. Therefore, a pretreatment step is critical to prepare the substrates for the downstream process. Combining pretreatment steps help to lower the severity of the drawbacks of a single pretreatment step. This paper systematically reviews the combined biological and chemical/physicochemical pretreatment based on fiber degradation and sugar yield. An energy-efficient biological pretreatment method combined with a chemical pretreatment that accelerates the pretreatment times has been seen to be efficient for fiber degradation and sugar yields. However, fungal species, culture conditions, biomass type, the severity of chemical pretreatment and the order of sequential pretreatment influences the relative component contents and sugar yield. Even the same biomass from different sources undergoing similar pretreatment conditions could result in a varying amount of digestibility.

Enzymatic Hydrolysis of Sugarcane Bagasse in Aqueous Two-Phase Systems (ATPS): Exploration and Conceptual Process Design

The enzymatic conversion of lignocellulosic material to sugars can provide a carbon source for the production of energy (fuels) and a wide range of renewable products. However, the efficiency of this conversion is impaired due to product (sugar) inhibition. Even though several studies investigate how to overcome this challenge, concepts on the process to conduct the hydrolysis are still scarce in literature. Aqueous two-phase systems (ATPS) can be applied to design an extractive reaction due to their capacity to partition solutes to different phases in such a system. This work presents strategies on how to conduct extractive enzymatic hydrolysis in ATPS and how to explore the experimental results in order to design a feasible process. While only a limited number of ATPS was explored, the methods and strategies described could easily be applied to any further ATPS to be explored. We studied two promising ATPS as a subset of a previously high throughput screened large set of ATPS, providing two configurations of processes having the reaction in either the top phase or in the bottom phase. Enzymatic hydrolysis in these ATPS was performed to evaluate the partitioning of the substrate and the influence of solute partitioning on conversion. Because ATPS are able to partition inhibitors (sugar) between the phases, the conversion rate can be maintained. However, phase forming components should be selected to preserve the enzymatic activity. The experimental results presented here contribute to a feasible ATPS-based conceptual process design for the enzymatic conversion of lignocellulosic material.

Impact of surfactant assisted acid and alkali pretreatment on lignocellulosic structure of pine foliage and optimization of its saccharification parameters using response surface methodology

In present study, two hybrid methods such as surfactant assisted acid pretreatment (SAAP) and surfactant assisted base pretreatment (SABP) of pine foliage (PF) were found efficient for removal of 59.53 ± 0.76% and 73.47 ± 1.03% lignin, respectively. Assessment of the impact of pretreatment over the structure of PF were studied by scanning electron microscopy, Fourier transform infrared and X-ray diffraction analysis. Parameters for saccharification of SAAP and SABP biomass were optimized by Box-Behnken design method and 0.588 g/g and 0.477 g/g of reducing sugars were obtained, respectively. The ethanol fermentation efficiency of Saccharomyces cerevisiae (NCIM 3288) of hydrolysates was increased by 16.1% and 6.01% in SAAP-PFF and SABP-PFF after detoxification with XAD-4 resin. The mass balance analysis of the process showed that 67.7% and 70.12% cellulose were utilized during SAAP and SABP, respectively. These results indicated that SAAP would be more economic for bioethanol production.

Solid-state fermentation in multi-well plates to assess pretreatment efficiency of rot fungi on lignocellulose biomass

The potential of fungal pretreatment to improve fermentable sugar yields from wheat straw or Miscanthus was investigated. We assessed 63 fungal strains including 53 white-rot and 10 brown-rot fungi belonging to the Basidiomycota phylum in an original 12 day small-scale solid-state fermentation (SSF) experiment using 24-well plates. This method offers the convenience of one-pot processing of samples from SSF to enzymatic hydrolysis. The comparison of the lignocellulolytic activity profiles of white-rot fungi and brown-rot fungi showed different behaviours. The hierarchical clustering according to glucose and reducing sugars released from each biomass after 72 h enzymatic hydrolysis splits the set of fungal strains into three groups: efficient, no-effect and detrimental-effect species. The efficient group contained 17 species belonging to seven white-rot genera and one brown-rot genus. The yield of sugar released increased significantly (max. 62%) compared with non-inoculated controls for both substrates.

Improved saccharification of steam-exploded Pinus radiata on supplementing crude extract of Penicillium sp

Commercially available enzymes do not contain all the necessary softwood-specific accessory enzymes to obtain high saccharification efficiency. In this work, six saprophytic fungi obtained from Pinus radiata plantation site were screened for the putative softwood-specific accessory enzyme, β-mannanase. A Penicillium sp. was found to produce β-mannanase in both solid (31.6 units/g of dry biomass) and liquid (117 units/g of dry biomass) cultures using locust bean gum as an inducer after 2 weeks of incubation. The saccharification of steam-exploded Pinus radiata was 7.8 % w/w improved when the crude extract of Penicillium sp. was added to a mixture of commercial enzymes.

A synergistic effect of pretreatment on cell wall structural changes in barley straw (Hordeum vulgare L.) for efficient bioethanol production

BACKGROUND

Barley straw (Hordeum vulgare L.) is an attractive lignocellulosic material and one of the most abundant renewable resources for fuel ethanol production. Although it has high cellulose and hemicellulose contents, there are several challenges and limitations in the process of converting it to fuel ethanol. High ash, silica and lignin contents in barley straw make it an inferior feedstock for enzymatic hydrolysis. Therefore pretreatment of barley straw could play an important role in inducing structural and compositional changes that increase the efficiency of enzymatic hydrolysis and make the whole process economically viable.

RESULTS

Saccharification was enhanced using various concentrations (0.0, 0.5, 1.0, 2.0 and 3.0% v/v) of a solution of sodium hypochlorite (NaClO) and hydrogen peroxide (H₂O₂) and various reaction times (15, 30 and 45 min) during pretreatment at 121 °C. The highest yield of glucose (447 mg g⁻¹) was achieved by pretreatment with 2.0% NaClO+H₂O₂ solution for 30 min, representing an increase of 65.99% compared with untreated barley straw (152 mg g⁻¹). During fermentation, the highest amount of ethanol (207 mg g⁻¹) was obtained under anaerobic plus 0.4 mmol L⁻¹ benzoic acid conditions, representing an increase of 57.49, 38.16 and 10.14% compared with untreated sample (88 mg g⁻¹), aerobic (128 mg g⁻¹) and anaerobic (186 mg g⁻¹) conditions respectively.

CONCLUSION

The results suggest that pretreatment with 2.0% NaClO+H₂O₂ solution disrupted the recalcitrant structure of barley straw and enhanced the glucose yield and subsequent bioethanol production.

Comparing lignocellulose physiochemistry after decomposition by brown rot fungi with distinct evolutionary origins

Among wood-degrading fungi, lineages holding taxa that selectively metabolize carbohydrates without significant lignin removal (brown rot) are polyphyletic, having evolved multiple times from lignin-removing white rot fungi. Given the qualitative nature of the 'brown rot' classifier, we aimed to quantify and compare the temporal sequence of carbohydrate removal among brown rot clades. Lignocellulose deconstruction was compared among fungi using distinct plant substrates (angiosperm, conifer, grass). Specifically, aspen, pine and corn stalk were harvested over a 16-week time series from microcosms containing Gloeophyllum trabeum, Fomitopsis pinicola, Ossicaulis lignatilis, Fistulina hepatica, Serpula lacrymans, Wolfiporia cocos or Dacryopinax sp. After quantifying plant mass loss, a thorough compositional analysis was complemented by a saccharification test to determine wood cell wall accessibility. Mass loss and accessibility varied depending on fungal decomposer and substrate, and trajectories of loss for hemicellulosic components and cellulose differed among plant tissue types. At any given stage of decomposition, however, lignocellulose accessibility and the fraction remaining of carbohydrates and lignin within a plant tissue type were generally the same, regardless of fungal isolate. This suggests that the sequence of plant component removal at this typical scale of characterization is shared among these brown rot lineages, despite their diverse genomes and secretomes.

Re-evaluation of the Genus Antrodia (Polyporales, Basidiomycota) in Korea

The wood decay fungi Antrodia P. Karst. play important ecological roles and have significant industrial and economic impacts as both wood degraders and sources of pharmaceutical and biotechnological products. Although each Antrodia species has distinct morphological characteristics, the misidentification rate is especially high due to their simple morphological characters. A combination of morphological and internal transcribed spacer region sequence analyses revealed that 27 of 89 specimens previously identified by morphology alone were correct, whereas 35 of these specimens were misidentified as other Antrodia species. We report here that seven Antrodia species exist in Korea (A. albida, A. heteromorpha, A. malicola, A. serialis, A. sinuosa, A. sitchensis, and A. xantha) and based on these specimens, we provide taxonomic descriptions of these species, except for A. serialis, which was only confirmed by isolate.

Effect of torrefaction for the pretreatment of rice straw for ethanol production

BACKGROUND

Rice straw is an attractive lignocellulosic material for ethanol production, since it is one of the most abundant renewable resources. It generally has high cellulose and hemicellulose contents that can be readily hydrolysed into sugars for subsequent ethanol fermentation. The pretreatment method plays an important role in increasing the efficiency of enzymatic saccharification, thereby making the whole process economically viable. Torrefaction is an appropriate pretreatment technique for enhancing the enzymatic reaction and subsequent ethanol production.

RESULTS

The effects of two important parameters, i.e. residence time (20, 40 and 60 min) and temperature (160, 180, 200, 220, 240 and 260 °C), were studied under an inert atmosphere. The highest yield of 351 ± 5.49 mg g(-1) total sugars was obtained after torrefaction treatment at 220 °C for 40 min, representing a 60.68% increase compared with the untreated sample. Based on ethanol studies conducted on rice straw, this estimated quantity of sugars could produce 150 ± 2.40 mg g(-1) ethanol, a 50.67% increase compared with the untreated sample under anaerobic conditions. The fermentation rate was enhanced by adding 0.4 mmol L(-1) benzoic acid.

CONCLUSION

The use of this waste material could reduce competition with food materials for ethanol production. It can be considered as an alternative sustainable waste management option.

A phylogenetic overview of the antrodia clade (Basidiomycota, Polyporales)

Phylogenetic relationships among members of the antrodia clade were investigated with molecular data from two nuclear ribosomal DNA regions, LSU and ITS. A total of 123 species representing 26 genera producing a brown rot were included in the present study. Three DNA datasets (combined LSU-ITS dataset, LSU dataset, ITS dataset) comprising sequences of 449 isolates were evaluated with three different phylogenetic analyses (maximum likelihood, maximum parsimony, Bayesian inference). We present a phylogenetic overview of the five main groups recovered: the fibroporia, laetiporus, postia, laricifomes and core antrodia groups. Not all of the main groups received strong support in the analyses, requiring further research. We were able to identify a number of well supported clades within the main groups.

Using a grass substrate to compare decay among two clades of brown rot fungi

Interest in the mechanisms of wood-degrading fungi has grown in tandem with lignocellulose bioconversion efforts, yet many potential biomass feedstocks are non-woody. Using corn stover (Zea mays) as a substrate, we tracked degradative capacities among brown rot fungi from the Antrodia clade, including Postia placenta, the first brown rot fungus to have its genome sequenced. Decay dynamics were compared against Gloeophyllum trabeum from the Gloeophyllum clade. Weight loss induced by P. placenta (6.2 %) and five other Antrodia clade isolates (average 7.4 %) on corn stalk after 12 weeks demonstrated inefficiency among these fungi, relative to decay induced by G. trabeum (44.4 %). Using aspen (Populus sp.) as a woody substrate resulted in, on average, a fourfold increase in weight loss induced by Antrodia clade fungi, while G. trabeum results matched those on stover. The sequence and trajectories of chemical constituent losses differed as a function of substrate but not fungal clade. Instead, chemical data suggest that characters unique to stover limit decay by the Antrodia clade, rather than disparities in growth rate or extractives toxicity. High p-coumaryl lignin content, lacking the methoxy groups characteristically cleaved during brown rot, is among potential rate-distinguishing characters in grasses. This ineptitude among Antrodia clade fungi on grasses was supported by meta-analysis of other unrelated studies using grass substrates. Concerning application, results expose a problem if adopting the strategy of the model decay fungus P. placenta to treat corn stover, a widely available plant feedstock. Overall, the results insinuate phylogenetically distinct modes of brown rot and demonstrate the benefit of using non-woody substrates to probe wood degradation mechanisms.

A novel surfactant-assisted ultrasound pretreatment of sugarcane tops for improved enzymatic release of sugars

The aim of this study was to develop a novel surfactant-assisted ultrasound pretreatment of sugarcane tops as well as to optimize the effect of various operational parameters on pretreatment and hydrolysis. A novel surfactant-assisted ultrasound pretreatment was developed which could effectively remove hemicelluloses and lignin and improve the reducing sugar yield from sugarcane tops. Operational parameters for pretreatment and hydrolysis were studied and optimized. Under optimal hydrolysis conditions, 0.661 g of reducing sugar was produced per gram of pretreated biomass. The structural changes of native and pretreated biomass were investigated by Scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transform infrared analysis (FTIR). The results indicate that surfactant-assisted ultrasound pretreated sugarcane tops can be used as a potential feed stock for bioethanol production.