Sporotrichum thermophile Growth, Cellulose Degradation, and Cellulase Activity

An experimental and modeling approach to describe the deactivation of cellulases at the air-liquid interface

Understanding the reaction mechanisms involved in the enzymatic hydrolysis of cellulose is important because it is kinetically the most limiting step of the bioethanol production process. The present work focuses on the enzymatic deactivation at the air-liquid interface, which is one of the aspects contributing to this global deactivation. This phenomenon has already been experimentally proven, but this is the first time that a model has been proposed to describe it. Experiments were performed by incubating Celluclast cocktail solutions on an orbital stirring system at different enzyme concentrations and different surface-to-volume ratios. A 5-day follow-up was carried out by measuring the global FPase activity of cellulases for each condition tested. The activity loss was proven to depend on both the air-liquid surface area and the enzyme concentration. Both observations suggest that the loss of activity takes place at the air-liquid surface, the total amount of enzymes varying with volume or enzyme concentration. Furthermore, tests performed using five individual enzymes purified from a Trichoderma reesei cocktail showed that the only cellulase that is deactivated at the air-liquid interface is cellobiohydrolase II. From the experimental data collected by varying the initial enzyme concentration and the ratio surface to volume, it was possible to develop, for the first time, a model that describes the loss of activity at the air-liquid interface for this configuration.

Construction of an enzyme-constrained metabolic network model for Myceliophthora thermophila using machine learning-based kcat data

BACKGROUND

Genome-scale metabolic models (GEMs) serve as effective tools for understanding cellular phenotypes and predicting engineering targets in the development of industrial strain. Enzyme-constrained genome-scale metabolic models (ecGEMs) have emerged as a valuable advancement, providing more accurate predictions and unveiling new engineering targets compared to models lacking enzyme constraints. In 2022, a stoichiometric GEM, iDL1450, was reconstructed for the industrially significant fungus Myceliophthora thermophila. To enhance the GEM's performance, an ecGEM was developed for M. thermophila in this study.

RESULTS

Initially, the model iDL1450 underwent refinement and updates, resulting in a new version named iYW1475. These updates included adjustments to biomass components, correction of gene-protein-reaction (GPR) rules, and a consensus on metabolites. Subsequently, the first ecGEM for M. thermophila was constructed using machine learning-based kcat data predicted by TurNuP within the ECMpy framework. During the construction, three versions of ecGEMs were developed based on three distinct kcat collection methods, namely AutoPACMEN, DLKcat and TurNuP. After comparison, the ecGEM constructed using TurNuP-predicted kcat values performed better in several aspects and was selected as the definitive version of ecGEM for M. thermophila (ecMTM). Comparing ecMTM to iYW1475, the solution space was reduced and the growth simulation results more closely resembled realistic cellular phenotypes. Metabolic adjustment simulated by ecMTM revealed a trade-off between biomass yield and enzyme usage efficiency at varying glucose uptake rates. Notably, hierarchical utilization of five carbon sources derived from plant biomass hydrolysis was accurately captured and explained by ecMTM. Furthermore, based on enzyme cost considerations, ecMTM successfully predicted reported targets for metabolic engineering modification and introduced some new potential targets for chemicals produced in M. thermophila.

CONCLUSIONS

In this study, the incorporation of enzyme constraint to iYW1475 not only improved prediction accuracy but also broadened the model's applicability. This research demonstrates the effectiveness of integrating of machine learning-based kcat data in the construction of ecGEMs especially in situations where there is limited measured enzyme kinetic parameters for a specific organism.

Staphylococcus aureus microbial biofilms degradation using cellobiose dehydrogenase from Thermothelomyces thermophilus M77

This work reports biochemical characterization of Thermothelomyces thermophilus cellobiose dehydrogenase (TthCDHIIa) and its application as an antimicrobial and antibiofilm agent. We demonstrate that TthCDHIIa is thermostable in different ionic solutions and is capable of oxidizing multiple mono and oligosaccharide substrates and to continuously produce H2O2. Kinetics measurements depict the enzyme catalytic characteristics consistent with an Ascomycota class II CDH. Our structural analyses show that TthCDHIIa substrate binding pocket is spacious enough to accommodate larger cello and xylooligosaccharides. We also reveal that TthCDHIIa supplemented with cellobiose reduces the viability of S. aureus ATCC 25923 up to 32 % in a planktonic growth model and also inhibits its biofilm growth on 62.5 %. Furthermore, TthCDHIIa eradicates preformed S. aureus biofilms via H2O2 oxidative degradation of the biofilm matrix, making these bacteria considerably more susceptible to gentamicin and tetracycline.

PFK2/FBPase-2 is a potential target for metabolic engineering in the filamentous fungus Myceliophthora thermophila

The key enzyme 6-phosphofructo-2-kinase (PFK2)/fructose-2,6-bisphosphatase (FBPase-2) is responsible for regulating the rates of glycolysis and gluconeogenesis in eukaryotes. However, its functions and mechanisms in filamentous fungi remain largely enigmatic. In this study, we systematically investigated the function of this enzyme in Myceliophthora thermophila, a thermophilic filamentous fungus with great capacity to produce industrial enzymes and organic acids. Our results showed that the M. thermophila genome encodes three isomers, all with the PFK2/FBPase-2 structure: pfk2-a, pfk2-b, and pfk2-c. Overexpression of each gene revealed that endogenous expression of pfk2-c (PFK2 activity) promoted glucose metabolism, while overexpression of pfk2-a (FBPase-2 activity) inhibited strain growth. Using knockouts, we found that each gene was individually non-essential, but the triple knockout led to significantly slower growth compared with the wild-type strain. Only the pfk2-a single knockout exhibited 22.15% faster sugar metabolism, exerted through activation of 6-phosphofructo-1-kinase (PFK1), thereby significantly promoting glycolysis and the tricarboxylic acid cycle. The FBPase-2 deletion mutant strain also exhibited overflow metabolism, and knocking out pfk2-a was proved to be able to improve the production and synthesis rate of various metabolites, such as glycerol and malate. This is the first study to systematically investigate the function of PFK2/FBPase-2 in a thermophilic fungus, providing an effective target for metabolic engineering in filamentous fungi.

Development of an Efficient C-to-T Base-Editing System and Its Application to Cellulase Transcription Factor Precise Engineering in Thermophilic Fungus Myceliophthora thermophila

Myceliophthora thermophila is a thermophilic fungus with great potential in biorefineries and biotechnology. The base editor is an upgraded version of the clustered regularly interspaced short palindromic repeats (CRISPR)-dependent genome-editing tool that introduces precise point mutations without causing DNA double-strand breaks (DSBs) and has been used in various organisms but rarely in filamentous fungi, especially thermophilic filamentous fungi. Here, for the first time, we constructed three cytosine base editors (CBEs) in M. thermophila, namely, evolved apolipoprotein B mRNA-editing enzyme catalytic subunit 1 (APOBEC1) cytosine base editor 4 max (Mtevo-BE4max), bacteriophage Mu Gam protein cytosine base editor 4 max (MtGAM-BE4max), and evolved CDA1 deaminase cytosine base editor (Mtevo-CDA1), and efficiently inactivated genes by precisely converting three codons (CAA, CAG, and CGA) into stop codons without DSB formation. The Mtevo-CDA1 editor with up to 92.6% editing efficiency is a more suitable tool for cytosine base editing in thermophilic fungi. To investigate the function of each motif of the cellulase transcription factor M. thermophila CLR-2 (MtCLR-2), we used the Mtevo-CDA1 editor. The fungal-specific motif of MtCLR-2 was found to be strongly involved in cellulase secretion, conidium formation, hyphal branching, and colony formation. Mutation of the fungus-specific motif caused significant defects in these characteristics. Thus, we developed an efficient thermophilic fungus-compatible base-editing system that could also be used for genetic engineering in other relevant filamentous fungi.

IMPORTANCE A CRISPR/Cas-based base-editing approach has been developed to introduce point mutations without inducing double-strand breaks (DSBs) and attracted substantial academic and industrial interest. Our study developed the deaminase-cytosine base-editing system to efficiently edit three target genes, amdS, cre-1, and the essential cellulase regulator gene Mtclr-2, in Myceliophthora thermophila. A variety of point mutations in the target loci of the DNA-binding domain and fungus-specific motif of M. thermophila CLR-2 (MtCLR-2) were successfully generated via our base editor Mtevo-CDA1 to elucidate its function. Here, we show that the DNA-binding domain of MtCLR-2 is important for the fungal response to cellulose conditions, while its fungus-specific motif is involved in fungal growth. These findings indicate that our base editor can be an effective tool for elucidating the functions of motifs of target genes in filamentous fungi and for metabolic engineering in the field of synthetic biology.

Study on dynamic changes of microbial community and lignocellulose transformation mechanism during green waste composting

There are few reports on the material transformation and dominant microorganisms in the process of greening waste (GW) composting. In this study, the target microbial community succession and material transformation were studied in GW composting by using MiSeq sequencing and PICRUSt tools. The results showed that the composting process could be divided into four phases. Each phase of the composting appeared in turn and was unable to jump. In the calefactive phase, microorganisms decompose small molecular organics such as FA to accelerate the arrival of the thermophilic phase. In the thermophilic phase, thermophilic microorganisms decompose HA and lignocellulose to produce FA. While in the cooling phase, microorganisms degrade HA and FA for growth and reproduction. In the maturation phase, microorganisms synthesize humus using FA, amino acid and lignin nuclei as precursors. In the four phases of the composting, different representative genera of bacteria and fungi were detected. Streptomyces, Myceliophthora and Aspergillus, maintained high abundance in all phases of the compost. Correlation analysis indicated that bacteria, actinomycetes and fungi had synergistic effect on the degradation of lignocellulose. Therefore, it can accelerate the compost process by maintaining the thermophilic phase and adding a certain amount of FA in the maturation phase.

Myceliophthora thermophila Xyr1 is predominantly involved in xylan degradation and xylose catabolism

BACKGROUND

Myceliophthora thermophila is a thermophilic ascomycete fungus that is used as a producer of enzyme cocktails used in plant biomass saccharification. Further development of this species as an industrial enzyme factory requires a detailed understanding of its regulatory systems driving the production of plant biomass-degrading enzymes. In this study, we analyzed the function of MtXlr1, an ortholog of the (hemi-)cellulolytic regulator XlnR first identified in another industrially relevant fungus, Aspergillus niger.

RESULTS

The Mtxlr1 gene was deleted and the resulting strain was compared to the wild type using growth profiling and transcriptomics. The deletion strain was unable to grow on xylan and d-xylose, but showed only a small growth reduction on l-arabinose, and grew similar to the wild type on Avicel and cellulose. These results were supported by the transcriptome analyses which revealed reduction of genes encoding xylan-degrading enzymes, enzymes of the pentose catabolic pathway and putative pentose transporters. In contrast, no or minimal effects were observed for the expression of cellulolytic genes.

CONCLUSIONS

Myceliophthora thermophila MtXlr1 controls the expression of xylanolytic genes and genes involved in pentose transport and catabolism, but has no significant effects on the production of cellulases. It therefore resembles more the role of its ortholog in Neurospora crassa, rather than the broader role described for this regulator in A. niger and Trichoderma reesei. By revealing the range of genes controlled by MtXlr1, our results provide the basic knowledge for targeted strain improvement by overproducing or constitutively activating this regulator, to further improve the biotechnological value of M. thermophila.

Direct production of commodity chemicals from lignocellulose using Myceliophthora thermophila

The production of fuels and chemicals from renewable plant biomass has been proposed as a feasible strategy for global sustainable development. However, the economic efficiency of biorefineries is low. Here, through metabolic engineering, Myceliophthora thermophila, a cellulolytic thermophilic fungus, was constructed into a platform that can efficiently convert lignocellulose into important bulk chemicals-four carbon 1, 4-diacids (malic and succinic acid), building blocks for biopolymers-without the need for extra hydrolytic enzymes. Titers of >200 g/L from crystalline cellulose and 110 g/L from plant biomass (corncob) were achieved during fed-batch fermentation. Our study represents a milestone in consolidated bioprocessing technology and offers a new and promising system for the cost-effective production of chemicals and fuels from biomass.

Thermostable multifunctional GH74 xyloglucanase from Myceliophthora thermophila: high-level expression in Pichia pastoris and characterization of the recombinant protein

A xyloglucanase of the GH74 family was identified in the thermophilic fungus strain Myceliophthora thermophila VKPM F-244, and its gene sequence was optimized for cloning and expression in Pichia pastoris. The recombinant xyloglucanase MtXgh74 exhibited the highest activity toward tamarind seed xyloglucan with a K _M value of 0.51 ± 0.06 mg/mL. The activities on barley β-glucan and carboxymethylcellulose were about 4 and 2%, respectively, compared to xyloglucan. Maximum xyloglucanase activity was observed at 70-75 °C and pH 6.5. After pre-incubation at 50 °C, pH 6.0 for 3 h, the enzyme retained 100% of its activity. The half-life of MtXgh74 at 60 °C, pH 6.0 was 40 min. In P. pastoris, MtXgh74 was produced in glycosylated form. The enzyme production in a 1 L bioreactor resulted in a yield of 118 U/mL or 5.3 g/L after 51 h fermentation. Kinetic studies of the hydrolysis product formation suggest that MtXgh74 has an endo-processive mode of action. The final products were the standard xyloglucan building blocks XXXG, XXLG, XLXG, and XLLG. Additionally, MtXgh74 hydrolyzed various linkages within the xyloglucan building blocks XXXG, XXLG, and XLXG (except XLLG) producing diverse low molecular weight oligosaccharides which may be identified by MALDI-TOF as XG, XX, XXG/GXX/XGX, XXX, LG, LX/XL, XLX/XXL, LLG, GXXXG, GXLLG, XLLGX. The unique combination of different activities within one enzyme along with its high thermostability and specificity toward xyloglucan makes MtXgh74 a promising candidate enzyme for industrial applications.

Recombinant expression of thermostable processive MtEG5 endoglucanase and its synergism with MtLPMO from Myceliophthora thermophila during the hydrolysis of lignocellulosic substrates

BACKGROUND

Filamentous fungi are among the most powerful cellulolytic organisms in terrestrial ecosystems. To perform the degradation of lignocellulosic substrates, these microorganisms employ both hydrolytic and oxidative mechanisms that involve the secretion and synergism of a wide variety of enzymes. Interactions between these enzymes occur on the level of saccharification, i.e., the release of neutral and oxidized products, but sometimes also reflected in the substrate liquefaction. Although the synergism regarding the yield of neutral sugars has been extensively studied, further studies should focus on the oxidized sugars, as well as the effect of enzyme combinations on the viscosity properties of the substrates.

RESULTS

In the present study, the heterologous expression of an endoglucanase (EG) and its combined activity together with a lytic polysaccharide monooxygenase (LPMO), both from the thermophilic fungus Myceliophthora thermophila, are described. The EG gene, belonging to the glycoside hydrolase family 5, was functionally expressed in the methylotrophic yeast Pichia pastoris. The produced MtEG5A (75 kDa) featured remarkable thermal stability and showed high specific activity on microcrystalline cellulose compared to CMC, which is indicative of its processivity properties. The enzyme was capable of releasing high amounts of cellobiose from wheat straw, birch, and spruce biomass. Addition of MtLPMO9 together with MtEG5A showed enhanced enzymatic hydrolysis yields against regenerated amorphous cellulose (PASC) by improving the release not only of the neutral but also of the oxidized sugars. Assessment of activity of MtEG5A on the reduction of viscosity of PASC and pretreated wheat straw using dynamic viscosity measurements revealed that the enzyme is able to perform liquefaction of the model substrate and the natural lignocellulosic material, while when added together with MtLPMO9, no further synergistic effect was observed.

CONCLUSIONS

The endoglucanase MtEG5A from the thermophilic fungus M. thermophila exhibited excellent properties that render it a suitable candidate for use in biotechnological applications. Its strong synergism with LPMO was reflected in sugars release, but not in substrate viscosity reduction. Based on the level of oxidative sugar formation, this is the first indication of synergy between LPMO and EG reported.

Development of a genome-editing CRISPR/Cas9 system in thermophilic fungal Myceliophthora species and its application to hyper-cellulase production strain engineering

BACKGROUND

Over the past 3 years, the CRISPR/Cas9 system has revolutionized the field of genome engineering. However, its application has not yet been validated in thermophilic fungi. Myceliophthora thermophila, an important thermophilic biomass-degrading fungus, has attracted industrial interest for the production of efficient thermostable enzymes. Genetic manipulation of Myceliophthora is crucial for metabolic engineering and to unravel the mechanism of lignocellulose deconstruction. The lack of a powerful, versatile genome-editing tool has impeded the broader exploitation of M. thermophila in biotechnology.

RESULTS

In this study, a CRISPR/Cas9 system for efficient multiplexed genome engineering was successfully developed in the thermophilic species M. thermophila and M. heterothallica. This CRISPR/Cas9 system could efficiently mutate the imported amdS gene in the genome via NHEJ-mediated events. As a proof of principle, the genes of the cellulase production pathway, including cre-1, res-1, gh1-1, and alp-1, were chosen as editing targets. Simultaneous multigene disruptions of up to four of these different loci were accomplished with neomycin selection marker integration via a single transformation using the CRISPR/Cas9 system. Using this genome-engineering tool, multiple strains exhibiting pronounced hyper-cellulase production were generated, in which the extracellular secreted protein and lignocellulase activities were significantly increased (up to 5- and 13-fold, respectively) compared with the parental strain.

CONCLUSIONS

A genome-wide engineering system for thermophilic fungi was established based on CRISPR/Cas9. Successful expansion of this system without modification to M. heterothallica indicates it has wide adaptability and flexibility for use in other Myceliophthora species. This system could greatly accelerate strain engineering of thermophilic fungi for production of industrial enzymes, such as cellulases as shown in this study and possibly bio-based fuels and chemicals in the future.

Myceliophthora thermophila syn. Sporotrichum thermophile: a thermophilic mould of biotechnological potential

Myceliophthora thermophila syn. Sporotrichum thermophile is a ubiquitous thermophilic mould with a strong ability to degrade organic matter during optimal growth at 45 °C. Both genome analysis and experimental data have suggested that the mould is capable of hydrolyzing all major polysaccharides found in biomass. The mould is able to secrete a large number of hydrolytic enzymes (cellulases, laccases, xylanases, pectinases, lipases, phytases and some other miscellaneous enzymes) employed in various biotechnological applications. Characterization of the biomass-hydrolyzing activity of wild and recombinant enzymes suggests that this mould is highly efficient in biomass decomposition at both moderate and high temperatures. The native enzymes produced by the mould are more efficient in activity than their mesophilic counterparts beside their low enzyme titers. The mould is able to synthesize various biomolecules, which are used in multifarious applications. Genome sequence data of M. thermophila also supported the physiological data. This review describes the biotechnological potential of thermophilic mould, M. thermophila supported by genomic and experimental evidences.

Genomic insights into the fungal lignocellulolytic system of Myceliophthora thermophila

The microbial conversion of solid cellulosic biomass to liquid biofuels may provide a renewable energy source for transportation fuels. Cellulolytic fungi represent a promising group of organisms, as they have evolved complex systems for adaptation to their natural habitat. The filamentous fungus Myceliophthora thermophila constitutes an exceptionally powerful cellulolytic microorganism that synthesizes a complete set of enzymes necessary for the breakdown of plant cell wall. The genome of this fungus has been recently sequenced and annotated, allowing systematic examination and identification of enzymes required for the degradation of lignocellulosic biomass. The genomic analysis revealed the existence of an expanded enzymatic repertoire including numerous cellulases, hemicellulases, and enzymes with auxiliary activities, covering the most of the recognized CAZy families. Most of them were predicted to possess a secretion signal and undergo through post-translational glycosylation modifications. These data offer a better understanding of activities embedded in fungal lignocellulose decomposition mechanisms and suggest that M. thermophila could be made usable as an industrial production host for cellulolytic and hemicellulolytic enzymes.

Transcriptome and exoproteome analysis of utilization of plant-derived biomass by Myceliophthora thermophila

Myceliophthora thermophila is a thermophilic fungus whose genome encodes a wide range of carbohydrate-active enzymes (CAZymes) involved in plant biomass degradation. Such enzymes have potential applications in turning different kinds of lignocellulosic feedstock into sugar precursors for biofuels and chemicals. The present study examined and compared the transcriptomes and exoproteomes of M. thermophila during cultivation on different types of complex biomass to gain insight into how its secreted enzymatic machinery varies with different sources of lignocellulose. In the transcriptome analysis three monocot (barley, oat, triticale) and three dicot (alfalfa, canola, flax) plants were used whereas in the proteome analysis additional substrates, i.e. wood and corn stover pulps, were included. A core set of 59 genes encoding CAZymes was up-regulated in response to both monocot and dicot straws, including nine polysaccharide monooxygenases and GH10, but not GH11, xylanases. Genes encoding additional xylanolytic enzymes were up-regulated during growth on monocot straws, while genes encoding additional pectinolytic enzymes were up-regulated in response to dicot biomass. Exoproteome analysis was generally consistent with the conclusions drawn from transcriptome analysis, but additional CAZymes that accumulated to high levels were identified. Despite the wide variety of biomass sources tested some CAZy family members were not expressed under any condition. The results of this study provide a comprehensive view from both transcriptome and exoproteome levels, of how M. thermophila responds to a wide range of biomass sources using its genomic resources.

Efficient plant biomass degradation by thermophilic fungus Myceliophthora heterothallica

Rapid and efficient enzymatic degradation of plant biomass into fermentable sugars is a major challenge for the sustainable production of biochemicals and biofuels. Enzymes that are more thermostable (up to 70°C) use shorter reaction times for the complete saccharification of plant polysaccharides compared to hydrolytic enzymes of mesophilic fungi such as Trichoderma and Aspergillus species. The genus Myceliophthora contains four thermophilic fungi producing industrially relevant thermostable enzymes. Within this genus, isolates belonging to M. heterothallica were recently separated from the well-described species M. thermophila. We evaluate here the potential of M. heterothallica isolates to produce efficient enzyme mixtures for biomass degradation. Compared to the other thermophilic Myceliophthora species, isolates belonging to M. heterothallica and M. thermophila grew faster on pretreated spruce, wheat straw, and giant reed. According to their protein profiles and in vitro assays after growth on wheat straw, (hemi-)cellulolytic activities differed strongly between M. thermophila and M. heterothallica isolates. Compared to M. thermophila, M. heterothallica isolates were better in releasing sugars from mildly pretreated wheat straw (with 5% HCl) with a high content of xylan. The high levels of residual xylobiose revealed that enzyme mixtures of Myceliophthora species lack sufficient β-xylosidase activity. Sexual crossing of two M. heterothallica showed that progenies had a large genetic and physiological diversity. In the future, this will allow further improvement of the plant biomass-degrading enzyme mixtures of M. heterothallica.

Lignin boosts the cellulase performance of a GH-61 enzyme from Sporotrichum thermophile

An enzyme belonging to the glycoside hydrolase family 61 from the thermophilic fungus Sporotrichum thermophile, was functionally expressed in the methylotrophic yeast Pichia pastoris under the transcriptional control of the alcohol oxidase (AOX1) promoter. The enzyme hydrolyzed barley β-glucan, carboxymethyl cellulose, lichenan, wheat arabinoxylan and birchwood xylan showing optimal activity at pH 8 and 65°C. A 2:1 mixture of Celluclast 1.5L and StCel61a was capable of increasing the degree of spruce conversion by 42%. The use of substrates with varying lignin content permitted the detection of a dependence of the enhancing capacity of StCel61a on the radical scavenging capacity of the different lignocellulosics. In the presence of a reductant, StCel61a boosted the efficiency of a mixture of purified cellulases (EGII, CBHI, β-GLUC) by 20%. The synergistic activity exhibited by StCel61a and its dependence on reducing substances provide guidelines for process design towards the production of economically viable bioethanol.

Substrate perturbation alters the glycoside hydrolase activities and community composition of switchgrass-adapted bacterial consortia

Bacteria modulate glycoside hydrolase expression in response to the changes in the composition of lignocellulosic biomass. The response of switchgrass-adapted thermophilic bacterial consortia to perturbation with a variety of biomass substrates was characterized to determine if bacterial consortia also responded to changes in biomass composition. Incubation of the switchgrass-adapted consortia with these alternative substrates produced shifts in glycoside hydrolase activities and bacterial community composition. Substantially increased endoglucanase activity was observed upon incubation with microcrystalline cellulose and trifluororacetic acid-pretreated switchgrass. In contrast, culturing the microbial consortia with ionic liquid-pretreated switchgrass increased xylanase activity dramatically. Microbial community analyses of these cultures indicated that the increased endoglucanase activity correlated with an increase in bacteria related to Rhodothermus marinus. Inclusion of simple organic substrates in the culture medium abrogated glycoside hydrolase activity and enriched for bacteria related to Thermus thermophilus. These results demonstrate that the composition of biomass substrates influences the glycoside hydrolase activities and community composition of biomass-deconstructing bacterial consortia.

Extracellular aldonolactonase from Myceliophthora thermophila

Fungi secrete many different enzymes to deconstruct lignocellulosic biomass, including several families of hydrolases, oxidative enzymes, and many uncharacterized proteins. Here we describe the isolation, characterization, and primary sequence analysis of an extracellular aldonolactonase from the thermophilic fungus Myceliophthora thermophila (synonym Sporotrichum thermophile). The lactonase is a 48-kDa glycoprotein with a broad pH optimum. The enzyme catalyzes the hydrolysis of glucono-δ-lactone and cellobiono-δ-lactone with an apparent second-order rate constant, k(cat)/K(m), of ~1 × 10(6) M(-1) s(-1) at pH 5.0 and 25°C but is unable to hydrolyze xylono-γ-lactone or arabino-γ-lactone. Sequence analyses of the lactonase show that it has distant homology to cis-carboxy-muconate lactonizing enzymes (CMLE) as well as 6-phosphogluconolactonases present in some bacteria. The M. thermophila genome contains two predicted extracellular lactonase genes, and expression of both genes is induced by the presence of pure cellulose. Homologues of the M. thermophila lactonase, which are also predicted to be extracellular, are present in nearly all known cellulolytic ascomycetes.

Cellodextrin transport in yeast for improved biofuel production

Fungal degradation of plant biomass may provide insights for improving cellulosic biofuel production. We show that the model cellulolytic fungus Neurospora crassa relies on a high-affinity cellodextrin transport system for rapid growth on cellulose. Reconstitution of the N. crassa cellodextrin transport system in Saccharomyces cerevisiae promotes efficient growth of this yeast on cellodextrins. In simultaneous saccharification and fermentation experiments, the engineered yeast strains more rapidly convert cellulose to ethanol when compared with yeast lacking this system.

Extremophiles in biofuel synthesis

The current global energy situation has demonstrated an urgent need for the development of alternative fuel sources to the continually diminishing fossil fuel reserves. Much research to address this issue focuses on the development of financially viable technologies for the production of biofuels. The current market for biofuels, defined as fuel products obtained from organic substrates, is dominated by bioethanol, biodiesel, biobutanol and biogas, relying on the use of substrates such as sugars, starch and oil crops, agricultural and animal wastes, and lignocellulosic biomass. This conversion from biomass to biofuel through microbial catalysis has gained much momentum as biotechnology has evolved to its current status. Extremophiles are a robust group of organisms producing stable enzymes, which are often capable of tolerating changes in environmental conditions such as pH and temperature. The potential application of such organisms and their enzymes in biotechnology is enormous, and a particular application is in biofuel production. In this review an overview of the different biofuels is given, covering those already produced commercially as well as those under development. The past and present trends in biofuel production are discussed, and future prospects for the industry are highlighted. The focus is on the current and future application of extremophilic organisms and enzymes in technologies to develop and improve the biotechnological production of biofuels.

Fungal bioconversion of lignocellulosic residues; opportunities & perspectives

The development of alternative energy technology is critically important because of the rising prices of crude oil, security issues regarding the oil supply, and environmental issues such as global warming and air pollution. Bioconversion of biomass has significant advantages over other alternative energy strategies because biomass is the most abundant and also the most renewable biomaterial on our planet. Bioconversion of lignocellulosic residues is initiated primarily by microorganisms such as fungi and bacteria which are capable of degrading lignocellulolytic materials. Fungi such as Trichoderma reesei and Aspergillus niger produce large amounts of extracellular cellulolytic enzymes, whereas bacterial and a few anaerobic fungal strains mostly produce cellulolytic enzymes in a complex called cellulosome, which is associated with the cell wall. In filamentous fungi, cellulolytic enzymes including endoglucanases, cellobiohydrolases (exoglucanases) and beta-glucosidases work efficiently on cellulolytic residues in a synergistic manner. In addition to cellulolytic/hemicellulolytic activities, higher fungi such as basidiomycetes (e.g. Phanerochaete chrysosporium) have unique oxidative systems which together with ligninolytic enzymes are responsible for lignocellulose degradation. This review gives an overview of different fungal lignocellulolytic enzymatic systems including extracellular and cellulosome-associated in aerobic and anaerobic fungi, respectively. In addition, oxidative lignocellulose-degradation mechanisms of higher fungi are discussed. Moreover, this paper reviews the current status of the technology for bioconversion of biomass by fungi, with focus on mutagenesis, co-culturing and heterologous gene expression attempts to improve fungal lignocellulolytic activities to create robust fungal strains.

Plant growth promotion by an extracellular HAP-phytase of a thermophilic mold Sporotrichum thermophile

Phytase of the thermophilic mold Sporotrichum thermophile Apinis hydrolyzed and liberated inorganic phosphate from Ca(+2), Mg(+2), and Co(+2) phytates more efficiently than those of Al(3+), Fe(2+), Fe(3+), and Zn(2+). The hydrolysis rate was higher at 60 degrees C as compared to 26 degrees Celsius. Among all the organic acids tested, citrate was more effective in enhancing solubilization of insoluble phytate salts by phytase than others. The dry weight and inorganic phosphate contents of the wheat plants were high when supplemented with phytase or fungal spores. The plants provided with 5 mg phytate per plant exhibited enhanced growth and inorganic phosphate. With increase in the dosage of phytase, there was increase in growth and inorganic phosphate of plants, the highest being at 20 U per plant. The compost made employing the combined native microflora of the wheat straw and S. thermophile promoted growth of the plants. The plant-growth-promoting effect was also higher with the compost made using S. thermophile than that from only the native microflora.

Feruloyl esterases as biotechnological tools: current and future perspectives

Feruloyl esterases represent a diverse group of hydrolases catalyzing the cleavage and formation of ester bonds between plant cell wall polysaccharide and phenolic acid. They are widely distributed in plants and microorganisms. Besides lipases, a considerable number of microbial feruloyl esterases have also been discovered and overexpressed. This review summarizes the latest research on their classification, production, and biophysicochemical properties. Special emphasis is given to the importance of that type of enzyme and their related phenolic ferulic acid compound in biotechnological processes, and industrial and medicinal applications.

Cellulose degrading enzymes and their potential industrial applications

Bioconversion of cellulose to soluble sugars and glucose is catalyzed by a group of enzymes called cellulases. Microorganisms including fungi, bacteria and actinomycetes produce mainly three types of cellulase components--endo-1,4-beta-D-glucanase, exo-1,4-beta-D-glucanase and beta-glucosidase--either separately or in the form of a complex. Over the last several decades, cellulases have become better understood at a fundamental level; nevertheless, much remains to be learnt. The tremendous commercial potential of cellulases in a variety of applications remains the driving force for research in this area. This review summarizes the present state of knowledge on microbial cellulases and their applications.

Avicel-adsorbable endoglucanase production by the thermophilic fungus Scytalidium thermophilum type culture Torula thermophila

Scytalidium thermophilum type culture Torula thermophila was isolated from mushroom compost and the total cellulase, endoglucanase, Avicel-adsorbable endoglucanase activities, as well as the fungal biomass generation and cellulose utilisation were analyzed in shake flask cultures with Avicel (microcrystalline cellulose) as the carbon source. Results were compared with an industrial strain of Scytalidium thermophilum type culture Humicola insolens. The pH and temperature optima for endoglucanase activities during enzyme assays were also analyzed for both organisms and determined to be pH 6.0 and 65 degrees C for type culture Torula thermophila, and pH 6.5 and 60 degrees C for type culture Humicola insolens. Analysis of the effect of growth temperature showed that type culture T. thermophila can grow and produce cellulases in the range of 35 to 55 degrees C although 40 to 50 degrees C seemed to favor growth and cellulase production. Although 45 degrees C was found optimal for fungal growth, both the specific endoglucanase and Avicel-adsorbable endoglucanase activities (U/mg protein) as well as the percentage of Avicel-adsorbable endoglucanase activity reached maxima at 50 degrees C and were higher as compared to type culture H. insolens. Results indicate that type culture T. thermophila, with further optimisations, is of potential use in the industrial production of cellulases.

Thermophilic fungi: their physiology and enzymes

Thermophilic fungi are a small assemblage in mycota that have a minimum temperature of growth at or above 20 degrees C and a maximum temperature of growth extending up to 60 to 62 degrees C. As the only representatives of eukaryotic organisms that can grow at temperatures above 45 degrees C, the thermophilic fungi are valuable experimental systems for investigations of mechanisms that allow growth at moderately high temperature yet limit their growth beyond 60 to 62 degrees C. Although widespread in terrestrial habitats, they have remained underexplored compared to thermophilic species of eubacteria and archaea. However, thermophilic fungi are potential sources of enzymes with scientific and commercial interests. This review, for the first time, compiles information on the physiology and enzymes of thermophilic fungi. Thermophilic fungi can be grown in minimal media with metabolic rates and growth yields comparable to those of mesophilic fungi. Studies of their growth kinetics, respiration, mixed-substrate utilization, nutrient uptake, and protein breakdown rate have provided some basic information not only on thermophilic fungi but also on filamentous fungi in general. Some species have the ability to grow at ambient temperatures if cultures are initiated with germinated spores or mycelial inoculum or if a nutritionally rich medium is used. Thermophilic fungi have a powerful ability to degrade polysaccharide constituents of biomass. The properties of their enzymes show differences not only among species but also among strains of the same species. Their extracellular enzymes display temperature optima for activity that are close to or above the optimum temperature for the growth of organism and, in general, are more heat stable than those of the mesophilic fungi. Some extracellular enzymes from thermophilic fungi are being produced commercially, and a few others have commercial prospects. Genes of thermophilic fungi encoding lipase, protease, xylanase, and cellulase have been cloned and overexpressed in heterologous fungi, and pure crystalline proteins have been obtained for elucidation of the mechanisms of their intrinsic thermostability and catalysis. By contrast, the thermal stability of the few intracellular enzymes that have been purified is comparable to or, in some cases, lower than that of enzymes from the mesophilic fungi. Although rigorous data are lacking, it appears that eukaryotic thermophily involves several mechanisms of stabilization of enzymes or optimization of their activity, with different mechanisms operating for different enzymes.

Purification and characterisation of an extracellular beta-glucosidase with transglycosylation and exo-glucosidase activities from Fusarium oxysporum

An extracellular beta-glucosidase from Fusarium oxysporum was purified to homogeneity by gel-filtration and ion-exchange chromatographies. The enzyme, a monomeric protein of 110 kDa, was maximally active at pH 5.0-6.0 and at 60 degrees C. It hydrolysed 1-->4-linked aryl-beta-glucosides and 1-->4-linked, 1-->3-linked and 1-->6-linked beta-glucosides. The apparent Km and kcat values for p-nitrophenyl beta-D-glucopyranoside (4-NpGlcp) and cellobiose were 0.093 (Km), 1.07 mM (kcat) and 1802 (Km), 461.5 min-1 (kcat), respectively. Glucose and gluconolactone inhibited the enzyme competitively with Ki values of 2.05 mM and 3.03 microM, respectively. Alcohols activated the enzyme; butanol showed maximum effect (2.2-fold at 0.5 M) while methanol increased the activity by 1.4-fold at 1 M. The enzyme catalysed the synthesis of methylglucosides, ethylglucoside and propylglucosides, as well as trisaccharides in the presence of different alcohols and disaccharides, respectively. In addition, the enzyme hydrolysed the unsubstituted and methylumbelliferyl cello-oligosaccharides [MeUmb(Glc)n] but the rate of hydrolysis decreased with increasing chain length. Analysis of products released from MeUmb(Glc)n as a function of time revealed that the enzyme attacked these substrates in a stepwise manner and from both ends. Thus, beta-glucosidase from F. oxysporum, with the above interesting properties, could be of commercial interest.

Substrate-velocity relationships for the Trichoderma viride cellulase-catalyzed hydrolysis of cellulose

The influence of substrate and enzyme concentrations on the rate of saccharification of two defined insoluble cellulose substrates, Avicel (FMC Corp., Philadelphia, Pa.) and Solka-Floc (James River Co., Berlin, N.H.), by the cellulase enzyme system of Trichoderma viride was evaluated. In the assays, enzyme concentrations ranging from 0.004 to 0.016 IU/ml and substrate concentrations up to 10% (wt/vol) were used. Analysis by initial velocity methods found the maximum velocity of saccharification to be nearly equivalent for the two substrates and the Km for the two substrates to be of a similar magnitude, i.e., 0.20% (wt/vol) for Solka-Floc and 0.63% (wt/vol) for Avicel. Studies in which relatively high substrate concentrations (greater than 15 times the Km) were used demonstrated that the enzyme exhibited very different apparent substrate inhibition properties for the two substrates. The rate of saccharification of Avicel at relatively high substrate concentrations was up to 35% lower than the maximum rate which was observed at lower substrate concentrations. The Avicel concentration corresponding to the maximum rate of saccharification was dependent on the enzyme concentration. In contrast to the results with Avicel, the enzyme did not exhibit substrate inhibition with the Solka-Floc substrate. Potential differences in the degree of substrate inhibition with different substrates, as reported here, are particularly relevant to the experimental design of comparative studies.

Regulatory aspects of cellulase biosynthesis and secretion

The cellulase enzyme system consists of cellobiohydrolase, endoglucanase, and beta-glucosidase and has been extensively studied with respect to its biosynthesis, properties, mode of action, application, and, most recently, secretion mechanisms. A knowledge of the factors governing the biosynthesis and secretion of these enzymes at the molecular level will be useful in maximizing enzyme productivity in extracellular fluid. Among other topics, the regulatory effects of sorbose (a noninducing sugar which is not a product of cellulose hydrolysis) on cellulase synthesis and release are described. Cellulase genes have recently been cloned into a number of microorganisms with a view to understanding the gene structure and expression and to obtaining the enzyme components in pure form. The factors governing biosynthesis and secretion of cellulases in recombinant cells are also discussed. Cellulases are known to be glycoproteins, therefore, the role of O- and N-linked glycosylation on enzyme stability and secretion is also detailed.