The Phanerochaete chrysosporium secretome: Database predictions and initial mass spectrometry peptide identifications in cellulose-grown medium

Identification of fungal lignocellulose-degrading biocatalysts secreted by Phanerochaete chrysosporium via activity-based protein profiling

Activity-based protein profiling (ABPP) has emerged as a versatile biochemical method for studying enzyme activity under various physiological conditions, with applications so far mainly in biomedicine. Here, we show the potential of ABPP in the discovery of biocatalysts from the thermophilic and lignocellulose-degrading white rot fungus Phanerochaete chrysosporium. By employing a comparative ABPP-based functional screen, including a direct profiling of wood substrate-bound enzymes, we identify those lignocellulose-degrading carbohydrate esterase (CE1 and CE15) and glycoside hydrolase (GH3, GH5, GH16, GH17, GH18, GH25, GH30, GH74 and GH79) enzymes specifically active in presence of the substrate. As expression of fungal enzymes remains challenging, our ABPP-mediated approach represents a preselection procedure for focusing experimental efforts on the most promising biocatalysts. Furthermore, this approach may also allow the functional annotation of domains-of-unknown functions (DUFs). The ABPP-based biocatalyst screening described here may thus allow the identification of active enzymes in a process of interest and the elucidation of novel biocatalysts that share no sequence similarity to known counterparts.

Retracted and Republished from: "Substrate-Specific Differential Gene Expression and RNA Editing in the Brown Rot Fungus Fomitopsis pinicola"

Wood-decaying fungi tend to have characteristic substrate ranges that partly define their ecological niche. Fomitopsis pinicola is a brown rot species of Polyporales that is reported on 82 species of softwoods and 42 species of hardwoods. We analyzed gene expression levels of F. pinicola from submerged cultures with ground wood powder (sampled at 5 days) or solid wood wafers (sampled at 10 and 30 days), using aspen, pine, and spruce substrates (aspen was used only in submerged cultures). Fomitopsis pinicola expressed similar sets of wood-degrading enzymes typical of brown rot fungi across all culture conditions and time points. Nevertheless, differential gene expression was observed across all pairwise comparisons of substrates and time points. Genes exhibiting differential expression encode diverse enzymes with known or potential function in brown rot decay, including laccase, benzoquinone reductase, aryl alcohol oxidase, cytochrome P450s, and various glycoside hydrolases. Comparing transcriptomes from submerged cultures and wood wafers, we found that culture conditions had a greater impact on global expression profiles than substrate wood species. These findings highlight the need for standardization of culture conditions in studies of gene expression in wood-decaying fungi. IMPORTANCE All species of wood-decaying fungi occur on a characteristic range of substrates (host plants), which may be broad or narrow. Understanding the mechanisms that allow fungi to grow on particular substrates is important for both fungal ecology and applied uses of different feedstocks in industrial processes. We grew the wood-decaying polypore Fomitopsis pinicola on three different wood species—aspen, pine, and spruce—under various culture conditions. We found that F. pinicola is able to modify gene expression (transcription levels) across different substrate species and culture conditions. Many of the genes involved encode enzymes with known or predicted functions in wood decay. This study provides clues to how wood-decaying fungi may adjust their arsenal of decay enzymes to accommodate different host substrates.

Omics analyses and biochemical study of Phlebiopsis gigantea elucidate its degradation strategy of wood extractives

Wood extractives, solvent-soluble fractions of woody biomass, are considered to be a factor impeding or excluding fungal colonization on the freshly harvested conifers. Among wood decay fungi, the basidiomycete Phlebiopsis gigantea has evolved a unique enzyme system to efficiently transform or degrade conifer extractives but little is known about the mechanism(s). In this study, to clarify the mechanism(s) of softwood degradation, we examined the transcriptome, proteome, and metabolome of P. gigantea when grown on defined media containing microcrystalline cellulose and pine sapwood extractives. Beyond the conventional enzymes often associated with cellulose, hemicellulose and lignin degradation, an array of enzymes implicated in the metabolism of softwood lipophilic extractives such as fatty and resin acids, steroids and glycerides was significantly up-regulated. Among these, a highly expressed and inducible lipase is likely responsible for lipophilic extractive degradation, based on its extracellular location and our characterization of the recombinant enzyme. Our results provide insight into physiological roles of extractives in the interaction between wood and fungi.

Glucose counteracts wood-dependent induction of lignocellulolytic enzyme secretion in monokaryon and dikaryon submerged cultures of the white-rot basidiomycete Pleurotus ostreatus

The secretome complexity and lignocellulose degrading capacity of Pleurotus ostreatus monokaryons mkPC9 and mkPC15 and mated dikaryon dkN001 were studied in submerged liquid cultures containing wood, glucose, and wood plus glucose as carbon sources. The study revealed that this white-rot basidiomycete attacks all the components of the plant cell wall. P. ostreatus secretes a variety of glycoside hydrolases, carbohydrate esterases, and polysaccharide lyases, especially when wood is the only carbon source. The presence of wood increased the secretome complexity, whereas glucose diminished the secretion of enzymes involved in cellulose, hemicellulose and pectin degradation. In contrast, the presence of glucose did not influence the secretion of redox enzymes or proteases, which shows the specificity of glucose on the secretion of cellulolytic enzymes. The comparison of the secretomes of monokaryons and dikaryons reveals that secretome complexity is unrelated to the nuclear composition of the strain.

Genome and secretome of Chondrostereum purpureum correspond to saprotrophic and phytopathogenic life styles

The basidiomycete Chondrostereum purpureum (Silverleaf fungus) is a saprotroph and plant pathogen commercially used for combatting forest "weed" trees in vegetation management. However, little is known about its lignocellulose-degrading capabilities and the enzymatic machinery that is responsible for the degradative potential, and it is not yet clear to which group of wood-rot fungi it actually belongs. Here, we sequenced and analyzed the draft genome of C. purpureum (41.2 Mbp) and performed a quantitative proteomic approach during growth in submerged and solid-state cultures based on soybean meal suspension or containing beech wood supplemented with phenol-rich olive mill residues, respectively. The fungus harbors characteristic lignocellulolytic hydrolases (GH6 and GH7) and oxidoreductases (e.g. laccase, heme peroxidases). High abundance of some of these genes (e.g. 45 laccases, nine GH7) can be explained by gene expansion, e.g. identified for the laccase orthogroup ORTHOMCL11 that exhibits a total of 18 lineage-specific duplications. Other expanded genes families encode for proteins more related to a pathogenic lifestyle (e.g. protease and cytochrome P450s). The fungus responds to the presence of complex growth substrates (lignocellulose, phenolic residues) by the secretion of most of these lignocellulolytic and lignin-modifying enzymes (e.g. alcohol and aryl alcohol oxidases, laccases, GH6, GH7). Based on the genetic and enzymatic constitution, we consider the 'marasmioid' fungus C. purpureum as a 'phytopathogenic' white-rot fungus (WRF) that possesses a complex extracellular enzyme machinery to accomplish efficient lignocellulose degradation during both saprotrophic and phytopathogenic life phases.

Screening of Fungi for Potential Application of Self-Healing Concrete

Concrete is susceptible to cracking owing to drying shrinkage, freeze-thaw cycles, delayed ettringite formation, reinforcement corrosion, creep and fatigue, etc. Continuous inspection and maintenance of concrete infrastructure require onerous labor and high costs. If the damaging cracks can heal by themselves without any human interference or intervention, that could be of great attraction. In this study, a novel self-healing approach is investigated, in which fungi are applied to heal cracks in concrete by promoting calcium carbonate precipitation. The goal of this investigation is to discover the most appropriate species of fungi for the application of biogenic crack repair. Our results showed that, despite the significant pH increase owing to the leaching of calcium hydroxide from concrete, Aspergillus nidulans (MAD1445), a pH regulatory mutant, could grow on concrete plates and promote calcium carbonate precipitation.

Substrate-Specific Differential Gene Expression and RNA Editing in the Brown Rot Fungus Fomitopsis pinicola

Wood-decaying fungi tend to have characteristic substrate ranges that partly define their ecological niche. Fomitopsis pinicola is a brown rot species of Polyporales that is reported on 82 species of softwoods and 42 species of hardwoods. We analyzed the gene expression levels and RNA editing profiles of F. pinicola from submerged cultures with ground wood powder (sampled at 5 days) or solid wood wafers (sampled at 10 and 30 days), using aspen, pine, and spruce substrates (aspen was used only in submerged cultures). Fomitopsis pinicola expressed similar sets of wood-degrading enzymes typical of brown rot fungi across all culture conditions and time points. Nevertheless, differential gene expression and RNA editing were observed across all pairwise comparisons of substrates and time points. Genes exhibiting differential expression and RNA editing encode diverse enzymes with known or potential function in brown rot decay, including laccase, benzoquinone reductase, aryl alcohol oxidase, cytochrome P450s, and various glycoside hydrolases. There was no overlap between differentially expressed and differentially edited genes, suggesting that these may provide F. pinicola with independent mechanisms for responding to different conditions. Comparing transcriptomes from submerged cultures and wood wafers, we found that culture conditions had a greater impact on global expression profiles than substrate wood species. In contrast, the suites of genes subject to RNA editing were much less affected by culture conditions. These findings highlight the need for standardization of culture conditions in studies of gene expression in wood-decaying fungi.IMPORTANCE All species of wood-decaying fungi occur on a characteristic range of substrates (host plants), which may be broad or narrow. Understanding the mechanisms that enable fungi to grow on particular substrates is important for both fungal ecology and applied uses of different feedstocks in industrial processes. We grew the wood-decaying polypore Fomitopsis pinicola on three different wood species, aspen, pine, and spruce, under various culture conditions. We examined both gene expression (transcription levels) and RNA editing (posttranscriptional modification of RNA, which can potentially yield different proteins from the same gene). We found that F. pinicola is able to modify both gene expression and RNA editing profiles across different substrate species and culture conditions. Many of the genes involved encode enzymes with known or predicted functions in wood decay. This work provides clues to how wood-decaying fungi may adjust their arsenal of decay enzymes to accommodate different host substrates.

VerSeDa: vertebrate secretome database

Based on the current tools, de novo secretome (full set of proteins secreted by an organism) prediction is a time consuming bioinformatic task that requires a multifactorial analysis in order to obtain reliable in silico predictions. Hence, to accelerate this process and offer researchers a reliable repository where secretome information can be obtained for vertebrates and model organisms, we have developed VerSeDa (Vertebrate Secretome Database). This freely available database stores information about proteins that are predicted to be secreted through the classical and non-classical mechanisms, for the wide range of vertebrate species deposited at the NCBI, UCSC and ENSEMBL sites. To our knowledge, VerSeDa is the only state-of-the-art database designed to store secretome data from multiple vertebrate genomes, thus, saving an important amount of time spent in the prediction of protein features that can be retrieved from this repository directly.

Database URL: VerSeDa is freely available at http://genomics.cicbiogune.es/VerSeDa/index.php

Metadata Analysis of Phanerochaete chrysosporium Gene Expression Data Identified Common CAZymes Encoding Gene Expression Profiles Involved in Cellulose and Hemicellulose Degradation

In literature, extensive studies have been conducted on popular wood degrading white rot fungus, Phanerochaete chrysosporium about its lignin degrading mechanisms compared to the cellulose and hemicellulose degrading abilities. This study delineates cellulose and hemicellulose degrading mechanisms through large scale metadata analysis of P. chrysosporium gene expression data (retrieved from NCBI GEO) to understand the common expression patterns of differentially expressed genes when cultured on different growth substrates. Genes encoding glycoside hydrolase classes commonly expressed during breakdown of cellulose such as GH-5,6,7,9,44,45,48 and hemicellulose are GH-2,8,10,11,26,30,43,47 were found to be highly expressed among varied growth conditions including simple customized and complex natural plant biomass growth mediums. Genes encoding carbohydrate esterase class enzymes CE (1,4,8,9,15,16) polysaccharide lyase class enzymes PL-8 and PL-14, and glycosyl transferases classes GT (1,2,4,8,15,20,35,39,48) were differentially expressed in natural plant biomass growth mediums. Based on these results, P. chrysosporium, on natural plant biomass substrates was found to express lignin and hemicellulose degrading enzymes more than cellulolytic enzymes except GH-61 (LPMO) class enzymes, in early stages. It was observed that the fate of P. chrysosporium transcriptome is significantly affected by the wood substrate provided. We believe, the gene expression findings in this study plays crucial role in developing genetically efficient microbe with effective cellulose and hemicellulose degradation abilities.

Time-scale dynamics of proteome and transcriptome of the white-rot fungus Phlebia radiata: growth on spruce wood and decay effect on lignocellulose

BACKGROUND

The white-rot Agaricomycetes species Phlebia radiata is an efficient wood-decaying fungus degrading all wood components, including cellulose, hemicellulose, and lignin. We cultivated P. radiata in solid state cultures on spruce wood, and extended the experiment to 6 weeks to gain more knowledge on the time-scale dynamics of protein expression upon growth and wood decay. Total proteome and transcriptome of P. radiata were analyzed by peptide LC-MS/MS and RNA sequencing at specific time points to study the enzymatic machinery on the fungus' natural growth substrate.

RESULTS

According to proteomics analyses, several CAZy oxidoreductase class-II peroxidases with glyoxal and alcohol oxidases were the most abundant proteins produced on wood together with enzymes important for cellulose utilization, such as GH7 and GH6 cellobiohydrolases. Transcriptome additionally displayed expression of multiple AA9 lytic polysaccharide monooxygenases indicative of oxidative cleavage of wood carbohydrate polymers. Large differences were observed for individual protein quantities at specific time points, with a tendency of enhanced production of specific peroxidases on the first 2 weeks of growth on wood. Among the 10 class-II peroxidases, new MnP1-long, characterized MnP2-long and LiP3 were produced in high protein abundances, while LiP2 and LiP1 were upregulated at highest level as transcripts on wood together with the oxidases and one acetyl xylan esterase, implying their necessity as primary enzymes to function against coniferous wood lignin to gain carbohydrate accessibility and fungal growth. Majority of the CAZy encoding transcripts upregulated on spruce wood represented activities against plant cell wall and were identified in the proteome, comprising main activities of white-rot decay.

CONCLUSIONS

Our data indicate significant changes in carbohydrate-active enzyme expression during the six-week surveillance of P. radiata growing on wood. Response to wood substrate is seen already during the first weeks. The immediate oxidative enzyme action on lignin and wood cell walls is supported by detected lignin substructure sidechain cleavages, release of phenolic units, and visual changes in xylem cell wall ultrastructure. This study contributes to increasing knowledge on fungal genetics and lignocellulose bioconversion pathways, allowing us to head for systems biology, development of biofuel production, and industrial applications on plant biomass utilizing wood-decay fungi.

A secretomic view of woody and nonwoody lignocellulose degradation by Pleurotus ostreatus

BACKGROUND

Pleurotus ostreatus is the second edible mushroom worldwide, and a model fungus for delignification applications, with the advantage of growing on woody and nonwoody feedstocks. Its sequenced genome is available, and this gave us the opportunity to perform proteomic studies to identify the enzymes overproduced in lignocellulose cultures.

RESULTS

Monokaryotic P. ostreatus (PC9) was grown with poplar wood or wheat straw as the sole C/N source and the extracellular proteins were analyzed, together with those from glucose medium. Using nano-liquid chromatography coupled to tandem mass spectrometry of whole-protein hydrolyzate, over five-hundred proteins were identified. Thirty-four percent were unique of the straw cultures, while only 15 and 6 % were unique of the glucose and poplar cultures, respectively (20 % were produced under the three conditions, and additional 19 % were shared by the two lignocellulose cultures). Semi-quantitative analysis showed oxidoreductases as the main protein type both in the poplar (39 % total abundance) and straw (31 %) secretomes, while carbohydrate-active enzymes (CAZys) were only slightly overproduced (14-16 %). Laccase 10 (LACC10) was the main protein in the two lignocellulose secretomes (10-14 %) and, together with LACC2, LACC9, LACC6, versatile peroxidase 1 (VP1), and manganese peroxidase 3 (MnP3), were strongly overproduced in the lignocellulose cultures. Seven CAZys were also among the top-50 proteins, but only CE16 acetylesterase was overproduced on lignocellulose. When the woody and nonwoody secretomes were compared, GH1 and GH3 β-glycosidases were more abundant on poplar and straw, respectively and, among less abundant proteins, VP2 was overproduced on straw, while VP3 was only found on poplar. The treated lignocellulosic substrates were analyzed by two-dimensional nuclear magnetic resonance (2D NMR), and a decrease of lignin relative to carbohydrate signals was observed, together with the disappearance of some minor lignin substructures, and an increase of sugar reducing ends.

CONCLUSIONS

Oxidoreductases are strongly induced when P. ostreatus grows on woody and nonwoody lignocellulosic substrates. One laccase occupied the first position in both secretomes, and three more were overproduced together with one VP and one MnP, suggesting an important role in lignocellulose degradation. Preferential removal of lignin vs carbohydrates was shown by 2D NMR, in agreement with the above secretomic results.

Characterization of a novel manganese dependent endoglucanase belongs in GH family 5 from Phanerochaete chrysosporium

The cDNA encoding a putative glycoside hydrolase family 5, which has been predicted to be an endoglucanase (PcEg5A), was cloned from Phanerochaete chrysosporium and expressed in Pichia pastoris. PcEg5A contains a carbohydrate-binding domain and two important amino acids, E209 and E319, playing as proton donor and nucleophile in substrate catalytic domain. SDS-PAGE analysis indicated that the recombinant endoglucanase 5A (rPcEg5A) has a molecular size of 43 kDa which corresponds with the theoretical calculation. Optimum pH and temperature were found to be 4.5-6.0, and 50°C-60°C, respectively. Moreover, rPcEg5A exhibited maximal activity in the pH range of 3.0-8.0, whereas over 50% of activity still remained at 20°C and 80°C. rPcEg5A was stable at 60°C for 12 h incubation, indicating that rPcEg5A is a thermostable enzyme. Manganese ion enhanced the enzyme activity by 77%, indicating that rPcEg5A is a metal dependent enzyme. The addition of rPcEg5A to cellobiase (cellobiohydrolase and β-glucosidase) resulted in a 53% increasing saccharification of NaOH-pretreated barley straw, whereas the glucose release was 47% higher than that cellobiase treatment alone. Our study suggested that rPcEg5A is an enzyme with great potential for biomass saccharification.

Mycobiota variation in stored rice straw and its cellulolytic profile

Rice Straw (RS) one of most important agrowaste worldwide. Variation in mycobiota inhabiting long stored RS and its cellulolytic profile were studied. The highest number of fungi (23 species) was recovered from 1st storage period (1-3 year). Alternaria alternata, Aspergillus sp., Cladosporium herbarum, Fusarium incarnatum, Geotrichum candidum, Penicillium sp., Stemphylium lycopersici and Ulocladium atrum are the most frequent genera. Among 21 fungal species recovered in the 2nd period (3-5 year), Cladosporium herbarum, Fusarium incarnatum, Stemphylium lycopersici and Ulocladium atrum recorded 100% frequency, whereas Ulocladium atrum, Veticillium lecanii, Stemphylium lycopersici and Penicillium sp., were the most frequent species in the 3rd period (> 5 years). Regarding the pathogenic fungal isolates, Nigrospora oryzae was the most frequent with high intensity in all samples of the three storage periods, whereas Alternaria padwikii reached the highest frequency and intensity in the 1st period and absent the 2nd and 3rd ones. The isolated fungal species showed a high production of cellulases comparing to previous studies with positive and significant correlation between FPase from one side and CMCase (r = 0.634, p ≤ 0.05) and β-glucosidase (r = 0.775, p ≤ 0.05) from the other side.

Methodologies and perspectives of proteomics applied to filamentous fungi: from sample preparation to secretome analysis

Filamentous fungi possess the extraordinary ability to digest complex biomasses and mineralize numerous xenobiotics, as consequence of their aptitude to sensing the environment and regulating their intra and extra cellular proteins, producing drastic changes in proteome and secretome composition. Recent advancement in proteomic technologies offers an exciting opportunity to reveal the fluctuations of fungal proteins and enzymes, responsible for their metabolic adaptation to a large variety of environmental conditions. Here, an overview of the most commonly used proteomic strategies will be provided; this paper will range from sample preparation to gel-free and gel-based proteomics, discussing pros and cons of each mentioned state-of-the-art technique. The main focus will be kept on filamentous fungi. Due to the biotechnological relevance of lignocellulose degrading fungi, special attention will be finally given to their extracellular proteome, or secretome. Secreted proteins and enzymes will be discussed in relation to their involvement in bio-based processes, such as biomass deconstruction and mycoremediation.

Plant-polysaccharide-degrading enzymes from Basidiomycetes

SUMMARY

Basidiomycete fungi subsist on various types of plant material in diverse environments, from living and dead trees and forest litter to crops and grasses and to decaying plant matter in soils. Due to the variation in their natural carbon sources, basidiomycetes have highly varied plant-polysaccharide-degrading capabilities. This topic is not as well studied for basidiomycetes as for ascomycete fungi, which are the main sources of knowledge on fungal plant polysaccharide degradation. Research on plant-biomass-decaying fungi has focused on isolating enzymes for current and future applications, such as for the production of fuels, the food industry, and waste treatment. More recently, genomic studies of basidiomycete fungi have provided a profound view of the plant-biomass-degrading potential of wood-rotting, litter-decomposing, plant-pathogenic, and ectomycorrhizal (ECM) basidiomycetes. This review summarizes the current knowledge on plant polysaccharide depolymerization by basidiomycete species from diverse habitats. In addition, these data are compared to those for the most broadly studied ascomycete genus, Aspergillus, to provide insight into specific features of basidiomycetes with respect to plant polysaccharide degradation.

Influence of Populus genotype on gene expression by the wood decay fungus Phanerochaete chrysosporium

We examined gene expression patterns in the lignin-degrading fungus Phanerochaete chrysosporium when it colonizes hybrid poplar (Populus alba × tremula) and syringyl (S)-rich transgenic derivatives. A combination of microarrays and liquid chromatography-tandem mass spectrometry (LC-MS/MS) allowed detection of a total of 9,959 transcripts and 793 proteins. Comparisons of P. chrysosporium transcript abundance in medium containing poplar or glucose as a sole carbon source showed 113 regulated genes, 11 of which were significantly higher (>2-fold, P < 0.05) in transgenic line 64 relative to the parental line. Possibly related to the very large amounts of syringyl (S) units in this transgenic tree (94 mol% S), several oxidoreductases were among the upregulated genes. Peptides corresponding to a total of 18 oxidoreductases were identified in medium consisting of biomass from line 64 or 82 (85 mol% S) but not in the parental clone (65 mol% S). These results demonstrate that P. chrysosporium gene expression patterns are substantially influenced by lignin composition.

Ethanol production via simultaneous saccharification and fermentation of sodium hydroxide treated corn stover using Phanerochaete chrysosporium and Gloeophyllum trabeum

Ethanol was produced via the simultaneous saccharification and fermentation (SSF) of dilute sodium hydroxide treated corn stover. Saccharification was achieved by cultivating either Phanerochaete chrysosporium or Gloeophyllum trabeum on the treated stover, and fermentation was then performed by using either Saccharomyces cerevisiae or Escherichia coli K011. Ethanol production was highest on day 3 for the combination of G. trabeum and E. coli K011 at 6.68 g/100g stover, followed by the combination of P. chrysosporium and E. coli K011 at 5.00 g/100g stover. SSF with S. cerevisiae had lower ethanol yields, ranging between 2.88 g/100g stover at day 3 (P. chrysosporium treated stover) and 3.09 g/100g stover at day 4 (G. trabeum treated stover). The results indicated that mild alkaline pretreatment coupled with fungal saccharification offers a promising bioprocess for ethanol production from corn stover without the addition of commercial enzymes.

Temporal alterations in the secretome of the selective ligninolytic fungus Ceriporiopsis subvermispora during growth on aspen wood reveal this organism's strategy for degrading lignocellulose

The white-rot basidiomycetes efficiently degrade all wood cell wall polymers. Generally, these fungi simultaneously degrade cellulose and lignin, but certain organisms, such as Ceriporiopsis subvermispora, selectively remove lignin in advance of cellulose degradation. However, relatively little is known about the mechanism of selective ligninolysis. To address this issue, C. subvermispora was grown in liquid medium containing ball-milled aspen, and nano-liquid chromatography-tandem mass spectrometry was used to identify and estimate extracellular protein abundance over time. Several manganese peroxidases and an aryl alcohol oxidase, both associated with lignin degradation, were identified after 3 days of incubation. A glycoside hydrolase (GH) family 51 arabinofuranosidase was also identified after 3 days but then successively decreased in later samples. Several enzymes related to cellulose and xylan degradation, such as GH10 endoxylanase, GH5_5 endoglucanase, and GH7 cellobiohydrolase, were detected after 5 days. Peptides corresponding to potential cellulose-degrading enzymes GH12, GH45, lytic polysaccharide monooxygenase, and cellobiose dehydrogenase were most abundant after 7 days. This sequential production of enzymes provides a mechanism consistent with selective ligninolysis by C. subvermispora.

SECRETOOL: integrated secretome analysis tool for fungi

The secretome (full set of secreted proteins) has been studied in multiple fungal genomes to elucidate the potential role of those protein collections involved in a number of metabolic processes from host infection to wood degradation. Being aminoacid composition a key factor to recognize secretory proteins, SECRETOOL comprises a group of web tools that enable secretome predictions out of aminoacid sequence files, up to complete fungal proteomes, in one step. SECRETOOL is freely available on the web at http://genomics.cicbiogune.es/SECRETOOL/Secretool.php .

Differential proteomic analysis of the secretome of Irpex lacteus and other white-rot fungi during wheat straw pretreatment

BACKGROUND

Identifying new high-performance enzymes or enzyme complexes to enhance biomass degradation is the key for the development of cost-effective processes for ethanol production. Irpex lacteus is an efficient microorganism for wheat straw pretreatment, yielding easily hydrolysable products with high sugar content. Thus, this fungus was selected to investigate the enzymatic system involved in lignocellulose decay, and its secretome was compared to those from Phanerochaete chrysosporium and Pleurotus ostreatus which produced different degradation patterns when growing on wheat straw. Extracellular enzymes were analyzed through 2D-PAGE, nanoLC/MS-MS, and homology searches against public databases.

RESULTS

In wheat straw, I. lacteus secreted proteases, dye-decolorizing and manganese-oxidizing peroxidases, and H2O2 producing-enzymes but also a battery of cellulases and xylanases, excluding those implicated in cellulose and hemicellulose degradation to their monosaccharides, making these sugars poorly available for fungal consumption. In contrast, a significant increase of β-glucosidase production was observed when I. lacteus grew in liquid cultures. P. chrysosporium secreted more enzymes implicated in the total hydrolysis of the polysaccharides and P. ostreatus produced, in proportion, more oxidoreductases.

CONCLUSION

The protein pattern secreted during I. lacteus growth in wheat straw plus the differences observed among the different secretomes, justify the fitness of I. lacteus for biopretreatment processes in 2G-ethanol production. Furthermore, all these data give insight into the biological degradation of lignocellulose and suggest new enzyme mixtures interesting for its efficient hydrolysis.

Genomewide analysis of polysaccharides degrading enzymes in 11 white- and brown-rot Polyporales provides insight into mechanisms of wood decay

To degrade the polysaccharides, wood-decay fungi secrete a variety of glycoside hydrolases (GHs) and carbohydrate esterases (CEs) classified into various sequence-based families of carbohydrate-active enzymes (CAZys) and their appended carbohydrate-binding modules (CBM). Oxidative enzymes, such as cellobiose dehydrogenase (CDH) and lytic polysaccharide monooxygenase (LPMO, formerly GH61), also have been implicated in cellulose degradation. To examine polysaccharide-degrading potential between white- and brown-rot fungi, we performed genomewide analysis of CAZys and these oxidative enzymes in 11 Polyporales, including recently sequenced monokaryotic strains of Bjerkandera adusta, Ganoderma sp. and Phlebia brevispora. Furthermore, we conducted comparative secretome analysis of seven Polyporales grown on wood culture. As a result, it was found that genes encoding cellulases belonging to families GH6, GH7, GH9 and carbohydrate-binding module family CBM1 are lacking in genomes of brown-rot polyporales. In addition, the presence of CDH and the expansion of LPMO were observed only in white-rot genomes. Indeed, GH6, GH7, CDH and LPMO peptides were identified only in white-rot polypores. Genes encoding aldose 1-epimerase (ALE), previously detected with CDH and cellulases in the culture filtrates, also were identified in white-rot genomes, suggesting a physiological connection between ALE, CDH, cellulase and possibly LPMO. For hemicellulose degradation, genes and peptides corresponding to GH74 xyloglucanase, GH10 endo-xylanase, GH79 β-glucuronidase, CE1 acetyl xylan esterase and CE15 glucuronoyl methylesterase were significantly increased in white-rot genomes compared to brown-rot genomes. Overall, relative to brown-rot Polyporales, white-rot Polyporales maintain greater enzymatic diversity supporting lignocellulose attack.

Cellobiose dehydrogenase modified electrodes: advances by materials science and biochemical engineering

The flavocytochrome cellobiose dehydrogenase (CDH) is a versatile biorecognition element capable of detecting carbohydrates as well as quinones and catecholamines. In addition, it can be used as an anode biocatalyst for enzymatic biofuel cells to power miniaturised sensor-transmitter systems. Various electrode materials and designs have been tested in the past decade to utilize and enhance the direct electron transfer (DET) from the enzyme to the electrode. Additionally, mediated electron transfer (MET) approaches via soluble redox mediators and redox polymers have been pursued. Biosensors for cellobiose, lactose and glucose determination are based on CDH from different fungal producers, which show differences with respect to substrate specificity, pH optima, DET efficiency and surface binding affinity. Biosensors for the detection of quinones and catecholamines can use carbohydrates for analyte regeneration and signal amplification. This review discusses different approaches to enhance the sensitivity and selectivity of CDH-based biosensors, which focus on (1) more efficient DET on chemically modified or nanostructured electrodes, (2) the synthesis of custom-made redox polymers for higher MET currents and (3) the engineering of enzymes and reaction pathways. Combination of these strategies will enable the design of sensitive and selective CDH-based biosensors with reduced electrode size for the detection of analytes in continuous on-site and point-of-care applications.

Cloning and characterization of a thermostable endo-arabinanase from Phanerochaete chrysosporium and its synergistic action with endo-xylanase

Putative arabinanase (PcARA) was cloned from cDNA of Phanerochaete chrysosporium. The gene sequencing indicated that PcARA consisted of 939 nucleotides that encodes for 312 amino acid arabinanase-polypeptide chain, including a signal peptide of 19 amino acids. Three-dimensional homology indicated that this enzyme is a five-bladed β-propeller, belonging to glycosidase family 43 and its secondary structure is consisted of 24 β-sheets. The PcARA-cDNA was expressed in Pichia pastoris using pPICZαC. SDS-PAGE of purified arabinanase showed a single band of 33 kDa that is very close to theoretical molecular mass of 33.9 kDa calculated by its amino acid content. Recombinant arabinanase (rPcARA) exhibited maximum activity at pH and temperature of 5.0 and 60 °C, respectively. End-product analysis of debranched arabinan hydrolysis by thin-layer chromatography indicated that rPcARA acted as endo-type. The synergistic action of rPcARA with recombinant xylanase resulted in 72 and 9.3 % release of total soluble sugar of arabinoxylan and NaOH-pretreated barley straw, respectively.

Cloning, expression, and characterization of a cellobiose dehydrogenase from Thielavia terrestris induced under cellulose growth conditions

The enzyme cellobiose dehydrogenase (CDH) is of considerable interest, not only for its biotechnological applications, but also its potential biological role in lignocellulosic biomass breakdown. The enzyme catalyzes the oxidation of cellobiose and other cellodextrins, utilizing a variety of one- and two-electron acceptors, although the electron acceptor employed in nature is still unknown. In this study we show that a CDH is present in the secretome of the thermophilic ascomycete Thielavia terrestris when grown with cellulose, along with a mixture of cellulases and hemicellulases capable of breaking down lignocellulosic biomass. We report the cloning of this T. terrestris CDH gene (cbdA), its recombinant expression in Aspergillus oryzae, and purification and characterization of the T. terrestris CDH protein (TtCDH). The TtCDH shows spectral properties and enzyme activity similar to other characterized CDH enzymes. Substrate specificity was determined for a number of carbohydrate electron donors in the presence of the two-electron acceptor 2,6-dichlorophenol-indophenol. The TtCDH also shows dramatic synergy with Thermoascus aurantiacus glycoside hydrolase family 61A protein in the presence of a β-glucosidase for the cleavage of cellulose.

Transcriptional response of the cellobiose dehydrogenase gene to cello- and xylooligosaccharides in the basidiomycete Phanerochaete chrysosporium

Cellobiose dehydrogenase (CDH) gene transcripts were quantified by reverse transcription-PCR (RT-PCR) in cultures of Phanerochaete chrysosporium supplemented with various cello- and xylooligosaccharides in order to elucidate the mechanism of enhanced CDH production in xylan/cellulose culture. Cellotriose and cellotetraose induced cdh expression, while xylobiose and xylotriose induced expression of cellobiohydrolase genes, especially cel7C.

Expression and regulation of genes encoding lignocellulose-degrading activity in the genus Phanerochaete

As white-rot basidiomycetes, Phanerochaete species are critical to the cycling of carbon sequestered as woody biomass, and are predicted to encode many enzymes that can be harnessed to promote the conversion of lignocellulose to sugars for fermentation to fuels and chemicals. Advances in genomic, transcriptomic, and proteomic technologies have enabled detailed analyses of different Phanerochaete species and have revealed numerous enzyme families required for lignocellulose utilization, as well as insight into the regulation of corresponding genes. Recent studies of Phanerochaete are also exemplified by molecular analyses following cultivation on different wood preparations, and show substrate-dependent responses that were difficult to predict using model compounds or isolated plant polysaccharides. The aim of this mini-review is to synthesize results from studies that have applied recent advances in molecular tools to evaluate the expression and regulation of proteins that contribute to lignocellulose conversion in Phanerochaete species. The identification of proteins with as yet unknown function are also highlighted and noted as important targets for future investigation of white-rot decay.

The putative endoglucanase PcGH61D from Phanerochaete chrysosporium is a metal-dependent oxidative enzyme that cleaves cellulose

Many fungi growing on plant biomass produce proteins currently classified as glycoside hydrolase family 61 (GH61), some of which are known to act synergistically with cellulases. In this study we show that PcGH61D, the gene product of an open reading frame in the genome of Phanerochaete chrysosporium, is an enzyme that cleaves cellulose using a metal-dependent oxidative mechanism that leads to generation of aldonic acids. The activity of this enzyme and its beneficial effect on the efficiency of classical cellulases are stimulated by the presence of electron donors. Experiments with reduced cellulose confirmed the oxidative nature of the reaction catalyzed by PcGH61D and indicated that the enzyme may be capable of penetrating into the substrate. Considering the abundance of GH61-encoding genes in fungi and genes encoding their functional bacterial homologues currently classified as carbohydrate binding modules family 33 (CBM33), this enzyme activity is likely to turn out as a major determinant of microbial biomass-degrading efficiency.

Significant alteration of gene expression in wood decay fungi Postia placenta and Phanerochaete chrysosporium by plant species

Identification of specific genes and enzymes involved in conversion of lignocellulosics from an expanding number of potential feedstocks is of growing interest to bioenergy process development. The basidiomycetous wood decay fungi Phanerochaete chrysosporium and Postia placenta are promising in this regard because they are able to utilize a wide range of simple and complex carbon compounds. However, systematic comparative studies with different woody substrates have not been reported. To address this issue, we examined gene expression of these fungi colonizing aspen (Populus grandidentata) and pine (Pinus strobus). Transcript levels of genes encoding extracellular glycoside hydrolases, thought to be important for hydrolytic cleavage of hemicelluloses and cellulose, showed little difference for P. placenta colonizing pine versus aspen as the sole carbon source. However, 164 genes exhibited significant differences in transcript accumulation for these substrates. Among these, 15 cytochrome P450s were upregulated in pine relative to aspen. Of 72 P. placenta extracellular proteins identified unambiguously by mass spectrometry, 52 were detected while colonizing both substrates and 10 were identified in pine but not aspen cultures. Most of the 178 P. chrysosporium glycoside hydrolase genes showed similar transcript levels on both substrates, but 13 accumulated >2-fold higher levels on aspen than on pine. Of 118 confidently identified proteins, 31 were identified in both substrates and 57 were identified in pine but not aspen cultures. Thus, P. placenta and P. chrysosporium gene expression patterns are influenced substantially by wood species. Such adaptations to the carbon source may also reflect fundamental differences in the mechanisms by which these fungi attack plant cell walls.

FunSecKB: the Fungal Secretome KnowledgeBase

The Fungal Secretome KnowledgeBase (FunSecKB) provides a resource of secreted fungal proteins, i.e. secretomes, identified from all available fungal protein data in the NCBI RefSeq database. The secreted proteins were identified using a well evaluated computational protocol which includes SignalP, WolfPsort and Phobius for signal peptide or subcellular location prediction, TMHMM for identifying membrane proteins, and PS-Scan for identifying endoplasmic reticulum (ER) target proteins. The entries were mapped to the UniProt database and any annotations of subcellular locations that were either manually curated or computationally predicted were included in FunSecKB. Using a web-based user interface, the database is searchable, browsable and downloadable by using NCBI’s RefSeq accession or gi number, UniProt accession number, keyword or by species. A BLAST utility was integrated to allow users to query the database by sequence similarity. A user submission tool was implemented to support community annotation of subcellular locations of fungal proteins. With the complete fungal data from RefSeq and associated web-based tools, FunSecKB will be a valuable resource for exploring the potential applications of fungal secreted proteins.

Database URL:http://proteomics.ysu.edu/secretomes/fungi.php

Identification and functional analysis of a gene encoding β-glucosidase from the brown-rot basidiomycete Fomitopsis palustris

The brown-rot basidiomycete Fomitopsis palustris is known to degrade crystalline cellulose (Avicel) and produce three major cellulases, exoglucanases, endoglucanases, and β-glucosidases. A novel β-glucosidase designated as Cel3A was identified from F. palustris grown at the expense of Avicel. The deduced amino acid sequence of Cel3A showed high homology with those of other fungal β-glucosidases that belong to glycosyl hydrolase (GH) family 3. The sequence analysis also indicated that Cel3A contains the N- and C-terminal domains of GH family 3 and Asp-209 was conserved as a catalytic nucleophile. The cloned gene was successfully expressed in the yeast Pichia pastoris and the recombinant protein exhibited β-glucosidase activity with cellobiose and some degree of thermostability. Considering the size and sequence of the protein, the β-glucosidase identified in this study is different from the protein purified directly from F. palustris in the previous study. Our results suggest that the fungus possesses at least two β-glucosidase genes.

Cellotriose and cellotetraose as inducers of the genes encoding cellobiohydrolases in the basidiomycete Phanerochaete chrysosporium

The wood decay basidiomycete Phanerochaete chrysosporium produces a variety of cellobiohydrolases belonging to glycoside hydrolase (GH) families 6 and 7 in the presence of cellulose. However, no inducer of the production of these enzymes has yet been identified. Here, we quantitatively compared the transcript levels of the genes encoding GH family 6 cellobiohydrolase (cel6A) and GH family 7 cellobiohydrolase isozymes (cel7A to cel7F/G) in cultures containing glucose, cellulose, and cellooligosaccharides by real-time quantitative PCR, in order to evaluate the transcription-inducing effect of soluble sugars. Upregulation of transcript levels in the presence of cellulose compared to glucose was observed for cel7B, cel7C, cel7D, cel7F/G, and cel6A at all time points during cultivation. In particular, the transcription of cel7C and cel7D was strongly induced by cellotriose or cellotetraose. The highest level of cel7C transcripts was observed in the presence of cellotetraose, whereas the highest level of cel7D transcripts was found in the presence of cellotriose, amounting to 2.7 x 10(6) and 1.7 x 10(6) copies per 10(5) actin gene transcripts, respectively. These numbers of cel7C and cel7D transcripts were higher than those in the presence of cellulose. In contrast, cellobiose had a weaker transcription-inducing effect than either cellotriose or cellotetraose for cel7C and had little effect in the case of cel7D. These results indicate that cellotriose and cellotetraose, but not cellobiose, are possible natural cellobiohydrolase gene transcription inducers derived from cellulose.

Proteomics of plant pathogenic fungi

Plant pathogenic fungi cause important yield losses in crops. In order to develop efficient and environmental friendly crop protection strategies, molecular studies of the fungal biological cycle, virulence factors, and interaction with its host are necessary. For that reason, several approaches have been performed using both classical genetic, cell biology, and biochemistry and the modern, holistic, and high-throughput, omic techniques. This work briefly overviews the tools available for studying Plant Pathogenic Fungi and is amply focused on MS-based Proteomics analysis, based on original papers published up to December 2009. At a methodological level, different steps in a proteomic workflow experiment are discussed. Separate sections are devoted to fungal descriptive (intracellular, subcellular, extracellular) and differential expression proteomics and interactomics. From the work published we can conclude that Proteomics, in combination with other techniques, constitutes a powerful tool for providing important information about pathogenicity and virulence factors, thus opening up new possibilities for crop disease diagnosis and crop protection.