The DNA-methyltransferase inhibitor 5-aza-2-deoxycytidine affects Humicola grisea enzyme activities and the glucose-mediated gene repression.

Humicola grisea var. thermoidea (Hgvt) is a thermophilic ascomycete that produces lignocellulolytic enzymes and it is proposed for the conversion of agricultural residues into useful byproducts. Drugs that inhibit the DNA methyltransferases (DNMTs) activity are employed in epigenetic studies but nothing is known about a possible effect on the production of fungal enzymes. We evaluated the effect of 5-aza-2'-deoxycytidine (5-Aza; a chemical inhibitor of DNMTs activity) on the secreted enzyme activity and on the transcription of cellulase and xylanase genes from Hgvt grown in agricultural residues and in glucose. Upon cultivation on wheat bran (WB), the drug provoked an increase in the xylanase activity at 96 h. When Hgvt was grown in glucose (GLU), a repressor of Hgvt glycosyl hydrolase genes, 5-Aza led to increased transcript accumulation for the cellobiohydrolases and for the xyn2 xylanase genes. In WB, 5-Aza enhanced the expression of the transcription factor CreA gene. Growth on WB or GLU, in presence of 5-Aza, led to a significant increase in transcripts of the pH-response regulator PacC gene. To our knowledge, this is the first report on the effect of a DNMT inhibitor in the production of fungal plant cell wall degradation enzymes.

Insights into the Lignocellulose-Degrading Enzyme System of Humicola grisea var. thermoidea Based on Genome and Transcriptome Analysis.

Humicola grisea var. thermoidea is a thermophilic ascomycete and important enzyme producer that has an efficient enzymatic system with a broad spectrum of thermostable carbohydrate-active (CAZy) enzymes. These enzymes can be employed in lignocellulose biomass deconstruction and other industrial applications. In this work, the genome of H. grisea var. thermoidea was sequenced. The acquired sequence reads were assembled into a total length of 28.75 Mbp. Genome features correlate with what was expected for thermophilic Sordariomycetes. The transcriptomic data showed that sugarcane bagasse significantly upregulated genes related to primary metabolism and polysaccharide deconstruction, especially hydrolases, at both pH 5 and pH 8. However, a number of exclusive and shared genes between the pH values were found, especially at pH 8. H. grisea expresses an average of 211 CAZy enzymes (CAZymes), which are capable of acting in different substrates. The top upregulated genes at both pH values represent CAZyme-encoding genes from different classes, including acetylxylan esterase, endo-1,4-ß-mannosidase, exoglucanase, and endoglucanase genes. For the first time, the arsenal that the thermophilic fungus H. grisea var. thermoidea possesses to degrade the lignocellulosic biomass is shown. Carbon source and pH are of pivotal importance in regulating gene expression in this organism, and alkaline pH is a key regulatory factor for sugarcane bagasse hydrolysis. This work paves the way for the genetic manipulation and robust biotechnological applications of this fungus. IMPORTANCE Most studies regarding the use of fungi as enzyme producers for biomass deconstruction have focused on mesophile species, whereas the potential of thermophiles has been evaluated less. This study revealed, through genome and transcriptome analyses, the genetic repertoire of the biotechnological relevant thermophile fungus Humicola grisea. Comparative genomics helped us to further understand the biology and biotechnological potential of H. grisea. The results demonstrate that this fungus possesses an arsenal of carbohydrate-active (CAZy) enzymes to degrade the lignocellulosic biomass. Indeed, it expresses more than 200 genes encoding CAZy enzymes when cultivated in sugarcane bagasse. Carbon source and pH are key factors for regulating the gene expression in this organism. This work shows, for the first time, the great potential of H. grisea as an enzyme producer and a gene donor for biotechnological applications and provides the base for the genetic manipulation and robust biotechnological applications of this fungus.

Proximate analysis of cold-press oil cakes after biological treatment with Trametes versicolor and Humicola grisea.

In order to increase the current knowledge on cold-press oil cakes composition, the present study aims to determine the chemical composition of oil cakes from hull-less pumpkin (Cucurbita pepo L.), flax (Linum usitatissimum L.), and hemp (Canabis sativa L.) before and after the biological treatment with Trametes versicolor and Humicola grisea using fungal-based solid-state technology. After 10 days of treatment, the content of ash, total nitrogen, total proteins, and total organic carbon increased in all the three oil cakes, while the content of ether extracts decreased. After treatment, the concentration of soluble carbohydrates decreased in pumpkin and hemp seed oil cakes, whereas it increased in flaxseed oil cake. During treatment with T. versicolor, the content of fructose significantly increased in hull-less pumpkin seed oil cake. Fiber content decreased in pumpkin and flaxseed oil cakes after treatment with both of the fungi, whereas it increased in flaxseed oil cake.

Characterization of a recombinant xylose tolerant ß-xylosidase from Humicola grisea var. thermoidea and its use in sugarcane bagasse hydrolysis.

One full-length ß-xylosidase gene (hxylA) was identified from the Humicola grisea var. thermoidea genome and the cDNA was successfully expressed by Pichia pastoris SMD1168. An optimization of enzyme production was carried out, and methanol was found to be the most important parameter. The purified enzyme was characterized and showed the optimal conditions for the highest activity at pH 7.0 and 50°C, being thermostable by maintaining 41% of its activity after 12h incubated at 50°C. HXYLA is a bifunctional enzyme; it showed both ß-xylosidase and α-arabinfuranosidase activities. The Km and Vmax values were 1.3mM and 39.1U/mg, respectively, against 4-nitrophenyl ß-xylopyranoside. HXYLA showed a relatively strong tolerance to xylose with high Ki value of 603mM, with the xylose being a non-competitive inhibitor. HXYLA was successfully used simultaneously and sequentially with an endo-xylanase for analysis of synergism in the degradation of commercial xylans. Furthermore, commercial cellulases supplementation with HXYLA during sugarcane bagasse hydrolysis increased hydrolysis in 29%. HXYLA is distinguished from other ß-xylosidases by the attractive characteristics for industrial applications such as thermostability, high tolerance xylose and saccharification of biomass by convert xylan into fementable monosaccharides and improve cellulose hydrolysis.

Purification and characterization of a new Xylanase from Humicola grisea var. Thermoidea

The thermophilic fungus Humicola grisea var. thermoidea secretes extracellular xylanase when grown on solid and in liquid media containing wheat bran and banana plant residue as substrates, respectively. At 55ºC, xylanase from the culture filtrate of H. grisea var. thermoidea grown on banana stalk retained 50% of its activity after 28 h of incubation. A xylanase (X2) was isolated from solid state cultures with wheat bran as the carbon source. It was purified to apparent homogeneity by ultrafiltration followed by ion-exchange and hydrophobic interaction chromatography on DEAE-Sepharose and Phenyl-Sepharose resins, respectively. The enzyme had an apparent molecular weight of 29 kDa, as determined by SDS-PAGE. The purified enzyme was most active at pH and temperature ranges of 4.5-6.5 and 55-60ºC, respectively. In addition, X2 showed thermostability at 60ºC with a half-life of approx. 5.5 h. The apparent Km values, using soluble and insoluble arabinoxylans as substrates, were 10.87 and 11.20 mg/ml, respectively.

O fungo termofílico Humicola grisea var. secreta xilanase extracelular quando cultivado em meios sólidos e líquidos contendo farelo de trigo e engaço de bananeira como substratos, respectivamente. À temperatura de 55ºC, xilanase do filtrado de meio de cultura de H. grisea var. thermoidea cultivado em engaço de bananeira reteve 50% de sua atividade após 28 de incubação. Uma xilanase (X2) foi isolada de culturas de estado sólido contendo farelo de trigo como fonte de carbono. X2 foi purificada por ultrafiltração, seguido por cromatografias de interação hidrofóbica e troca iônica em resinas de Phenyl-Sepharose e DEAE-Sepharose, respectivamente. A enzima apresentou peso molecular de 29 kDa, como determinado por SDS-PAGE. A enzima purificada foi mais ativa em intervalos de pH e temperatura de 4,5-6,5 and 55-60ºC, respectivamente. Além disso, X2 mostrou termoestabilidade a 60ºC com meia vida de aproximadamente 5,5 h. Os valores de Km aparente, utilizando arabinoxilanas solúveis e insolúveis, foram 10,87 and 11,20 mg/ml, respectivamente.