Transcriptome analysis of Aspergillus fumigatus grown on sugarcane bagasse

Abstract

In Brazil, the ethanol production from sugarcane is more than 25 billion liters per year, which represents approximately 33% of all world production, highlighting it in an important role in future demand for this fuel. To maintain in this position investments are required for generation of new technologies in the conversion of sugarcane for ethanol. Currently, ethanol production occurs from first-generation technologies that utilize sucrose from sugarcane as an energy source. Approximately one third of plant energy is used to production of ethanol and sugar, while the rest remains in the field as straw and bagasse, producing the largest Brazilian agricultural industry waste. The large amount of sugarcane bagasse, the easy availability and low cost, stimulates studies the production of ethanol from bagasse, pointing Brazil in a great power in the development of second generation ethanol. Second generation biofuels can be produced from sugars released from the cell wall of plant wastes, such as bagasse from sugarcane. The biomass of sugarcane is made of lignocellulosic material, primarily hemicellulose and cellulose, polysaccharides which are sugars and high energy that can be converted into ethanol. However, the association between cellulose, hemicellulose and pectin imposes great difficulties in recovering the constituent sugars in the form of monomers with high purity. Due to this recalcitrant characteristic of bagasse, a major challenge in the production of second generation biofuels is the conversion of lignocellulosic substrates in fermentable sugars. With this, effective mechanical or chemical pre-treatment are necessary, aimed to destroy the cellular structure of the pulp for subsequent enzymatic hydrolysis. In nature, bacteria and fungi play an important role in the degradation of plant biomass, since secrete specific enzymes for the constituent polysaccharides. Many of these enzymes are studied, characterized and cataloged in the CAZy database, and the most abundant class is glycoside hydrolases (GH) and carbohydrate esterases (CE). However, little is known about the response for fungi to different lignocellulosic materials and the production of enzymes and accessory proteins required for the breakdown of plant biomass. The most studied enzymes are from fungi such as Aspergillus niger and Trichoderma reesei. However, other members of the genus Aspergillus are able to secrete hydrolytic enzymes of greatest importance, among them the A. fumigatus. Although A. fumigatus is a pathogenic fungus, is considered an important enzymes producer such as cellulases, xylanases and lipases, whose synergistic effect increases the efficiency of hydrolytic enzymes secreted, but little is known about these enzymes, facts that emphasize the importance of better understanding of this mechanism in A. fumigatus. Accordingly, the main objectives of this work are: (i) the analysis of the transcriptional profile of A. fumigatus when grown in the presence of sugarcane bagasse, through techniques of RNA-seq; (ii) identification of secreted enzymes in the medium by LC-MS / MS (secretome); (iii) characterization in S. cerevisiae PE-2 of the 5 most hydrolytic enzymes expressed in RNA-seq. These analysis of RNA-seq, and the determination of the secretome of these species, may bring new knowledge of hydrolytic enzymes that support their industrial applicability, with emphasis on second generation ethanol. (AU)