Global gene expression of Aspergillus niger grown on bagasse and culm of sugarcane

Author(s)

Camila Cristina Sanchez

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2016-05-20

Examining board members

Fabio Marcio Squina; Roberto Ruller; Rosana Goldbeck

• Advisor: Fabio Marcio Squina

Abstract

The increased energy demand and the increasing consensus on the reduce emissions of greenhouse gases and dependence on fossil fuels is boosting the development and improvement of biofuels production. Currently, ethanol is the most widely used biofuel and it is obtained from the fermentation of sugars mainly extracted from sugarcane (Brazil) and corn (US), and these two countries account for approximately 83% of world production. The Brazilian harvest of sugarcane in 2015/2016 was estimated at 655 million tons, and approximately 366 million was destined to ethanol production (yielding about 28 billion liters). Despite this large production, to meet the global demand for biofuel, pronounced efforts are being made to increase these numbers, and one of the options is the production of so-called second-generation (2G) ethanol. This ethanol is produced by fermentation of sugars released from complex polysaccharides found in plant biomass. In this sense, as a byproduct of the sugar-energy sector, it is estimated to be generated about 178 million tons of bagasse annually, the agro-industrial waste produced in larger abundance in Brazil. And studies suggest that 8% are used to produce ethanol, Brazil could increase about 40% of this biofuel production. However, is necessary that several biotechnological challenges are overcome to use this bagasse and increase 2G ethanol production, especially reducing the cost of the hydrolysis of this material. Accordingly, many studies aiming to understand the metabolism of microorganisms which naturally evolved to use plant cell wall as carbon source, and to know the enzymes involved in breaking down polysaccharides (called CAZymes) produced by them. The fungus "Aspergillus niger" stands out as a great producer and secretor of these enzymes, and although several studies have already been performed, little is known about its metabolism. Thus, the present work studies the transcriptome (using RNA-Seq) and secretome (by mass spectrometry) of "A. niger" grown in culm in natura and pretreated bagasse for 6, 12 and 24 hours. The results showed that the hydrolysis of substrates begins within 6 hours after inoculation, observed through the presence of monomers (mainly xylose and glucose) in the supernatants. In addition, 237 genes encoding CAZymes were found up-regulated, which represents more than 50% of CAZymes encoded by the A. niger genome. Besides, about half of CAZymes up-regulated were found in the supernatant. The main cellulases, hemicellulases were transcribed and secreted, and in general, the expression levels were already highest in initial growth points. Most of the genes encoding the CAZymes were up-regulated in both substrates, but some qualitative and quantitative differences were observed, which may be due to differences in the composition of the culm and bagasse. Furthermore, it was found up-regulated several transporters of sugars, putative transcription factors and genes without known function, and the product of these genes can be directly or indirectly related to the saccharification process. This work may enable the discovery of novel proteins related to the degradation of plant biomass, which can result in the improvement of enzyme cocktail, reducing the production cost of 2G ethano (AU)

• FAPESP's process: 13/09541-4 - Genomic studies of global gene expression of Aspergillus niger grown on sugarcane bagasse and stem
• Grantee: Camila Cristina Sanchez
• Support Opportunities: Scholarships in Brazil - Master