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The search for renewable sources of energy requires a worldwide effort in order to decrease the harmful effects of global climate change, as well as to satisfy the future energy demands. In this context, biofuels are emerging as a new source of energy derived from biomass. The production of biofuels could decrease effectively the impact of pollutants in the atmosphere, in addition to assisting in the management for tons of biomass waste. Biomass (plant matter) can be referred to "traditional biomass", which is used in inefficient ways such as the highly pollutant primitive cooking stoves (wood), and "modern biomass" that refers to biomass produced in a sustainable way and used for electricity generation, heat production and transportation of liquid fuels [1]. In addition to these definitions, The International Energy Agency (IEA) defines biomass as any plant matter that could be used directly as fuel or con‐ verted into fuels, electricity or heat. Therefore, in order to provide useful management of bi‐ omass, it is clear that one needs to learn how to extract energy from plants.

Plant cells are mainly composed by lignocellulosic material, which includes cellulose, hemi‐ cellulose and lignin (lignocellulosic complex). The hydrolysis of lignocellulose to glucose is a major bottleneck in cellulosic biofuel production processes [2]. In nature, microorganisms, especially fungi, are able to degrade the plant cell wall through a set of acting synergistically enzymes. This phenomenon leads to glucose being released in a free form, which can enter the metabolism of the microorganism, providing its energy. A great challenge is to modify the architecture of the plant cell walls and/or the ability of the microorganisms to degrade it, by modifying their genomes. For instance, researchers can generate genetically engineered microorganisms able to degrade efficiently the polymers in the plant cells, producing sugars monomers that can be fermented directly by yeasts, generating ethanol. This chapter will describe the composition of plant cell walls and how microorganisms cope with the lignocel‐ lulosic material. The main focus will be on fungi cell wall degrading enzymes (CWDEs) and their genetic regulation. The aim of this chapter is to guide scientists in order to genetically

© 2013 de Souza; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2013 de Souza; licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

improve microorganisms that can be able to efficiently degrade the plant biomass. Also, new strains could be great producers of CWDEs, providing enzymatic cocktails that can be intro‐ duced commercially. Finally, the future perspectives will demonstrate how far we are from cellulosic ethanol and other biomass-derived chemical compounds, regarding to research of microorganisms.
