**Author details**

posting, human and animal feeding, economically important chemical compounds and bio‐ mass fuel production are among some industrial applications derived from microbial

232 Sustainable Degradation of Lignocellulosic Biomass - Techniques, Applications and Commercialization

Global climate change and future energy demands initiate a race in order to achieve sustain‐ able fuels derived from biomass residues. Conversion of sugars to ethanol is already cur‐ rently done at very low cost from sugarcane in Brazil, and from corn, in United States. However, the challenge is how to obtain the biofuel from the wastes generated from the mills producing ethanol. Residues such as sugarcane bagasse and corncobs contain large amounts of lignocellulosic material and therefore can be transformed into biofuels. A major advantage of using residues to produce biofuels is to reduce the competition between fuels and food. In this context, hydrolytic enzymes such as cellulases contribute for the large cost of cellulosic ethanol nowadays. The great bottleneck to achieve cellulosic biofuels is the plant biomass recalcitrance, and overcome such barrier is the key for the development of feasible industrial processes for biofuels production. For instance, it was recently demon‐ strated that *Aspergillus niger* growing on steam-exploded sugarcane bagasse was able to pro‐ duce and secrete a high number of (hemi)cellulases [98]. The challenge is to adapt the process of steam explosion of a waste residue, such as sugarcane bagasse, with its hydroly‐ sis by the fungi. The steam-explosion is a pretreatment that can decrease biomass recalci‐

The comprehension of the machinery behind the enzymatic systems of fungi able to degrade plant cell wall polysaccharides favors the use of the microorganisms in industrial applications. Currently, through advanced molecular techniques, it is possible to engineer new microbial strains by insertion or deletion of genes involved in important metabolic pathways responsible for biomass degradation. The useful host cells to develop the synthetic bioengineering should have versatile genetic tools, resources and suitability for bio-refinery processes, such as stress tolerance. Therefore, a strain development in future requires insertion, deletion and expression controls of multiple genes and it is a difficult task to achieve. However, integrated advanced techniques could be able to overcome these challenges, including computational simulation of metabolic pathways, genome synthesis, directed evolution and minimum genome factory. The synthesis of the whole genome has already been done [160, 162] and, as discussed in reference [153], in a near future the synthesis of very large fragments of DNA will make it possible to de‐ sign a whole yeast artificial chromosome (YAC) encoding a number of genes. According to these authors, the *de novo* synthesis of YAC should be a breakthrough methodology for the fu‐ ture synthetic bioengineering, and cloning of individual genes and a construction of plasmid vectors would be obsolete. A rational design of metabolic pathways along with customized de‐ sign of genes with optimized expression may be obtained, making it possible to produce a

As said by Lee Lynd, a pioneering researcher in the field of biomass: "the first step toward realiz‐ ing currently improbable futures is to show that they are possible". These technologies descri‐ bed above are currently available for scientific community and, along with advances in industrial processes, endorse the possibility to take energy from plant biomass using microor‐ ganisms. Thus, the Humanity has never been so close to use new and sustainable ways of energy.

trance, allowing the fungi to penetrate deeply within the biomass.

whole sequence of the artificial chromosome [153, 163].

lignocellulosic degradation.

Wagner Rodrigo de Souza\*

Address all correspondence to: wagnerusp@gmail.com

Institute of Biology, State University of Campinas (UNICAMP), Brasil
