Biological pretreatment has low energy requirements and mild environmental conditions (Table 4.5). However, most of these processes are too slow, which lim­its their application at an industrial level for ethanol production process. Fungi are enzyme producers when they grow on the surface of wood and other lignocel — lulosic materials. Brown-rot fungi mostly attack the cellulose, while white — and soft-rot fungi attack both cellulose and lignin. As many white-rot fungi degrade the lignin, they have been employed for production of ligninases and degradation of lignocellulosics. Evans et al. (1994) describe how enzymes released by these fungi attack lignocellulosic materials and emphasized the role of small molecular agents involved in this process. These authors point out that the most important fungi of this class are Phanerochaete chrysosporium and Phlebia radiate, which synthesize significant amounts of extracellular peroxidases. Lee (1997) reports on the main microorganisms producing lignin-degrading enzymes and suggests the fermentation processes for producing them through both submerged culture and solid-state fermentation. In fact, the fungus P. chrysosporium has been proposed in the patent of Zhang (2006) for degrading lignin in a biomass-to-ethanol process scheme involving the separate fermentation of pentoses and hexoses (Sanchez and Cardona, 2008). The cellulases required by the process for bioethanol production can be obtained from lignocellulosic materials in which the fungi grow. Tengerdy and Szakacs (2003) and Kang et al. (2004) highlight the viability of producing cellulases and hemicellulases by solid-state fermentation compared to conven­tional submerged fermentation (Warzywoda et al., 1992).