Even though the process of wood decay by many common white — and rot fungi has been well character­ized, other types of decay caused by soft-rot fungi or bacteria are still not well understood (Blanchette et al., 2002, 2004). Soft rot is caused by fungi taxonomically classified in the phylum Ascomycota, including related asexual taxa. The term soft rot is used because it was first identified from soft, decayed wood surfaces in contact with excessive moisture (Findlay, 1984). Soft rot can also occur in dry environments (Blanchette, 2000) and seems to predominate in extreme environments such as excessively wet or dry sites, where white — and brown-rot fungi growth is inhibited, and in substrates that do not favor the growth and development of other types of fungi (Blanchette, 1995; Blanchette et al.,

2004) . Soft-rot fungi attack the lignocellulose matrix in wood by formation of cavities (type I) or cell wall erosion (type II). Cellulases and hemicellulases, but not ligninases, are involved in soft-rot attack leading to extensive loss of the carbohydrate polymers; high amounts of lignin remain even in advanced stages of soft rot (Blanchette, 1995; Eriksson et al., 1990; Nilsson et al, 1989). The most studied and applied soft-rot fungus, Trichoderma reesei, and its mutants, are mainly used for large-scale commercial production of cellulases and hemicellulases (Durand et al., 1988; Esterbauer et al., 1991; Tomme et al., 1988).

Bacteria

Bacteria degrade plant cell walls through three main morphological forms: tunneling, erosion, and cavitation (Blanchette, 1995; Daniel et al., 1987; Singh and Butcher, 1991, 1985; Singh et al., 1990). An early study has confirmed that the Gram-positive filamentous bacte­rium Streptomyces viridosporus degrades softwood lignin into low molecular weight fragments (Crawford et al., 1982). Furthermore, enzymes similar to the fungal sys­tem such as peroxidases, ligninases and manganese per­oxidases have been implicated in bacterial biomass delignification (Glenn and Gold, 1983; Kirk et al., 1986). Interestingly, some bacteria can attack high lignin-containing hard wood that is considered durable and resistant to fungal decay (Nilsson et al., 1992; Singh and Butcher, 1991). However, compared to fungi, bacte­ria are not as efficient for lignocellulosic biomass pre­treatment, as shown by a recent work comparing eight microorganisms including fungi and bacteria, for pre­treatment of sugarcane waste (Singh et al., 2008).