In biological pretreatment process, bacteria and actinomycetes are not as efficient as white — and brown-rot fungi. Very few bacteria, such as filamentous bacteria be­longing to the genus Streptomycetes are well known degraders of lignin, have been studied for pretreatment. These bacteria have been found to have some role in final mineralization of lignin. Non-filamentous bacteria Pseudomonas degrade very little amount of lignin. Since these bacteria do not have extra cellular oxidoreductase, which is one of the very essential enzymes for delignification and cannot be utilized in biological pretreatment. Actinomycetes are bacteria which form multicellular fila­ments; thus, they resemble fungi, also produce extracellular peroxidase as white-rot and brown-rot fungi, for example LiP-type enzyme. Streptomyces sp. EC1 produces peroxidase and cell-bound demethylase requiring H2O2 and Mn2+, both have been produced at relatively high levels in the presence of Kraft lignin or wheat straw [49]. Bacteria actinomycetes Streptomyces viridosporus have also been studied up to some extent [95]. Godden et al. [96] studied activity of peroxidase and catalase in six actinomycetes strains.

Thermophilic actinomycetes have been isolated from a wide range of natural sub­strates, for example from desert sand and compost. The genera of the thermophilic actinomycetes isolated from compost include Nocardia, Streptomyces, Thermoacti — nomyces, and Micromonospora. Actinomycetes degrade lignin as their primary metabolic activity and at high nitrogen levels compared to white-rot fungi, most of which degrade lignin via their secondary metabolism [97].

The lignin-degrading actinomycete species examined till date have been shown to oxidatively de-polymerize lignin. The primary degradative activity of actinomycetes is solubilization of lignin, with low levels of mineralization compared with the white — rot fungi. The depolymerization reactions produce a modified water-soluble, acid precipitable polymeric lignin as the principal lignin degradation product. The range of actinomycete species capable of metabolizing lignin is still unknown. Moreover, the strains examined thus far solubilize lignin to an acid-precipitable polymeric lignin-like product.