Brown-rot fungi and biomimetic systems as a pretreatment for bioethanol production from wood

Fungal pretreatments to the conversion of lignocellulosic biomass into ethanol have been proposed, mainly using white-rot fungi to decay lignin and expose cellulose fibers, however, brown-rot fungi (BRF) have an even better wood deconstructing machinery where is possible to observe losses in mechanical properties before significant mass loss can be detected. The wood biodegradation system of BRF starts with non-enzymatic oxidative reactions that result in an efficient process that facilitates the further enzymatic hydrolysis. BRF developed a mechanism that reduce Fe(III) to Fe(II) and produce hydrogen peroxide, which are the Fenton reaction reagents. In Fenton reaction ·OH radical is produced by the reduction of H₂O₂ and oxidation of Fe(II), in an acidic medium (Fe(II) + H₂O₂ -> Fe (III) +^.OH + OH⁻). The oxidative reaction produces a progressive decrease in wood strength due to selective carbohydrate removal, mainly hemicelluloses. The synergy between the pretreatment of lignocellulose by brown rot fungi and saccharification has been demonstrated. Also, it is possible to biomimic the BRF process and uses it as pretreatment of wood. A pretreatment that combine wood oxidation followed by hydrothermolysis or organosolv pretreatment was evaluated and it could be a promising alternative to reduce the severity of the process and cellulases consumption. The main advantage of this pretreatment is an important reduction on time of the enzymatic hydrolysis to obtain similar or higher yields of glucose.

Acknowledgements: The financial support of this work was provided by project FONDECYT 1130693.