Application of fractional factorial design to study the short-term biological pretreatment of sugarcane bagasse by novel ligninolytic strains

The development of sustainable and green technologies is necessary to preserve the environment. The substitution of gasoline for ethanol is a promising measure for reducing CO₂ emissions that contribute to the greenhouse effect. Second generation ethanol may be produced from fermentable sugars inherent in agro-residues. These sugars, polymerized into cellulose and hemicellulose, are surrounded by a protective barrier of lignin that hinders the access of cellulolytic and xylanolytic enzymes. Ligninolytic microorganisms compromise the lignin barrier increasing accessibility of sugars to enzyme treatment. In this study, the performance of four novel fungal strains was evaluated for their ability to degrade sugarcane bagasse lignin. A fractional factorial design 2^4-1 was used to assess the impact of agitation (0-100 rpm), sugarcane bagasse size (20-60 mesh), culture medium volume (dampened-submerged) and pH (5.5-8.5) on the activities of cellulase, xylanase, lignin peroxidase (LiP), laccase (LAC) and acid precipitable polymeric lignin (APPL) concentration over 21 days. The strains exhibited low LAC and LiP activities but did not produce cellulase. APPL appeared to be metabolized by all strains tested. Initially, high xylanase activity (up to 30 U/mg of protein) was observed but through optimization of culture conditions was reduced to 5 U/mg of protein. The best culture conditions for low xylanase activity were 100 rpm, 20 mesh size, dampened and pH 8.5 for all strains. Therefore the optimal culture conditions were determined in which the novel strains were able to metabolize lignin in a short period of time with no significant consumption of fermentable sugars.