Pretreatment of lignocellulosic material with fungi capable of higher lignin degradation and lower carbohydrate degradation improves substrate acid hydrolysis and the eventual conversion to ethanol

Phanerochaete chrysosporium, Pycnoporus cinnobarinus, and fungal isolates RCK-1 and RCK-3 were tested for their lignin degradation abilities when grown on wheat straw (WS) and Prosopis juliflora (PJ) under solid-state cultivation conditions. Fungal isolate RCK-1 degraded more lignin in WS (12.26% and 22.64%) and PJ (19.30% and 21.97%) and less holocellulose in WS (6.27% and 9.39%) and PJ (3.01% and 4.58%) after 10 and 20 days, respectively, than other fungi tested. Phanerochaete chrysosporium caused higher substrate mass loss and degraded more of holocellulosic content (WS: 55.67%; PJ: 48.89%) than lignin (WS: 18.89%; PJ: 20.20%) after 20 days. The fungal pretreatment of WS and PJ with a high-lignin-degrading and low-holocellulose-degrading fungus (fungal isolate RCK-1) for 10 days resulted in (i) reduction in acid load for hydrolysis of structural polysaccharides (from 3.5% to 2.5% in WS and from 4.5% to 2.5% in PJ), (ii) an increase in the release of fermentable sugars (from 30.27 to 40.82 g.L-1 in WS and from 18.18 to 26.00 g-L-1 in PJ), and (iii) a reduction in fermentation inhibitors (total phenolics) in acid hydrolysate of WS (from 1.31 to 0.63 g.L-1) and PJ (from 2.05 to 0.80 g.L-1). Ethanol yield and volumetric productivity from RCK-1-treated WS (0.48 g.g(-1) and 0.54 g.L-1.h(-1), respectively) and PJ (0.46 g.g(-1) and 0.33 g.L-1.h(-1), respectively) were higher than untreated WS (0.36 g.g(-1) and 0.30 g-L-1.h(-1), respectively) and untreated PJ (0.42 g.g(-1) and 0.21 g.L-1.h(-1), respectively).