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 cinnabarinus ,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).