Conditions for pretreatment of cotton stalks using P. chrysosporium by SSC have also been explored. While substrate moisture content significantly affects lignin degradation, supplementation with modified salts did not affect the reaction process. Over a period of 14 days, SSCat 75% moisture content without salts resulted in 27.6% lignin degradation, 71.1% solids recovery and 41.6% availability of carbohydrates, suggesting that mi­crobial pretreatment by SSC has the potential to be a low-cost, environmentally friendly alternative to chemi­cal approaches (Shi et al., 2008).

RICE STRAW

Fungal pretreatment of rice straw for improved enzy­matic saccharification has been reported. Yamagishi et al. (2011) tested 17 C. stercoreus isolates for their ability to treat rice straw for improved enzymatic hydrolysis. A negative correlation was found between cellulase and xylanase activity in these isolates and enzymatic saccharification yields in the pretreated straw. A 25-day pretreatment with the strain C. stercoreus TY-2 led to a more than fivefold increase in enzymatic saccharification yield compared to untreated control samples, suggesting this isolate has the potential for biological pretreatment of rice straw under conditions of low energy input. A 15-day pretreatment of rice straw with P. chrysosporium in an optimized media resulted in a treated biomass with an enzymatic digestibility of 64.9% of the theoretical maximum glucose yield. When the fungal-pretreated rice straw was used as a substrate in simultaneous saccharifi­cation and fermentation (SSF), a 9.49 g/l ethanol concen­tration, 58.2% of the theoretical maximum production yield, and 0.40 g/l/h productivity were achieved after 24 h and a 62.7% of the theoretical maximum ethanol yield was expected after 96 h (Bak et al., 2009).

When rice straw was pretreated with the wood-rot fun­gus, Dichomitus squalens, for 15 days, an enzymatic digest­ibility of 58.1% of theoretical glucose yield was reached for the treated biomass. When the pretreated rice straw was used as a substrate for ethanol production in SSF, the ethanol production yield and productivity were 54.2% of the theoretical maximum and 0.39 g/l/h, respectively, after 24 h (Bak et al., 2009). Taniguchia et al. (Taniguchi et al., 2005) reported the effect on rice straw composition and susceptibility to enzymatic hydrolysis after pretreat­ment with four white-rot fungi (P. chrysosporium, Trametes versicolor, C. subvermispora, and P. ostreatus). Among the four strains, P. ostreatus selectively degraded the lignin fraction of rice straw rather than the cellulose compo­nent. A 60-day pretreatment of rice straw with P. ostreatus led to a total weight loss of 25% and 41% lignin degrada­tion, but only a 17% loss of cellulose and a 48% loss of hemicellulose. A 48-h enzymatic hydrolysis lead to 52% holocellulose and 44% cellulose solubilization in the pretreated rice straw corresponding to a net sugar yield of 33% from holocellulose and 32% from cellulose.

PADDY STRAW

A recent report of a study on the pretreatment of paddy straw with the white-rot fungus T. hirsuta (Micro­bial Type Culture Collection) MTCC 136 showed high ligninase and low cellulase activities. It showed that within 10 days of solid state fermentation, the carbohy­drate content was enhanced by 11.1% and a much higher yield of sugars was obtained after enzymatic hydrolysis. Saccharification efficiency of the biologically pretreated paddy straw with the commercial enzyme Acceler — ase®1500 reached 52.69% within 72 h suggesting the delignification potential of T. hirsuta for pretreatment of lignocellulosic substrate and facilitating efficient enzymatic digestibility of cellulose (Saritha et al., 2012b).