Ammonia fiber explosion (AFEX) treatment of corn stover and effects of AFEX treatment on plant-produced heterologous cellulase

The ammonia fiber explosion (AFEX) process treats lignocellulosic biomass with liquid ammonia under pressure followed by explosive pressure release to enhance conversion of structural carbohydrates (cellulose and hemicellulose) to fermentable sugars. The potential of ammonia fiber explosion (AFEX) treatment for enhancing the enzymatic conversion of lignocellulosic biomass is well recognized. However, optimizing the process conditions and parameters such as ammonia loading, moisture content of biomass, temperature and residence time is necessary for maximum effectiveness of this process. The effectiveness of the AFEX treatment was measured by the extent of enzymatic hydrolysis of the treated corn stover and also by the amount of ethanol produced during simultaneous saccharification and fermentation (SSF) process from these samples. Approximate optimal pretreatment conditions for corn stover were found to be temperature, 90°C; kg of ammonia: kg of dry corn stover, 1:1; moisture content of corn stover, 60% (dry weight basis [dwb]); and residence time (holding at target temperature), 5 minutes. Approximately 97% of the theoretical glucose yield was obtained during enzymatic hydrolysis of the optimal treated corn stover using 60 filter paper unit (FPU) of cellulase enzyme /g of glucan. The ethanol yield of optimally AFEX-treated corn stover has been increased up to 2.2 times over that of an untreated sample.; The cost of enzymes used for saccharification of cellulosic residues is dominant in the overall bioconversion process. One way to decrease this cost is to produce these enzymes in transgenic plants. In an effort to produce heterologous cellulases in transgenic corn plant, a research group from the Crop and Soil Sciences Department (at Michigan State University) and I constructed several different plasmid DNAs to target these enzymes to different compartments (cytosol or chloroplasts) of transgenic corn plants.; We have also investigated the effects of AFEX pretreatment, employing a range of treatment temperatures, moisture contents and ammonia loadings on the activity of plant-produced heterologous cellulase. The plant materials included transgenic tobacco plants expressing E1 (endoglucanase from Acidothermus cellulolyticus). The E1 activity was measured in untreated and AFEX-treated tobacco leaves to investigate the effects of the treatment on the activity of this enzyme. The maximum observed percent of retention of activity was about 36% for transgenic tobacco plant treated at 60°C, 0.5:1 ammonia loading ratio, and 60% moisture content (dwb).