Comparative analysis of bioethanol production involving saccharification by mixed recombinant clostridial enzymes using sugarcane leaves and kans grass as sustainable feed stocks from North-east India

Abstract

The present study involves bioethanol production from sugarcane (<em>Saccharum officinarum</em>) leaves (SL) and Kans grass (<em>Saccharum spontaneum</em>) (KG), under two separate approaches of fermentation, i) SHF (separate hydrolysis &amp; fermentation) and ii) SSF (simultaneous saccharification &amp; fermentation). The H₃PO₄-acetone pretreatment strategy was performed for effective lignin removal and enhanced porosity, confirmed by FT-IR (fourier transform infrared spectroscopy) and FESEM (field emission scanning electron microscopy). Saccharification was performed by involving recombinant cellulase GH5 (family 5 of glycoside hydrolase) and hemicellulase GH43 (family 43 of glycoside hydrolase) from <em>Clostridium thermocellum</em>, expressed and isolated from <em>Escherichia coli</em>. Successively, the bioethanol producers <em>Saccharomyces cerevisiae</em> (NCIM 3215) and <em>Candida shehatae</em> (NCIM 3500) were employed. Comparative SHF trials with 1% (w/v) pretreated KG and SL gave bioethanol titre of 0.52 and 0.64 g/L, respectively, whereas SSF experiments resulted in bioethanol titre of 0.8 and 1.0 g/L, respectively at 100 mL shake flask. An increased feedstock concentration of 5% (w/v) KG in shake flask resulted in increased bioethanol titre (4.2 g/L) in SSF. However, the increased substrate concentration of 5% (w/v) SL in individual shake flask resulted in 1.4 fold more bioethanol titre (5.7 g/L) in comparison to KG, and its scale up in bioreactor with 1 L working volume gave bioethanol titre of 11.4 g/L and yield of 0.267 g of bioethanol/g of pretreated SL.