Integrated genetic and chemical modification with rice straw for maximum bioethanol production

Abstract

Crop straw provides huge lignocellulose residues that are transformable for bioethanol production and biochemicals. However, lignocellulose recalcitrance fundamentally causes a costly biomass process that is unapplicable for bioethanol conversion at industrial level with potential waste release. Here, this study selected the transgenic rice (Oryza sativa L.) lines that overexpressed AtCesA6, a typical gene involved in cellulose biosynthesis of primary cell walls in Arabidopsis (Arabidopsis thaliana L Heynh.). This work then examined significantly improved lignocellulose substrates along with much soluble sugars deposition in the transgenic rice straws. By performing green-style pretreatments with mature rice straws using two recyclable and relatively low-cost alkali chemicals (NH3·H2O, CaO) and liquid hot water, this work determined almost complete enzymatic saccharification in the transgenic rice lines. Notably, under two optimal alkali pretreatments, the transgenic rice samples could achieve either bioethanol yields of more than 20 % (% dry matter) or bioethanol concentrations at 18.3 g/L and 19.1 g/L from one-pot relatively high solid loading saccharification, being much higher than those of wild type (Nipponbare). Furthermore, this study examined how the lignocellulose recalcitrance was significantly reduced for remarkably raised enzymatic saccharification in the transgenic rice straws. It also explicated that the maximum bioethanol yield obtained in the transgenic straws should mainly be subjective to near-complete enzymatic saccharification and much directly-fermentable soluble sugars accumulation. Therefore, this study has provided a novel strategy for high bioethanol production by integrating genetically-improved lignocellulose substrates with optimal one-pot-process technology in bioenergy crops.