Neither 1 G nor 2 G fuel ethanol: setting the ground for a sugarcane-based biorefinery using an iSUCCELL yeast platform

First-generation (1 G) fuel ethanol production in sugarcane-based biorefineries is an established economic enterprise in Brazil. Second-generation (2 G) fuel ethanol from lignocellulosic materials, though extensively investigated, is currently facing severe difficulties to become economically viable. Some of the challenges inherent to these processes could be resolved by efficiently separating, and partially hydrolysing the cellulosic fraction of the lignocellulosic materials into the disaccharide cellobiose. Here we propose an alternative biorefinery, where the sucrose-rich stream from the 1 G process is mixed with a cellobiose-rich stream in the fermentation step. The advantages of mixing are threefold: 1) decreased concentrations of metabolic inhibitors that are typically produced during pretreatment and hydrolysis of lignocellulosic materials; 2) decreased cooling times after enzymatic hydrolysis prior to fermentation; 3) decreased availability of free glucose for contaminating microorganisms and undesired glucose repression effects. The iSUCCELL platform will be built upon the robust Saccharomyces cerevisiae strains currently present in 1 G biorefineries, which offer competitive advantage in non-aseptic environments, and into which intracellular hydrolyses of sucrose and cellobiose will be engineered. It is expected that high yields of ethanol can be achieved in a process with cell recycling, lower contamination levels and decreased antibiotic use, when compared to current 2 G technologies.