In-situ corn fiber conversion method unlocks the role of viscosity on enhancing ethanol yield by reducing side-product glycerol

Abstract In-situ corn fiber conversion enables to greenly convert corn fiber into bioethanol with saving energy and capital expenditure. However, the remaining challenge is to understand how the additive cellulases improve substrate utilization efficiency but reduce the side-product glycerol concentration. Herein, we investigated a comprehensive responses pattern of cellulases-assisted ethanol production on fermentation properties and transcriptomic level. Two determinants, glucose release rate and viscosity, were identified to govern ethanol/glycerol ratio disturbance. The transcriptomic studies revealed three genes in ethanol synthetic and two genes in synthetic glycerol pathway present remarkably up-regulated (up to 4.28-fold) and down-regulated (up to 4.81-fold) under cellulases condition, respectively. Interestingly, 15 upregulated/downregulated genes were commonly obtained in (non-)cellulases and (non-)sodium-polyacrylate transcriptomic landscape, suggesting the reduced glycerol concentration most likely result from the decreased broth viscosity. This obtained knowledge unmask molecular mechanisms of cellulases-assisted ethanol improvement and empower engineers to rationally optimize the biofuel process for higher ethanol concentration.