Biobutanol production from rice straw using a redox-modulated fungal-bacterial consortium: Transcriptional regulation and process integration.

Abstract

Producing butanol from lignocellulosic biomass is a key strategy for addressing climate change and the energy crisis. Consolidated bioprocess (CBP), which combines enzyme production, hydrolysis, and fermentation into a single step, offers an effective way to lower the production costs of biobutanol. Despite the crucial role of fungi in cellulolytic decomposition, developing efficient fungal-bacterial consortia for butanol production remains challenging due to the fundamental conflict between the aerobic nature of fungi and the strict anaerobicity of solventogenic clostridia. In this study, a microbial consortium comprising the lignocellulose degrader Trichoderma reesei RUT-C30 and the butanol producer Clostridium beijerinckii NCIMB 8052 was developed, enabling direct butanol production from alkali-pretreated rice straw (RS). The butanol-producing ability of fungal-bacterial consortia was demonstrated using microcrystalline cellulose (MCC) as a substrate. After optimizing RS loading and l-cysteine, the consortium achieved a butanol titer of 3.09 ± 0.20 g/L with a yield of 0.069 g/g initial pretreated RS and a productivity of 0.018 g/(L·h), at 4.5% (w/v) RS loading and 0.5 g/L l-cysteine. Transcriptomic analysis revealed that T. reesei RUT-C30 adapted to hypoxia by enhancing ethanol fermentation and hydrolysis of cellulose and hemicellulose. Additional l-cysteine probably altered carbon flow to the non-oxidized pentose phosphate pathway and enhanced butyrate production and acid reabsorption in C. beijerinckii NCIMB 8052. This study provides new insights for optimizing cooperation between microbes with differing oxygen requirements, advancing butanol production from lignocellulosic biomass.