Formation and multiple catalysis of copper-cysteine complex enhance butanol fermentation from rice straw

Butanol production from rice straw via Acetone-Butanol-Ethanol (ABE) fermentation has been considered a sustainable and cost-effective approach to cope with energy crisis and environmental issues. However, a number of factors, particularly low butanol production and energy-intensive separation, impede its industrial application. In this study, Cu²⁺, Zn²⁺, Fe²⁺, and Ni²⁺ were individually induced into the ABE fermentation system of Clostridium beijerinckii NCIMB 8052 with butyric acid and sugars both from rice straw as co-substrates to increase the specific butanol yield. The results demonstrated that the additional 0.20 g/L Cu²⁺ (i.e. 1.25 mmol/L) significantly increased SBY and butanol/acetone to 0.194 ± 0.006 g/g rice straw and 3.90 ± 0.21, respectively, compared to those of 0.126 ± 0.004 g/g rice straw and 2.61 ± 0.17 in control system. The improved butanol production was attributed to the formation of Cu²⁺-cysteine/Cu⁺-cysteine complex, which enhanced the adsorption of butyrate from rice straw by upgrading the activity of key enzyme (ctfAB) and NADH/NAD⁺. The study provides a reinforcement strategy for efficient lignocellulosic butanol production.