Enhancing Butanol Production By Co-culture Of Clostridium Acetobutylicum And Shewanella Oneidensis

In recent years,due to the aggravation of fossil fuels and environmental issues,people pay more attention to the development of clean energy.Butanol has gained extensive attention due to its superior properties.Butanol is mainly obtained by acetone-butanol-ethanol(ABE)fermentation.However,there are still many problems existing in ABE fermentation,which limit butanol yield.In this paper,a new co-cultured system with Clostridium clostridium and Shewanella oneidensis was used for ABE fermentation.It is expected that the two strains can enhance the fermentation performance through material and energy exchange,thereby increasing the butanol ratio and butanol yield.As s new type of fermentation method,co-culture can utilize different metabolic pathways of two strains to achieve a mutually beneficial symbiosis,obtaining a similar consequence as complex DNA recombination in vitro.From raw materials to fermentation processes,mixed fermentation of butanol has many potentials to explore.This study hopes to enhance the ABE fermentation of Clostridium acetobutylicum by co-culturing with Shewanella oneidensis.The main research contents and results are as follows:(1)The Shewanella was cultured separately under different conditions,and it was found that the cells could grow normally only when the oxygen was sufficient.The study also found that Shewanella could only maintain activity at first 24 h under the full anaerobic condition,without any growing.When the medium was not deoxygened,Shewanella oneidensis can grow till the oxygen inside the medium was exhausted,and the cells remain active at the next24 h.(2)Shewanella oneidensis cultured in an oxygen-containing medium can provide an aerobic environment for Clostridium acetobutylicum by consuming the oxygen,thereby enhancing the ABE fermentation of Clostridium acetobutylicum.Compared with 11.4 g/L butanol obtained by separate culture of Clostridium acetobutylicum,13.3 g/L butanol was produced by co-cultured fermentation with an improved butanol yield of 16% and productivity of 33.33%.(3)Taking the separate culture of Clostridium acetobutylicum as a control,different proportions of Shewanella oneidensis were added into Clostridium acetobutylicum-contained medium respectively at the solvent period of Clostridium acetobutylicum.It is found that when the dry weight ratio of Shewanella oneidensis and Clostridium acetobutylicum was 1:2,butanol concentration was the highest,reaching to 14.7 g/L.Compared with the control group,the butanol yield increased by 28.94%,and the productivity increased by 58.93%.(4)As the optimum pH of the two strains are different,the research work explored the effect of pH on the co-cultured fermentation.It was found that when the pH was controlled to6.0,Clostridium acetobutylicum produced more acids instead of ABE solvents.Besides,Shewanella oneidensis lost its activity within a shorter time of 6 h.(5)Two-compartment co-culture of Shewanella oneidensis and Clostridium acetobutylicum showed that the butanol concentration was 6.4 g/L when there was no external electron exchange in the co-culture process,and the butanol concentration increased to 7.5g/L after accessing an external electron pathway.Also,the concentration of acetone with external electron exchange increased by 31%.In summary,it is feasible to enhance the ABE fermentation by co-cultures of Clostridium acetobutylicum and Shewanella oneidensis,and it also proved that the co-culture process can significantly improve the butanol yield and productivity with a reduced cost.