As the demand for alternative fuel sources has increased, there has been renewed interest in the production of butanol from microorganisms such as the bacterium Clostridium tyrobutyricum. Butanol is a promising alternative due to its ability to integrate easily into current systems, however the production process must be optimized before commercial application becomes viable. The production of butanol from C. tyrobutyricum is examined and altered by implementing techniques of metabolic engineering. Multiple plasmids have been constructed and used to create high performance C. tyrobutyricum mutants by improving the central butanol formation pathway and decreasing byproducts.
Furthermore, the fermentation process was examined and the knowledge acquired will facilitate more effective fermentation in the future. One of the main goals of butanol fermentation using microorganisms is to utilize lignocellulosic materials due to their availability and low cost. However, the lignin, cellulose, and hemicellulose cannot be consumed by Clostridium species without pretreatment. The pretreatment process releases microbial inhibitors that reduce the fermentation yield and productivity, including weak acids, derivatives of furan, and phenolic compounds. The inhibitory effects of two representative compounds, furfural and phenol, have been examined in batch fermentations of C. tyrobutyricum for butanol production. Both cell growth and butanol formation were sensitive to inhibitor concentrations, and resistance under low concentrations was observed, indicating that the inhibition effects can be alleviated or avoided through detoxification of the pretreated biomass. Future work will focus on optimizing the construction and fermentation of high performance mutants to generate high yields of butanol.
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