Researchers at Feng Chia University in Taiwan have engineered the bacterium Escherichia coli to produce n-butanol from crude glycerol—a byproduct of the production of biodiesel.
In an open-access paper in the journal Biotechnology for Biofuels, they report that under microaerobic conditions, the engineered strain produced 6.9 g/L n-butanol from 20 g/L crude glycerol. The conversion yield and the productivity reached 87% of the theoretical yield and 0.18 g/L/h, respectively. Overall, the team concluded, the technology platform may be useful for the economic viability of glycerol-related industries.
Among alternative fuels, n-butanol is superior to ethanol in terms of energy density, volatility, and hygroscopicity. It can be transported by the existing infrastructure and readily used in gasoline blends. Clostridium bacteria have long been used for the mass production of n-butanol via the acetone–butanol–ethanol (ABE) fermentation process. However, classic ABE fermentation—which has a biphasic process: acidogenesis followed by solventogenesis—can be technically challenging, the authors noted.
To address that issue, in earlier work, the Feng Chia team engineered metabolic pathways in E. coli for the effective production of n-butanol.
A commercialized bioprocess of n-butanol can be readily realized by a cost-effective feedstock. Biodiesel has been utilized as an alternative fuel for transportation. The annual production yield of biodiesel increases substantially with the pressing need for renewable fuels. Glycerol is a byproduct generated in the production process of biodiesel. The extending market demand has resulted in a large amount of glycerol currently available in the market. The glycerol surplus greatly reduces the price of crude glycerol, which negatively affects the economic viability of the glycerol-producing, oleochemical, and biodiesel industries. The situation is even worsened by the additional cost for disposal of glycerol waste. Therefore, it is appealing to develop a technology platform that converts crude glycerol to the value-added products.
Used as a feedstock, glycerol is attractive because it has the highly reduced carbon atoms and enables generation of more reducing equivalents than glucose. This advantage of glycerol makes it more favorable for production of reduced compounds. However, glycerol metabolism is less effective than glucose metabolism in E. coli. In this study, E. coli was engineered for the production of n-butanol from glycerol. This was systematically carried out by manipulation of central metabolism and glycerol catabolism. Consequently, the proposed approach conferred the strain with the ability to produce n-butanol from crude glycerol in an effective manner.
Mukesh Saini, Ze Win Wang, Chung-Jen Chiang and Yun-Peng Chao (2017) “Metabolic engineering of Escherichia coli for production of n-butanol from crude glycerol” Biotechnology for Biofuels 10:173 doi: 10.1186/s13068-017-0857-2