Sunday, May 3, 2009
2-75
Microbial Conversion of Bio-Oils to Fuels and Chemicals: A new Biorefinery Paradigm
Clementina Dellomonaco1, Paul Campbell2, Carlos Rivera2, and Ramon Gonzalez1. (1) Chemical and Biomolecular Engineering, Rice University, 6100 Main ST, MS-362, Houston, TX 77005, (2) Glycos Biotechnologies Inc, 711 Leverkuhn St., Houston, TX 77007
The use of oils and fats as renewable resources for the production of chemicals and fuels is a promising avenue to establish biorefineries. The highly reduced nature of carbon atoms in these feedstocks, as compared to sugars, would ensure the production of chemicals and fuels at higher yields. However, metabolism of free fatty acids (FAs), the main constituents of fats and oils, requires the presence of an external electron acceptor, which in turn would preclude the synthesis of metabolic products. We propose a new hybrid paradigm to balance cell growth and synthesis of reduced products by using micro-respiratory conditions that lead to a respiro-fermentative metabolic mode.
Ethanol and succinate were chosen as model products and E. coli as model organism to illustrate the feasibility of the above approach. The maximum theoretical yields for the synthesis of ethanol and succinate from FAs are 1.33 g/g and 1.85 g/g, respectively, compared to 0.51 g/g (ethanol) and 1.12 g/g (succinate) for their production from sugars (i.e. 2.6- and 1.7-fold increase by using FAs). To increase the production of ethanol, a mutant of the enzyme acetaldehyde/alcohol dehydrogenase (r-AdhE) was created that is functional in the presence of oxygen. Overexpression of r-AdhE in wild-type E. coli MG1655 grown under micro-respiratory conditions led to a yield of 0.60 g ethanol/g FAs, which already surpasses the maximum theoretical from sugars. Similar improvements in the synthesis of succinate were achieved by engineering the TCA cycle and the glyoxylate shunt to prevent succinate degradation and enhance its synthesis.
Ethanol and succinate were chosen as model products and E. coli as model organism to illustrate the feasibility of the above approach. The maximum theoretical yields for the synthesis of ethanol and succinate from FAs are 1.33 g/g and 1.85 g/g, respectively, compared to 0.51 g/g (ethanol) and 1.12 g/g (succinate) for their production from sugars (i.e. 2.6- and 1.7-fold increase by using FAs). To increase the production of ethanol, a mutant of the enzyme acetaldehyde/alcohol dehydrogenase (r-AdhE) was created that is functional in the presence of oxygen. Overexpression of r-AdhE in wild-type E. coli MG1655 grown under micro-respiratory conditions led to a yield of 0.60 g ethanol/g FAs, which already surpasses the maximum theoretical from sugars. Similar improvements in the synthesis of succinate were achieved by engineering the TCA cycle and the glyoxylate shunt to prevent succinate degradation and enhance its synthesis.