Engineering Microbes for Optimized Biofuel Production
Redirecting a microbe’s metabolic pathways to make desired products frequently results in slower growth, lower yield, and other negative impacts that reduce production efficiency. This is often related to the accumulation of toxic intermediates at metabolic “bottlenecks” in microbes lacking natural pathways to use, redirect, or dispose of these compounds. Researchers at the DOE Joint Bioenergy Institute (JBEI) have observed this phenomenon in E. coli strains expressing an engineered pathway for the synthesis of terpene, a precursor of several different hydrocarbon biofuels. To alleviate this toxicity, the team screened genome databases to identify variants of the enzyme in other organisms that are able to process the problematic compound. The enzymes were expressed in vitro and assayed for activity, and genes encoding the most promising candidates were engineered into E. coli. This produced a set of strains with varying synthesis properties under different growth conditions. Subsequent manipulation of gene expression levels, cofactor pools, and redox conditions resulted in a 120% improvement in terpene production over the initial strain. These results further improve an already promising industrial microbe and demonstrate the potential of coupled systems biology and targeted metabolic engineering for enhancing biofuel production.
Maa, S. M., D. E. Garcia, A. M. Redding-Johanson, G. D. Friedland, R. Chan, T. S. Batth, J. R. Haliburton, D. Chivian, J. D. Keasling, C. J. Petzold, T. Lee, and S. R. Chhabra. 2011. “Optimization of a Heterologous Mevalonate Pathway Through the Use of Variant HMG-CoA Reductases,” Metabolic Engineering 13(5), 588-97. (DOI: 10.1016/j.ymben.2011.07.001)