Metabolic Engineering for Biocatalyst Robustness to Organic Inhibitors

Abstract

Microbial production of biorenewable fuels and chemicals is often limited by inhibition of the biocatalyst, either by increasing concentrations of the product compound or by contaminant compounds in the biomass-derived sugars. This inhibition can interfere with economically viable production. Here we discuss typical mechanisms of inhibition and methods for improving biocatalyst robustness. Inhibition often takes the form of inhibition of enzyme activity, depletion of cofactor pools, and membrane damage; methods are discussed for mitigating each of these types of inhibition. Various evolutionary schemes have been developed and implemented on a variety of inhibitory compounds, including butanol, acetic acid, furfural, and ethanol. Reverse engineering of these improved strains can provide insight into new metabolic engineering strategies.

Turning the Screw: Engineering Extreme pH Resistance in Escherichia coli through Combinatorial Synthetic Operons

“…Indeed, different molecular strategies have been used for the rational improvement of microbial robustness under conditions such as temperature, pH, and inhibitor concentrations. , In recent years, synthetic biology approaches used to this end include the development of genetic devices composed of heat shock proteins (HSPs) and superoxide dismutases that were able to improve ethanol fermentation at high temperatures in Saccharomyces cerevisiae , synthetic circuits composed of RNA thermometers allied to quorum-sensing systems to regulate expression both of HSPs and cell death in E. coli , and the development of pH-sensing riboswitches to regulate mRNA translation in bacteria under specific acidity conditions . Our work contributes to this growing field by showing the feasibility of employing combinatorial operon constructions to obtain resistance devices that greatly enhance exponentially growing E. coli survival under acidic stress even without prior adaptation to acidic pH or media supplementation.…”