Identifying the Best Biofuel-Producing Microbes
To use a microbe as a factory to make a desired product, a bacterial strain that already produces the compound is treated to generate many mutants, some of which may produce more of the product. From all these new variants, the challenge is to identify those microbes that make the largest amounts of the desired compound. This is particularly difficult when the target compound (e.g., a biofuel) does not confer any selective advantage to the microbe. To solve this problem, researchers at the U.S. Department of Energy’s (DOE) Lawrence Berkeley National Laboratory and DOE Joint BioEnergy Institute designed a “biosensor”—a genetic regulator that “senses” the presence of the desired product (e.g., butanol). The expression of a gene that confers an advantage to the microbe, such as resistance to the antibiotic tetracycline, is then induced by the presence of the biosensor. Butanol biosensor-containing Escherichia coli cells, for example, grow in the presence of the antibiotic only if the medium also contains butanol. Finally, plasmids capable of synthesizing various amounts of butanol were introduced into E. coli containing the butanol biosensor and growing in tetracycline-containing medium. High butanol-producing cells could readily be identified by their faster growth rates. This approach will facilitate the selection of microbial strains that produce large quantities of any small molecule, an important step toward the development of renewable biofuels.
Dietrich, J. A., D. L. Shis, A. Alikhani, and J. D. Keasling. 2012. “Transcription Factor-Based Screens and Synthetic Selections for Microbial Small-Molecule Biosynthesis,” ACS Synthetic Biology, DOI: 10.1021/sb300091d.