Living bacterial cells contain thousands of genes. However, only a part of the genes are activated (expressed) at any given time. Bacterial cells activate or repress a specific set of genes to optimally respond to or adapt to the dynamic environment. When engineering bacterial cells to produce useful chemicals or proteins (metabolic engineering), to detect and measure speficic compounds (biosensors), or to metabolize environmental toxins (bioremediation), we need versatile gene switches or circuits that can turn on or turn off genes in response to chemical or physical signals. We developed a powerful technique called dual genetic selection that allows us to efficiently design such gene switches in E. coli.
Synthetic Bacterial Riboswitches
Riboswitches are RNA-based sensors found in bacteria that detect small molecule metabolites such as vitamins, nucleobases, and amino acids. When a riboswitch binds to the associated metabolite molecule, the structure of the RNA changes, resulting in a change in the level of gene expression. In other words, bacteria use RNA to recognize certain metabolites and turn on or turn off a set of genes that are involved in the synthesis or removal of the metabolites. We are using the dual genetic selection technique developed in our lab to engineer natural riboswitches. For example, we took a vitamin B1 (thiamine) riboswitch from E. coli that turns off gene expression when there is excess vitamin, and reengineered the riboswitch to turn on gene expression when the vitamin is available. The engineered riboswitches may be useful for measuring metabolite levels inside cells or to redesign metabolic pathways.
