Engineered bacteria for propionate-repressed expression of sfGFP and GM-CSF

Abstract

Inflammatory bowel diseases (IBD) are chronic diseases that currently have no cure. Certain beneficial bacteria in the gut microbiome are able to ferment dietary fibers and produce short chain fatty acids, such as propionate, that help protect intestinal integrity and prevent the colonization of pathogens. These are found in reduced concentrations in people who suffer from IBD. Bacteria have been engineered to detect specific biomarkers which can be used as complimentary diagnostic tools and as drug delivery vehicles, helping to increase target specificity and avoid harmful side effects. In this work, we develop a two plasmid system in E. coli DH5α that detects and responds to decreasing concentrations of propionate. We observed that the genetic circuit functions between 0-110 mM of propionate with at least 0.1 mM generating a response. We then cloned the gene for the cytokine, granulocyte macrophage-colony stimulating factor (GM-CSF) into the system, which was chosen due to its reported effects in strengthening the intestinal epithelium barrier. Considerable concentrations of GM-CSF were produced after 4 hours of growth, likely being degraded soon afterward. Overall, the reporter strain may function as a complementary diagnostic tool for quantifying propionate and the therapeutic strain may work as a delivery vehicle for GM-CSF.