UC San Diego

The cryptic bgl operon in E. coli can be activated via mutation under starvation conditions to enable the uptake and metabolism of β-glucosides as a carbon source for growth and division. I found that the expression of one of the ix genes in this operon, bglG, leads to an increase in operon mutation frequency that confers the Bgl+ (β-glucoside utilizing) phenotype. I compared the mutation rates of a single copy, constitutive bglG expressing BW25113 E. coli strain to a wild type BW25113 strain on various agar plate mutation assays and used colony PCR to analyze differences in mutation frequencies. Then, I performed mutation assays on cells grown on a good carbon source (glycerol) and incubated on a poor carbon source (propanediol) to show that these differences arising from bglG expression are isolated to the bgl operon. To identify a plausible mechanism, I generated native promoter bglG-lacZ fusions as a reporter and analyzed promoter activity under different conditions. I found that bglG expression specifically increases bgl-activating mutations and that this effect is dependent on the presence of β-glucosides.