IS1 transposition is enhanced by translation errors and by bacterial growth at extreme glucose levels

Transposition of insertion sequences (IS) is an enzyme-mediated process that only occurs in a minority of cells within a bacterial culture. Transposition is thus a rare event, but transposition frequency may vary depending on experimental conditions. For instance in a rich broth, IS elements are known to transpose during stationary phase but not during exponential growth. Using a reporter system which involves the activation of the cryptic bgl operon in Escherichia coli, we show that the frequency of IS1 transposition is a function of glucose concentration in the growth medium, it is increased by streptomycin amounts that are below minimum inhibitory concentration (sub-MIC) and is inhibited in an rpsL150 strain with high translation accuracy. Since starved cells are known to enhance ribosome frameshifting, our data suggests that growth conditions applied in this study could affect IS1 transposition by increasing translation infidelity.