Activation of the bgl operon by adaptive mutation

Area of Science:

• Microbiology
• Genetics
• Molecular Biology

Background:

• The cryptic bgl operon in Escherichia coli K12 is typically inactive.
• Activation of the bgl operon allows utilization of beta-glucoside sugars like arbutin.
• IS element insertions are known to activate gene expression.

Purpose of the Study:

• To investigate the mechanisms of bgl operon activation in Escherichia coli K12.
• To explore the role of IS elements in adaptive mutagenesis.
• To characterize late-arising mutations during selection on arbutin.

Main Methods:

• Selection of Bgl+ mutants in Escherichia coli K12.
• Analysis of IS element insertions in the bglR control region.
• Characterization of mutations in late-arising mutants, including sequencing of the hns locus.

Main Results:

• IS1 or IS5 insertions in the bglR region activate the bgl operon in 98% of cases.
• Prolonged selection on arbutin, especially during carbon starvation, leads to adaptive mutations.
• A significant portion (20%) of late-arising adaptive mutations occurred at the hns locus.

Conclusions:

• This study provides the first direct evidence for adaptive mutagenesis mediated by IS element insertions.
• The bgl operon system in E. coli offers a model for studying IS-element-driven adaptive mutagenesis.
• The findings are applicable to diverse genetic backgrounds, including natural E. coli isolates.