Compensatory evolution in rifampin-resistant Escherichia coli

Area of Science:

• Microbiology
• Evolutionary Biology
• Molecular Biology

Background:

• Antibiotic resistance is a growing clinical concern.
• Mutations conferring antibiotic resistance can impose a fitness cost on bacteria.
• Understanding the evolution of antibiotic resistance requires studying the fitness costs and compensatory adaptations.

Purpose of the Study:

• To quantify the intrinsic fitness burden of rifampin resistance mutations in Escherichia coli.
• To investigate the mechanisms of adaptation to the fitness costs of rifampin resistance.
• To explore the evolutionary dynamics of antibiotic resistance and compensatory mutations.

Main Methods:

• Isolation and characterization of 28 independent rifampin-resistant (Rif(r)) mutants of Escherichia coli K12 (MG1655).
• Measurement of per-generation fitness burden in the absence of rifampin.
• Serial transfer evolution experiments in the presence and absence of rifampin.
• Analysis of compensatory mutations and transcription efficiency using RT-PCR.

Main Results:

• The fitness burden of Rif(r) mutations ranged from 0-28%, with a median of 6.4%, and no correlation with resistance level.
• In the absence of rifampin, evolved clones showed increased fitness due to compensatory mutations, not reversion.
• In the presence of rifampin, both resistance levels and relative fitness generally increased, with some mutants showing enhanced transcription efficiency.

Conclusions:

• Bacterial populations can adapt to the fitness costs of antibiotic resistance through compensatory mutations.
• Increased transcription efficiency is a potential mechanism for adaptation to rifampin resistance.
• These findings have implications for understanding adaptive molecular evolution and managing antibiotic resistance.