High mutation rates limit evolutionary adaptation in Escherichia coli

Area of Science:

• Evolutionary Biology
• Microbial Genetics
• Genomics

Background:

• Mutation is the source of genetic variation essential for evolution.
• Elevated mutation rates are observed across various organisms, from viruses to human tumors.
• Increased mutation rates can lead to both harmful and beneficial genetic changes.

Purpose of the Study:

• To investigate the impact of significantly increased genomic mutation rates on adaptive evolution in Escherichia coli.
• To determine how varying mutation rates influence adaptation in both ancestral and novel environments.

Main Methods:

• Evolving multiple replicate populations of E. coli with four distinct mutation rates for 3000 generations.
• Assessing evolved populations' growth in ancestral and over 90 novel chemical environments.
• Performing whole-genome sequencing on evolved populations to identify genetic changes.

Main Results:

• Higher mutation rates generated greater genetic diversity.
• Modestly increased mutation rates enhanced adaptation speed and performance in some novel environments.
• Very high mutation rates resulted in reduced adaptation, poor performance across environments, and a spontaneous decrease in mutation rate.

Conclusions:

• Mutation rate critically influences the balance between deleterious and beneficial mutations.
• The study identifies a tipping point for mutation rates affecting fitness, even at levels found in nature.
• Experimental findings challenge some theoretical models regarding mutation rate optima in evolution.