Transposable elements as mutator genes in evolution

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Mutator genes in Escherichia coli confer evolutionary advantages in chemostat competition by increasing mutation rates.
• Transposable elements, such as transposon Tn5, have been previously shown to increase E. coli fitness in chemostats, but the mechanism remains unclear.

Purpose of the Study:

• To investigate whether the transposable element Tn10 confers a similar evolutionary advantage to E. coli in chemostat competition.
• To determine if the advantage conferred by Tn10 is linked to increased mutation rates and transposition events.

Main Methods:

• Competition experiments in chemostats using E. coli strains with and without the transposon Tn10.
• Monitoring of strain frequencies and analysis of Tn10 transposition events within the host genome.

Main Results:

• Transposon Tn10 confers a frequency-dependent evolutionary advantage to E. coli in chemostats.
• Tn10 transposition, likely involving IS10 sequences, occurs when Tn10 strains are favored and insert into a specific genomic site.
• No Tn10 transpositions were detected when the Tn10 population lost in competition.

Conclusions:

• Transposon Tn10 enhances the evolutionary fitness of E. coli by increasing the host bacterium's mutation rate.
• The observed advantage is frequency-dependent and mediated by the mutagenic activity of Tn10, leading to adaptive mutations.