Genomic GC content drifts downward in most bacterial genomes

Area of Science:

• Genomics
• Evolutionary Biology
• Microbial Genetics

Background:

• Spontaneous deamination of cytidine leads to frequent GC-to-AT transitions across life.
• Eukaryotic genomes counteract GC loss via biased gene conversion during recombination.
• Bacterial genomes lack observed biased gene conversion, prompting investigation into GC content dynamics.

Purpose of the Study:

• To test the hypothesis that GC-to-AT transitions reduce prokaryotic genomic GC content evolutionarily.
• To analyze GC content trends in bacterial genomes using a phylogenetic approach.

Main Methods:

• Phylogenetic analysis of closely related bacterial genomes.
• Comparison of genomic GC content across different bacterial lineages.
• Detailed examination of mobile element impact on GC content in Caulobacter genomes.

Main Results:

• Bacterial genomes with GC content >= 40% show a downward drift in GC content.
• Genomes with GC content < 40% exhibit stable or increasing GC content.
• Acquisition of mobile elements can reduce overall genomic GC content.

Conclusions:

• GC-to-AT transitions are a significant factor in reducing bacterial genomic GC content over evolutionary timescales.
• The rate of GC-to-AT mutation and existing GC content influence the direction of genomic drift.
• Mobile element acquisition can further decrease genomic GC content in bacteria.