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Evolution in bacteria: evidence for a universal substitution rate in cellular genomes
1Department of Biochemistry, University of California, Berkeley 94720.
Journal of Molecular Evolution
|January 1, 1987
Summary
This study establishes a bacterial evolution timeline using ribosomal RNA divergence and geological events. It estimates Salmonella typhimurium and Escherichia coli diverged 120-160 million years ago, revealing similar molecular clock rates across diverse life forms.
Area of Science:
- Evolutionary Biology
- Molecular Evolution
- Genomics
Background:
- Establishing accurate molecular clocks is crucial for understanding evolutionary timelines.
- Bacterial evolutionary history is complex and often difficult to date precisely.
- Previous studies have lacked a robust temporal framework for bacterial divergence.
Purpose of the Study:
- To construct a temporal scale for bacterial evolution.
- To estimate divergence times for bacterial lineages.
- To compare molecular substitution rates between prokaryotes and eukaryotes.
Main Methods:
- Constructing a temporal scale by correlating ecological events with bacterial phylogenetic trees.
- Utilizing 16S ribosomal RNA (rRNA) gene sequences from eubacteria, mitochondria, and chloroplasts.
- Analyzing protein-coding DNA for divergence at synonymous sites and estimating substitution rates.
Main Results:
- Salmonella typhimurium and Escherichia coli diverged between 120 and 160 million years ago.
- Silent substitution rates in bacteria are comparable to those in eukaryotes (0.7-0.8%/Myr).
- Bacterial 16S rRNA and 5S rRNA substitution rates align with those in vertebrates and plants.
Conclusions:
- A reliable temporal scale for bacterial evolution can be established using rRNA divergence.
- Molecular clock rates are remarkably conserved across prokaryotes and eukaryotes for both rRNA and protein-coding genes.
- Bacterial amino acid replacement rates are significantly lower than silent substitution rates, more so than in mammals.