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Proceedings of the National Academy of Sciences of the United States of America

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Bacterial genetics, Escherichia coli -- Growth, Bacterial genomes


Bacteria display considerable variation in their overall base compositions, which range from 13% to over 75% G+C. This variation in genomic base compositions has long been considered to be a strictly neutral character, due solely to differences in the mutational process; however, recent sequence comparisons indicate that mutational input alone cannot produce the observed base compositions, implying a role for natural selection. Because bacterial genomes have high gene content, forces that operate on the base composition of individual genes could help shape the overall genomic base composition. To explore this possibility, we tested whether genes that encode the same protein but vary only in their base compositions at synonymous sites have effects on bacterial fitness. Escherichia coli strains harboring G+C-rich versions of genes display higher growth rates, indicating that despite a pervasive mutational bias toward A+T, a selective force, independent of adaptive codon use, is driving genes toward higher G+C contents.


This is the publisher's final PDF. Copyright (2012) Highwire PressThis is an open access article distributed under the Creative Commons License:, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Version of record can be found at

*At the time of publication, Professor Raghavan was affiliated with Yale University.



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