Codon bias, tRNA pools, and horizontal gene transfer

Abstract

Horizontal Gene Transfer (HGT) is a major force in bacterial evolution. Bacteria are under a strong selection to optimize their growth rate by improving features related to their codon usage. In a recent study we have shown that these two forces are coupled: 1) the codon bias of transferred genes has a strong influence on the probability that they will become fixed in the new genome, and 2) frequent HGTs may increase the similarity in the tRNA pools of organisms within the same community. Thus, methods for inferring HGTs probably underestimate their number. We believe that that the principles that affect microorganisms may also apply to mobile genetic elements (including plasmids, viruses, and transposons).

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Acknowledgements

T.T. is supported by the Koshland center for basic research. We would like to thank Ms. Hadas Zur, Dr. Uri Gophna, Prof. Martin Kupiec and Prof. Eytan Ruppin for their helpful comments.

Figures and Tables

Figure 1 Relations between translation efficiency and horizontal gene transfer. (A) Transferred genes with neutral function but with codons that are adapted to the host have a smaller effect on the fitness of the host as they recruit less ribosomes (left) than genes with codons that are not adapted to the host (slower codons; right). (B) A duplication or horizontal transfer of a tRNA that recognizes rare codons in the transferred genes may improve the translation efficiency of these genes and thus decrease their ribosomal density. After such a change in the tRNA pool, the number of available ribosomes increases, and thus the fitness of the host is augmented (right vs. left).

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