Codon bias, tRNA pools and horizontal gene transfer.

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).