Evolutionary Responses to Translational Challenges imposed by Horizontal Gene Transfer

Stéphanie BEDHOMME
CNRS, Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), Montpellier stephanie.bedhomme@cefe.cnrs.fr 

(Seminar in English)

Horizontal gene transfer is a powerful mechanism for antibiotic resistance spread. However, the maintenance of a horizontally transferred gene is not granted. In particular, transferred genes usually have codon preferences differing from the ones of the receiving genome, potentially triggering a translational challenge. It is predicted that, if maintained, such a gene will undergo an amelioration process, i.e. the evolution of its codon usage towards the host one and/or a fine tuning of its expression and of the expression of interacting genes.

To test these predictions, synonymous versions of an antibiotic resistance gene were transformed in Escherichia coli. We verified that mismatch in codon usage induced a fitness cost and then experimentally evolved these populations. At the phenotypic level, the cost of codon usage mismatch was totally compensated. At the genotypic level, no amelioration process was observed but various genetic changes occurred: mutations in the regulatory region, gene loss, plasmid copy number reduction and diverse types of chromosomal mutations. Horizontal transfer thus reveals itself, not only as a spreading highway for these genes but also as a powerful mechanism pushing bacteria to explore new ways of functioning.

Recent publication:

Bedhomme et al. (2017) Plasmid and clonal interference during post-horizontal gene transfer evolution. Molecular Ecology, 26: 1832–1847.