Experimental Determination of Evolutionary Barriers to Horizontal Gene Transfer

Horizontal gene transfer, the acquisition of genes across species boundaries, is a major source of novel phenotypes. Several barriers have been suggested to impede the likelihood of horizontal transmission; however experimental evidence is scarce. We measured the fitness effects of genes transferred from Salmonella enterica serovar Typhimurium to Escherichia coli , and found that most result in strong fitness costs. Previously identified evolutionary barriers — gene function and the number of protein-protein interactions — did not predict the fitness effects of transferred genes. In contrast, dosage sensitivity, gene length, and the intrinsic protein disorder significantly impact the likelihood of a successful horizontal transfer. While computational approaches have been successful in describing long-term barriers to horizontal gene transfer, our experimental results identified previously underappreciated barriers that determine the fitness effects of newly transferred genes, and hence their short-term eco-evolutionary dynamics.