The evolutionary fate of a horizontal gene transfer (HGT) event is determined by its fitness on the recipient cell, i.e., whether it is beneficial, neutral or deleterious. The distribution of fitness effects (DFE), thus is a fundamental predictor of the outcome of an HGT event.
The environment plays a considerable role in determining the fitness cost of a horizontally transferred gene. We have studied the fitness effects of genes transferred from Salmonella enterica serovar Typhimurium to Escherichia coli in six environments, that potentially represent the conditions experienced by the two species. The data suggests high variability of genes in different environments. Genes, whose fitness varies substantially between environments, may be able to persist in populations while being deleterious in one environment, they may be neutral or even beneficial in another environment, suggesting that environmental fluctuations may increase the likelihood of HGT.
In addition to the in vitro environments, we are also looking at, how changes in the intrinsic environment of a cell, after an HGT event, could affect fitness. An increase in protein dosage due to functional similarity of the horizontally transferred gene to the endogenous gene can cause an imbalance in the cell, thereby leading to a negative fitness effect. By comparing the growth rates of each ortholog gene with the wild type strain, we can elucidate when gene dosage acts as a barrier to HGT.
Determining the interaction status and evolutionary fate of duplicated homomeric proteins
