Reassessing Microbial Evolution in Light of Horizontal Gene Transfer

University Of Connecticut, Storrs CT

Investigators

Abstract

Horizontal or lateral gene transfer (HGT) denotes the exchange of genetic information between organisms as opposed to vertical inheritance, i.e. the passing of genes from parent to daughter cells. This project will study the relative contributions of HGT and vertical inheritance to microbial evolution. First, the extent of intra-gene mosaicism will be explored. Individual genes can be mosaic as a result of recombination. Preliminary data indicate that in the case of ribosomal RNA intra-gene mosaicism might not be a rare event. Statistical tests will be developed to assess how frequently intra-gene mosaicism occurred during microbial evolution. These tests will utilize simulated sequence evolution incorporating different models with varying amounts of HGT and recombination. Second, genome evolution will be simulated to address the following question: Are the confidently detected instances of HGT the tip of an iceberg, the bulk of which remains below the detection limit? Or are many of the alleged transfer events artifacts due to compositional bias, convergent evolution and unrecognized gene duplications? The simulations will include different frequencies of recombination and will utilize different models to simulate sequence evolution. Simulations that take the detection levels for horizontal gene transfer and intra-gene mosaicism into consideration will move the study of horizontal gene transfer beyond a compilation of anecdotal evidence. Third, a relaxed molecular clock model will be used to analyze the early evolution of prokaryotic life. Time estimates and their credibility intervals will be obtained for individual gene families. Dates for key evolutionary events estimated from compatible datasets will be combined to achieve more accurate divergence time estimates