Speaker
Description
The passage of genes from parents to offspring is a fundamental rule of heredity. However, bacteria violate this rule of strict vertical inheritance by shuttling DNA between cells through horizontal gene transfer (HGT). Common vehicles for HGT are conjugative plasmids, extrachromosomal pieces of DNA encoding the machinery for their own transfer. In addition to standard vertical transmission, genes on such plasmids can move between different strains or even different species of bacteria. This partial “uncoupling” of the evolutionary trajectory of plasmid-borne genes from the evolution of their host has interesting consequences for the ecology and evolution of mobile genes, which will be the focus of this presentation. These consequences revolve around the feature of horizontal transfer itself. First, I will discuss some challenges in measuring the rate of transfer, and I will present a novel estimate derived from a branching process framework and implemented through an adjustment of the classic fluctuation analysis of Luria and Delbrück. Second, I will discuss the impact that cross-species HGT has on protein evolution, focusing on a gene encoding an enzyme that degrades a common class of antibiotics, revisiting Wright’s fitness landscape metaphor in the process. Third, I will touch on how gene mobility at different levels—between cells and within a genome—interact to influence the evolution of different forms of mobility. I will conclude with a philosophical discussion on how mobile gene evolution connects to host-pathogen coevolution, egalitarian major transitions, multi-level selection, and the nature of biological individuality.
