Population dynamics and population genetics of recombination in bacteria

Although a rare event and unnecessary for reproduction, for many species of bacteria, recombination broadly defined to include the acquisition of genes from other, at times very divergent, organisms plays a fundamental role as a source of variation for adaptive evolution. What about more mundane horizontal gene transfer (HGT) events: homologous gene recombination (HGR) among members of the same population? While there no question about central role of HGR has played as tool for understanding the genetics and molecular biology of bacteria, the role of this kind of gene shuffling for the evolution of bacteria is not at all clear. The motivation for the research in this dissertation was to increase our understanding of the contribution of HGR to adaptive evolution in bacteria, reviewed in the background Chapter 1. And, save for serendipitous observation, the profound toxin-mediated oscillations in the densities of Streptococcus pneumoniae in continuous culture described in Chapter 2, the population and evolutionary dynamics of HGR in bacteria is the focus of this dissertation. The third chapter explores the factors that constrain the extent to which different strains of S. pneumoniae engage in shuffling their genes by HGR. The fourth chapter, we use a semi-stochastic simulation of mutation, selection and recombination to ascertain the conditions under which, and extent to which, HGR accelerates the rate at which bacterial populations adapt to their environment. More importantly, we assess the conditions under which the capacity to increase rates of adaptive evolution will select for the evolution and maintenance of mechanisms for HGR while competing recombining vs non-recombining populations.