Effect of environmental DNA exposure on bacterial adaptation rates

The increasing amount of DNA sequence data available reveals that horizontal gene transfer (HGT) events have been frequent in most bacterial species. This observation identifies HGT as a major driving force in bacterial evolution. Whereas many studies hav e addressed the dynamics and mechanisms of microbial evolution in asexual bacterial populations, few studies exist on the evolutionary dynamics between the processes of HGT and bacterial adaptation. HGT through natural transformation provides bacteria wit h potential access to huge reservoirs of genetic information. The importance of an improved understanding of the evolutionary impact of HGT is underscored by the fact that most microbes of importance to humans are known to be recombinogenic. It is a fact that HGT plays an important role in the acquisition of and spread of antibiotic resistance genes and virulence determinants in pathogenic microbes causing severe problems in clinical settings worldwide. Thus, it is crucial to increase our quantitative und erstanding of how HGT contribute to rapid microbial evolution. In this project, we determine the relative contribution of HGT by natural transformation on bacterial adaptation to a novel and constant environment. Our model organism is the gram-negative b acterium Acinetobacter baylyi strain ADP1 (also designated Acinetobacter sp. BD413) that is competent for natural genetic transformation. We will determine the effect of exposure to DNA of different origins on the adaptation of this bacterium in a novel e nvironment and quantify relative fitness changes by comparison with the ancestral clone under asexual experimental conditions. We will also investigate possible shifts in recombination rates, and how presence of foreign DNA influences on the genetic varia bility during environmental adaptation.