The bacterial plant pathogen Pseudomonas syringae is a highly diverse species complex that can infect and cause disease on a wide range of hosts. Despite this broad host range, individual strains of P. syringae are highly host specific. In this thesis, we used in planta serial passaging to experimentally evolve twelve independent lineages of P. syringae pathovar phaseolicola (Pph) 1448A, a bean pathogen, on the novel host Arabidopsis thaliana (Arabidopsis), with the goal of characterizing the early adaptive steps towards host adaptation. Twelve hypermutating lineages of Pph 1448A were constructed for this experiment to increase the evolvability of lineages, and to efficiently study mutations associated with adaptation towards Arabidopsis. After eighty days of passaging on the novel host, lineage 7 has shown a significant gain in fitness on Arabidopsis. Population sequencing of this lineage may provide novel insights into the adaptive processes underlying host specificity in P. syringae.M.Sc
