Among the main mechanisms of evolution we find adaptation, genetic drift, gene flow, mutation, natural selection and speciation. The following thesis explores bacterial mutation rate, mutants, mutators, and how competition acts as a driving force of adaptation. In chapter 1, the system used in reference for mutation is the devolopment of Pseudomonas aeruginosa antibacterial resistance in the Cystic Fibrosis patients. Current methods for determining mutation rate are quite involved mathematically or complicated experimentally. A new method for estimating mutation rate is discussed and compared with two other widely used methods. In chapter 2, a microarray data set of different strains are compared. We find that the data set has strains that ...