University of Washington genome scientist, Maynard Olson, spoke this weekend at a symposium at Cold Spring Harbor Laboratory in honor of the 60th anniversary of the phage course, where he discussed molecular evolution in chronic bacterial infections. Analysis of whole genome sequences of Pseudomonas aeruginosa, a pathogen responsible for chronic lung colonization in patients with cystic fibrosis, reveals an evolutionary ?weakening? of the bacterium over time, resulting in a much less virulent organism. Comparing sequences from P. aeruginosa isolates obtained from a patient at 6 months and 96 months of age, with a 97% detection rate, found that 68 mutations had occurred in the late isolate compared to the original wild type. Many mutations were found in virulence genes. One large deletion removed 139 genes. Furthermore, the mutant isolate was sickly and difficult to grow in vitro. ?You overwhelmingly see loss of function mutations,? says Olson. ?There is positive selection...

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