Genetic Variation of a Bacterial Pathogen within Individuals with Cystic Fibrosis Provides a Record of Selective Pressures

            In the paper from Lieberman et al, the bacterial pathogen B. dulosa was studied to find out whether mutations within the bacteria’s genome led to a genetic fix in the population or resulted in more genetic diversity. The two different models the hypothesis was based on were the dominant-lineage model, which suggested that that the presence of more beneficial mutations would eventually select for superior dominant lineages of genes, and the diverse-community model, which stated that adaptive lineages reached an intermediate frequency in the population, leading to general genetic diversity with many coexisting gene lineages. The study that the researchers conducted found that the B. dulosa that colonized in the patients with cystic fibrosis had been colonizing with multiple genetic lineages for at least 5 years, showing that they had been developing like that for quite some time. They additionally found that many of the selective pressures acting on the pathogens were the same across all of the patients, showing that the diverse mutations were fairly stable across the sample population. Overall, the study’s support of the diverse-community model allowed them to conclude that in bacterial populations, the beneficial mutations that emerge and compete with each other actually prevent any one dominant lineage from becoming fixed in the population, and rather evolve together to fight off common selective forces. 

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