Dynamics of the Bacterial Genome: Rates and Mechanisms of Mutation

Bacterial chromosomes are highly dynamic, frequently changing with regards to gene content and size via a number of processes, including deletions which lead to gene loss. How deletions form and at what rates has been the main focus of this report. In paper II we looked into how chromosomal location impacts chromosomal deletion rates in S. typhimurium. Deletion rates varied more than 100-fold between different chromosomal locations and some large deletions considerably increased the exponential rate of growth of the cells. Our results indicate that the chromosome is heterogeneous with regards to deletion rates and that deletions may be genetically fixed as a consequence of natural selection instead of drift or mutational biases. In paper I we analyzed in a laboratory setting how swiftly reductive evolution, i.e. gene loss, could occur. Utilizing a serial passage approach, we demonstrated that extensive genome reduction potentially could occur on a very short evolutionary time scale. For most deletions we noticed little or no homology at the deletion endpoints, suggesting that spontaneous deletions often form through a RecA independent process…


Salmonella enterica
The bacterial genome
The eukaryotic cell as a growth niche
Reductive evolution
Chromosome organization
Mechanisms of reductive evolution
Homologous recombination
Illegitimate recombination
Mechanisms of deletion formation
DNA breaks and deletion formation
Mutagenesis and DNA repair
Origins of change
Fidelity of DNA replication
Sources of DNA damage
Maintaining genome integrity
Base excision repair (BER)
Nucleotide excision repair (NER)
Methyl directed mismatch repair
Cellular responses to stress
The adaptive mutation controversy
Present investigations
Reductive evolution can be a rapid process in laboratory settings
Mechanism of genome reduction
Mechanism of deletion formation
Large variation in deletion rate at different chromosomal locations
Fitness effects of large chromosomal deletions…

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