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Where are the pseudogenes in bacterial genomes?
J G Lawrence1, R W Hendrix, S Casjens
1Pittsburgh Bacteriophage Institute and Dept of Biological Sciences, University of Pittsburgh, PA 15260, USA. jlawrenc+@pitt.edu
Most bacteria maintain high DNA deletion rates to purge harmful genetic elements. Intracellular parasites, shielded from these elements, exhibit lower deletion rates and more pseudogenes.
Area of Science:
- Genomics
- Microbial Evolution
Background:
- Bacterial genomes are typically compact with few pseudogenes.
- Intracellular parasites like Rickettsia prowazekii and Mycobacterium leprae are notable exceptions with higher pseudogene loads.
Purpose of the Study:
- To investigate the evolutionary pressures shaping bacterial genome size and pseudogene accumulation.
- To propose a model explaining the difference in pseudogene content between free-living and intracellular bacteria.
Main Methods:
- Comparative genomic analysis of bacterial genomes.
- Theoretical modeling of DNA influx and deletion rates.
Main Results:
- Most bacterial genomes maintain a balance between DNA influx and deletion.
- Free-living bacteria face constant influx of mobile genetic elements (transposons, phages).
- Intracellular parasites experience a reduced influx of dangerous genetic elements due to their sheltered environment.
Conclusions:
- High deletion rates in most bacteria act as a selective pressure against detrimental genetic elements.
- The sheltered lifestyle of intracellular parasites reduces the need for high deletion rates, leading to pseudogene accumulation.
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