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Base composition bias might result from competition for metabolic resources.
Eduardo P C Rocha1, Antoine Danchin
1Atelier de BioInformatique, Université Pierre et Marie Curie, 12, rue Cuvier, 75005 Paris, France. erocha@abi.snv.jussieu.fr
Trends in Genetics : TIG
|June 5, 2002
Summary
Obligatory intracellular bacteria and their associated genetic elements, such as phages and plasmids, exhibit a higher proportion of Adenine (A) and Thymine (T) bases. This AT richness may be linked to the energetic costs and availability of nucleotides.
Area of Science:
- Microbial genomics
- Molecular evolution
- Bioenergetics
Background:
- Bacterial genome guanine-cytosine (GC) content exhibits wide variation (25-75%), with underlying reasons largely unknown.
- GC content influences genome stability, replication, and gene expression, but its evolutionary drivers remain debated.
Purpose of the Study:
- To investigate the correlation between bacterial lifestyle and genome composition, specifically GC content.
- To explore the AT/GC content of bacterial viruses (phages), plasmids, and insertion sequences in relation to their hosts.
Main Methods:
- Comparative genomic analysis of bacterial species with varying host dependencies.
- Analysis of nucleotide composition in bacterial phages, plasmids, and insertion sequences.
- Correlation of AT/GC content with host-pathogen or host-symbiont relationships.
Main Results:
- Genomes of bacteria with obligate host reliance (pathogens, symbionts) are significantly AT-rich.
- Bacterial phages, plasmids, and insertion sequences also display a marked AT-richness compared to their bacterial hosts.
- A strong inverse correlation was observed between host dependency and GC content.
Conclusions:
- The AT-richness of obligate intracellular bacterial genomes and associated mobile genetic elements is a consistent observation.
- The energetic cost and limited availability of guanine (G) and cytosine (C) over adenine (A) and thymine (T)/uracil (U) are proposed as a potential explanation for observed nucleotide composition differences.