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Biol Lett. Jun 23, 2009; 5(3): 429–432.
Published online Mar 11, 2009. doi:  10.1098/rsbl.2008.0793
PMCID: PMC2679921
The α-proteobacteria: the Darwin finches of the bacterial world
Thijs J.G. Ettema and Siv G.E. Andersson*
Department of Molecular Evolution, Evolutionary Biology Center, 752 36 Uppsala, Sweden
*Author for correspondence (siv.andersson/at/
Received January 7, 2009; Accepted February 12, 2009.
The α-proteobacteria represent one of the most diverse bacterial subdivisions, displaying extreme variations in lifestyle, geographical distribution and genome size. Species for which genome data are available have been classified into a species tree based on a conserved set of vertically inherited core genes. By mapping the variation in gene content onto the species tree, genomic changes can be associated with adaptations to specific growth niches. Genes for adaptive traits are mostly located in ‘plasticity zones’ in the bacterial genome, which also contain mobile elements and are highly variable across strains. By physically separating genes for information processing from genes involved in interactions with the surrounding environment, the rate of evolutionary change can be substantially enhanced for genes underlying adaptation to new growth habitats, possibly explaining the ecological success of the α-proteo-bacterial subdivision.
Keywords: adaptation, expansion, reduction, bacterial genomes, genomic islands
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