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Trends Microbiol. 2008 Apr;16(4):142-8. doi: 10.1016/j.tim.2008.01.009. Epub 2008 Mar 28.

Do Salmonella carry spare tyres?

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Graduate Program in Population Biology, Ecology and Evolution, Emory University, Atlanta, GA 30322, USA.


Salmonellae are enterobacteria that have the unique ability to change their flagellar composition by switching expression among two loci that encode the major flagellin protein. This property is not available to all Salmonella, but is species, subspecies and serotype specific. Curiously, the subsequent loss of the second locus in some lineages of Salmonella has apparently been tolerated and, indeed, has led to considerable success for some lineages. We discuss here an evolutionary model for maintenance of this unique function and the possible evolutionary advantages of loss or preservation of this mechanism. We hypothesize that the second flagellin locus is a genetic 'spare tyre' used in particular environmental circumstances.

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