Potential for hitchhiking in theeda-edd-zwfgene cluster ofEscherichia coli

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Abstract
SUMMARY: The locieda, eddandzwfform a tightly linked cluster inE. colithat functions in the metabolism of galacturonate, gluconate and glucose. This cluster has been transferred from six natural isolates into the genetic background ofE. coliK12 and examined with regard to effects on growth rate in chemostats. Although the naturally occurringedaandzwfalleles are selectively neutral, theeddalleles are not. Theeddalleles fall into three functional classes distinguished by their effects on growth rate in gluconate medium, the most common classes differing in fitness by approximately 1% per hour. This extensive non-neutral genetic variation ofeddis discussed in light of the evident rarity of gluconate as a natural substrate. We propose that gluconate selection is intermittent in space or time, providing the population an opportunity to accumulate non-neutral genetic variants during periods of relaxed selection. Such genetic variants will eventually be sorted out by the intermittent periods of gluconate selection, and during these periods the linkededaandzwfalleles will experience pronounced hitchhiking effects.