A conservative test of genetic drift in the endosymbiotic bacterium Buchnera: slightly deleterious mutations in the chaperonin groEL.

Published

Journal Article

The obligate endosymbiotic bacterium Buchnera aphidicola shows elevated rates of sequence evolution compared to free-living relatives, particularly at nonsynonymous sites. Because Buchnera experiences population bottlenecks during transmission to the offspring of its aphid host, it is hypothesized that genetic drift and the accumulation of slightly deleterious mutations can explain this rate increase. Recent studies of intraspecific variation in Buchnera reveal patterns consistent with this hypothesis. In this study, we examine inter- and intraspecific nucleotide variation in groEL, a highly conserved chaperonin gene that is constitutively overexpressed in Buchnera. Maximum-likelihood estimates of nonsynonymous substitution rates across Buchnera species are strikingly low at groEL compared to other loci. Despite this evidence for strong purifying selection on groEL, our intraspecific analysis of this gene documents reduced synonymous polymorphism, elevated nonsynonymous polymorphism, and an excess of rare alleles relative to the neutral expectation, as found in recent studies of other Buchnera loci. Comparisons with Escherichia coli generally show patterns predicted by their differences in N(e). The sum of these observations is not expected under relaxed or balancing selection, selective sweeps, or increased mutation rate. Rather, they further support the hypothesis that drift is an important force driving accelerated protein evolution in this obligate mutualist.

Full Text

Duke Authors

Cited Authors

  • Herbeck, JT; Funk, DJ; Degnan, PH; Wernegreen, JJ

Published Date

  • December 2003

Published In

Volume / Issue

  • 165 / 4

Start / End Page

  • 1651 - 1660

PubMed ID

  • 14704156

Pubmed Central ID

  • 14704156

Electronic International Standard Serial Number (EISSN)

  • 1943-2631

International Standard Serial Number (ISSN)

  • 0016-6731

Language

  • eng