Insights into the origins and evolution of mutualistic insect-bacterial symbioses

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Title Insights into the origins and evolution of mutualistic insect-bacterial symbioses
Publication Type dissertation
School or College College of Science
Department Biological Sciences
Author Oakeson, Kelly F.
Date 2014-05
Description A diverse array of insect species harbor maternally transmitted mutualistic bacterial endosymbionts that perform a variety of functions within their hosts. Many of these associations are obligate in nature with the insect relying on the bacterial symbiont to provide nutrients that are lacking in the insect's natural diet. These obligate endosymbionts often show a highly reduced genome size and maintain only a small fraction of the gene inventory of free-living bacteria. Some of the smallest known bacterial genomes are from obligate endosymbionts that have been associated with their insect hosts for long periods of time. In addition to their small size, the genomes of ancient obligate symbionts also show an increased rate of DNA and polypeptide sequence evolution as well as a nucleotide composition bias that results in an increased ratio of adenine and thymine residues. Despite extensive study of these ancient endosymbionts, little is known about their origins. To address this issue and to better understand the forces shaping genomes in the early stages of an endosymbiotic association, this work focuses on two bacteria: strain HS, a recently characterized free-living bacterium that likely served as a progenitor to the Sodalis-allied clade of bacterial endosymbionts, and the Sitophilus oryzae primary endosymbiont (SOPE), a very recent established maternally transmitted obligate endosymbiont of the rice weevil. The complete genome sequencing of these two bacteria along with comparative genomic analyses revealed that SOPE has undergone a very rapid degeneration of its genome, losing nearly half of its coding capacity, a massive expansion of insertion sequence (IS) elements and numerous intragenomic rearrangements facilitated by the IS elements. Surprisingly, these changes have happened very recently since strain HS and SOPE shared a common ancestor approximately 28,000 years ago.
Type Text
Publisher University of Utah
Subject Insects; Bacterial endosymbionts
Dissertation Institution University of Utah
Dissertation Name Doctor of Philosophy
Language eng
Rights Management Copyright © Kelly F. Oakeson 2014
Format application/pdf
Format Medium application/pdf
Format Extent 1,919,166 Bytes
Identifier etd3/id/2965
ARK ark:/87278/s6g19838
Setname ir_etd
ID 196534
Reference URL https://collections.lib.utah.edu/ark:/87278/s6g19838
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