Characterization and Phylogenetic Relationships of XENORHABDUS BOVIENII Strains (ENTERORBACTERIACEAE, y-PROTEOBACTERIA) Based on Sequence Data of Two Protein Coding Genes

Date of Award

2009

Document Type

Thesis

Degree Name

Bachelors

Department

Natural Sciences

First Advisor

Gilchrist, Sandra

Keywords

Steinernema nematode, Xenorhabdus Bovienii, Entomopathogenic

Area of Concentration

Biology

Abstract

Xenorhabdus spp. are Gram negative gamma-proteobacteria that have a mutualistic association with entomopathogenic nematodes in the genus Steinernema. These bacteria are symbiotically harbored in the intestine of the only free-living stage of nematodes, the infective juvenile. This pair is pathogenic for a range of insects and has been integrated into biological control programs worldwide. Each Steinernema species has an apparent specific association with only one Xenorhabdus species, though a single Xenorhabdus bacterial species may be associated with multiple nematode species. This is the case of X. bovienii, which is present in nine different Steinernema spp. However, why these nematode species share the same bacterial symbiont is not understood. It has been speculated that sharing of X. bovienii could have happened by horizontal transfer of symbionts during co-infection of an insect host. Phylogenies based upon 16S rRNA sequences for Xenorhabdus spp. indicate some variation exists among X. bovienii isolates from different Steinernematids. Nevertheless, this gene is considered too conservative to reflect intraspecific variation. We considered two protein coding genes, rec-A and ser-C, to examine intraspecific variation across nine X. bovienii strains and interpret evolutionary relationships with other Xenorhabdus spp.

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