Term of Award

Spring 2009

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (open access)


Department of Biology

Committee Chair

Laura B. Regassa

Committee Member 1

Lorenza Beati

Committee Member 2

Oscar J. Pung


Spiroplasmas are among the smallest self replicating organisms known. They are helical, motile descendents of Gram-positive bacteria that have evolved to occupy broad host ranges including plants, insects and crustaceans. Spiroplasmas are the causative agent of several economically important agricultural diseases, but most host-microbe interactions appear to be commensal. Given the ubiquitous nature of these microbes, a methodical approach that focused on serologically distinct isolates from a single host family was used as an initial step in understanding spiroplasma diversity and distribution. Tabanid-associated spiroplasmas represent the most thoroughly studied group to date, so this project examined a spiroplasma field isolate collection (>200 isolates) that was obtained from tabanid flies in Costa Rica, Ecuador, Australia, and the United States. The 16S rRNA, 23S rRNA, and rpoB genes and the 16S-23S rRNA spacer region were successfully used to establish evolutionary relationships of the closely related spiroplasma isolates. Phylogenetic analyses and non-genetic character mapping indicated that all study isolates belonged to the Apis clade; arginine hydrolysis was a strong indicator of evolutionary relatedness; surface serology and phylogenetic placement were congruent; and neither host specificity nor geographical ranges were strict.