Term of Award

Spring 2013

Degree Name

Master of Science in Biology (M.S.)

Document Type and Release Option

Thesis (restricted to Georgia Southern)

Department

Department of Biology

Committee Chair

Laura B. Regassa

Committee Member 1

Lorenza Beati

Committee Member 2

Quentin Q. Fang

Abstract

Spiroplasmas are helical, motile bacteria that are associated with plants and arthropods. Traditionally, they were classified into groups based on serology; however, the recent loss of antisera repositories led to the suspension of the requirement to complete serological analysis. Therefore, Spiroplasma taxonomy needs to transition from serology to DNA characters for species circumscription. Thus, it is essential to determine the congruency between serology and phylogeny. This study examined a set of closely related strains to evaluate the level of congruency between serology and phylogeny. As a case study, the utility of maintaining serology as a character to delineate strain clusters was also investigated. A total of 26 strains were used in this study. Serological data and DNA sequences were obtained using deformation tests and GenBank, respectively. Bayesian and maximum parsimony trees were constructed using partial 16S rDNA and concatenated sequences. UPGMA trees were constructed based on the serological data. Comparative analysis of the serological and phylogenetic trees indicated that they lacked overall congruency but most tight phylogenetic clusters were conserved. When serology was used in conjunction with phylogeny to place novel isolates, members within each supported cluster exhibited serological, phylogenetic, and phenotypic relatedness. These consistent patterns for closely related strains indicated the existence of strain complexes; each complex may represent a single “species”. Although serology is incongruent with phylogeny at deeper evolutionary levels, it may be informative for the delineation of strain clusters. By undertaking a more comprehensive, balanced polyphasic approach, Spiroplasma classification may lead to a more coherent set of "species".

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