Identification, distribution and evolution of three type III secretion systems and their effectors in the pathogen, Pantoea stewartii sp. stewartii DC283

Date
2012-12
Authors
Kirzinger, Morgan William Bruce
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Faculty of Graduate Studies and Research, University of Regina
Abstract

The type III secretion system (T3SS) is an extracellular appendage used primarily by bacteria for pathogenesis in both plants and animals, including humans. Related to the bacterial flagellum, this nanomachine uses an extracellular pilus to actively transport effector proteins from Gram-negative bacteria directly into the host cell to cause disease. One genus that uses the T3SS is Pantoea, which comprises several well-studied plant pathogenic species, as well as opportunistic human pathogenic species. Three T3SSs were identified in a diverse collection of Pantoea representing plant, clinical and environmental samples: a plant-specific T3SS Hrc 1, and two animal-specific T3SSs, SPI-1 and SPI-2. A PCR-based genetic survey identified 17 Hrc 1 systems, 12 SPI-1 systems, and 9 SPI-2 systems in 9 species, 5 species from the genus Pantoea. Phylogenetic analysis together with GC content and comparative genomic analyses of the T3SS genomic islands revealed that the evolution of the plant is more consistent with vertical inheritance, whereas the SPI-1 and SPI-2 systems appear to have been acquired later though horizontal gene transfer. Most interestingly, however, was the identification of the plant T3SS in clinical isolates and the presence of the animal T3SSs in plant isolates. The Pantoea stewartii subsp. stewartii DC283 genome was also analyzed for the presence of type III secreted effectors (T3SEs), which resulted in the identification of 5 novel T3SEs. The evolutionary analysis of the three T3SSs and the identification of known and novel T3SEs highlights the importance of these secretion systems and their effectors in the biology of Pantoea.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology, University of Regina. x, 154 p.
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