Date Thesis Awarded

5-2016

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Mark H. Forsyth

Committee Member

Kurt Williamson

Committee Member

Shanta Hinton

Committee Member

Lisa Landino

Abstract

Helicobacter pylori is a gram-negative bacterium that colonizes the human gastric mucosal layer of 50% of the world’s population. H. pylori utilizes a variety of adhesin proteins to adhere to the gastric epithelial layer, allowing the bacterium to successfully colonize its host, gain access to nutrients, and persist even during gastric mucosal shedding. The present study investigates transcriptional regulation of adhesin-encoding genes sabA and hopZ in the H. pylori strain J99. Several adhesin-encoding genes, including sabA and hopZ, possess a repeating homopolymeric nucleotide tract within their promoter region and a poly-cytosine-thymine (poly-CT) tract downstream of the translational start site. Strain J99's sabA promoter homopolymeric tract consists of 18 thymines, whereas the hopZ promoter has a poly-adenine tract composed of 14 adenines. Both sabA and hopZ are phase-off , i.e., full-length protein cannot be synthesized, in the wild-type based upon poly-CT tract repeat lengths of 8 and 6 respectively. We used site directed mutagenesis to extend and truncate the poly-thymine or poly-adenine tract to determine whether altering lengths of these homonucleotide tracts affects transcription frequency of sabA or hopZ. Using qRT-PCR, we found that extending or truncating the poly-thymine tract of sabA or the poly-adenine tract of hopZ by five thymines or adenines respectively increases transcription frequency of these adhesin-encoding genes. In addition, alterations in the poly-CT tract of sabA to switch phase status to phase-on led to significant increases in transcription frequency of sabA. However, phase-on and poly-T tract extension mutations did not have synergistic effects on sabA transcription frequency. Phase-on mutations, but not poly-thymine tract mutations, increased H. pylori’s adhesion to human gastric epithelial cells. Not only did the phase-on mutants increase H. pylori adhesion, but also induced more inflammatory cytokine interleukin-8 (IL-8) production by the human gastric epithelial cells. Overall, the present study examines different mechanisms of H. pylori adherence regulation at the genetic level and effects on the host inflammatory immune response.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.

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