Date Thesis Awarded

7-2012

Document Type

Honors Thesis

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Mark H. Forsyth

Committee Member

Kurt E. Williamson

Committee Member

Oliver Kerscher

Committee Member

Randolph A. Coleman

Abstract

Helicobacter pylori is a gram negative gastric pathogen that infects the mucosal lining of the human stomach and is present is nearly half of the human population. H. pylori is the etiologic agent of peptic ulcer disease, and infection is highly associated with the development of gastric cancer. The H. pylori genome encodes three complete two-component signal transduction systems (TCSTs): ArsRS, CrdRS, and FlgRS. Each system regulates many genes in response to environmental stimuli. The genome also encodes an essential orphan response regulator, HP1021. Previous transcriptional profiling experiments indicate that each of these TCSTs regulates the expression of virulence genes. The acetone carboxylase operon, acxABC, is associated with virulence and is regulated by all H. pylori TCSTs and HP1021. We characterized the TCST-mediated transcriptional regulation of acxABC expression by examining the physical interaction of response regulators ArsR and HP1021, a repressor and activator of acxABC transcription, respectively, with the promoter region of acxA. Electrophoretic mobility shift assays suggest that both ArsR and HP1021 bind upstream and downstream of the -35 hexamer promoter element, with ArsR binding two distinct sites and HP1021 binding as many as six sites. All of the ArsR binding sites overlap with HP1021 binding sites, suggesting possible binding competition. Also, acxA expression was assayed via quantitative real-time PCR in H. pylori strains 26695 and J99 under both neutral and acidic conditions. Under neutral conditions, abrogation of arsS in H. pylori strain J99 resulted in a 4.4-fold increase in acxA transcription, however no significant change in transcription was observed in strain 26695. Grown under acidic conditions, the J99 arsS null mutant exhibited approximately a 2.6-fold increase in acxA transcription with no significant differential regulation occurring in the 26695 arsS null mutant. Collectively, this study suggests that H. pylori uses multiple TCSTs to regulate the expression of the acxABC operon, forming an overlapping regulatory network that allows finely tuned control over transcriptional regulation. This multi-layered mechanism of regulation may apply to other H. pylori virulence genes and represents a unique way for H. pylori, a bacterium with a relative paucity of TCSTs, to maintain tight control over gene expression. Inter-strain variation in the ArsRS-mediated regulation of acxA occurs between H. pylori strains J99 and 26695, offering the acxABC operon as a model for understanding strain-specific variation in TCST-mediated regulation of virulence factors.

Creative Commons License

Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 License.

Comments

Thesis is part of Honors ETD pilot project, 2008-2013. Migrated from Dspace in 2016.

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