Date Thesis Awarded
Honors Thesis -- Access Restricted On-Campus Only
Bachelors of Science (BS)
The carcinogenic bacterium Helicobacter pylori is a leading cause of human Peptic Ulcer Disease and Gastric Cancer, and regulation of its gene expression and disease pathogenesis is heavily strain dependent. There is a growing body of literature that indicates that methylation by restriction-modification systems plays a key role in the ability for H. pylori to adapt to and maintain colonization of the gastric epithelium. The study aimed to further investigate various environmental regulatory factors affecting Type I DNA methyltransferase hsdM1 (HP0463) expression, to identify the DNA motif methylated by the encoded methyltransferase, as well as identifying targets of epigenetic regulation via hsdM1-dependent promoter methylation. We demonstrated that hsdM1 transcription is dependent on metabolic and quorum sensing gene luxS, with repression of hsdM1 transcription in luxS deletion mutants. This regulation of hsdM1 was shown to be independent of the role of luxS in quorum sensing, with no correlation between presence of quorum sensing molecule AI-2 in media and transcription of hsdM1, suggesting that any regulatory action by LuxS is likely related to its role in the activated methyl cycle and detoxification of hsdM1 activation byproduct S-adenosyl-L-homocysteine (SAH). We also utilized methylome sequencing data from H. pylori 26695 control and hsdM1 deletion mutants to identify the methylation target motif of HsdM1 and select three potential targets of hsdM1-mediated promoter methylation (HP0054, HP0731, and HP1121). Transcriptional levels of the three potential hsdM1 targets were analyzed via qRT-PCR and it was demonstrated that for HP0731 and HP1121 hsdM1-dependent promoter methylation had a significant effect on transcription. The DNA methyltransferase hsdM1 in H. pylori strain 26695 is luxS but not AI-2 sensitive, and shown to have significant effect on mRNA transcription through methylation of antisense promoters, potentially contributing to epigenetic plasticity and aiding the bacterium in decades-long colonization of the harsh and ever-changing environment of the human gastric epithelium.
Ramsey, Erin, "Characterizing Environmental Regulation of Type I DNA Methyltransferase hsdM1 (HP0463) in Helicobacter pylori" (2023). Undergraduate Honors Theses. William & Mary. Paper 2014.
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