Non-coding small RNAs (sRNAs) are integral to post-transcriptional gene regulation in bacteria. The function of an sRNA is dependent on both secondary structure and the sequence of its unstructured seed region. The sRNA seed region typically base-pairs with target mRNAs to down-regulate the expression of target genes by blocking the ribosome-binding site or by promoting RNase-mediated degradation of the sRNA-mRNA complex. sRNAs have also been shown to increase expression of target genes by releasing RNA secondary structures that block ribosome-binding sites. Selective pressure to maintain sRNA function conserves the sequence of the sRNA seed region, but mutations in mRNA sequences to match sRNA seed regions lead to the accumulation of new targets by an sRNA. In this study, the author identified a unique scenario where a 53-nucleotide insertion event occurred in the seed region of the sRNA MgrR in Escherichia fergusonii. This PhoP/PhoQ-regulated sRNA is conserved in most enteric bacteria and is known to increase bacterial resistance to the antimicrobial peptide polymyxin B by controlling the expression of the phosphethanolamine transferase gene eptB. The analyses shows that MgrR does not regulate the expression of eptB in E. fergusonii, as observed in E. coli. Instead, MgrR likely regulates the glycerol utilization pathway glpABCFKTQ-frdABCD, and the pentose phosphate sugar pathway ulaABÂ-tktC that produces NADPH. Cell sensitivity to oxidative stress is affected by the production of NADPH, and an mgrR-deletion strain of E. fergusonii was highly sensitive to hydrogen peroxide (H2O2) and deoxycholic acid in vitro and displayed a severe loss of fitness within murine gut. The ulaAB-tktC pathway is not present in E. coli MG1655 and deletion of MgrR did not cause any sensitivity to H2O2. This work demonstrates that sRNAs could evolve divergent functions in closely related bacteria.
| Identifer | oai:union.ndltd.org:pdx.edu/oai:pdxscholar.library.pdx.edu:open_access_etds-5804 |
| Date | 27 December 2018 |
| Creators | Wright, Austin Paul |
| Publisher | PDXScholar |
| Source Sets | Portland State University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Dissertations and Theses |
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