Medina, Diana Natalie (2019-10). Characterization of Novel Small Regulatory RNAs In Borrelia burgdorferi and Their Role in Lyme Disease Pathogenesis. Doctoral Dissertation.
Thesis
The causative agent of Lyme disease Borrelia burgdorferi, is maintained in nature in an enzootic cycle involving a tick vector and a mammalian host. In order to cycle between two vastly different hosts, B. burgdorferi tightly regulates its gene expression by sensing environmental cues. In bacteria, small regulatory RNAs (sRNAs) have emerged as post-transcriptional regulators of genes associated in different cell processes such as chemotaxis, metabolism and virulence. The sRNAs bind to transcripts and affect their translation and/or stability, thus, modulating and fine-tuning gene expression. Recently, in B. burgdorferi, a repertoire of sRNAs has been identified and a significant number of them are differentially expressed at temperatures in vitro that mimic the tick vector or mammalian host, suggesting a potential role in the enzootic cycle. In this work, we tested the role of seven putative sRNAs of B. burgdorferi in the experimental mouse model of infection. Of those, two were further examined in more detail. The genetic inactivation of the sRNA in between the gene bbd04 and the pseudogene bbd05a of linear plasmid 17 (lp17), designated SR0725, was dispensable for borrelial mouse infection. However, the genetic inactivation of the sRNA between the genes bbd18 and bbd21 of linear plasmid 17 (lp17), denoted SR0736, resulted in an attenuated phenotype in the mouse model. RNA-seq studies revealed 19 dysregulated transcripts in the sRNA mutant strain compared to the parent. Global proteomics and western blot analysis revealed two proteins were significantly less abundant in the sRNA mutant than in the parent. Taken together, this study describes a novel trans-acting sRNA potentially involved in posttranscriptional regulation of multiple genes by stabilizing transcripts and/or targeting mRNAs for degradation in B. burgdorferi. Our work highlights the importance of a trans-acting sRNA for optimum infection in the Lyme disease spirochetal bacterium, Borrelia burgdorferi.
