Doctor of Philosophy (PhD)
Department of Biological Sciences
The rise of multi-drug resistant bacteria combined with a decreasing pool of effective antibiotics has placed an increasing need for the development of novel antibiotics. Bacterial natural products or secondary metabolites have been the greatest source for development of novel antibiotics. The genus Burkholderia has recently emerged as a source of promising compounds with antibacterial, antifungal, and anti-cancer activities. Bacterial secondary metabolites provide added advantage to bacteria under stressful environments such as during host infection, evading predators or nutrient deficient conditions. However, genes involved in synthesis of these novel compounds remain silent under normal laboratory growth, creating a hurdle in isolation and characterization of these compounds. Understanding the underlying mechanism of how these genes are regulated could hold the key to unlocking the production of the secondary metabolites.
A large number of biosynthetic gene clusters in Burkholderia thailandensis are known to be under direct or indirect control of the global regulator, MftR (Major facilitator transport regulator). MftR, a MarR (Multiple antibiotics resistance regulator) homolog, is conserved even in the pathogenic strains. My work focuses specifically on the role of MftR in regulation of genes encoding proteins required for production two secondary metabolites involved in increasing fitness of the bacteria through increased virulence a) malleilactone, a cytotoxic compound, and b) malleobactin, the major siderophore. The data presented here indicate that under normal growth conditions MftR directly represses the expression of genes encoding local activators, MalR and ECF (extra-cytoplasmic sigma factor), which are essential for production of malleilactone and malleobactin, respectively. Further, my work shows disruption of the purine metabolic pathway induced by sub-lethal dosage of trimethoprim in B. thailandensis, and that such disruption leads to increased virulence as indicated by increased killing of Caenorhabditis elegans by bacterial cells grown with trimethoprim. Moreover, disruption of mftR makes B. thailandensis more virulent as indicated by increased motility, biofilm production, siderophore production, killing of C. elegans, and rot on onion bulb.
Overall, the work conducted so far not only addresses the role of secondary metabolites, malleilactone and malleobactin, in virulence of bacterial physiology, but also that targeting a global regulator could be an effective way of eliciting production of secondary metabolites. Moreover, the role of a global regulator in increasing bacterial fitness under antibiotic stress through production of secondary metabolites is highlighted.
Thapa, Sudarshan Singh, "From Regulation of Secondary Metabolites to Increased Virulence under Sublethal Dosage of Antibiotics: An Unprecedented Role of Global Regulator, MftR, in Burkholderia thailandensis" (2020). LSU Doctoral Dissertations. 5382.