Chemical Investigation of Bacterial Interactions Involving Pathogens
Chemical communication mediates the vast majority of collective bacterial behaviors, orchestrating gene expression and community functions. A fundamental understanding of how pathogens are able to do this underlies the philosophy of natural product chemistry, providing insights into novel mechanisms for controlling pathogenic bacterial infections. To increase the effectiveness of antibiotics, alternative therapeutic approaches can be used that target bacterial phenotypes associated with infections, including swarming motility and quiescence. This dissertation explores molecules that interfere with such phenotypes in two different pathogens: uropathogenic Escherichia coli (UPEC) and Vibrio parahaemolyticus. Increased understanding of how bacterial behaviors can be modulated in pathogens may significantly improve our ability to tackle these diseases. The first study, which is reported in chapter two, describes the role of peptidoglycan, a ubiquitous bacterial cell wall component, in facilitating the reversal of quiescence in UPEC. This study uses an in vitro model of the quiescent state to test isolated peptidoglycan as a chemical signaling molecule that reverses dormancy. A single purified peptide was isolated from cultures of UPEC using bioassay-guided fractionation and enzyme treatment. The tetrapeptide, Ala-Glu-DAP-Ala was found to be a potent proliferant that reverses quiescence in UPEC. This is the first reported compound to possess this bioactivity. Chapter three describes an investigation to better understand chemically-mediated bacteria-bacteria interactions between the marine bacteria Bacillus pumilus YP001 and Vibrio parahaemolyticus PSU5429. The investigational approach used a combination of experimental methods, emphasizing Matrix-Assisted Laser Desorption Ionization-Time of Flight Imaging Mass Spectrometry (MALDI-TOF IMS), whole genome analysis, and chemical isolations. The main finding showed that multiple compounds produced by the B. pumilus may act in concert to effect a lethal outcome on V. parahaemolyticus cells. When B. pumilus was grown in close proximity to the V. parahaemolyticus on an agar surface, secreted secondary metabolites induced swarming motility in the vibrio, chemically attracting toward a lethal zone containing an antibiotic. Chapter four describes whole genome sequencing and bioinformatics based secondary metabolite profiling of genetically unique bacteria strains isolated from the American lobster Homarus americanus. This body of work implicates potentially important genetic pathways for both pathogenic and commensal bacteria. Furthermore, these studies exemplify the use of next generation sequencing and biosynthetic pathways tools to probe the potential for bacteria to produce unique natural products.
Hilary Joan Grant Ranson,
"Chemical Investigation of Bacterial Interactions Involving Pathogens"
Dissertations and Master's Theses (Campus Access).