Understanding the Relationship Between Nanoparticles and Bacterial Group Behavior: Autolysis and Quorum Sensing

Nano-sized materials are being used to address some of humanities greatest challenges— cancer therapy, food and water security, and environmental remediation. While extremely promising for these applications, the production, use, and disposal of nanomaterials have resulted in their release into environmental compartments. One major concern of any novel contaminant is how it interacts with bacteria. Bacteria play essential roles in human health, engineered systems, and ecological functioning. Bacteria are capable of macro-scale influence because they have evolved communication systems that enable coordinated behaviors. Communication among cells involves chemical signals that enter the environment, where they are subjected to its biogeochemistry, which now includes novel nanomaterials. The overall goal of this thesis was to improve understanding of the relationship between nanoparticles and cell-to-cell signaling behavior in bacteria focusing on two population-level behaviors: autolysis and quorum sensing. Specifically, this project sought to: (1) improve our understanding of how metal-oxide nanoparticles affect the autolytic process in Bacillus subtilis, by elucidating the biological response of the interactions between titanium dioxide nanoparticles and biomolecules; (2) reveal the interactions between quorum sensing signaling molecules and metal cations commonly used in antimicrobial nanomaterials, silver and copper; and (3) demonstrate the potential of quorum sensing-regulated cyanide production to affect oxidation and dissolution of gold nanoparticles in an environmentally relevant system. By addressing these objectives, the work demonstrated that: 1. TiO2 nanoparticles disrupt the autolytic process by delaying the onset of autolysis, and intercepting released autolytic enzymes, preventing the enzymes from degrading peptidoglycan in neighboring cells. 2. Quorum sensing signaling molecules form complexes with Ag+ and Cu2+, removing the most bioavailable form (free HHL, Ag+, and Cu2+) from the cells’ environment. 3. Quorum sensing-regulated cyanide production induces oxidative dissolution in Au nanoparticles, which were previously assumed to be inert in environmental systems. Taken together, this body of work highlights the relationship between nanoparticles and population-level behavior in bacteria. The presence of nanoparticles can have significant effects on population-level behaviors, and the activity of population-level behaviors can have significant effects on nanoparticles behavior. This inter-connected relationship, where the nanoparticles are both acted on and act upon their environment, must be considered in nanoparticle-based studies and applications.