The primary mode of growth for bacteria in the environment and during infection is as a biofilm–multicellular assemblages encased in a self-produced matrix. Bacteria growing in biofilms must contend with the difficulties of resource limitation and competition in order to reap the benefits of increased protection from external stresses including the antibiotics used against them.
With the rise in multi-drug resistance, understanding the interplay of the complicated processes that make this growth style possible will help us develop better treatment options. Cells must maintain redox homeostasis in order to carry out metabolism and avoid death. In the pathogen Pseudomonas aeruginosa, oxygen is the preferred terminal electron acceptor used for this purpose. However, oxygen is often scarce under natural growth conditions, where opposing rates of diffusion and consumption lead to the formation of steep gradients.
Under conditions of oxygen limitation, the metabolically versatile P. aeruginosa can use two major redox balancing strategies: (i) denitrification (i.e., respiration of exogenous nitrate) and (ii) reduction of endogenous redox-active pigments called phenazines. The work in this thesis describes novel regulatory mechanisms for redox homeostasis with an emphasis on the biofilm lifestyle.
Chapter 1 will introduce the necessary background about redox pathways and homeostasis in P. aeruginosa, and how this organism senses chemical cues and transduces this information into physiological adjustments that support metabolic activity and survival. Chapter 2 highlights the remarkable versatility of P. aeruginosa in producing multiple terminal oxidases, particularly the cbb3-type terminal oxidases encoded by partially redundant operons, which have the potential to generate 16 isoforms. The interaction between small-molecule virulence factors, such as cyanide, and the respiratory chain adds complexity to this system. This study uncovers the regulatory role of MpaR, a predicted pyridoxal phosphate-binding transcription factor, in governing expression of a cbb3-type terminal oxidase subunit in response to endogenous cyanide.
Chapter 3 demonstrates that pyocyanin, a terminal phenazine product, promotes metabolic activity at a depth in biofilms. However, production of pyocyanin and precursor products is stressful to cells particularly when electron donors are limiting. This work presents the global regulators RpoS and Hfq/Crc as regulators of phenazine production to balance toxicity and metabolic support. Finally, Chapter 4 identifies the first member of the P. aeruginosa phosphotransferase system, PtsP, as an oxygen-independent regulator of phenazine production and denitrification.
The research presented in this thesis sheds light on P. aeruginosa’s adaptive tactics for thriving under adverse conditions. Understanding the physiology of this bacterium under conditions relevant to biofilm-based infection provides insights into its strategies for long-term colonization in host environments and opens the door for development of more effective antimicrobials in the face of a world-wide antibiotic crisis.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/5ewq-8289 |
| Date | January 2023 |
| Creators | Smiley, Marina K. |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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