Lactate is an important metabolic intermediate in mammals, and increased lactate production has been shown to occur under inflammatory conditions. Invading bacteria can utilize this lactate as a carbon source for growth and persistence in infection contexts, and a deeper understanding of bacterial lactate metabolism is therefore essential for treating such infections. One bacterial species that can utilize lactate for growth and that is often found in environments where lactate accumulates is the opportunistic pathogen Pseudomonas aeruginosa. P. aeruginosa is most known for its colonization of the lungs of people with cystic fibrosis and of chronic wounds, environments where lactate concentrations can range from 10-40 mM. This thesis uncovers the details of lactate metabolism in P. aeruginosa, including the regulation of its lactate utilization genes, and elucidates several aspects of cell metabolism found to influence lactate consumption.
Chapter 1 provides a background into the prevalence of lactate as a major metabolic intermediate in mammals and the rationale for why it has become such a well-studied compound. This chapter also touches on the diversity of lactate utilization enzymes and their regulation across various bacterial species, and takes a closer look at P. aeruginosa’s ability to cause infection. Since much of P. aerugionsa’s success as a pathogen is linked to aspects of its metabolism, a comprehensive picture of the core pathways that support its growth and survival has the potential to reveal drug targets or inform therapeutic strategies.
Chapter 2 dives deeper into the regulatory mechanisms underpinning lactate utilization in P. aeruginosa and explores the reasoning behind P. aeruginosa’s possession of two, seemingly redundant L-lactate dehydrogenase genes: lldD and lldA. The chapter discusses how the two unique regulators of these genes - LldR and LldS, respectively - confer distinct conditional sensitivities on the expression of lldD and lldA, especially with respect to iron and glycolate concentrations. These diverse inputs allow P. aeruginosa to adapt its lactate utilization to specific environments.
Chapter 3 takes a closer look at glycolate metabolism in P. aeruginosa, since glycolate is structurally similar to lactate and, as described in Chapter 2, has been identified as a potent inhibitor of LldD-dependent lactate metabolism. Although evidence suggests glycolate is also present in infection sites, little is known about its metabolism, especially in pathogenic bacteria. Within this chapter, my co-authors and I demonstrate that expression of the P. aeruginosa glcDEFG operon is responsive to glycolate, and that the operon is expressed in the absence of added glycolate, suggesting that this metabolite is produced endogenously. We speculate that the main source of this glycolate is glyoxal/methylglyoxal detoxification, a process whereby toxic metabolic byproducts are converted into either glycolate or lactate. The fact that glyoxal/methylglyoxal detoxification produces both glycolate and lactate underscores the high degree of cross-talk between the bioactivities of these two metabolites.
Finally, Chapter 4 goes into more detail about a core theme introduced in the other chapters - how P. aeruginosa adapts its metabolism in response to changing oxygen and nutrient conditions. P. aeruginosa possesses two rubredoxin genes, which encode small soluble electron carriers believed to help it cope with oxidative stress. This chapter demonstrates that induction of the rubredoxin genes in liquid culture may occur at key time points associated with oxidative stress and metabolic shifts, and may be linked to changes in lactate and glycolate metabolism.
This thesis lays the groundwork for understanding aspects of P. aeruginosa physiology that have yet to be fully explored, including the regulatory relationships between detoxification mechanisms and central metabolism, the condition-dependent control of metabolic pathways that affects physiological differentiation in multicellular structures and in infection sites, and the potential for neighboring species in polymicrobial infections to influence P. aeruginosa physiology and virulence. This work will hopefully bring to light the need to study these metabolic and regulatory pathways, not just in Pseudomonas spp., but in other organisms as well, as many of these core biochemical processes are evolutionarily conserved.
| Identifer | oai:union.ndltd.org:columbia.edu/oai:academiccommons.columbia.edu:10.7916/fwrx-sg42 |
| Date | January 2024 |
| Creators | Florek, Lindsey |
| Source Sets | Columbia University |
| Language | English |
| Detected Language | English |
| Type | Theses |
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