The Bioenergetics of a Low-Power, Phenazine-Dependent Maintenance Metabolism in Pseudomonas aeruginosa

Citation

Ciemniecki, John Alan (2024) The Bioenergetics of a Low-Power, Phenazine-Dependent Maintenance Metabolism in Pseudomonas aeruginosa. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/n992-ey51. https://resolver.caltech.edu/CaltechTHESIS:04152024-205944516

Abstract

A common feature of all life is the metabolic transformation of energy from the environment to biochemical energy in the organism. While this process is well-characterized in molecular detail for fast-growing or otherwise fast-metabolizing organisms such as humans, many microorganisms subsist in the environment around us with little to no exogenous energy for extended periods, and we have only vague ideas how. Questions about the metabolic mechanisms and rates underpinning these astounding survival capabilities speak to the fundamental question of the lower energetic limits of life. Motivated by this big-picture question in biology, this thesis represents one line of physiological inquiry into a specific anaerobic survival metabolism of Pseudomonas aeruginosa, an opportunistic bacterial pathogen. Pseudomonas is perhaps best known for its characteristic production of colorful, redox-active, secondary metabolites called phenazines that allow a metabolic process called extracellular electron transfer. Phenazine extracellular electron transfer has been previously shown to unlock a slow, anaerobic glucose catabolism that facilitates the survival of energy-limited populations of cells. My thesis work has elucidated the predominant membrane-bound protein complexes involved in phenazine reduction and the predominant subcellular location of reduction for each of the main phenazines produced by Pseudomonas. I show that the survival metabolism powered by these phenazines places them in a true maintenance state where there is no detectable growth in the population at the single-cell level. The metabolic rate of this maintenance was measured and found to be 1,000 times slower than when the cells are growing in aerobic culture, 100 times slower than estimates of maintenance rates made in continuous culture, and 10 times slower than the mean basal metabolic rate estimated across all life on the planet. These results open the door to investigations of metabolic attenuation, a physiological state that underpins microbial survival in nature and disease. In pursuit of these discoveries, various new experimental assays that allow further investigation into the bioenergetics and biochemistry of phenazine metabolism were developed. Finally, intellectual frameworks are presented that, in conjunction with the discoveries made and methods developed, collectively bring us steps closer to understanding the bioenergetic basis of microbial resiliency.

Thesis Files