Characterization of The Ato Gene Family In Alternative Carbon Metabolism

<p>As a commensal colonizer and opportunistic pathogen, <em>Candida albicans </em>is the most clinically important human associated fungus. Systemic infection carries an unacceptably high mortality rate of ~40% in the growing population of immunocompromised individuals. Macrophages are important innate immune cells that limit the niches in the human body in which <em>C. albicans </em>can persist through phagocytic removal. However, following phagocytosis <em>C. albicans</em> readily escapes from the immune cell by differentiating into filamentous hyphae, a process that should be inhibited in the normally acidic phagolysosome. We have shown that <em>C. albicans</em> induces germination by neutralizing the phagolysosome. To better understand this process we compared transcript profiles of cells in conditions that promote<em> </em>alkalinization <em>in vitro</em> to macrophage phagocytosed cells, which revealing an overlapping set of up-regulated genes, including several members of the poorly understood <em>ATO </em>family. This family is greatly expanded in <em>C. albicans </em>relative to other fungi and has been implicated in both ammonia release (Ammonia Transport Outward) and acetate metabolism. I hypothesized that the Ato proteins are important effectors of the pH change <em>in vitro</em> and in macrophages. Deletion of one of the 10 homologs, <em>ATO5, </em>or the over-expression of a dominant negative <em>ATO1^G53D </em>allele<em> </em>results in a delay in environmental alkalinization <em>in vitro</em>, a defect in hyphal formation. Further, these strains form fewer hyphae after phagocytosis, have a reduced ability to escape macrophages, and reside in more acidic phagolysosomal compartments than wild-type cells. Analysis of an <em>ato5Δ ATO1^G53D</em>double mutant strain revealed additive <em>in vitro</em> defects, similar in magnitude to the<em> stp2∆</em> mutant. Additionally, over-expression of many <em>ATO </em>genes in a wild-type background significantly increases alkalinization and ammonia release, strongly suggesting functional overlap between them. In a complementary approach we examined Ato function in <em>S. cerevisiae </em>Ato proteins as important to weak acid stress tolerance and cytosolic pH homeostasis; revealing that <em>ato</em> mutants are sensitive to weak acid stress and are unable to maintain cytosolic pH homeostasis. This defect was largely dependent upon ScAto1. Taken together, we conclude that Ato proteins are important mediators of the host-pathogen interaction by regulating pH in some host niches.</p>

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation (PhD)

Year dc:date.available

2016

Author dc:creator

• Danhof, Heather A

Contributors dc:contributor

• Michael C. Lorenz
• Jeffrey Actor
• Ziyin Li

• Metabolism
• Macrophages
• Fungi
• Candida albicans
• Saccharomyces cerevisiae
• acetate
• transport
• Pathogenic Microbiology

Repository record dc:identifier

https://digitalcommons.library.tmc.edu/utgsbs_dissertations/677

OAI identifier oai:identifier

oai:digitalcommons.library.tmc.edu:utgsbs_dissertations-1722