The Characterization of Coccidioides posadasii During the Parasitic Life Stage
Coccidioides posadasii and Coccidioides immitus are both dimorphic fungal species responsible for the disease coccidioidomycosis known as Valley Fever. Located in the arid southwestern part of the United States, Coccidioides’ environmental form is found in the soil. When the soil is aerosolized, arthroconidia, the spores produced in the saprophytic phase (environmental form) are released and inhaled by the host. Once arthroconidia are inhaled, cells undergo a lifecycle change called the parasitic phase also known as the spherule/endospore phase. The spherules are round cells that grow and produce endospores. When spherules rupture, they release endospores in the host and each endospore can grow into a new spherule, continuing the cycle in the host. Despite previously published investigations regarding the stimuli needed to induce the parasitic lifecycle and understanding the pathogenesis of the spherule/endospore phase, not much is known about the surface proteins that play a role in dissemination, host-evasion, and other virulence factors. My dissertation research has focused on characterizing the parasitic lifecycle of Coccidioides posadasii by investigating the secreted extracellular proteome of the parasitic lifecycle, characterizing the growth and morphology of a strain that remains in the spherule/endospore phase, and developing the foundational research for the development of a noninvasive diagnostic platform. Based on our lab’s previous experience characterizing the surface proteome of Cryptococcus neoformans, characterization of the secreted surface proteome of spherules from Coccidioides was warranted. Using a trypsin-shaving approach, we were able to cleave off spherule surface proteins, identify them via mass spectrometry, and identified catalytic pathways potentially involved in virulence. Additionally, we were able to characterize the growth dynamics of a strain of C. posadasii that remains in the spherule/endospore phase in various in vivo- like media. We were able to use this strain to perform immunofluorescence to develop a noninvasive diagnostic platform for the identification of fungal nodules in the lung caused by coccidioidomycosis. Taken together, these studies contribute a foundational understanding of potential mechanisms involved in virulence, a model organism for the study of the parasitic lifecycle, and the basis for a novel diagnostic for the Coccidioides research community.