Deletion of Core Septin Gene aspB in Aspergillus fumigatus Results in Fungicidal Activity of Caspofungin

Author

Rebecca Jean Busch, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Master of Science

Department

Molecular Biology Microbiology and Biochemistry

First Advisor

Vargas-Muñiz, José

Abstract

Septins are a family of GTP-binding proteins, and although highly conserved throughout many eukaryotes, their functions vary across species. In Aspergillus fumigatus, the etiological agent of invasive aspergillosis, septins participate in a variety of roles such as cell wall organization of conidia, septation, and response to anti-cell wall stress. Previous studies determined that the ∆aspB strain had a greater sensitivity to anti-cell wall drugs, especially the echinocandin caspofungin, yet mechanisms behind this augmented sensitivity are unknown. We performed cell viability staining post-caspofungin exposure and found that the ∆aspA, ∆aspB, and ∆aspC strains showed significant reduction in cell viability. Concomitant with the reduced viability, deletion strains are more susceptible to caspofungin on solid media. These results indicate that the septin cytoskeleton is important for A. fumigatus survival in the presence of caspofungin. Due to the potential of improved therapeutic outcome, we followed up using a neutropenic murine model of invasive aspergillosis. Deletion of the aspB gene resulted in improved survival when treated with caspofungin when compared to the akuBKU80 wild-type or untreated ∆aspB strains. Quantitative proteomics analyses were used to find proteins involved in the septin-dependent adaptation to caspofungin. We identified four candidates with roles in cell wall integrity. Deletion of these candidate genes resulted in increase in susceptibility to caspofungin and moderate reduction in viability post drug exposure. Taken together, these data suggest that septin AspB is essential in mediating the fungistatic response to caspofungin.