Theses and Dissertations

Dayna Emrick

Issuing Body

Mississippi State University

Advisor

Gordon, Donna M.

Committee Member

Smith, James Leif

Committee Member

Lu, Shien

Committee Member

Munn, Giselle Thibaudeau

Committee Member

Welch, Mark E.

Other Advisors or Committee Members

Travis, Rick

Date of Degree

8-9-2019

Original embargo terms

Visible to MSU only for 3 years

Document Type

Dissertation - Open Access

Major

Biological Sciences

Degree Name

Doctor of Philosophy

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Arts and Sciences

College

College of Arts and Sciences

Department

Department of Biological Sciences

Department

Department of Biological Sciences

Abstract

Fungal infections have a significant impact on the world population, with estimates of over 1.6 million deaths a year. One contributing factor is the increasing number of fungi resistant to the current clinical treatments, including the last approved family of antifungal compounds introduced into the market over a decade ago. This is driving the search for new antifungals with different biological targets. A new potential antifungal occidiofungin, is a cyclic glycolipopeptide isolated from the soil bacterium Burkholderia contaminans MS14 with a broad spectrum of activity against both human and plant pathogens. Kill kinetics demonstrated that this compound is fungicidal and activates the cell wall integrity pathway at suboptimal dosing as determined by Mkc1 MAPK phosphorylation studies. As three of the four classes of currently available antifungals target ergosterol or ergosterol biosynthesis, the bioactivity of occidiofungin was assayed in the presence of ergosterol containing DOPC vesicles and was shown to retain antifungal properties. Occidiofungin was also found to have a similar activity profile against the S. cerevisiae -1,3-glucan synthesis mutant, indicating that it does not share a target with the fourth class of antifungals. Stability testing showed occidiofungin retained in vitro potency in the presence of human serum, across a broad range of pH and temperature conditions, and was resistant to gastric proteases. Based on cell morphology, occidiofungin did not target a specific stage of the yeast cell cycle, however cells were smaller in size and acquired ‘dancing bodies’, both properties of apoptosis. This was confirmed with data showing concentration dependent increases in DNA fragmentation, reactive oxygen species, and extracellular localization of phosphatidylserine. In addition to these findings, cells deleted for the yeast caspase gene exhibit a 2old resistance to occidiofungin. While SEM showed no morphological differences between treated and untreated cells, TEM did identify a thinning of the cell wall and inclusion bodies in cells treated with occidiofungin. As a stable fungicidal compound that induces apoptosis in yeast, occidiofungin has a great potential to become a new candidate drug for clinical use in treating fungal infections, including those resistant to current antifungals.

URI

https://hdl.handle.net/11668/14573

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