Searching for microbial antagonists to Coccidioides immitis, the Valley Fever fungus
Authors:Joe Baal, Derrick Chung Sang, Abdelhamid Dalia
Mentor:Antje Lauer, Professor of Biology, California State University of Bakersfield
Coccidioidomycosis, also known as Valley Fever, is a respiratory infection caused by the fungal pathogen Coccidioides spp. Coccidioides immitis, is thought to be endemic in the arid and semi-arid soils of California’s San Joaquin Valley. Previous studies, along with our group’s prior investigation, have supported the idea that C. immitis grows in an irregular distribution, with negative growth spots scattered within the fungus’ natural habitat. While there are several biological parameters that could be influencing this spotty distribution, the absence of C. immitis in some areas may be primarily the result of microbial antagonism. This project focused on the isolation of bacteria from loamy soils in Bakersfield, CA. C. immitis negative soil samples from a confirmed cocci-growth site were diluted and plated on low nutrient R2A medium supplemented with soil extract to provide a variety of nutrients to the soil bacterial community. All different colony-morphology types were re-streaked on R2A plates until pure cultures were obtained. The pure cultures were then tested against the fungus Uncinocarpus resii, which is a non-pathogenic close relative to C. immitis. Zones of inhibition (ZOI) were observed after growing the challenge assays at 24 ºC for 2-3 weeks. All pure cultures that exhibited strong ZOI against U. resii were then challenged against C. immitis in collaboration with the Biosafety-3 lab of Dr. Guibert (Department of Public Health in Monterey, CA). The final challenge assays showed around 10 bacterial isolates (most of which were of Bacillus and Streptomyces species) that strongly inhibited the growth of C. immitis. The discovery of these anti-cocci bacterial species opens new topics to explore such as the identification of antifungal metabolites or a venture in a bioremediation project.