Date of Completion

Spring 5-15-2020

Thesis Advisor(s)

Joerg Graf

Honors Major

Molecular and Cell Biology




The yeast Cryptococcus neoformans is present in the microbiota of many plants and animals and produces melanin, a compound that protects cells against UV light and promotes virulence. Melanin production can be induced by exogenous tyrosine, homogentisic acid, catecholamines, or their precursors such as L-DOPA, all of which may be produced by bacteria. The goal of this study was to investigate the interaction between Enterobacter hormaechei (a mosquito gut isolate) and C. neoformans with respect to the production of melanin by C. neoformans in the presence of E. hormaechei, potentially due to the production of L-DOPA or other metabolites by this bacterium. After performing transposon mutagenesis, over 7000 E. hormaechei mutants were screened, resulting in the transcription factor TyrR being identified as necessary for E. hormaechei to promote C. neoformans melanization. TyrR is a transcription factor known to regulate genes involved in amino acid metabolism and L-DOPA synthesis. In future studies, TyrR will be characterized in E. hormaechei for its role in inducing C. neoformans melanogenesis through gene complementation, melanization assays, mass spectrometry, and melanin particle analysis.

Included in

Microbiology Commons