When Aaron Mitchell took an undergraduate genetics course at Carnegie Mellon University in 1975, he was hooked. “I thought that subject was the coolest thing I’d ever heard in my life,” says Mitchell, now a professor at University of Georgia and the recipient of this year’s George W. Beadle Award. This course spurred a career-long fascination with yeast genetics where he developed many of the pivotal tools mycologists used to study Candida albicans, which forms biofilms on human surfaces or on medical devices and causes opportunistic infections, while at Columbia University, Carnegie Mellon, and University of Georgia. 

Inspired by the genetics course, Mitchell began his research career in Saccharomyces cerevisiae as an undergraduate and worked on the organism for almost 20 years, studying the regulation of meiosis and pH sensing. When Mitchell first started studying S. cerevisiae, there weren’t many genetic tools available and scientists were just starting to understand how to transform the yeast with DNA.

Developing genetic tools for C. albicans

Mitchell became interested in C. albicans when he was director of the Cold Spring Harbor course on yeast genetics in 1992 and has been studying how C. albicans biofilms ever since. Because he saw how S. cerevisiae as a model organism grew over the years, he wanted to do the same thing for C. albicans: develop the tools to study it, share the reagents, and strengthen the use of genetics in the mycology community.

As one of the pioneers who made C. albicans genetically tractable, Mitchell developed a gene disruption method based on short regions of homology and a URA3 gene cassette for creating unmarked homozygous mutants that have both become widely used. He created a C. albicans transcription factor mutant library and shared it with the mycology community via the Fungal Genetics Stock Center. “I don’t want to be the gatekeeper for what people do with these mutants,” he says. In his own lab, he’s used them to study C. albicans host interactions such as adherence and biofilm formation. 

In 2018, Mitchell’s lab identified the impact of strain variation on biofilms. In this study, the team mutated four biofilm transcription factor genes in five clinical isolates. They found that mutations had varying effects among the different strains. “We’re among the first groups to try to exploit strain variation [for] genotype-phenotype studies to learn something that you couldn’t just learn from the reference strain alone,” he says.

Strengthening the use of genetics in mycology

Aside from gaining an interest in C. albicans while directing the Cold Spring Harbor yeast genetics course, Mitchell gained experience and made connections that were critical to the co-founding of the Molecular Mycology course at the Marine Biological Laboratory in 1997. The course was designed to explore modern experimental techniques in pathogenic fungi, foster collaborations between mycologists, and to develop the next generation of mycologists.

It was there that Mitchell met longtime collaborator David Andes, a physician scientist from University of Wisconsin. Andes was a student in the course in 2002 and the labs began collaborating on research shortly after. In the last 20 years, the pair has published 21 papers together on the regulation of biofilm-related genes, the formation of the extracellular matrix that holds biofilm cells together, and the variation in regulatory networks among C. albicans strains. Andes notes the long-lasting impact that the course had on him and the field in general: “Aaron continued to foster people’s careers, the focus of their research, and mentor folks to really help develop the field.”

Mitchell directed the course until 2010 and has seen its tremendous impact on the mycology community over the years. “If you look at the first class, many of those graduates are leaders in the medical mycology field now,” says Mitchell.

Commitment to mentoring

The same commitment to developing people and fostering ideas has also defined his mentorship style. One of his trainees was Saranna Fanning, now an assistant professor in neurology at Harvard Medical School and Brigham and Women’s Hospital. Fanning became part of Mitchell’s lab as a research technician and went on to work with Mitchell both as a graduate student and as a postdoc. “Aaron’s way of teaching genetics was just so all-consumingly inspiring that I just really wanted that to be part of my training,” she says. “He’s very invested as a teacher, whether that’s in a classroom or in a lab. He is an exceptionally invested mentor.” She recalls how he’d always drop by the lab bench and help troubleshoot experiments. “He seemed to have worked out how to give you this perfect balance in terms of independence and encouragement with the space to thrive, but also feeling like you were very much supported,” she says.

From trainees to longtime collaborators, Mitchell’s influence runs deep. “He’s a brilliant scientist for sure and his contributions have moved the field forward, but I think [he’s] an equally important mentor to not just individuals, but to the field,” says Andes.

Join us in congratulating Aaron Mitchell on receiving the George W. Beadle Award for his contributions to the molecular mycology field including creating and disseminating new genetic tools to the community and shaping the next generation of mycologists.

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