An orange-colored yeast species isolated from a Baltimore sidewalk several years ago could be the basis of eco-friendly mosquito traps that reduce malaria transmission, according to a new study from researchers at the Johns Hopkins Bloomberg School of Public Health.
Yeasts and other fungal species are known to have an intertwined relationship with insects. Much as plants lure animals to consume their fruits and spread their seeds, fungi lure insects to land on them and pick up and spread their cells and spores. In the study, the researchers investigated the ability of common yeasts to attract mosquitoes. They discovered that a yeast called Rhodotorula taiwanensis can, with its scent and sticky quality, lure and even trap the Anopheles gambiae, the principal malaria-transmitting mosquito in Africa.
The study was published online June 15 in the Proceedings of the National Academy of Sciences.
In addition to being found in Maryland, R. taiwanensis is present in other regions around the world, commonly in soil and on plants. It also occurs on the surface of sugar cane and rice leaves, on the stems of mugwort herbs, on blueberries, as well as in fermentation starter cultures used for traditional alcohol production in India and Korean soy sauce.
"Our findings suggest that this common yeast could be the basis for safe and inexpensive mosquito-control strategies," says study co-senior author Conor McMeniman , PhD, an associate professor in the W. Harry Feinstone Department of Molecular Microbiology and Immunology at the Bloomberg School. McMeniman is also faculty at the Johns Hopkins Malaria Research Institute.
The study's other co-senior author was Arturo Casadevall , MD, PhD, MS, a Bloomberg Distinguished Professor of Molecular Microbiology and Immunology and Infectious Diseases, and the Alfred and Jill Sommer Professor and Chair of the W. Harry Feinstone Department of Molecular Microbiology and Immunology at the Bloomberg School.
Malaria remains one of the world's leading causes of death, with more 600,000 fatalities in 2024, according to the World Health Organization. Despite advances in vaccines and surveillance strategies, malaria transmission remains difficult to control. The parasites that cause the disease frequently develop resistance to antimalarial drugs. Malaria-carrying mosquitoes have become increasingly resistant to insecticides. The two malaria vaccines in use are only modestly effective. Finally, mosquito traps are still considered an emerging technology.
The McMeniman Lab studies disease-transmitting mosquitoes and the sensory cues that influence their behavior. The Casadevall Lab studies fungi and other microbes. For this project, the two teams collaborated to investigate the potential mosquito-attraction capabilities of various common yeast species.
Only one of the seven yeast species tested stood out for its ability to attract female A. gambiae mosquitoes which can transmit malaria: R. taiwanensis strain 200S, an orange-colored yeast that Casadevall's Lab isolated in 2023 in a study of fungi found in the city of Baltimore.
The researchers characterized this yeast's blend of scent chemicals, finding that it consists mainly of the organic compounds acetone and 3-methyl-1-butanol—a distinct and simple mix compared to those found in other common yeasts including baker's yeast Saccharomyces cerevisiae. Further tests in A. gambiae mosquitoes and Drosophila fruit flies—which were also attracted to Rhodotorula, and even liked to eat it—confirmed that the yeast's attraction worked largely via the insect sense of smell, specifically a class of insect olfactory sensors called odorant receptors.
Experiments also showed that both the mosquitoes and the fruit flies tended to disperse Rhodotorula throughout a test area. This finding is consistent with the idea that this yeast's insect-luring ability is part of an evolved strategy for enhancing its proliferation.
The team isolated two closely related Rhodotorula species, R. mucilaginosa and R. toruloides, from Anopheles mosquitoes at a malaria-endemic field site in Zambia, demonstrating that Rhodotorula and Anopheles are in contact in the wild.
"Rhodotorula yeasts appear to be common elements of the fungal populations—or 'mycobiomes'—found on insects, and are widely present in the environment," Casadevall says.
The researchers observed that both female and male Anopheles mosquitoes often become trapped in the sticky biofilms formed by R. taiwanensis, akin to quicksand, suggesting that this yeast's slimy surface may also be useful to develop biodegradable glue for mosquito traps.
The researchers now are considering developing Rhodotorula-based traps for malaria control, leveraging the fragrant and sticky qualities of these yeasts. The researchers are currently evaluating the attractiveness of R. taiwanensis to other species of malaria mosquitoes as well as nuisance-biting mosquitoes found in the U.S. The findings, they say, also suggest the value of more comprehensive explorations of the close relationships between insects and fungi.
" Scent and Adhesion Drive Insect Dispersal of Environmental Yeast " was co-authored by Diego Giraldo, Daniel Smith, Sébastien Ortiz, Stephanie Rankin-Turner, Mary Gebhardt, Lusajo Mwakibete, Ziyang Chen, Reneé Ali, Douglas Norris, Sean Zhang, Arturo Casadevall and Conor McMeniman.
Support for the research was provided in part by the inaugural MMI Noetic Award created by Lisa Walborn from the W. Harry Feinstone Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health; by the National Institute of Allergy and Infectious Diseases (U19AI089680); and by the Johns Hopkins Malaria Research Institute and Bloomberg Philanthropies.
