A new study from Johns Hopkins University suggests that common fungal species living in cities are evolving to tolerate higher temperatures, raising concerns about the potential emergence of new disease-causing pathogens. The research, published in ISME Communications, examined fungal populations within Baltimore, finding that those living in warmer areas exhibit traits associated with heat adaptation.
The Risk of Heat-Adapted Fungi
Fungi, typically molds and yeasts, generally struggle to survive at temperatures close to human body temperature. However, scientists are increasingly worried that climate change may be driving fungal species to adapt to rising temperatures, potentially creating new threats to human health. Candida auris, a particularly concerning multi-drug resistant yeast responsible for thousands of infections annually, exemplifies this risk. Researchers like Arturo Casadevall, senior author of the study, have proposed that C. auris ‘s unusual heat tolerance might have developed relatively recently, potentially linked to global warming.
The Baltimore Study: Finding Adaptation in the City
Cities are particularly vulnerable to extreme heat events, prompting the researchers to investigate whether urban fungi are showing signs of adapting to warmer conditions. To do so, they used a unique method: sticky taffy-like candies to collect microbes directly from sidewalks at four sites in Baltimore representing different temperature ranges: warm, above average, average, and cool.
The findings revealed that fungal species collected from the warmest site exhibited lighter pigmentation compared to those from cooler sites. This lighter pigmentation is thought to help prevent overheating and indicates possible adaptation to warmer environments.
Further laboratory experiments confirmed these observations. Fungal species from warmer sites demonstrated greater heat resistance when exposed to elevated temperatures compared to their counterparts from cooler sites.
Key Findings & Species of Concern
The study identified a significant correlation between site temperature and fungal adaptation. Molds and yeasts from the warmest site absorbed less heat experimentally—and had significantly less pigmentation—compared to those from the coolest site. Several fungal species from warm sites also showed increased survival after heat exposure.
Notable findings included:
- Rhodotorula mucilaginosa: A common environmental yeast but rare human pathogen, was more viable after heat exposure when isolated from the warmest site.
- Cystobasidium minutum: A fungus isolated from a 38.4°C (101°F) sidewalk, displayed the highest resistance to heat stress and even grew at 37°C (98.6°F)—human body temperature.
Future Research and Implications
Researchers expect similar results from studies conducted in other cities. However, they emphasize that further investigation is needed, acknowledging limitations such as variations in sun exposure, foot traffic, and wildlife.
“These findings suggest that the high temperatures within urban environments can prompt fungal species to develop heat adaptations, potentially making them more likely to cause human infections,” said Daniel Smith, first author and postdoctoral student.
Ultimately, the study highlights the potential for fungi to evolve rapidly in response to environmental changes and underscores the need for continued research into how urban ecosystems are shaping the evolution of fungal pathogens. It’s preliminary data, but a crucial first step towards understanding and mitigating the risk of heat-adapted fungal infections in a warming world
