Thermal and pigment characterization of environmental fungi in the urban heat island of Baltimore City

Abstract

One of the major barriers of fungal infections of mammals is the inability to grow and/or survive at mammalian body temperature, typically around 37°C. This has provided mammals an advantage over fungi. However, environmental fungi may soon adapt to persist at higher temperatures, consistent with mammalian body temperature, due to thermal selection pressures imposed by climate change, global warming, and increased frequency of extreme heat events. Consequently, there is a need for more updated information about the thermal tolerance range of fungi near humans, such as in urban areas. The heat island effect suggests that cities are up to 8°C warmer than their suburban counterparts because of increased heat production, asphalt coatings and reduced greenspace among other factors, and it is more common in lower income and marginalized urban communities. Thus, urban centers are at increased risk for the emergence of heat tolerant fungi. In this study, we developed a methodology to collect and archive fungal isolates from sidewalk and soil samples in both warmer and cooler neighborhoods in Baltimore, Maryland. We demonstrate a novel methodology for fungal sample collection from sidewalks, employing the use of standardized and commercially available taffy. Analysis of fungal isolates collected from warmer neighborhoods revealed greater thermal tolerance and lower pigmentation, suggesting local adaptation to heat. Lower pigmentation in hotter areas is consistent with the notion that fungi use pigmentation to help regulate their temperature. Further, we identified the robust presence of the polyextremotolerant fungusAureobasidium pullalansfrom the warmest neighborhood in Baltimore, further showing that the extreme conditions of cities can drive proliferation of extremotolerant fungi. This study develops new techniques for environmental fungal collection and provides insight on the fungal census in an urban setting that can inform future work to study how urban environments may drive stress/thermotolerance in fungi, which could alter fungal interactions with humans and impact human health.

Wake-up Call: Rapid Increase in Human Fungal Diseases under Climate Change

“…He argues that the heat island effect (urban areas that are several degrees warmer than the surrounding region due to buildings, traffic, and other factors 30 ) means fungi there could face more selective pressures for thermotolerance. Accordingly, in a study available in preprint, 31 he and his team, led by postdoctoral fellow Daniel Smith, sampled the fungal population of four sidewalks in Baltimore, Maryland. They found fungi from hotter sidewalks were lighter-colored and absorbed less heat than those isolated from cooler, shadier sidewalks.…”

“…These findings could inform future studies on “how urban environments may drive stress/thermotolerance in fungi, which could alter fungal interactions with humans and impact human health,” wrote the researchers. 31 …”

Advanced genetic techniques in fungal pathogen research

“…Nevertheless, fungal pathogens can also cause disease in individuals with various chronic illnesses or other infections, such as asthma, COPD, diabetes, liver disease, tuberculosis, influenza, and COVID-19 ( 6 ). Furthermore, accumulating evidence suggests that climate change and urbanization not only increase the endemic area of many pathogens but can directly impact and increase the pathogenic potential of fungal species ( 7 , 8 ). Histoplasmosis, blastomycosis, and coccidioidomycosis, traditionally restricted to specific areas in the United States ( Histoplasma along the Mississippi river basin, Coccidioides in the Southwest, and Blastomyces in the Midwest and the Central South), are now found throughout the continental United States ( 9 ).…”