Assessing heatwave impacts on fungal spore emissions with real-time detection and next generation sequencing technologies

Bioaerosols are ubiquitous airborne microorganisms comprised of bacteria, fungi, pollen, virus and their constituents. Fungi have been associated with negative health effects ranging in severity from allergic reactions to asthma and serious infection, where susceptible individuals are at greater risk of life-threatening health outcomes resulting from exposure. While airborne fungi are abundant, they are poorly characterized due to the low temporal resolution of traditional offline sampling methods, limiting our understanding of key emission drivers in critical micro-environments and their impacts on air quality.

There is a critical need to better characterize background fungal aerosol concentrations to build baselines to explore exposure assessment. Here we investigate the utility of emerging real-time detection methods in conjunction with offline sampling during a two-week pilot study to characterize the outdoor concentrations of key aeroallergenic fungi at high time resolution.

A Multiparameter Bioaerosol Spectrometer (MBS) was deployed at UKHSA Chilton alongside a Burkard sampler during summer 2022, capturing the extreme European-wide heatwave which occurred 9-15^th of August; The MBS is a biofluorescence spectrometer that classifies and quantifies bioaerosols on a single particle basis via their autofluorescent signatures, allowing for fungal aerosol concentrations to be derived at 5-minute time resolution; Next Generation Sequencing (NGS) was performed on daily integrated Burkard samples to provide broader fungal compositional context. Meteorological data was also recorded.

Clear diurnal behaviour in Cladosporium- and Penicillium-like aerosol was observed with the MBS, with maximums occurring in the late afternoon and early morning respectively. These characteristic diurnal emission features would not be evident from sample integrations typical of offline sampling.

Splitting the MBS real-time data into pre-heatwave and heatwave periods revealed that during heatwave conditions the environment was too hot and dry for the typical day time sporulation and emission of Cladosporium to occur, where the emission was delayed until the early morning when temperatures dropped and subsequently critical humidity levels had recovered; The typical early morning release of Penicillium was largely unaffected by the heatwave, however, daytime concentrations dropped to zero during the hottest and driest periods.

Analysis of the daily NGS data showed that the abundance of key species such as Alternaria and Cladosporium were enhanced during the heatwave, while Aureobasidium and Epicoccum are suppressed by heatwave conditions in our observations.

We demonstrate the utility of a complimentary real-time and offline NGS dual approach to gain deeper insights into fungal spore emissions. This allowed us for the first time to investigate the impacts of heatwave conditions on the emissions of key aeroallergenic species, providing insight into how diurnal emissions may be impacted by a warming climate. We also suggest that this approach shows promise for routine fungi monitoring to assess impacts on public health.