Ergosterol as a biomarker for the quantification of the fungal biomass in atmospheric aerosols

Abstract

The prevailing warm and humid climate in subtropical cities favors fungal growth in the ambient environment. Fungal growth has implications for public health because fungal cells, spores and their metabolites are allergenic and potential health hazards. In this regard, better and quicker alternatives than the available sampling and species identification methods are needed for quantifying fungal communities in atmospheric aerosols. In this study, the fungal membrane ergosterol was used as a biomarker for assessing the abundance and mass loading of fungi in atmospheric aerosols. Gas chromatography-mass spectrometry (GC-MS) was utilized for quantification of this biomarker in fine (PM 2.5) and coarse (PM 2.5–10) particulates collected by high volume samplers simultaneously at a rural site and an urban site in Hong Kong. The geometric means of the total ergosterol concentrations at the rural and urban sites were 120.2 and 93.9 pg m −3 in the PM 10 (calculated as the sum of PM 2.5 and PM 2.5–10) particulates. The significantly higher ergosterol loading at the rural site was related to the vegetation coverage around the sampling site. Ergosterol loading was higher in the autumn at both sites, which correlated with seasonal drops in the relative humidity below 70%. Approximately 65–66% of the ergosterol in PM 10 is associated with fine particulates, indicating that atmospheric fungi likely lead to chronic respiratory symptoms. The mass loading of the fungal spores on the dry mass was on the order of 10–10 2 ng m −3. The geometric mean concentration of the fungal spores was estimated as 46 and 36 spores m −3, which was one-sixth of the measured viable samplings of 292 and 247 CFU m −3 at the rural and urban sites, respectively. This underestimation leads to the need for establishing proper conversion factors from conditions identical to or simulating the study system of interest when markers are quantified and estimated for microbial mass loading in ambient aerosols. This study was the first to utilize the fungal biomarker ergosterol in monitoring and assessing ambient fungal loading and prevalence in atmospheric aerosols for a period of eight months. It confirms that biomarkers can provide quantitative information on microbial communities in atmospheric aerosols.