Airborne and Grain Dust Fungal Community Compositions Are Shaped Regionally by Plant Genotypes and Farming Practices

Abstract

Chronic exposure to airborne fungi has been associated with different respiratory symptoms and pathologies in occupational populations, such as grain workers. However, the homogeneity in the fungal species composition of these bioaerosols on a large geographical scale and the different drivers that shape these fungal communities remain unclear. In this study, the diversity of fungi in grain dust and in the aerosols released during harvesting was determined across 96 sites at a geographical scale of 560 km 2 along an elevation gradient of 500 m by tag-encoded 454 pyrosequencing of the internal transcribed spacer (ITS) sequences. Associations between the structure of fungal communities in the grain dust and different abiotic (farming system, soil characteristics, and geographic and climatic parameters) and biotic (wheat cultivar and previous crop culture) factors were explored. These analyses revealed a strong relationship between the airborne and grain dust fungal communities and showed the presence of allergenic and mycotoxigenic species in most samples, which highlights the potential contribution of these fungal species to work-related respiratory symptoms of grain workers. The farming system was the major driver of the alpha and beta phylogenetic diversity values of fungal communities. In addition, elevation and soil CaCO 3 concentrations shaped the alpha diversity, whereas wheat cultivar, cropping history, and the number of freezing days per year shaped the taxonomic beta diversity of these communities.

Emerging Insights into the Occupational Mycobiome

“…Additional sources of worker exposure to the Ascomycota in waste sorting environments have been resolved and included Tricothecium [21] and Davidiella [18], as well as yeasts such as Candida and Blastobotrys species [20••]. Clinically relevant fungal taxa placed in the order Pleosporales that expresses homologous Alt a 1 allergen [58] were identified in a wheat grain production facility and included Epicoccum nigrum , Alternaria ethzedia , and Didymella exitialis (Table 1) [22]. Sequences placed in the Basidiomycota were also resolved in these occupational environments and included the Agaricomycetes in biomethanization facilities [18], as well as Wallemia species and Cryptococcus victoriae in a waste sorting plant [19] and wheat production facility [22], respectively.…”

“…Clinically relevant fungal taxa placed in the order Pleosporales that expresses homologous Alt a 1 allergen [58] were identified in a wheat grain production facility and included Epicoccum nigrum , Alternaria ethzedia , and Didymella exitialis (Table 1) [22]. Sequences placed in the Basidiomycota were also resolved in these occupational environments and included the Agaricomycetes in biomethanization facilities [18], as well as Wallemia species and Cryptococcus victoriae in a waste sorting plant [19] and wheat production facility [22], respectively. Studies of outdoor biowaste and agricultural commodity processing demonstrate the ubiquity of pre-established fungal contaminants such as A. fumigatus but additionally highlight overlooked fungal sources placed in the Ascomycota and Basidiomycota to be more prevalent than previously estimated and contribute to worker exposures.…”

Frequent Occupational Exposure to Fusarium Mycotoxins of Workers in the Swiss Grain Industry

“…Indeed, there is a good correlation between grain and wheat dust for the presence of DON and ZEN [8,9], as well as of fungi that might produce them between grain dust and aerosols [10]. Although high exposure to grain dust is inevitable during direct handling of grain or straw or during the cleaning of surfaces contaminated by grain dust [1,3], the identification of determinants of high exposure to mycotoxins may help employers to optimize the safety of workstations.…”

Exposure to field vs. storage wheat dust: different consequences on respiratory symptoms and immune response among grain workers

“…Blood was systematically sampled to determine sensitization markers (specific IgE, IgG, and precipitins) to specific biological agents in field or stored wheat. The presence of the respective fungal species in the workers' environment was researched in settled dust by high-throughput sequencing and those results were described in detail elsewhere (Pellissier et al 2016).…”

“…Fungi act as irritants, toxins, aeroallergens, or pathogens that cause infection depending on underlying disease, species, and form (Wiszniewska et al 2013;Vacher et al 2015;Kuhn and Ghannoum 2003). Certain molds abundant in freshly harvested wheat are known to be allergenic, such as Alternaria alternata and Cladosporium cladosporioides (Pellissier et al 2016;Madsen et al 2015;Flannigan 1978;Gora et al 2009;Swan and Crook 1998), or toxigenic, such as Fusarium graminearum and Fusarium culmorum, two mycotoxin-producing fungal species (Pellissier et al 2016). The microflora of freshly harvested wheat differs from that of −3 stored grain and straw which contains "storage fungi", such as Penicillium brevicompactum, and Eurotium amstelodami (Swan and Crook 1998).…”