The Inhalable Mycobiome of Sawmill Workers: Exposure Characterization and Diversity

Abstract

Exposure to fungal spores has been associated with respiratory symptoms and allergic alveolitis among sawmill workers, but the complexity of sawmill workers’ fungal exposure has been poorly studied. We characterized the fungal diversity in air samples from sawmill workers’ breathing zones and identified differences in the richness, diversity, and taxonomic composition between companies, departments, wood types, and seasons. Full-shift personal inhalable dust samples (n = 86) collected from 11 industrial sawmill, sorting mill, and planer mill companies processing spruce and/or pine were subjected to DNA metabarcoding using the fungal internal transcribed spacer (ITS) region 2. The workers were exposed to a higher total number of operational taxonomic units (OTUs) in summer than in winter and when processing spruce than when processing pine. Workers in the saw department had the richest fungal exposure, followed by workers in the planing department and sorting of dry timber department. Sawmills explained 11% of the variation in the fungal community composition of the exposure, followed by season (5%) and department (3%). The fungal compositions of the exposures also differed between seasons, sawmills, wood types, and departments at the taxonomic level, ranging from the phylum to the species level. The differences in exposure diversity suggest that the potential health effects of fungal inhalation may also be different; hence, a risk assessment based on the fungal diversity differences should be performed. This study may serve as a basis for establishing a fungal profile of signature species that are specific for sawmills and that can be measured quantitatively in future risk assessments of sawmill workers. IMPORTANCE To gain more knowledge about exposure-response relationships, it is important to improve exposure characterization by comprehensively identifying the temporal and spatial fungal composition and diversity of inhalable dust at workplaces. The variation in the diverse fungal communities to which individuals are exposed in different seasons and sawmills suggests that variations in exposure-related health effects between seasons and companies can be expected. More importantly, the distinct fungal profiles between departments across companies indicate that workers in different job groups are differently exposed and that health risks can be department specific. DNA metabarcoding provides insight into a broad spectrum of airborne fungi that may serve as a basis for obtaining important knowledge about the fungi to which workers are exposed.

The airborne mycobiome and associations with mycotoxins and inflammatory markers in the Norwegian grain industry

“…This result may be somewhat surprising, considering that autumn may represent more favorable growth conditions and higher rate of spore dispersal due to higher temperature and nutrient sources. It is also in contrast to other studies that have shown seasonal differences in fungal communities associated with sawmills 31 , plant leaves 32 , roots 33 and soil 34 . However, the grain dust generated in winter results from handling more heterogeneous grain types received during winter than grain types that are received during autumn.…”

“…A greater relative abundance of sequences placed in the phylum Ascomycota than Basidiomycota was detected in winter and autumn samples, which is in line with the view of Ascomycota species are more tolerant to environmental stress. In this case, this would not mean the harsh winter conditions, as previously indicated for the mycobiome in Norwegian sawmills 31 , but more likely the production process-related strain that fungi are exposed to during drying and moving the grain at the elevators and feed mills. However, we observed seasonal differences at the order and genus levels that may be explained by different nutrient preferences or tolerances of the identified fungi.…”

“…DNA was extracted from dust collected in the Eppendorf tube part of the sampling equipment. 150 µL cetyl trimethylammonium bromide (CTAB) buffer were initially added, and the DNA was extracted as previously reported 49 . Fungal ITS2 rRNA gene region was amplified using the fITS7a and ITS4 50 , 51 primer combination.…”

“…Fungal ITS2 rRNA gene region was amplified using the fITS7a and ITS4 50 , 51 primer combination. We followed similar PCR reactions setup and conditions as well as amplicon library preparation method as mentioned previously 49 . In addition to the 24 samples, individual cultured species, 4 parallels of a mock community, 2 field blanks, and a PCR negative control were also included in the sequencing run as control samples, and were used while curating the final OTU tables as shown before 31 .…”

“…We followed similar PCR reactions setup and conditions as well as amplicon library preparation method as mentioned previously 49 . In addition to the 24 samples, individual cultured species, 4 parallels of a mock community, 2 field blanks, and a PCR negative control were also included in the sequencing run as control samples, and were used while curating the final OTU tables as shown before 31 . The mock community comprised fungal cultures of Rhizopus microsporous , Cladosporium allicinum , Penicillium variotii , Fusarium graminearum , Aspergillus fumigatus and Wallemia sebi, with known genome size, and was used to estimate index jumping in the sequencing run.…”