Microbial diversity in bioaerosol samples causing ODTS compared to reference bioaerosol samples as measured using Illumina sequencing and MALDI-TOF.

The importance of the microbial diversity of bioaerosols in relation to occupational exposure and work related health symptoms is not known. The aim of this paper is to gain knowledge on the bacterial and fungal communities in dust causing organic dust toxic syndrome (ODTS) and in reference dust not causing ODTS. Bacterial and fungal communities were described in personal exposure samples from grass seed workers developing ODTS, in dust generated from grass seeds causing ODTS and in dust generated from reference seeds not causing ODTS. Amplicon sequencing of the bacterial 16S rRNA gene and the fungal ITS region, as well as matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) were used for identification of fungi and bacteria in personal exposure samples and in dust samples from grass seeds causing ODTS and in dust from reference grass seeds. Furthermore, activities of enzymes were measured in the same samples. The sequencing data revealed more than 150 bacterial and 25 fungal genera present in each sample. Streptomyces spp., Aspergillus fumigatus and Rhizopus microsporus were dominating in the dust causing ODTS but not in the reference dust. The dustiness in terms of Mucor sp. and R. microsporus were 100-1000 times higher for problematic seeds compared to reference seeds. The bacterial species in the dust causing ODTS included pathogenic species such as Klebsiella pneumonia and Streptomyces pneumonia, and it contained increased concentrations of total protein, serine protease, chitinase, and β-glucosidase. Twenty-three bacterial genera covered more than 50% of the total reads in the personal and problematic seed dust. These 23 genera accounted for less than 7% of the total reads in the reference seed dust. The microbial community of the dust from the problematic seeds showed great similarities to that from the personal air samples from the workers. In conclusion, we have shown for the first time a shift in the microbial community in aerosol samples that caused ODTS compared to the reference samples that did not cause the ODTS. Furthermore, elevated enzyme activities were found in the dust causing ODTS.