Characterization of fungi in office dust: Comparing results of microbial secondary metabolites, fungal internal transcribed spacer region sequencing, viable culture and other microbial indices

Abstract

Recent developments in molecular and chemical methods have enabled the analysis of fungal DNA and secondary metabolites, often produced during fungal growth, in environmental samples. We compared 3 fungal analytical methods by analysing floor dust samples collected from an office building for fungi using viable culture, internal transcribed spacer (ITS) sequencing and secondary metabolites using liquid chromatography-tandem mass spectrometry. Of the 32 metabolites identified, 29 had a potential link to fungi with levels ranging from 0.04 (minimum for alternariol monomethylether) to 5700 ng/g (maximum for neoechinulin A). The number of fungal metabolites quantified per sample ranged from 8 to 16 (average = 13/sample). We identified 216 fungal operational taxonomic units (OTUs) with the number per sample ranging from 6 to 29 (average = 18/sample). We identified 37 fungal species using culture, and the number per sample ranged from 2 to 13 (average = 8/sample). Agreement in identification between ITS sequencing and culturing was weak (kappa = -0.12 to 0.27). The number of cultured fungal species poorly correlated with OTUs, which did not correlate with the number of metabolites. These suggest that using multiple measurement methods may provide an improved understanding of fungal exposures in indoor environments and that secondary metabolites may be considered as an additional source of exposure.

Keywords: DNA sequencing; culture; fungi; internal transcribed spacer region; office building; secondary metabolites.

Figure 1

Prevalence of metabolites in floor dust (n=28) * Only one among 28 samples was above LOD.

Figure 2

Levels of metabolites in floor dust. Alternariol MME=Alternariol monomethylether. * Only one among 28 samples was above LOD.

Figure 3

The number of fungal OTUs, cultured species, and secondary metabolites for each analyzed sample and the correlation between them. In the first bar graph: * Samples were not analyzed for fungal DNA due to insufficient quantity of dust available for the analysis.

Figure 4

Prevalence (%) and average level (geometric mean CFU/g: colony forming unit per gram of dust) of each fungal species identified in 28 dust samples with culture. Fungi with no error bars in the geometric mean bar graph indicate that they were identified in only one sample. The upper limit of Acremoniumstrictum is off-scale (5.5×10⁷ CFU/g)