Assessment of fungal diversity in a water-damaged office building

Abstract

Recent studies have described fungal communities in indoor environments using gene sequencing-based approaches. In this study, dust-borne fungal communities were elucidated from a water-damaged office building located in the northeastern region of the United States using internal transcribed spacer (ITS) rRNA gene sequencing. Genomic DNA was extracted from 5 mg of floor dust derived from 22 samples collected from either the lower floors (n = 8) or a top floor (n = 14) of the office building. ITS gene sequencing resolved a total of 933 ITS sequences and was clustered into 216 fungal operational taxonomic units (OTUs). Analysis of fungal OTUs at the 97% similarity threshold showed a difference between the lower and top floors that was marginally significant (p = 0.049). Species richness and diversity indices were reduced in the lower floor samples compared to the top floor samples and there was a high degree of compositional dissimilarity within and between the two different areas within the building. Fungal OTUs were placed in the phyla Ascomycota (55%), Basidiomycota (41%), Zygomycota (3%), Glomeromycota (0.4%), Chytridiomycota (0.3%), and unassigned fungi (0.5%). The Ascomycota classes with the highest relative abundances included the Dothideomycetes (30%) and Eurotiomycetes (16%). The Basidiomycota consisted of the classes Ustilaginomycetes (14%), Tremellomycetes (11%), and Agaricomycetes (8%). Sequence reads derived from the plant pathogen Ustilago syntherismae were the most abundant in the analysis as were obligate Basidiomycota yeast species that accounted for 12% and 11% of fungal ITS sequences, respectively. ITS gene sequencing provides additional insight into the diversity of fungal OTUs. These data further highlight the contribution of fungi placed in the phylum Basidiomycota, obligate yeasts, as well as xerophilic species that are typically not resolved using traditional culture methods.

Keywords: Exposure assessment; fungus; gene sequencing; occupational; office building.

Figure 1.

Operational Taxonomic Unit (OTUs) analysis of samples derived from the State Office Building lower floor and top floor samples. OTUs were defined at 97% similarity threshold. (A) Bar graph representing the mean number of fungal OTUs identified for all, lower floor and top floor samples. Error bars represent standard deviation. (B) Rarefaction analysis (reference samples solid shapes) of fungi for lower floors (denoted by a solid triangle) and top floor (denoted by a solid circle) samples. Hollow symbols with dotted lines represent extrapolation up to three times the sample size. Grey error bars represent 95% confidence interval.

Figure 2.

Relative abundance of the fungal phyla identified in the analysis of 22 floor dust samples. The x-axis represents the percentage of 765 fungal sequences.

Figure 3.

Rank order of the ten most abundant fungal classes and orders identified in the analysis of twenty-two-floor dust samples. Y-axes represent the rank order of relative abundance of sequences placed in Ascomycota class, Basidiomycota class, Ascomycota order, and Basidiomycota order. Not included in this figure are the Chytridiomycota and Glomeromycota that were identified to phylum level. The Zygomycota was composed of species placed in one Order, the Mucorales. The x-axis represents the percentage of 765 fungal sequences.

Figure 4.

The relative abundance of identified fungal OTUs (sequences with 97% similarity) that accounted for greater than 1% of all fungal clone libraries (n = 765). Not included in this figure is the Basidiomycota genus Cryptococcus that accounted for 4.31% of total fungal sequences.