Supplementary Figure 2 Chao Estimated Richness Across the Different Classrooms, with Standard

Supplementary Figure 1 Characteristics of the sampled building. A. Floor plan of building and the classrooms sampled. Eight petri dish samplers were per used room, two at each of four spots (marked with an X). Samplers collected passively settled dust on top of shelves for the duration of the teaching semester, approximately three months. B. All outgoing air from the second floor teaching laboratory classrooms exit the building as exhaust through a plume on the roof. The supply air is a combination of return air from the first floor lecture rooms and outdoor air, which enters the ventilation system through grills above the second floor.

A.

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Supplementary Figure 2 Chao Estimated Richness across the different Classrooms, with standard deviation shaded.

Supplementary Figure 3 A rank “frequency” distribution of indoor air fungal OTUs in teaching classrooms. The OTUs are ranked in descending order based on how frequently they appeared in the samples, with the most frequent OTUs appearing on the left of the graph. The maximum number of samples is 34, and the majority of OTUs appeared in only one sample.

Supplementary Figure 4 Nonmetric multidimensional scaling showing the relationship between the composition of fungal communities in different teaching classrooms, based on the Morisita-Horn dissimilarity index. Observed samples (top: black) showed the greatest distance between samples. In the manipulations, puffball taxa were reassigned to typical indoor taxa (middle: green) and the abundances of the puffball taxa were equalized with non-puffball taxa (bottom: coral). Classroom E samples, circled in each, are distinct from other classroom samples in all cases but to a lesser degree in the manipulations than in the observed.

Supplementary Table 1 OTUs present in negative controls and removed from all other samples.

Supplementary Table 2 Details of the data manipulations to vary either the quantitative (Manipulation 1) or qualitative (Manipulation 2) differences between Classroom E and the other classrooms.

Supplementary Table 3 Characterization of the taxa identified using a BLAST search. Abundance rank 1-20 follows the order in Figure 1c.

Supplementary Table 4 Differences, based on three dissimilarity indices, between Classroom E and all other Classrooms. Significance (p-value) and variation explained (R2) of the fungal community composition between the Classrooms determined by analysis of variance based on distance matrices (adonis). Also included is the mean value difference between Classrooms.