Spores indoors

One of our broad goals at BIMERC, the UC Berkeley group funded by Sloan, is to look at what microbes are found indoors and why. We first tackled this in homes and decided to survey in a university family housing complex – in essence, getting replication in the built environment while eliminating potential sources of variation in buildings, such as design, building material, age, etc.

Sampling one-month collections of airborne dust at two different seasons, we found some things we expected, and others we didn’t.

Our study site – a university family house complex

First, the unsurprising. When you don’t limit sampling to what will grow in culture, you can a shocking number of taxa. In our case, over 1000 fungal “species” were detected indoors, the far majority of which were clearly coming in from the outdoors. For example, types like a puffball known as the “dog-turd” and Glomeromycota that (for what we can tell) are obligate symbiotic associates with plants.

Dog Turd Fungus
Pisolithus tinctorius, aka the dog turd fungus

What we didn’t expect to see was that the features of the dust sample and the unit — for example, what kind of room the sample came from or how often the residents clean — had no effect on what kinds of fungi were found indoors. Instead, the airborne fungi indoors were singularly dominated by what was coming in from the outdoors.

And what is coming in from outdoors in this housing complex that spans hundreds of meters is not a uniform source pool. Instead, the fungi appear to dispersal limited on even this small geographic scale, so that two air samples separated by 100 meters have more species in common that two air samples separated by 400 meters.  While this “distance-decay” effect would not be surprising across regions, its occurrence for airborne propagules of microbes on this small scale is practically undocumented.

Model for fungi indoors – Figure 3 of paper

Turns out, those fungi that make our homes sick or unsightly are just a tiny fraction of what can end up inside. It would be interesting to do this in a different region than the Bay Area, where the climate is not so conducive for “natural” ventilation year around. Davis, CA?

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