Every week, I take the time to learn something about the mycological world. It’s great. I’d like to do it more, but this summer has been overwhelming to say the least. After finally closing on a house, I feel I’ll have more time to allocate towards uncovering this realm of biology. While cleaning my new basement, I started thinking of the fungi that probably live down there. I anxiously reminded myself of the opportunistic black mold, lurking undetected, waiting for dark basements to become moist! There are horror stories of black, Stachybotrys mold ruining homes. I pulled myself together, and started to ponder. I came to the realization that my entire home is an ecosystem and there will be resident fungi and bacteria everywhere, no matter how hard I scrub. Like the communities of ‘foreign’ microorganism living in our bodies, these fungi living on residential surfaces too have intimate interactions with us.
In 2013, Rachel Adams and her team published a paper regarding these residential fungi. They tested two hypotheses regarding fungal and bacterial growth. Before this paper, it was thought that the assemblages of fungi occurring on resident surfaces are just a subset of wind-blown spores that make their way into our homes. Bacteria on the other hand enter our homes the same way, but additionally hitch a ride on us. So bacterial communities living on our indoor surfaces can be vectored in by us, while fungal assemblages can’t. This is the original hypothesis.
After sampling different surfaces including drains, windowsills and human foreheads, it turns out this original hypothesis should stand. Although the researchers found that drains are occupied by some human vectored fungi, the fungi in our homes are still mainly structed by the outside air, and their ability to grow on nutrient poor surfaces like our countertops. Bacterial residents mirror both the communities from the outside air, and human and pet skin, fur, hair ect. The human forehead had a surprising diversity of fungi that was dissimilar to the assemblages living on indoor surfaces, showing how little influence we have at structuring indoor mycological communities.
The fungi living in drains had some human vectored species, but conditions here select for thermotolerant species. Drains are mainly occupied by a low diversity of fungi including species of Exophiala, Candida, and Fusarium; all of which can withstand the drastic temperature fluctuations present in this residential niche. Windowsills, and countertops were made up of fungal communities very similar to species found in outside air. Surprisingly, human foreheads had a wide diversity of non-residential fungi, including the crop pathogen Claviceps purperea more commonly known as ergot!
All in all, these researches revealed that most surfaces inside your home are occupied by fungi. These surfaces passively collect these airborne fungi from the outside. Bacteria too make their way on residential surfaces like this, but are also structured by the communities that live on our own skin. If these researchers sampled my new home, especially my office, I think they would be completely shook. My collection of dried fungi is pretty immense, so I predict that my desk surface mirrors the forest floor of a temperate old growth forest. The next time you wipe down a countertop or clean out a drain, remember that our fungal friends are there, will be there and there’s little we can do about it.