There aren’t just two species in this photo (Image: Sarah Small/Getty)
Every nook and every cranny of our houses and flats is an invisible ecosystem of bacteria, fungi and archaea. And it’s only now that we are beginning to get a true picture of this ecosystem.
Biologist at North Carolina State University in Raleigh has conducted the . His team is sequencing the DNA on swabs sent to him by volunteers from 1430 houses and apartments across North America to identify what’s living on door frames, pillows and kitchen counters. “Some live with goats, some live in fraternities with 40 other dirty stinky guys, some live with kids,” says Dunn. “Every single one has microbial DNA on every surface we swabbed.”
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Dunn and his team discovered phenomenal diversity amongst the microbes. To sequence the full genomes of every beastie would have been impossibly slow. So Dunn’s team analysed sections of DNA and classified the microbes into loose categories known as operational taxonomic units (OTUs).
The results were still surprising. They found , 35,000 OTUs of fungi and 350 OTUs of archaea across all the homes. “With the fungi, that’s of the order of magnitude of all of the named fungi on Earth. It’s astonishing really,” says Dunn.
His team went on to study a subset of homes in more detail – and found much, much more. “There was a couple of thousand kinds of arthropod in houses and they include amazing things,” says Dunn. Among them is the drain fly, which inhabits many kitchen drains and whose larvae live off the waste at the bottom. “We also found a parasitoid wasp in almost every house,” says Dunn (see diagram).
The microbes we shed from our skin, such as Staphylococcus and Corynebacterium, live in every room in our homes. “Everyone tends to worry about the toilet seat but the truth is that everywhere we put our bodies tends to have a set of ‘you’ microbes,” says Dunn.
This is borne out by other research. at the University of Oregon in Eugene investigated the bacteria on floors, desks and chairs in a university classroom and says the results apply to our homes too. “When you look at the bacteria on the seat of a chair, it’s not just skin-associated bacteria, there’s also stuff associated with the human gut and the vagina,” says Meadow. “Whether we like to admit it or not, we’re incredibly leaky animals and our clothes are definitely not the impermeable barrier we like to think they are.”
“Chairs hold bacteria from the human gut and vagina. We are leaky animals”
While some bacteria are widespread, there are also geographic variations. Dunn’s team has found some plant pathogens only in houses in corn-growing regions. “We’re seeing this really beautiful replication of everything biologically that’s going on around us seeping through our windows into our homes,” says Dunn. There are also differences within each home based on the climatic conditions we create in each room and what we do there.
The effect of all these microbes we share our rooms with is far from clear. “There’s been a lot of research into the bad things, the pathogens,” says Meadow. “But the majority of microbes have no impact on our health or a positive effect.” While research into the health effect of the microbial ecosystem is still at an early stage, one study carried out in 2013 gives an insight into its influence. Mice exposed to dust from homes with dogs were less likely to develop asthma than mice exposed to dust from dog-free homes. The protected mice were found to have higher levels of the bacterium Lactobacillus johnsonii in their intestines, which .
We are also pretty ignorant of the effect we are having on our home’s microbes too – especially when it comes to cleaning with bleach and other products. “We’re choosing the ecosystems we have around us and mostly we’re doing it pretty blindly,” says Dunn. “We go to war against these invisible lifeforms and we think we’re creating an environment that’s free from them. Instead, we’re creating an environment in which we favour those few species able to withstand our assaults.”
Dunn hopes further research will show us how to “garden” our home’s microbial ecosystems so they contain the right mix of species to keep us healthy. “It’s stupid not to,” he says.
Read more: “The secret life of your home“
This article appeared in print under the headline “Home but not alone”
