The spotlight
There I was: teetering on the top of a ladder with my headlamp and a sampling vial, ready to brave the bats, cockroaches, and spiders in the attic of my family’s Florida home, in search of an even smaller — and infinitely more mysterious — lifeform. I knew up here, somewhere in the dusty bowels of our home, was a condensation line for the heating and cooling system. And where there’s moisture, there’s bacteria. Could this innocuous household appliance yield a tiny biological marvel with quirks that could help humans fight climate change?
Recently, scientists have been searching for such “extremophiles,” which are microorganisms that have evolved unique traits to match the extreme environments that they grow in. In places with plentiful carbon dioxide, for example, some microorganisms might have evolved the ability to eat it, which might make them useful tools in cleaning up our atmosphere and other polluted environments.
A sample that came from my family’s dishwasher. Sachi Kitajima Mulkey / Grist
When we think of extreme environments, our minds might go to deserts or volcanoes or deep ocean trenches. And researchers have discovered extremophiles in places like those — including Chonkus, a cyanobacteria with a voracious appetite for carbon dioxide recently found in volcanic vents off the coast of Sicily. But extremes can also exist closer to home.
The human home has long been a place thought to be so ecologically mundane that science has largely ignored it, leaving the majority of the tiny life forms that live with us unstudied. But in our perfectly controlled environments, home appliances — like dishwashers — create conditions that are relatively rare in nature. There are potentially tens of thousands of microbes in these spaces left to be discovered, and many could prove useful.
The Two Frontiers Project, a nonprofit research organization dedicated to microbial exploration and the same group that found Chonkus, is trying to fill this gap. A new citizen science project, Extremophiles: In Your Home, invites volunteers to look for unusual growth of bacteria and algae — what we might commonly think of as slime or gunk — in their houses and send samples in for the scientists to test for unique carbon-capture abilities.
“Most of what we could know about the home we don’t know. We have just not historically studied the home in the way that we would study other places,” said Rob Dunn, a microbiologist who has dedicated his career to studying the small species embedded in our daily lives. In 2019, The Guardian called him the “David Attenborough of the domestic sphere.”
According to Dunn, this knowledge gap began when early ecologists decided to focus on studying a natural world defined by the absence of people. Although research of human environments has been increasing in recent decades, “it’s still true that we know more about warblers than human pathogens,” he said. When scientists have studied household bacteria, food, and insects, he said, it has often been in an effort to sterilize the environment — not understand it ecologically.
“Hundreds of millions, if not a billion cells, fit in a space this small,” said James Henriksen, holding up his fingers, boxed into the size of a quarter. Henriksen is a microbiologist at Colorado State University and co-founder of the Two Frontiers Project. It’s helpful to remember that “an entire ecosystem is occurring in these little bits of slime,” he added.
Take Thermus aquaticus, a bacteria whose enzymes helped unlock modern genetic sequencing technology, and became essential in COVID-19 PCR tests. The bacteria was originally found in the thermal pits of Yellowstone National Park — but could have been just as readily, and perhaps more easily, found in household hot-water heaters, Henriksen and Dunn told me, if anyone had thought to look.
Braden Tierney, a microbiologist and another co-founder of the Two Frontiers Project, calls microbes “nature’s alchemists,” thanks to their billions of genes that come with different functions tailored for survival in their environment. If there’s an abundant molecule — like carbon dioxide — a microbe will have evolved to eat it, Tierney explained during a presentation to the participants of the extremophiles citizen science project. And if a microbe can eat CO2, it can potentially be used to help suck up the carbon dioxide humans are pumping into the Earth’s atmosphere, thereby helping to mitigate warming. According to Tierney, microbial life is already responsible for fixing, or storing away, a significant portion of the carbon in the atmosphere.
“That means there are naturally evolved microbial mechanisms out there that are really, really good at cleaning up the environment,” he said. According to the World Economic Forum, microbial carbon capture is one of the world’s top emerging technologies, although it’s still in early stages of research and development.
After signing up on the website for the extremophiles project, participants are prompted to take photos of “slime, crusty mats, stringy growth,” in their homes, particularly in places that have extreme hot-cold cycles. Some recommended hunting grounds include washing machines, refrigerator drip lines, hot-water heaters, solar panels, and showerheads. Henriksen is especially interested in a substance called “pan pudding” that accumulates in the drip trays under air-conditioning units. And while microbes are everywhere, he said, growths that are visible to the naked eye are more likely to have genetic properties that researchers can put to use. Around 35 observations have been uploaded to the project so far by citizen scientists, and over 80 members have signed up.
If the researchers see something promisingly unusual, they’ll mail the volunteer a testing kit with empty sample tubes, gloves, and a scraper, and a prepaid envelope to send it back. Then, the researchers test the DNA of the sample, and the results will be added to an open-source database of microbes. By cataloguing the diversity of these tiny life forms, the hope is that some may one day become useful for human endeavors — like tackling greenhouse gas emissions, or cleaning up pollution.
It was with this hope that I scooped up the gloppy film in my dishwasher, the flaky gunk at the bottom of my rain barrel, and the speckled water from the air-conditioning pipes in my attic, and sent the microscopic ecosystems of my home off to a lab for testing.
The sampling kit that arrived at my home after I uploaded photos of the grime in my surroundings. Sachi Kitajima Mulkey / Grist
But even observations that don’t end up being sampled fill in important gaps of scientific understanding, Henriksen said.
Dunn agrees. “It’s amazing, people are seeing totally different things in their homes in different places,” he said. And even if the citizen science data isn’t as standardized as research done in a lab, “it’s still the best data we have,” he said. Dunn’s lab in North Carolina runs citizen science projects too, such as a survey on the microbiomes in showerheads, armpits, and sourdough bread, with the goal of “engaging as many people as possible” in the discovery of daily life.
“We simply can’t do this kind of broad survey without the help of a larger community,” said Sarah Newman, manager of the extremophiles citizen science project and director of operations at CitSci.org, where the project is hosted. “It’s giving people a place to be a part of science where there wasn’t one in the past.”
And in a way, we’ve already all been participating. “Our houses are actually a very strange environment, if you think about it. Right under our noses, we’ve been contributing to centuries-long experiments of setting up these strange places,” said Henriksen.
It may be weeks or months until I hear back from the Two Frontiers team about the sample I sent in — the precise lab work required to identify genetically distinct organisms takes time. But perhaps lurking in the guts of my Florida home, or in some chunky slime hiding in yours, could be the next single-celled ally in the fight against climate change.
— Sachi Kitajima Mulkey
More exposure
A parting shot
Another power of microorganisms is their ability to break down all kinds of materials — which makes them potentially useful for things like decontamination and waste processing. Here, biotechnologist Nadac Reales del Canto shows an experiment at a mining site in Antofagasta, Chile, in 2021. The extremophiles that Reales and her team were studying managed to eat a nail in just three days.
