“CAN I ask what all this is for?” The pharmacy assistant is eyeing me suspiciously. I have just asked for some covid tests, urine sample pots and sterile scalpel blades. Oh, and some latex gloves, please. “I want to see if there are extreme life forms hiding in my dishwasher,” I explain. “I see,” she says carefully, before scurrying off to consult a colleague.
It is an unusual shopping list, I’ll admit. To explain it, I need to rewind to June, when I spotted a study about bacteria that can live in what humans consider to be extreme conditions, such as high temperatures, caustic liquids or intense radiation. Normally, scientists head to exotic locations to find these microbes, such as the scalding volcanic springs of Yellowstone National Park or the frozen deserts of Antarctica. But you don’t have to go to the ends of the earth to find them, this study said. Chances are, extreme-loving microbes are not only surviving, but thriving, .
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That was it. I had to find out whether my kitchen really was home to microbes whose adaptations are like a list of superhero powers. In the process, I gained a new appreciation of the diversity of life – and won’t see my coffee machine in quite the same way again.
Extreme-loving microbes are a goldmine for bioprospectors who pan the natural world for biotechnology innovations. Covid PCR tests, for example, rely on a DNA-copying enzyme first isolated from a bacterium called Thermus aquaticus that lives in hot springs, tolerating temperatures hot enough to poach an egg.
As well as surviving extremes of heat, microbes can thrive in bitter cold – even living in ice and snow. Some flourish in high salt concentrations, others in rivers as acidic as your stomach. A few hardy ones can even resist radiation and desiccation. You might think it impossible for any organism to survive such conditions, says Manuel Porcar at the University of Valencia in Spain, yet these microbes show it is indeed possible.
There are extreme environments in your home, too. Temperature-wise, many houses are kept at around 20°C (68°F). But our kitchens contain appliances that run much hotter: 70 or 80°C (176°F) or more. Some operate using harsh chemicals. “So from an ecological perspective, they are closer to Yellowstone than to your bedroom,” says Porcar.
Coffee machine microbiome
And in them is life. Over the years, researchers have found “extremophile” microbes in appliances such as , washing machines and . Even your coffee machine has its inhabitants. “It’s like a world in itself, with different cycles of temperature and caffeine,” says Porcar. His team has shown how a microbial community can form. In theory, microbes could even cling to life in your microwave oven, enduring repeated pulses of microwave radiation, desiccation and heat.
Which begs the question: how did they get there? Many microbes are great travellers, borne around the world by wind and water. They can settle anywhere, but only thrive where the environment is right for each particular species. It is well known in microbial ecology circles that ““. In other words, the microbes you find thriving in a given spot tend to be influenced less by geography and more by the particular conditions of that environment.
Intriguingly, this also holds for human-made habitats. Porcar and his team have shown that not only can certain , but the communities you find there are the same on panels in locations as different as Spain, California and the north and south poles. This insight led them to suggest the concept of the Microbiome of Things, the idea that appliances around the world share common selection pressures. So, the microbiome of a microwave oven or dishwasher in the UK should be similar to that of one in Australia, Canada or even an Antarctic base.
Microbe-hunting at home
Eaten up with curiosity as to what might be living in my kitchen, I contacted Porcar, who also heads a bioprospecting company called . He and his colleague Adriel Latorre agreed to analyse samples from my kitchen. This was easier said than done, as I didn’t have the usual lab equipment. But a trip to the pharmacy and one startled assistant later, I had what I needed.
The covid tests supplied sterile solution and swabs that I used to takes samples. Anything that looked like a microbial film, I scraped off with a scalpel and put in the urine pots. I then froze everything, couriered it to Spain and crossed my fingers that we would find something interesting.
After a nail-biting few weeks of waiting, the results from my kitchen are in. The Darwin team successfully extracted DNA from the samples and sequenced parts of a gene called 16S rRNA, which allows bacteria to be identified down to the level of their genus. This won’t allow us to unequivocally prove the presence of a specific extremophilic species – that would involve prolonged, expensive experimental tests – but the analysis gives a pretty strong steer, says Latorre.
The appliance that topped the list in terms of the total number of different microbes was my dishwasher, which hosted 70 genera, or groups, of bacteria. This machine subjects its microbial denizens to 65°C (149°F) heat, water stress, detergent, dishwasher salt and dry periods, and was the main source of heat-loving or heat-tolerant bacteria in my kitchen. These include Exiguobacterium, a genus containing that grow in a range of harsh environments, including hot springs, glaciers and salt lakes, Priestia, which can form spores highly resistant to heat, and Paracoccus, which has been found in hot springs. There was biotech potential there too: Bacillus, a genus that promises applications such as antimicrobial compounds and heat-stable enzymes needed by the detergent industry, and Acinetobacter, which includes the bioremediation of heavy metals and fuel spills among its many talents.
Biotech potential
Next up is my coffee machine, home to 53 unique genera. The most abundant, , contains species known to metabolise caffeine, as do two other genera found alongside it, Acinetobacter and Pseudomonas. Fermenting coffee beans with microbes like these could be a new and improved way of producing decaffeinated coffee.
Bringing up the rear is my washing machine (not strictly a kitchen appliance, I know, but it does create extreme conditions within the home) with six detected genera, including some, such as Pseudomonas putida, known to break down pollutants and organic molecules.
Are these results surprising? “Yes and no,” says Porcar. The microbial diversity found in my appliances is consistent with previous studies, but there are intriguing findings, such as Methylobacterium-Methylorubrum being the most abundant genus in my coffee machine, which is not what Porcar’s previous studies have found. The team might try to grow it in their lab to find out more about it.
For me, the experiment highlights the astonishing versatility of life and how much there is yet to be discovered in unexpected places.
Now then, who’s for coffee?
