The view from where soil samples were collected near a camp on the South Col. Credit: Baker Perry
In forensic science, Locard's exchange principle holds that—no matter what—the perpetrator of a crime will bring something into the crime scene and leave with something from it.
Researchers at the University of Colorado Boulder have shown that principle is true even 5 miles above sea level in the Himalayan mountains. But instead of investigating a crime, Steve Schmidt and colleagues were investigating the hardy human microbes left behind by hikers scaling Mt. Everest.
In an area known as South Col, the dip between Mount Everest and its sister peak Lhotse, adventurers pitch their final camp before attempting to climb the world’s tallest peak from its southeastern side. The research team was not surprised to find microorganisms left at South Col by humans, but they were surprised by the microbes’ ability to withstand the extreme Himalayan environment—which is radically different than the microbes’ normal living conditions of the human nose and mouth.
Schmidt studies the cryobiosphere: Earth’s cold regions and the limits to life in them. He and his team have sampled soils everywhere from Antarctica and the Andes to the Himalayas and the high Arctic. Typically, human-associated microbes don’t show up in these places to the extent they appeared in the Mt. Everest samples from the latest study.
In fact, scientists have been unable to conclusively identify human-associated microbes in samples collected above 26,000 feet. The University of Colorado Boulder-led study, published in Arctic, Antarctic, and Alpine Research, marks the first time next-generation sequencing was used to analyze soil from such a high elevation—giving the team unprecedented insight.
Collecting extreme samples
In May 2019, a team of researchers was headed up to South Col to set up the planet’s highest weather station, established by the National Geographic and Rolex Perpetual Planet Everest Expedition. Schmidt connected with the team and asked them to collect soil samples while up there.
So, Baker Perry, professor of geography at Appalachian State University and a National Geographic Explorer, hiked as far away from the South Col camp as possible to scoop up soil samples to send back to Schmidt.
With next-generation sequencing, Schmidt and team were able to identify almost all living or dead microbes in the soil. They then carried out extensive bioinformatics analyses of the DNA sequences to determine the diversity of organisms.
Most of the microbial DNA sequences detected were of no surprise to the research team. According to the study’s findings, most were “extremophilic” organisms that had previously been detected in other high-elevation sites in the Andes and Antarctica. For example, the most abundant organism detected was a fungus in the genus Naganishia that can withstand extreme levels of cold and UV radiation—environmental aspects that kill most other microbes.
However, the scientists also found microbial DNA for organisms heavily associated with humans, including Staphylococcus, one of the most common skin and nose bacteria, and Streptococcus, a dominant genus in the human mouth.
“If somebody blew their nose or coughed, that's the kind of thing that shows up,” said Schmidt.
Since those microbes normally thrive in warm, wet environments like noses and mouths, Schmidt said it was “impressive” to see they were resilient enough to survive in a dormant state in such harsh conditions.
Luckily, the researchers don’t expect these human-associated microbes to significantly affect Everest’s environment. But, the work does carry implications for the potential for life beyond Earth—if one day humans step foot on Mars or beyond.
“We might find life on other planets, and cold moons,” said Schmidt. “We’ll have to be careful to make sure we’re not contaminating them.”