Scientists used to believe that the soil microbes found in the deserts of Antarctica were the same as those found in the Amazon rainforest, but studies showed that, like all organisms, soil microbes are highly adapted to local conditions. For this reason, Lennon doesn’t think the Earth has a global microbial seed bank. Instead, each soil community, such as the dirt in Centralia, has its own local seed bank. Local microbes deposit themselves into the seed bank when conditions are less than ideal. Microbes from elsewhere can also hitchhike into the area, arriving on the feet and feathers of birds or blowing in on the wind. Some of them may try to make a go of it and either thrive or die out, but others will hunker down and wait.

The microbial ecologist Genoveva Esteban of Bournemouth University in the U.K. saw the microbial seed bank at work in Priest Pot, a 10,000-year-old pond in northern England’s Lake District. Esteban brought samples of microbial eukaryotes (small, single-celled organisms with a nucleus) from Priest Pot back to the lab to grow. Like their nucleus-deficient prokaryotic brethren, eukaryotes are challenging to grow in culture. Most just don’t want to grow in the lab. When Esteban peeked at drops of lake water under the microscope, she saw hundreds of types of swirling and swimming creatures. In the lab, she could identify only 20 species growing in the culture bottle. Then she divided the culture and grew it in a range of environments. (“We really squeezed our imaginations” to come up with every possible combination of conditions, Esteban said.) Three months later, she had 135 species.

“There were all these hidden organisms, just waiting for the right conditions to appear,” she said.

The same thing happened when Esteban took samples from Andalusia’s salt pans, those hypersaline remnants of ancient seas in what is now southern Spain. Initially, she could detect only seven microbial species in samples from six different salt flats. She gradually diluted those samples and let them grow for five weeks or more, and the number of species shot up to 95.

In a sense, Esteban’s deliberate environmental manipulations mimicked what happens when conditions shift in the natural world — including what happens as the climate continues to warm. High in the Alaskan Arctic, Janet Jansson, a microbiologist at Pacific Northwest National Laboratory outside of Richland, Washington, was tracking how global warming was affecting microbes in Hess Creek. For thousands of years, the subsurface soil in the area had been permanently frozen, but global warming is changing that, causing the underground soil layers to begin to thaw.

In this colored scanning electron micrograph of the bacterium Viridibacillus arvi, the yellow, more bulbous cells are dormant spores. The green, more rod-shaped cells are beginning to germinate and return to more active life. Dennis Kunkel Microscopy/Science Photo Library

In results published in Nature in 2011, Jansson found that after thawing a sample for just 48 hours, she could begin to see a shift in the community’s DNA. This hinted at a rise in the abundance of carbon-eating bacteria, as opposed to the type of microbe that’s usually found in the permafrost, eking out a living by using iron as an energy source.

Later sampling of both thawed and frozen sites, backed up by RNA analysis, confirmed that the DNA wasn’t lying. In the thawed soil, the iron-reducing microbes had been largely replaced by others using organic carbon for food. These differences, Jansson found, were inherent in the system.

“It’s a very extreme difference in function,” she said. “These organisms are already there, just in low numbers. The environment selects for what’s able to thrive.”

From an ecological perspective, Loy says, seed banks provide the system with a kind of insurance policy. “If you take antibiotics, those with resistance genes can grow and take over those empty niches,” Loy said. Seed banks function the same way, with dormant organisms becoming dominant when environmental conditions change. Tobin and Shade hypothesized that a microbial seed bank could explain some of what they were seeing in Centralia. Their long-term experiments were cranking along, giving them the perfect opportunity to test this idea, when suddenly, disaster struck.

A Backup Plan for Ecosystems

Just as Centralia has attracted plenty of oddball microbes, it has also attracted weirdos of the more bipedal variety. During the freezing afternoon Tobin and I spent traipsing around Centralia, several cars pulled off Locust Avenue to ask us for directions to the fire. “This always happens,” she told me as the cars drove off, disappointed to learn that they wouldn’t be able to see any flames. The old Route 61, which partially collapsed for the final time in 1993 and forced the state to build a bypass, still exists as an asphalt canvas for graffiti artists. Their work ranges from the prosaic “L+L 4EVER” to pieces of a more scatological and sexual nature.