Our Warming Planet Is a Petri Dish for New and Deadly Microbes

On a sweltering morning last July, Vernon Spear, a burly eighty-five-year-old with thinning gray hair, went to check a chicken-wire crab trap that was hanging from a dock in Cambridge, Maryland. Spear is a lifelong resident of the Eastern Shore, near where the Choptank River flows into the Chesapeake Bay. He lives less than fifty yards from the dock. He was pleased to find that the trap held six feisty blue crabs, a local delicacy that he likes to steam and sprinkle with Old Bay. As Spear reached in, however, he scraped his arm on some metal, drawing blood. He wasn’t worried; he’d been scratched many times before. But, in the hours that followed, Spear’s arm began to turn violent shades of purple and red. His wife, Lea, thought it looked like he’d been badly burned. Soon his arm swelled up—liquid appeared to be pooling under the skin—and he rushed to his local emergency room. A clinician suspected an infection of Vibrio vulnificus, which under a microscope looks like a kidney bean with a tail. It is popularly known as flesh-eating bacteria.When V. vulnificus enters a wound, it damages blood vessels, causing them to leak plasma into surrounding tissues. The immune system tries to protect the body by calling in clotting cells to halt the leaking; in the process, the cells cut off blood flow, prompting flesh to become necrotic. The bacteria can cause shock, sepsis, and multi-organ failure. Infections that reach the bloodstream prove deadly at least fifty per cent of the time.A medical helicopter arrived within twenty minutes. Spear was flown to the R Adams Cowley Shock Trauma Center at the University of Maryland Medical Center, in Baltimore. There was no question that he would need surgery. Rather, his doctors wondered if they would be able to save his life. Antibiotics on their own are of limited use against a V. vulnificus infection. The best way to control the bacteria is to cut away the affected flesh. Surgeons worked quickly to excise layers from Spear’s forearm. When he regained consciousness, hours later, he was aghast. He could see into his arm; the muscle and bone were exposed. “It was just a big hole,” he told me.

For most of Spear’s lifetime, infections of V. vulnificus north of Georgia were rare. Lately, however, the bacteria have killed people as far north as New York and Rhode Island. “What has happened is that the environment has changed,” Rita Colwell, a ninety-one-year-old microbiologist at the University of Maryland, told me. It’s not that the bacteria are migrating, she said. Low levels are always present where freshwater and salt water mix. But when water warms above fifty-nine degrees Fahrenheit V. vulnificus becomes more abundant, and above seventy-seven degrees its population soars.When Colwell started sampling microorganisms in the Chesapeake Bay, in the late sixties, she occasionally heard about V. vulnificus infections in the area. A deadly case in the eighties made the Washington Post and the Baltimore Sun. “It was an astounding rarity,” she told me. Nowadays, about a dozen cases are confirmed in Maryland each year; the number increased by more than fifty per cent in the span of fourteen years. A 2023 study found that the season in which the bacteria are detectable now starts in early spring and extends into the fall. “This is insidious, and it’s happening to us,” Colwell said.Climate change affects every life-form on Earth, but we tend to focus on how it impacts certain vulnerable species: polar bears, sea turtles, corals. Microorganisms are often omitted from the story of warming, even though they far outnumber plants and animals. In 2019, an international group of thirty-three scientists warned in the journal Nature that the “unseen majority” of life was being transformed by rising temperatures, and that humans would have to contend with the consequences. Microorganisms that infect us could become more common, and appear in new places. Billions of other microbe species could be affected, too. How would they respond when their environments shifted? “We’re dealing with the first life on Earth,” Antje Boetius, a co-author of the Nature paper, who serves as the president and C.E.O. of the Monterey Bay Aquarium Research Institute, told me. “Our planet is the test tube. We make it a bit warmer, everything will change.”When scientists depict all of Earth’s species on a tree of life, the lineage of humans looks like a twig.

Microbes—biological entities that are too small to see without a microscope, including bacteria, fungi, viruses, protozoa, algae, and archaea—take up most of the tree. Microorganisms are not passive occupants of our planet—they are co-creators of our environment. Microscopic algae produce much of the oxygen that we breathe. Various microbes process almost all the dead plants on the planet. “Without that very basic function, we’d all be sitting in a pile of leaves,” Steven D. Allison, an ecologist at the University of California, Irvine, told me. Microorganisms partner with plant roots, and with leaves that regulate the amount of carbon in the atmosphere; they are “the architects and the wardens of life on this planet,” A. Murat Eren, a microbial ecologist and computer scientist at the Helmholtz Institute for Functional Marine Biodiversity, in Germany, told me. (A soil bacterium is even responsible for making a compound called geosmin, Greek for “earth” and “odor,” which generates the distinctive scent that follows rain.)What virtually all microbes have in common is that they are ubiquitous. Microbial ecologists have a saying, Boetius told me: Everything is everywhere. A single drop of seawater, for example, can contain a million microbes, including a hundred or more species of bacteria. Microbes colonize every plant and animal, living and dead; they live on frozen mountaintops, in searing volcanoes, and at the bottoms of the deepest caves and oceans. When scientists sampled clean rooms where NASA builds spacecraft, they managed to find two hundred and fifteen bacterial strains on the floors alone. Microbes even have their own microbes.Meanwhile, microbes are constantly evolving. Many bacteria divide numerous times a day—and, crucially, accumulate mutations in the process. “Every division is an experiment in survival, with a slightly different genetic roll of the dice,” Eren said. Different types of microbes reproduce in different ways: bacteria and archaea duplicate themselves; viruses hijack the cells of other species; and some fungi reproduce sexually, whereas others transfer their DNA by releasing spores. But all of them can gain new traits over time, just as plants and animals do—only the microbes are much faster at it. (

The gap between the rate of human evolution and the rate of microbial evolution, Eren said, is like “the difference between a drifting tectonic plate and an F-16 fighter jet.”)In the late nineteenth century, William Dallinger, an English minister who experimented with microscopes, cultivated microbes called flagellates in warm water. He gradually increased the temperature to a hundred and fifty degrees, a level that once would have killed them. They adapted to such an extent that when they were put back in cooler water they died. Nearly a century later, scientists at Michigan State University bred Escherichia coli in a stark environment that contained barely any food. More than thirty thousand bacterial generations later, an E. coli lineage developed the ability to consume molecules known as citrates, which were previously inedible. The change was as extreme, a biological mathematician wrote, as if humans had developed the capacity to eat wood.Our bodies, in turn, are constantly adapting to the trillions of microbes that surround us. Each of us has a microbiome—a universe of microorganisms living on us and in us—that helps digest food, stop infections, and make chemicals that the body needs. When microbes are beneficial or benign, we say that they’ve colonized us. When they are harmful, we say that they’ve infected us. Even then, our bodies adjust to their presence. Our immune systems develop new defenses, trying to kill germs that might otherwise kill us. But, in an era when the microbial world is changing rapidly, plants and animals may struggle to keep up. “We always ask: How are we going to adapt to a changing world?” Eren said. “The real question is: How are we going to coexist with microbes that have adapted to the new world?”“So, the queen died, and after a brief period of anarchy a fledgling democracy started to emerge, but then there was a coup and the eventual rise of a brutal strongman, and long story short the honey tastes lousy.”Cartoon by Emily FlakeSpear ultimately spent eight days in the hospital. Doctors watched carefully for any further darkening of the skin, which would indicate that the V. vulnificus infection was still spreading. The six blue crabs had been left in a pot on the stove. “Never got to eat them,” Spear told me.In October, I watched Spear undergo a follow-up surgery in Maryland.

He was under anesthesia, covered with drapes. Only his right arm and left leg were visible. I could see the aftermath of the infection: the entire length of his forearm was shiny and pink, like prosciutto. William Chiu, an acute-care surgeon, explained that he would be covering the wound with a thin layer of Spear’s own skin. (They sourced the skin from his left leg because he has a tattoo on his right.) I watched as another doctor slid what looked like a potato peeler along Spear’s thigh. He then rolled the resulting strip of skin through a mesher, an instrument that cuts geometric holes into tissue so it can expand to cover a larger area. Finally, he handed the skin graft to Chiu, who delicately stretched it over Spear’s arm.After the surgery, I sat with Spear and his wife in the shock-trauma unit. He had an I.V. in his arm. He still seemed stunned that dipping his hand in the local river had nearly killed him. “We’ve never heard anything about not going into the water,” he told me. Despite the circumstances, he was in good spirits. He and his wife shared stories they’d heard about other V. vulnificus infections. A friend had said that his brother, a waterman, lost his leg to an infection. Their electrician had told them about a man on nearby Hoopers Island who contracted a fatal infection after being nicked by a crab shell. Spear’s wife worried about families who vacationed on the Eastern Shore. How would they know to avoid the water when they had open cuts or scrapes?In the middle of our conversation, Spear suddenly exclaimed, “I don’t believe in global warming.” There was an awkward silence. I asked if he thought the weather had changed during his lifetime. He mulled this over and said, “It’s warm now, and it’s, what, October?” He leaned back onto his pillow and exchanged a glance with his wife. “We don’t have as harsh winters anymore,” he added.In the opening scene of “The Last of Us,” a post-apocalyptic HBO series that débuted in 2023, an epidemiologist goes on TV to share his greatest fear: that fungi will adapt to warmer and warmer temperatures.