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  • Writer's pictureP.K. Peterson

Extremophiles: Microbes That Love Extremes

“Microbes run this world. We just live in it.”

- Dan Rothman, geochemist, Massachusetts Institute of Technology

“For small creatures such as we, the vastness [of the universe] is made bearable only through love.”

- Carl Sagan, American astronomer, author

Recently, researchers reported two exciting discoveries in the field of microbiology that involve an extraordinary group of microbes called extremophiles. In the January 6th Science article “Oxygen and nitrogen production by an ammonia-oxidizing archaeon,” scientists described a microbe named Nitrosopumilus marbimus that is able to survive in dark, oxygen-depleted environments by producing oxygen on its own using a biological process that has never been seen before. The second discovery, announced on January 25 in an article in New Scientist, “Microbes survive deep below the seafloor at temperatures up to 120 C,” researchers found that samples of sediments 1.2 kilometers below the seafloor contain an abundant supply of living microbes. For readers who thought that temperatures well above boiling, such as 120 C (248 F), would kill everything, well, think again. As Tina Treude, UCLA Professor of Marine Geomicrobiology, commented: “Life seems to be everywhere. I would speculate that wherever there’s energy that can be exploited by microorganisms, life finds a way.”

Extremophiles are the focus of this week’s Germ Gems post.

What and where are the extremophiles? An extremophile (from Latin extremus meaning “extreme” and Greek philia meaning “love’) is an organism that is able to live (and in some cases thrive) in extreme environments, that is, environments that make survival challenging, such as extremely high or low temperatures, pH levels, radiation, or salinity. Because many of the technologies needed to detect and define the nature of extremophiles didn’t even exist until the past half century, scientists only recently recognized the outsized importance of extremophiles in the evolutionary history of our planet.

As I’ve underscored in previous Germ Gems posts, University of Illinois microbiologist, Carl Woese and his colleagues’ development of metagenomics was pivotal. This technology led to the discovery of genetic material from a staggering number of microbial species in the environment—more than 99% of which we hadn’t even known existed. (Currently, it’s estimated that there are as many as 1 trillion different species now alive on Earth.) It also led to the landmark discovery of Archaea (from the Greek word archaios, meaning ancient)—a domain of single-celled microorganisms whose cells lack a nucleus.

It is postulated that life on Earth began in what is called the Archaeon eon, 3.8 billion years ago, when our “last universal common ancestor” (dubbed LUCA) emerged, perhaps in a hydrothermal vent somewhere in the Pacific Ocean. The ability of this extremophile to thrive in extremely hot and chemically aggressive environments was a prerequisite for the subsequent evolution of life on Earth.

Extremophiles continue to populate our planet today. They’ve been found living in the cold and dark, in a lake buried a half mile deep under the ice in Antarctica, in the deepest spot on Earth at the bottom of the Mariana Trench in the Pacific Ocean, in hot springs, and inside rocks up to 1,500 feet beneath the sea floor under 8,500 feet of ocean. (Archaea are also plentiful members of the human gut microbiome, an environment that may not be quite so extreme, but certainly seems hostile.)

Origin of oxygen in Earth’s atmosphere. We have an extremophile known as cyanobacteria to thank for this life-sustaining gas. It wasn’t until about 2.45 billion years ago that, for the first time, oxygen was becoming a significant component of the Earth’s atmosphere. This was a critical development for all life forms that depend on oxygen such as all animal species, Homo sapiens among them. Scientists refer to the appearance of sufficient oxygen to allow aerobic existence as the “Great Oxygenation Event.” Currently, about 70% of Earth’s oxygen comes from plants and plant-like organisms in oceans while the remainder comes from trees.

Extremophiles and greenhouse gases. Permafrost is another extreme environment that sustains countless extremophiles. Permafrost refers to any type of ground—from soil to sediment to rock—that has been frozen continuously for a minimum of two years or as many as hundreds of thousands of years. It can extend down beneath the Earth’s surface from a few feet to more than a mile—covering entire regions such as the Arctic tundra, or a single, isolated spot, such as a mountaintop.

In many parts of the world, the Earth’s permafrost is now turning out to be not so permanent. This development has been capturing growing scientific attention. As global temperatures rise, the once always-frozen ground, or permafrost, that covers a good portion of the world’s northern latitudes is thawing. This is alarming because as the underground ice begins to melt, it’s exposing long-hidden threats to our climate, ecosystems, and health.

All across the Artic, ecosystems are shifting from carbon sinks, which absorb more greenhouse gases than they release, to carbon sources in the form of the greenhouse gases, carbon dioxide and methane. For an excellent analysis of this global threat, I recommend Joshua Yaffa’s January 10, 2022 article in The New Yorker, “The Great Siberian Thaw: Permafrost contains microbes, mammoths, and twice as much carbon as Earth’s atmosphere. What happens when it starts to melt?”

That which was first shall also be last. In previous Germ Gems posts, I’ve emphasized the enormous importance of microbes in evolution and in human biology. In this week’s post, I’ve highlighted the fact that without an extraordinary group of microbes called extremophiles, we wouldn’t even exist. Extremophiles will continue to exist and survive. Will Homo sapiens?

Over the past several decades, evolutionary biologists provided evidence that the Earth has witnessed five Mass Extinctions, referred to as the “Big Five”—periods when at least 70% of all living creatures were snuffed out. The largest of these five mass extinctions occurred at the end of the Permian period, about 250 million years ago, when 90% of all species disappeared from the planet. (This mass extinction is aptly referred to as “The Great Dying”.) Massachusetts Institute of Technology geochemist Dan Rothman and his research colleagues suggest that a methane-spurting archaean, Methanosarcina, played a key role in climate change that brought down most of the rest of the living world.

Many scientists now believe we are living in the Sixth Extinction, or the Anthropocene Epoch— the most recent period in Earth's history when human activity started impacting the planet’s climate and ecosystems. Homo sapiens played a singularly important role in igniting the Anthropocene and our species is now challenged with stopping it.

The good news is that there’s mounting evidence that with human ingenuity extremophiles can be harnessed to help us out of this predicament. For example, scientists recently discovered a species of extremophiles that consumes methane for its energy use that could be used to reduce methane emissions from landfills. And some agricultural researchers feel that extremophiles hold the answer to engineering crops that can withstand a wider range of environmental conditions in order to feed a growing human population.

The origin of our species is deeply rooted in the emergence of ancient extremophiles. Perhaps they also hold a key to discoveries that will enable our species to continue to exist on this planet.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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