The Earth beneath our feet teems with life invisible to the naked eye, and the discovery of an unfamiliar type of soil-dwelling microbe adds to the complexity of this hidden world. A recent study has dug up evidence of a new phylum of microbes — called CSP1-3 — in a part of Earth referred to as the critical zone. This layer of the planet is where air, water, soil, rocks, and plants interact to create the living skin of Earth.
The study, published in the Proceedings of the National Academy of Sciences, found that CSP1-3 plays a crucial role in purifying water that flows down through the deep soil where it thrives. Researchers are now hoping to find out how these microbes are able to flourish in such an environment.
The Critical Zone’s Value
Earth’s critical zone, extending from trees on the surface down to soil 700 feet underground, is home to several chemical and biological processes that uphold ecosystems. Microbes are among the most important inhabitants of this zone, breaking down minerals and helping plants grow.
“This zone supports most life on the planet as it regulates essential processes like soil formation, water cycling and nutrient cycling, which are vital for food production, water quality and ecosystem health,” said James Tiedje, a microbiologist at Michigan State University, in a statement. “Despite its importance, the deep critical zone is a new frontier because it’s a major part of the Earth that is relatively unexplored.”
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From Water to Soil
The new phylum was unearthed by researchers as they analyzed soil samples from locations in Iowa and China at depths of 70 feet below the surface. They say that these separate areas share a similar kind of deep soil, which is why CSP1-3 was present in both.
The origin story of CSP1- 3 shows how environmental changes caused the microbes to evolve and settle in deep soil. Millions of years ago, the microbes’ ancestors resided in hot springs and fresh water. Over time, major habitat changes led them to relocate to topsoil, and they would eventually move further down into deep soil.
An unexpected twist in this study, according to the researchers, is that the modern microbes of CSP1-3 are not rare but abundant in parts of deep soil, sometimes making up 50 percent or more of the communities there.
“I believe this occurred because the deep soil is such a different environment, and this group of organisms has evolved over a long period of time to adapt to this impoverished soil environment,” Tiedje said.
CSP1-3 has found its niche in deep soil communities, where it cleans up the residue from water that passes through soil. The topsoil isn’t able to fully purify rainwater, leaving CSP1-3 to absorb leftover carbon and nitrogen.
Recreating Microbial Environments
The full extent of CSP1-3’s physiology — granting them the ability to live in deep soil — is not yet known. Researchers hope to grow CSP1-3 cultures in a laboratory, but this may be a challenging task given the difficulties of replicating the conditions in which microbes live.
Attempting to grow CSP1-3 at high temperatures could potentially be an effective method, considering the microbes' ancestors once resided in hot springs. This may even bring forth key information that could have real ecological applications.
“CSP1-3’s physiology, driven by their biochemistry, is different, so there may be some interesting genes of value for other purposes,” Tiedje said. “For example, we don’t know their capacities for metabolizing tough pollutants and, if we could learn that, we can help solve one of the Earth’s most pressing problems.”
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Proceedings of the National Academy of Sciences. Diversification, niche adaptation, and evolution of a candidate phylum thriving in the deep Critical Zone
Development in Earth Surface Processes. Chapter 1 - Introduction to the Critical Zone
Jack Knudson is an assistant editor at Discover with a strong interest in environmental science and history. Before joining Discover in 2023, he studied journalism at the Scripps College of Communication at Ohio University and previously interned at Recycling Today magazine.
