Revealing Earth’s Concealed Realm: Scientists Chart the Vast Subterranean Microbial Universe
Professor Magdalena Osburn, seen here during a site visit in August, has undertaken a pioneering expedition. Image credit: Sanford Underground Research Facility.
An abandoned goldmine serves as a portal for the exploration of microscopic life hidden deep within the Earth’s crust.
If we were to aggregate the mass of all microorganisms inhabiting the Earth’s subsurface, their collective biomass would surpass that of all marine life in our oceans.
Nevertheless, due to the challenges associated with reaching these depths, this thriving subterranean ecosystem remains largely uncharted and enigmatic. Leveraging a repurposed goldmine in South Dakota’s Black Hills as their laboratory, a team of researchers from Northwestern University has meticulously mapped the most comprehensive overview to date of these elusive and extraordinary subterranean microorganisms beneath our feet.
In total, the research team characterized nearly 600 microbial genomes, a portion of which are entirely novel to science. Among this array, Northwestern geoscientist Magdalena Osburn, who spearheaded the study, asserts that the majority of these microorganisms can be categorized into one of two groups: “minimalists,” which have streamlined their existence by subsisting on a consistent diet day in and day out, and “maximalists,” which are opportunistic, readily seizing any available resources.
This groundbreaking study was recently published in the journal Environmental Microbiology.
An exterior view of the former goldmine, now known as the Sanford Underground Research Facility. Image credit: Sanford Underground Research Facility.
The significance of this new research extends beyond the deep underground realm, hinting at potential lifeforms that might someday be discovered on Mars. Given that these microorganisms thrive on resources found within rocks and water sources physically separated from the surface, it raises the possibility that similar organisms could endure beneath the Martian surface.
“The deep subsurface biosphere is vast; it represents an immense expanse of space,” remarked Osburn, an associate professor of Earth and planetary science at Northwestern’s Weinberg College of Arts and Sciences. “We employed the mine as a conduit to access this biosphere, which is challenging to reach no matter the approach. The strength of our study lies in the multitude of genomes we obtained, including many from underexplored groups. By scrutinizing their DNA, we can decipher which organisms inhabit the subterranean realm and gain insights into their activities. These organisms are often elusive in laboratory settings, earning them the moniker ‘microbial dark matter’ due to our limited knowledge.”
A Portal to the Earth’s Crust
For the past decade, Osburn and her team have regularly ventured into the former Homestake Mine in Lead, South Dakota, where they collected geochemical and microbial samples. Renamed the Sanford Underground Research Facility (SURF), this subterranean laboratory now hosts diverse research experiments across various disciplines. In 2015, Osburn established six experimental sites collectively known as the Deep Mine Microbial Observatory within SURF.
“The mine has evolved into a facility dedicated to subterranean science,” Osburn noted. “Researchers primarily conduct high-energy particle physics experiments here. However, they also permit us to investigate the subterranean ecosystems within the rocks. We can set up controlled experiments at this dedicated site and revisit them months later, a luxury we wouldn’t have in an active mine.”
By drilling into the rocks within the mine, Osburn and her team collect fracture fluids containing water and dissolved gases. Some of these fluids have been isolated for up to 10,000 years and harbor a thriving microbial community that largely goes unnoticed.
In the recent study, Osburn and her team procured eight fluid samples from various depths throughout the mine, spanning from the surface to depths of approximately 1.5 kilometers. This assortment of samples offers a glimpse into the gradient of microbial life at different depths.
Minimalists vs. Maximalists
Back in Osburn’s laboratory at Northwestern, the researchers sequenced the microbial DNA extracted from the samples. Among the nearly 600 genomes characterized, the microorganisms belonged to 50 distinct phyla, including 18 candidate phyla.
Within this diverse microbial community, Osburn observed that each lineage eventually adopts one of two life strategies: becoming a minimalist or a maximalist.
“Many of the microorganisms we encountered were either minimalists—highly specialized with a singular, well-defined function that they excel at in collaboration with a select group of partners—or maximalists, which possess a versatile array of capabilities,” Osburn explained. “Maximalists are prepared to harness any available resource. Their genomes reveal a multitude of options. In resource-scarce environments, they can synthesize what they need.”
Osburn elaborated that minimalists typically share resources with specialized allies, collectively contributing to their mutual success.
“Some of these lineages lack the genes necessary to produce their own lipids, which is astonishing,” Osburn remarked. “How can a cell function without lipids? It’s analogous to humans not being able to synthesize every amino acid, thus relying on dietary protein for the essential amino acids we cannot produce ourselves. Nevertheless, this represents an extreme case. Minimalists are highly specialized, collaborating extensively without redundancy.”
Implications for Earth and Beyond
As we contemplate the possibility of life beyond our planet, Osburn posits that these subterranean microbes may offer insights into the potential existence of life elsewhere.
“I am enthralled by the evidence of microbial life flourishing independently of us, devoid of plants, oxygen, or surface atmospheres,” she declared. “Such lifeforms could conceivably subsist deep within Mars or within the icy moon oceans at this very moment. These life forms shed light on what may inhabit other regions of our solar system.”
Furthermore, these findings hold implications for our own planet. As industries explore locations for long-term carbon storage, many companies are investigating the possibility of injecting carbon dioxide deep underground.
In the midst of these endeavors, Osburn emphasizes the importance of considering the impact on subterranean microbial life.
“We must be mindful of life in the deep subsurface and how human activities, such as mining and carbon storage, could influence it,” she cautioned. “If we store carbon dioxide underground, there are microbes capable of metabolizing it to produce methane, for instance. There exists a subterranean biosphere that, depending on perturbations, has the potential to affect surface conditions.”
Reference: “A metagenomic view of novel microbial and metabolic diversity found within the deep terrestrial biosphere at DeMMO: A microbial observatory in South Dakota, USA” by Lily Momper, Caitlin P. Casar, and Magdalena R. Osburn, 14 November 2023, Environmental Microbiology.
DOI: 10.1111/1462-2920.16543
This study received support from NASA Exobiology (grant numbers NNH14ZDA001N, NNX15AM086), the David and Lucile Packard Foundation, and the Canadian Institute for the Advancement of Research — Earth 4D.
Table of Contents
Frequently Asked Questions (FAQs) about Subterranean Microbial Universe
What is the main focus of this research?
The main focus of this research is to explore and map the diverse microbial life thriving deep within the Earth’s subsurface, shedding light on their unique characteristics and ecological roles.
How was this research conducted?
Researchers conducted this study by collecting microbial samples from a repurposed goldmine in South Dakota’s Black Hills, now known as the Sanford Underground Research Facility. They extracted fracture fluids from rocks at various depths within the mine, then sequenced the microbial DNA within these samples.
What are “minimalists” and “maximalists” in the context of this study?
In this study, “minimalists” refer to microorganisms that have specialized and streamlined functions, often collaborating with others to share resources. “Maximalists” are microorganisms with versatile capabilities, ready to utilize a wide range of resources as needed.
How might this research have implications beyond Earth?
The research suggests that similar microbial lifeforms found in the Earth’s subsurface could provide insights into potential life on other celestial bodies, such as Mars or icy moon oceans. These microorganisms thrive in environments without the need for plants, oxygen, or surface atmospheres, making them relevant to astrobiology.
Why is it important to consider subterranean microbial life in activities like carbon storage?
Subterranean microbial life can play a significant role in processes like carbon storage. For instance, when carbon dioxide is injected underground, certain microbes can metabolize it to produce methane. Understanding these interactions is crucial when assessing the environmental impact of such activities.
More about Subterranean Microbial Universe
- Environmental Microbiology Journal – The journal where the study was published.
- Northwestern University – The institution where the researchers conducted their study.
- Sanford Underground Research Facility (SURF) – The underground laboratory where the research was conducted.
- NASA Exobiology – The organization that provided support for this research.
- David and Lucile Packard Foundation – The foundation that contributed to funding this study.
- Canadian Institute for the Advancement of Research — Earth 4D – Another organization that supported this research.
