Fats Reveal How Microbes Survive the Harshest Corners of the Deep Sea
Scientists have discovered that even in some of the most extreme environments on Earth—where conditions would crush, dissolve, or starve most life—tiny microorganisms are not only surviving but thriving. A team from the University of Bremen’s MARUM – Center for Marine Environmental Sciences has found biochemical traces of life in two newly discovered mud volcanoes deep in the Pacific Ocean. These volcanoes lie within the Mariana forearc, a region of the seafloor where the Pacific Plate dives beneath the Philippine Sea Plate, forming part of the Mariana subduction zone.
What makes this discovery extraordinary is that the environment inside these mud volcanoes is almost unthinkably extreme. The pH levels reach 12, one of the highest values ever recorded in a natural ecosystem. To put that in perspective, it’s about as caustic as household bleach. On top of that, the area experiences tremendous pressure, low nutrient availability, and minimal organic carbon—a combination that would make it seem completely inhospitable.
Discovering Microbial Life in a Harsh World
The research team, led by Palash Kumawat, used lipid biomarker analysis to uncover the survival strategies of microbes living in these conditions. Lipid biomarkers are essentially fats—molecules that form the membranes of microbial cells. Unlike DNA, which can quickly degrade in such extreme environments, fats can persist long after a cell dies, leaving behind a biochemical fingerprint.
Traditional DNA-based methods often fail when the number of living cells is too low to detect, but lipids can tell their own story. By examining the structure and isotopic composition of these fats, the scientists were able to determine how these microorganisms obtain their energy and how long they might have lived in these mud volcanoes.
The study found that these microbial communities metabolize carbon from inorganic sources deep within the Earth. Rather than relying on sunlight or organic matter sinking from above, they draw energy from minerals and gases such as hydrogen (H₂) and carbon dioxide (CO₂). Through chemical reactions, they can produce methane (CH₄)—a greenhouse gas that is both a product of and a fuel for microbial life in these environments.
The Role of Fats as Life’s Fingerprints
The fats detected by Kumawat’s team serve as chemical evidence of life, revealing both modern and ancient microbial activity. When these lipids remain intact, it means the cells were living or recently alive. When they degrade, they become geomolecules, marking fossilized microbial communities from the past.
By comparing the ratios of carbon isotopes in the lipids, the researchers observed a shift from hydrogen-based methanogenesis (where microbes use hydrogen and carbon dioxide to make methane) to sulfate-dependent anaerobic methane oxidation, a process where other microbes consume methane in the absence of oxygen. This finding indicates that multiple microbial communities have existed there over time, evolving as conditions changed.
The lipids themselves are chemically diverse. The team identified unsaturated diether lipids, acyclic and branched tetraether lipids, and both isoprenoidal and non-isoprenoidal glycosidic lipids. These molecular structures are hallmarks of microbial adaptation. Their unique chemical configurations help maintain membrane stability and fluidity under extreme pH and pressure, allowing these organisms to endure conditions that most life forms cannot tolerate.
A Window Into Earth’s Early Biosphere
The extreme conditions in these deep-sea mud volcanoes may resemble those of early Earth, when life first emerged billions of years ago. High alkalinity, abundant hydrogen, and rock-water interactions are all believed to have played key roles in the origin of life.
The researchers suggest that similar serpentinite-hosted systems could have provided the right combination of energy sources and chemical gradients for primitive microbes to evolve. This also ties the study to astrobiology—the search for life beyond Earth. Environments like this may exist on Mars, Europa, or Enceladus, where rock-water interactions are known to produce hydrogen and methane. Discovering microbial biospheres in Earth’s deep serpentinite mud volcanoes strengthens the idea that life could exist elsewhere under similar conditions.
How Serpentinization Fuels Life
At the heart of this discovery is a geological process called serpentinization. This occurs when ultramafic rocks from Earth’s mantle (rich in minerals like olivine and pyroxene) react with seawater. The reaction releases hydrogen and other reduced gases, making the surrounding fluids highly alkaline and rich in chemical energy.
When these fluids rise through the crust and erupt through mud volcanoes, they bring with them a mix of serpentine minerals, brucite, and magnetite, along with gases like hydrogen and methane. These gases then provide the foundation for chemosynthetic ecosystems—where microbes extract energy from chemical reactions instead of sunlight.
The Mariana forearc is particularly special because its mud volcanoes allow scientists to study mantle materials and fluids that would normally be locked away deep inside the Earth. By analyzing cores taken from the seafloor—such as samples GeoB24917-1 and GeoB24930-1 collected by the Research Vessel Sonne during Expedition SO 292/2 in 2022—the researchers could directly sample this rare environment.
Why These Findings Matter
The implications of this research go far beyond the Mariana Trench. It expands our understanding of life’s boundaries. The discovery proves that biological systems can operate in hyper-alkaline, low-carbon, high-pressure environments.
Such findings challenge our assumptions about where life can exist. Microbial metabolisms based on hydrogen, methane, and sulfate can function independent of the ocean’s surface or sunlight. This hints at a deep biosphere that may extend far beneath the seafloor—an unseen microbial world that contributes to the global carbon cycle by producing and consuming greenhouse gases.
These results also emphasize the importance of using chemical biomarkers to detect life in extreme environments. When DNA evidence fades, fats remain. This makes lipid analysis a valuable tool not just for deep-sea exploration but for searching for ancient life in planetary samples or fossil sediments.
The Limits and Next Steps
While the lipid biomarkers reveal a lot, there’s still more to learn. The team notes that cell numbers in these environments are incredibly low—possibly among the lowest anywhere on Earth. Future research could focus on genetic sequencing and metabolic modeling to better understand the precise microbial players involved.
There’s also the question of energy limitation. How do these microbes maintain basic cellular function when nutrients are so scarce? How often do they replicate—or are some living in metabolic standby, waiting for favorable conditions?
Understanding the temporal changes in lipid composition might also reveal how these biospheres evolve over geological time. The current evidence of a shift from methane production to methane oxidation shows that deep microbial communities can change their dominant metabolisms as chemical conditions fluctuate.
The Bigger Picture
This research builds on years of work showing that life and geology are deeply intertwined. Wherever water and rock interact, there’s potential for chemistry that sustains life. The Mariana mud volcanoes demonstrate that even Earth’s most chemically extreme environments can host self-sustaining microbial ecosystems.
And while the work was focused on a specific corner of our planet, it also broadens our imagination about where else life could be found. If microbes can thrive in fluids as caustic as bleach, buried kilometers below the ocean floor, then the possibilities for life beyond Earth just became a little more tangible.
Research Reference:
Biomarker evidence of a serpentinite chemosynthetic biosphere at the Mariana forearc – Communications Earth & Environment (2025)
