Two miles underground, strange bacteria are found thriving
by Chad Boutin
Oct. 20, 2006
A Princeton-led research group has discovered an isolated community of bacteria nearly two miles underground that derives all of its energy from the decay of radioactive rocks rather than from sunlight. According to members of the team, the finding suggests life might exist in similarly extreme conditions even on other worlds.
The self-sustaining bacterial community, which thrives in nutrient-rich groundwater found near a South African gold mine, has been isolated from the Earth’s surface for several million years. It represents the first group of microbes known to depend exclusively on geologically produced hydrogen and sulfur compounds for nourishment. The extreme conditions under which the bacteria live bear a resemblance to those of early Earth, potentially offering insights into the nature of organisms that lived long before our planet had an oxygen atmosphere.
The scientists, who hail from nine collaborating institutions, had to burrow 2.8 kilometers beneath our world’s surface to find these unusual microbes, leading the scientists to their speculations that life could exist in similar circumstances elsewhere in the solar system.
“What really gets my juices flowing is the possibility of life below the surface of Mars,” said Tullis Onstott, a Princeton University professor of geosciences and leader of the research team. “These bacteria have been cut off from the surface of the Earth for many millions of years, but have thrived in conditions most organisms would consider to be inhospitable to life. Could these bacterial communities sustain themselves no matter what happened on the surface? If so, it raises the possibility that organisms could survive — even on planets whose surfaces have long since become lifeless.”
Onstott’s team published its results in the Oct. 20 issue of the journal Science. The research group includes first author Li-Hung Lin, who performed many of the analyses as a doctoral student at Princeton and then as a postdoctoral researcher at the Carnegie Institution.
“These bacteria are truly unique, in the purest sense of the word,” said Lin, now at National Taiwan University. “We know how isolated the bacteria have been because analyses of the water that they live in showed that it’s very old and hasn’t been diluted by surface water. In addition, we found that the hydrocarbons in the environment did not come from living organisms, as is usual, buet rather that the source of the hydrogen needed for their respiration comes from the decomposition of water by radioactive decay of uranium, thorium and potassium.”
Because the groundwater the team sampled to find the bacteria comes from several different sources, it remains difficult to determine specifically how long the bacteria have been isolated. The team estimates the time frame to be somewhere between three and 25 million years, implying that living things are even more adaptable than once thought.
“We know surprisingly little about the origin, evolution and limits for life on Earth,” said biogeochemist Lisa Pratt, who led Indiana University Bloomington’s contribution to the project. “Scientists are just beginning to study the diverse organisms living in the deepest parts of the ocean, and the rocky crust on Earth is virtually unexplored at depths more than half a kilometer below the surface. The organisms we describe in this paper live in a completely different world than the one we know at the surface.”
That subterranean world, Onstott said, is a lightless pool of hot, pressurized salt water that stinks of sulfur and noxious gases humans would find unbreathable. But the newly discovered bacteria, which are distantly related to the Firmicutes division of microbes that exist near undersea hydrothermal vents, flourish there.
“The radiation allows for the production of lots of sulfur compounds that these bacteria can use as a high-energy source of food,” Onstott said. “For them, it’s like eating potato chips.”
But the arrival of the research team brought one substance into the underground world that, though vital to human survival, proved fatal to the microbes — air from the surface.
“These critters seem to have a real problem with being exposed to oxygen,” Onstott said. “We can’t seem to keep them alive after we sample them. But because this environment is so much like the early Earth, it gives us a handle on what kind of creatures might have existed before we had an oxygen atmosphere.”
Onstott said that many hundreds of millions of years ago, some of the first bacteria on the planet may have thrived in similar conditions, and that the newly discovered microbes could shed light on research into the origins of life on Earth.
“These bacteria are probably close to the base of the tree for the bacterial domain of life,” he said. “They might be genealogically quite ancient. To find out, we will need to compare them to other organisms such as Firmicutes and other such heat-loving creatures from deep-sea vents or hot springs.”
The research team is building a small laboratory 3.8 kilometers beneath the surface in the Witwatersrand region of South Africa to conduct further study of the newly discovered ecosystem, said Onstott, who hopes the findings will be of use when future space probes are sent to seek life on other planets.
“A big question for me is, how do these creatures sustain themselves?” Onstott said. “Has this one strain of bacteria evolved to possess all the characteristics it needs to survive on its own, or are they working with other species of bacteria? I’m sure they will have more surprises for us, and they may show us one day how and where to look for microbes elsewhere.”
Other authors of this work include Johanna Lipmann-Pipke of GeoForschungsZentrum, Potsdam, Germany; Erik Boice of Indiana University; Barbara Sherwood Lollar of the University of Toronto; Eoin L. Brodie, Terry C. Hazen, Gary L. Andersen and Todd Z. DeSantis of Lawrence Berkeley National Laboratory, Berkeley, Calif.; Duane P. Moser of the Desert Research Institute, Las Vegas; and Dave Kershaw of the Mponeng Mine, Anglo Gold, Johannesburg, South Africa.
Pratt and Onstott have collaborated for years as part of the Indiana-Princeton-Tennessee Astrobiology Institute (IPTAI), a NASA-funded research center focused on designing instruments and probes for life detection in rocks and deep groundwater on Earth during planning for subsurface exploration of Mars. IPTAI’s recommendations to NASA will draw on findings discussed in the Science report.
This work was also supported by grants from the National Science Foundation, the U.S. Department of Energy, the National Science Council of Taiwan, the Natural Sciences and Engineering Research Council of Canada, Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) and the Killam Fellowships Program.
More information about this discovery can be found at http://newsinfo.iu.edu/news/page/normal/4229.html and http://www.carnegieinstitution.org/news_releases/news_2006_1019.html
Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome
By Li-Hung Lin, Pei-Ling Wang, Douglas Rumble, Johanna Lippmann-Pipke, Erik Boice, Lisa M. Pratt, Barbara Sherwood Lollar, Eoin L. Brodie, Terry C. Hazen, Gary L. Andersen, Todd Z. DeSantis, Duane P. Moser, Dave Kershaw, and T. C. Onstott
Geochemical, microbiological, and molecular analyses of alkaline saline groundwater at 2.8 kilometers depth in Archaean metabasalt revealed a microbial biome dominated by a single phylotype affiliated with thermophilic sulfate reducers belonging to Firmicutes. These sulfate reducers were sustained by geologically-produced sulfate and hydrogen at concentrations sufficient to maintain activities for millions of years with no apparent reliance on photosynthetically-derived substrates.
Microbes deep beneath seafloor survive on byproducts of radioactive process
Results have implications for life on Mars
NARRAGANSETT, R.I. – February 26, 2021 – A team of researchers from the University of Rhode Island’s Graduate School of Oceanography and their collaborators have revealed that the abundant microbes living in ancient sediment below the seafloor are sustained primarily by chemicals created by the natural irradiation of water molecules.
The team discovered that the creation of these chemicals is amplified significantly by minerals in marine sediment. In contrast to the conventional view that life in sediment is fueled by products of photosynthesis, an ecosystem fueled by irradiation of water begins just meters below the seafloor in much of the open ocean. This radiation-fueled world is one of Earth’s volumetrically largest ecosystems.
The research was published today in the journal Nature Communications.
“This work provides an important new perspective on the availability of resources that subsurface microbial communities can use to sustain themselves. This is fundamental to understand life on Earth and to constrain the habitability of other planetary bodies, such as Mars,” said Justine Sauvage, the study’s lead author and a postdoctoral fellow at the University of Gothenburg who conducted the research as a doctoral student at URI.
The process driving the research team’s findings is radiolysis of water – the splitting of water molecules into hydrogen and oxidants as a result of being exposed to naturally occurring radiation. Steven D’Hondt, URI professor of oceanography and a co-author of the study, said the resulting molecules become the primary source of food and energy for the microbes living in the sediment.
“The marine sediment actually amplifies the production of these usable chemicals,” he said. “If you have the same amount of irradiation in pure water and in wet sediment, you get a lot more hydrogen from wet sediment. The sediment makes the production of hydrogen much more effective.”
Why the process is amplified in wet sediment is unclear, but D’Hondt speculates that minerals in the sediment may “behave like a semiconductor, making the process more efficient.”
The discoveries resulted from a series of laboratory experiments conducted in the Rhode Island Nuclear Science Center. Sauvage irradiated vials of wet sediment from various locations in the Pacific and Atlantic Oceans, collected by the Integrated Ocean Drilling Program and by U.S. research vessels. She compared the production of hydrogen to similarly irradiated vials of seawater and distilled water. The sediment amplified the results by as much as a factor of 30.
“This study is a unique combination of sophisticated laboratory experiments integrated into a global biological context,” said co-author Arthur Spivack, URI professor of oceanography.
The implications of the findings are significant.
“If you can support life in subsurface marine sediment and other subsurface environments from natural radioactive splitting of water, then maybe you can support life the same way in other worlds,” said D’Hondt. “Some of the same minerals are present on Mars, and as long as you have those wet catalytic minerals, you’re going to have this process. If you can catalyze production of radiolytic chemicals at high rates in the wet Martian subsurface, you could potentially sustain life at the same levels that it’s sustained in Earth’s marine sediment.”
Sauvage added, “This is especially relevant — given that the Perseverance Rover has just landed on Mars, with its mission to collect Martian rocks and to characterize its habitable environments.”
D’Hondt said the research team’s findings also have implications for the nuclear industry, including for how nuclear waste is stored and how nuclear accidents are managed. “If you store nuclear waste in sediment or rock, it may generate hydrogen and oxidants faster than in pure water. That natural catalysis may make those storage systems more corrosive than is generally realized,” he said.
The next steps for the research team will be to explore the effect of hydrogen production through radiolysis in other environments on Earth and beyond, including oceanic crust, continental crust and subsurface Mars. They also will seek to advance the understanding of how subsurface microbial communities live, interact and evolve — when their primary energy source is derived from the natural radiolytic splitting of water.
This study was supported by the U.S. National Science Foundation and the U.S. National Aeronautics and Space Administration. The project is also affiliated with the Center for Dark Energy Biosphere Investigations.
COMMENT: In discussions with evolutionary biologists, we learned recently that “not all animals and fungi use oxygen and give off carbon dioxide”; and, on the other hand, “not all plants use carbon dioxide and give off oxygen.” It turns out there are exceptions — if one includes deviations seen in bacteria.
The first article below (posted in 2006) noted that “some baceria live off radioactive decay in rocks” — which were discovered deep in South African gold mines. The second article below (posted in 2021) noted that “some microbes that live in the marine sediment use chemicals that are made from the irradiation of water — hydrogen and oxidants created when naturally-occurring radiation splits apart water molecules.”
It had been thought that “most marine-sediment microbes lived off the products of photosynthesis” — but it looks like these types of indirectly-radiation-fed microbes are extremely common — and may even be dominant in the seafloor. Time to change the biology textbooks. Life is getting more complicated, and weird. ☹ ☹ 😊 😊