A study published today in Science by researchers from the U.S. Department of Energy’s Argonne National Laboratory may dramatically shift our understanding of the complex dance of microbes and minerals that takes place in aquifers deep underground. This dance affects groundwater quality, the fate of contaminants in the ground and the emerging science of carbon sequestration.
Deep underground, microbes don’t have much access to oxygen. So they have evolved ways to breathe other elements, including solid minerals like iron and sulfur.
The part that interests scientists is that when the microbes breathe solid iron and sulfur, they transform them into highly reactive dissolved ions that are then much more likely to interact with other minerals and dissolved materials in the aquifer. This process can slowly but steadily make dramatic changes to the makeup of the rock, soil and water.
“That means that how these microbes breathe affects what happens to pollutants — whether they travel or stay put — as well as groundwater quality,” said Ted Flynn, a scientist from Argonne and the Computation Institute at the University of Chicago and the lead author of the study.
About a fifth of the world’s population relies on groundwater from aquifers for their drinking water supply, and many more depend on the crops watered by aquifers.
For decades, scientists thought that when iron was present in these types of deep aquifers, microbes who can breathe it would out-compete those who cannot. There’s an accepted hierarchy of what microbes prefer to breathe, according to how much energy each reaction can theoretically yield. (Oxygen is considered the best overall, but it is rarely found deep below the surface.)
According to these calculations, of the elements that do show up in these aquifers, breathing iron theoretically provides the most energy to microbes. And iron is frequently among the most abundant minerals in many aquifers, while solid sulfur is almost always absent.
But something didn’t add up right. A lot of the microorganisms had equipment to breathe both iron and sulfur. This requires two completely different enzymatic mechanisms, and it’s evolutionarily expensive for microbes to keep the genes necessary to carry out both processes. Why would they bother, if sulfur was so rarely involved?
The team decided to redo the energy calculations assuming an alkaline environment—“Older and deeper aquifers tend to be more alkaline than pH-neutral surface waters,” said Argonne coauthor Ken Kemner—and found that in alkaline environments, it gets harder and harder to get energy out of iron.
“Breathing sulfur, on the other hand, becomes even more favorable in alkaline conditions,” Flynn said.
The team reinforced this hypothesis in the lab with bacteria under simulated aquifer conditions. The bacteria, Shewanella oneidensis, can normally breathe both iron and sulfur. When the pH got as high as 9, however, it could breathe sulfur, but not iron.
There was still the question of where microorganisms like Shewanella could find sulfur in their native habitat, where it appeared to be scarce.
The answer came from another group of microorganisms that breathe a different, soluble form of sulfur called sulfate, which is commonly found in groundwater alongside iron minerals. These microbes exhale sulfide, which reacts with iron minerals to form solid sulfur and reactive iron. The team believes this sulfur is used up almost immediately by Shewanella and its relatives.
“This explains why we don’t see much sulfur at any fixed point in time, but the amount of energy cycling through it could be huge,” Kemner said.
Indeed, when the team put iron-breathing bacteria in a highly alkaline lab environment without any sulfur, the bacteria did not produce any reduced iron.
“This hypothesis runs counter to the prevailing theory, in which microorganisms compete, survival-of-the-fittest style, and one type of organism comes out dominant,” Flynn said. Rather, the iron-breathing and the sulfate-breathing microbes depend on each other to survive.
Understanding this complex interplay is particularly important for sequestering carbon. The idea is that in order to keep harmful carbon dioxide out of the atmosphere, we would compress and inject it into deep underground aquifers. In theory, the carbon would react with iron and other compounds, locking it into solid minerals that wouldn’t seep to the surface.
Iron is one of the major players in this scenario, and it must be in its reactive state for carbon to interact with it to form a solid mineral. Microorganisms are essential in making all that reactive iron. Therefore, understanding that sulfur—and the microbe junkies who depend on it—plays a role in this process is a significant chunk of the puzzle that has been missing until now.
The study, “Sulfur-Mediated Electron Shuttling During Bacterial Iron Reduction,” appears online today in the May 1 edition of Science Express and will be published in Science at the end of the month. Other authors on the study were Argonne scientists Bhoopesh Mishra (also of the Illinois Institute of Technology) and Edward O’Loughlin and Georgia Tech scientist Thomas DiChristina.
Funding for the research was provided by the U.S. Department of Energy’s Office of Science. The Advanced Photon Source (APS) is also supported by the DOE’s Office of Science. The team conducted X-ray analysis at the APS GeoSoilEnviroCARS beamline 13-ID-E, which is operated by the University of Chicago and jointly supported by the National Science Foundation and the DOE’s Office of Science. Additional support came from the National Institutes of Health and the National Science Foundation.
The Computation Institute (CI), a joint institute of the University of Chicago and Argonne National Laboratory, is an intellectual nexus for scientists and scholars pursuing multi-disciplinary research, and a resource center for developing and applying innovative computational approaches. Founded in 1999, it is home to over 200 faculty, fellows, and staff researching complex, system-level problems in such areas as biomedicine, energy and climate, astronomy and astrophysics, computational economics, social sciences and molecular engineering. CI is home to diverse projects including the Center for Robust Decision Making on Climate and Energy Policy, the Center for Multiscale Theory and Simulation, the Urban Center for Computation and Data and Globus.
The Advanced Photon Source at Argonne National Laboratory is one of five national synchrotron radiation light sources supported by the U.S. Department of Energy’s Office of Science to carry out applied and basic research to understand, predict, and ultimately control matter and energy at the electronic, atomic, and molecular levels, provide the foundations for new energy technologies, and support DOE missions in energy, environment, and national security. To learn more about the Office of Science X-ray user facilities, visit the user facilities directory.
Argonne National Laboratory seeks solutions to pressing national problems in science and technology. The nation's first national laboratory, Argonne conducts leading-edge basic and applied scientific research in virtually every scientific discipline. Argonne researchers work closely with researchers from hundreds of companies, universities, and federal, state and municipal agencies to help them solve their specific problems, advance America's scientific leadership and prepare the nation for a better future. With employees from more than 60 nations, Argonne is managed by UChicago Argonne, LLC for the U.S. Department of Energy's Office of Science. For more, visit www.anl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, visit science.energy.gov
Brian Grabowski | Eurek Alert!
Memories Influence Choice of Food
22.05.2015 | Universität Basel
Memories Influence The Decision in Choosing Certain Foods
21.05.2015 | Universitätsklinikum Hamburg-Eppendorf
Physicists have developed an innovative method that could enable the efficient use of nanocomponents in electronic circuits. To achieve this, they have developed a layout in which a nanocomponent is connected to two electrical conductors, which uncouple the electrical signal in a highly efficient manner. The scientists at the Department of Physics and the Swiss Nanoscience Institute at the University of Basel have published their results in the scientific journal “Nature Communications” together with their colleagues from ETH Zurich.
Electronic components are becoming smaller and smaller. Components measuring just a few nanometers – the size of around ten atoms – are already being produced...
Development and implementation of an advanced automobile parking navigation platform for parking services
To fulfill the requirements of the industry, PolyU researchers developed the Advanced Automobile Parking Navigation Platform, which includes smart devices,...
The world's first electrical car and passenger ferry powered by batteries has entered service in Norway. The ferry only uses 150 kWh per route, which...
On Tuesday, 19 May 2015 the research icebreaker Polarstern will leave its home port in Bremerhaven, setting a course for the Arctic. Led by Dr Ilka Peeken from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) a team of 53 researchers from 11 countries will investigate the effects of climate change in the Arctic, from the surface ice floes down to the seafloor.
RV Polarstern will enter the sea-ice zone north of Spitsbergen. Covering two shallow regions on their way to deeper waters, the scientists on board will focus...
Nanoengineers at the University of California, San Diego developed a gel filled with toxin-absorbing nanosponges that could lead to an effective treatment for skin and wound infections caused by MRSA (methicillin-resistant Staphylococcus aureus), an antibiotic-resistant bacteria. This "nanosponge-hydrogel" minimized the growth of skin lesions on mice infected with MRSA - without the use of antibiotics. The researchers recently published their findings online in Advanced Materials.
To make the nanosponge-hydrogel, the team mixed nanosponges, which are nanoparticles that absorb dangerous toxins produced by MRSA, E. coli and other...
20.05.2015 | Event News
18.05.2015 | Event News
12.05.2015 | Event News
22.05.2015 | Materials Sciences
22.05.2015 | Information Technology
22.05.2015 | Materials Sciences