Bacteria use iron and manganese oxide to

In addition to sulfate, iron and manganese compounds can play an important role in converting methane to carbon dioxide and ultimately carbonate in Earth's oceans, according to a research group of anaerobic sediments. These compounds may be crucial for methane depletion in the early, oxygen-free period of our planet.

"We often believe that bacteria only consume methane in marine anaerobic sediments if there is a sulfate occurrence," said Emily Beal, a graduate student in geological sciences in Penn State . But electrons, such as iron and manganese, are more energy-friendly than sulfates. '

Bacteria or bacteria groups use sulfate to metabolize methane.Recently researchers have discovered bacteria that use nitrogen forms in freshwater environments to convert methane.

Beal said: 'Many people have suspected that iron and manganese may have been used, but no one has shown this to be' by living 'in living organisms'.

Beal, working with Christopher H. House, professor of geoscience, Penn State University, and Victoria J. Orphan, professor of geology, California Institute of Technology, studying a variety of marine sediments to identify. Whether these bacteria can convert methane into carbon dioxide without using any sulfur compound. They reported their findings in the July issue of Science.

Using sedimentary specimens turning 20 miles off California waters at a depth of 1800 feet near the methane sludge in the Pacific Ocean, Beal brewed many sediment systems including a non-fertile form of steaming (group control), a sample with controlled sample sulfate, and a sample of live sulfate without iron oxide and manganese oxide. She also incubates samples without sulfate but contains iron oxide and manganese oxide. She placed methane gas containing 13 isotopes of non-radioactive carbon in an empty space in the tanks above the sediment and examined any carbon dioxide produced by the sample. All carbon dioxide has carbon isotope 13 which is due to the methane sample.

This is the Alvin submarine used to collect sediments (from methane sludge at the Eel River basin, Calif) used in the study. (Photo: Emily Beal)

The control group did not show any activity, while the iron and manganese oxide samples without sulfate showed very little activity. As expected, the sulfate group showed the most activity.

House, director of Penn State's Center for Astrobiology, said: ' We don't think iron and manganese are more important than sulfates, but they're not useless ingredients. They can play an important role in today's carbon cycle. '

One reason they play an important role is that some of the carbon dioxide produced reacts with both manganese and iron to form carbonates that precipitate and sequester carbon in the sea. Even if carbon dioxide is released into the atmosphere, it is a greenhouse gas less dangerous than methane.

In the early Earth, when oxygen was absent in the atmosphere, sulfate was rare. No sulfate, iron and manganese oxide may be needed for the conversion of methane to carbon dioxide.
Beal said: 'Sulfate comes mainly from the oxidation of rocks. Oxygen is essential for this process'.

While manganese and iron oxide are produced in today's oxygen atmosphere, they are also produced by photochemical reactions in a rare oxygen atmosphere.These oxides can be much richer than sulfates in the oceans in the early Earth.

While Beal classified more than 12 microorganisms living in sediment used, she still did not know which bacteria were responsible for consuming methane. It could be a bacterium, or a cluster of bacteria. She is trying to identify this microorganism.

The National Science Foundation and NASA Space Biology Institute funded the study.