A protein essential for photosynthesis was in use by lifeforms long before oxygen was commonly available. This discovery could re-write much of what scientists believe about the biology of plants.
Researchers from Virginia Tech examined chemical processes occurring in a variety of methane-forming bacteria called methanogens. These bacteria are found in areas lacking in oxygen. In order to carry out the study, the group looked at Methanocaldococcus jannaschii, an ancient methanogen that lives in underwater hydrothermal vents and volcanoes. Areas like these mimic many of these same conditions as those present on the early Earth.
When examining the life cycle of the bacteria, researchers found that the protein thioredoxin (Trx), which switches photosynthesis on in present-day cells, repaired proteins damaged by oxygen. Because these methanogens thrived well before oxygen was present in the atmosphere, ancient jannaschii may have regulated their respiration using Trx.
Researchers believe the substance was used by ancient microbes, which produced methane as a waste product. Methane is one of the main components of natural gas. It is also a powerful greenhouse gas. The study reveled the chemical was in use by the tiny organisms two-and-a-half billion years ago. Oxygen was not readily available in the atmosphere of the Earth until 2.4 billion years ago. This was caused by the proliferation of cyanobacteria, commonly known as blue-green algae. The Great Oxygenation Event killed off much of the life on Earth, for whom oxygen acted as a poison.
These new findings may assist researchers studying the formation of natural gas, as well as provide solutions to agricultural challenges. The production of meat and milk could be increased, since methanogens play a critical role in the digestion of food by livestock. Even human medicine may benefit from this new discovery.
"By looking at this one mechanism that was not previously studied, we will be able to develop new basic information that potentially has broad impact on contemporary issues ranging from climate change to obesity," Biswarup Mukhopadhyay, associate professor of biochemistry at the Virginia Tech College of Agriculture and Life Sciences said.
After plants die in areas where oxygen is rare, such as under bodies of water, methanogens feed on the biological material, producing methane in the process. This gas is then consumed by other organisms, which excrete carbon dioxide. This gas is then used for respiration by plants, and oxygen is one of the end products. When carried out under controlled conditions, this same process can be used to recycle organic waste into gas, meant to power homes and businesses.
"Trx may now be considered a critical participant in the global carbon cycle, climate change, and bioenergy production," researchers wrote in an article announcing the results.
The study was detailed in an online edition of the Proceedings of the National Academy of Sciences.