Scientists have found the cause of the greenhouse effect

Up to four percent of methane on Earth comes from oxygen-rich ocean water, but scientists have been unable to pinpoint the exact source of the greenhouse gas until now. Now, researchers say they have found it.

The scientists who made the discovery weren’t looking to study ocean geochemistry. They were looking for new antibiotics. The National Institutes of Health-funded project was investigating an unusual class of potential antibiotics called phosphonates, which are already used in agriculture and medicine.

"We study all kinds of antibiotics that have carbon-phosphorus bonds," explains William Metcalf, a professor of microbiology at the University of Illinois and the project's leader, and Wilfried van der Donk, a professor at the Institute for Genomic Biology. "We found genes in microbes that we thought would make an antibiotic. But they weren't doing that. They were doing something completely different."

The microbe was Nitrosopumilus maritimus, one of the most common organisms on the planet, an inhabitant of the oxygen-rich waters of the open ocean. Scientists found genes in these microbes that could supposedly produce potential antibiotics - phosphonic acids. Taking the necessary fragment of Nitrosopumilus maritimus DNA, the researchers transferred copies of it into the genome of Escherichia coli (intestinal bacillus), but this modified bacterium began to produce not an antibiotic, as scientists had hoped, but methylphosphonic acid (methylphosphonate).

The substance was used by researchers to confirm a previously unpopular hypothesis that methane in the ocean is the product of bacteria that break down methyl phosphonate into methane and phosphoric acid.

"There was just one problem with this theory," says van der Donk. "Methylphosphonic acid had never been detected in marine ecosystems before. Based on known chemical reactions, it was difficult to understand how this compound could be produced without using unusual biochemistry."

By growing Nitrosopumilus maritimus in large quantities in the lab along with other ocean-dwelling bacteria, scientists found that methylphosphonate accumulated in the cell walls of Nitrosopumilus maritimus. When the organism died, other bacteria broke the carbon-phosphorus bond of methylphosphonate to gobble up phosphorus, an element that is rare in the oceans but essential for life. Thus, when the carbon-phosphorus bond in methylphosphonate is broken, methane is released.

Scientists note that their discovery will allow them to better understand the nature of climate change on the planet.

"We know that 20 percent of the greenhouse effect comes from methane, four percent of which comes from a previously unknown source. We need to know where the methane is produced and what happens to it to understand what will happen when the climate changes," said William Metcalf.

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