UI, MIT research team may have solved oceans' methane 'paradox'

UI, MIT research team may have solved oceans' methane 'paradox'

Tue, 12/26/2017 - 7:00am | Adalberto Toledo

Photo by: The News-Gazette

A team of researchers from the University of Illinois and the Massachusetts Institute of Technology may have answered one of the biggest mysteries in climate science: the "oceanic methane paradox."
In researching new forms of antibiotics, Wilfred van der Donk and his colleagues stumbled upon an abundant enzyme in marine microbes that may be responsible for the production of the greenhouse gas.
For years, scientists have known that 4 percent of the global methane budget consists of methane that is released from the Earth's oceans into the atmosphere — but not its exact source, hence the paradox.
Of course, many microbes produce methane as a byproduct of their metabolism, but most of them live inside other organisms or in deep parts of the ocean where oxygen is scarce. None live near the ocean's surface.
But in 2012, van der Donk and others published a paper in Science magazine that gave them a clue to the mystery. It examined one enzyme structure — methylphosphonate synthase (MPnS) — in one marine organism that produces a compound known to convert to methane.
Using the genetic sequence of the enzyme, researchers culled databases of organisms with similar genomes and found the enzyme exists in some of the most abundant marine microbes.
Then they hit a dead-end.
"Much to our chagrin, the enzymes didn't make methylphosphonate," van der Donk said. "So now we had a problem."
Van der Donk called his colleague, Catherine Drennan, an MIT professor of chemistry and biology. He asked her to see if she could reveal the structure of MPnS in hope of finding more variants of the enzyme in other microbes.
They found microbes that have nearly identical enzymes, van der Donk said, separated only by one tiny element that made all the difference. It was a eureka moment. By changing just one aspect of the enzyme's structure, scientists were able to make an enzyme produce MPnS when it would not have otherwise with the same efficiency.
So now, scientists can see which organisms produce MPnS, and therefore methane, and which do not.
Through tests, they found that one microbe in particular — which in the summer can cover up to 50 percent of the cells in temperate ocean surface waters — could also produce the enzyme.
"We now have a better idea of which enzyme will make methylphosphonate," van der Donk said. "So for someone who is trained as a chemist, it's very satisfying that we can make a prediction and it be right."
With methane contributing so much to the greenhouse gases said to be warming the planet, preventing the enzymes from producing methane seems like an attractive idea. Van der Donk set the record straight.
"I think it's probably a bad idea to say, 'Let's prevent that methane from being produced in the ocean,'" he said. "If we prevent it from being produced, we're going to be preventing a lot of organisms from getting the phosphorus they need, since methane is a byproduct of that process. We could really be messing with the overall ocean if we did."
The more important applications: The experiments have provided chemists with clues on how one can direct radical reactions to a desired outcome. Soon, chemists could be able to mimic nature's processes.