Sulfur-scavenging bacteria could be key to making common component in plastic

Scientists at the Department of Energy’s Oak Ridge National Laboratory and Ohio State University discovered a new microbial pathway that produces ethylene, providing a potential avenue for biomanufacturing a common component of plastics, adhesives, coolants and other everyday products.

Scientists have discovered how microbes in waterlogged soils produce high levels of ethylene, which can adversely affect agricultural crops and bioenergy feedstocks like switchgrass. This new knowledge can be used to develop treatments for healthier crops. Credit: Andy Sproles/ORNL, U.S. Dept. of Energy

The discovery, published in Science, sheds light on a long-standing mystery about how ethylene is produced in anaerobic, or oxygen-deprived, soils and points to potential paths to prevent crop damage from high levels of ethylene. The study also outlines a previously unknown way bacteria generate methane, a powerful greenhouse gas.

The research team found that ethylene and methane are byproducts of a bacterial process that makes methionine, an amino acid necessary for building proteins. When their environment is anaerobic and low in sulfur, bacteria are forced to scavenge sulfur from cellular waste products, triggering this new pathway.

ORNL’s Bob Hettich used a specialized mass spectrometry technique to characterize the proteomes of microbial systems. Credit: Carlos Jones/ORNL, U.S. Dept. of Energy

“For about a decade, researchers have studied the biological production of ethylene through a different mechanism that occurs in oxygenated environments,” said Ohio State research scientist Justin North. “There is a technical hurdle to scaling up that process as ethylene and oxygen mixed at industrial scales could be explosive. This new anaerobic pathway clears that hurdle, but there is still work to do in scaling it up.”

The research began at Ohio State where Robert Tabita leads an ongoing study of carbon fixation and nitrogen and sulfur metabolism in photosynthetic bacteria. As part of Tabita’s team, North decided to measure the gasses being consumed and emitted by Rhodospirillum rubrum and other microbes in the same family when they were starved for sulfur. He was surprised to detect ethylene.

“We know these bacteria are producing hydrogen and consuming carbon dioxide,” North said. “But, lo and behold, they were making copious amounts of ethylene gas. And we thought, well, that’s weird.”

North and his Ohio State colleagues studied this new metabolic process using radioactive compounds to track the precursors and the production of methionine and ethylene in microbes. But a different type of analytical biotechnology was needed to make the critical link between the pathway and the proteins called enzymes that drive it.

Source: ORNL


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