Researchers have found a pathway allowing bacteria to make a key ingredient in plastic, which they say could lead to methods of making plastic that don't require fossil fuels. File Photo by Russell Shively/Shutterstock
Aug. 27 (UPI) -- Scientists have identified a new microbial pathway in bacteria for the production of ethylene, a common component of plastics, adhesives and other products.
In addition to potentially offering a new way to biomanufacture ethylene, the discovery could help researchers develop new strategies for protecting flooded crops from ethylene-forming bacteria.
Until now, scientists knew of only two proteins in bacteria that produced ethylene, and both proteins require oxygen.
"Unfortunately, oxygen and ethylene, when combined, are highly flammable and explosive," lead researcher Justin North, a microbiologist at Ohio State University, told UPI in an email. "This presents a significant engineering challenge making it difficult to make ethylene at large scales."
All living organisms need carbon, nitrogen, sulfur and phosphorous to grow and build cells, but sulfur is often locked away in organic compounds like dimethyl sulfide or methylthio-ethanol.
Scientists found the new microbial pathway for the production of ethylene -- described Thursday in the journal Science -- while investigating the survival strategies of photosynthetic freshwater and soil bacteria, which often inhabit environs where sulfur is limited or hard to access.
"Surprisingly, when these bacteria like Rhodospirillum rubrum and Rhodopseudomonas palustris were deprived of oxygen they started making copious amounts of methane from dimethyl sulfide and ethylene from methylthio-ethanol," North said. "This led us on an entirely new pathway and to an entirely new discovery of a complex protein that removes the needed sulfur from these compounds giving us methane or ethylene as a useful byproduct."
Scientists identified the new pathway by exposing microbes to different chemical environs, and using mass spectrometry to measure differences in the ratios of proteins produced by the bacteria. The data showed the production of nitrogenase-like skyrocketed in low-sulfur environs.
"Looking at what proteins a cell makes in one environment and looking at what proteins a cell makes in a different environment can give us amazing clues into what a particular function of a protein may be," North said.
After finding evidence that nitrogenase-like proteins were likely involved in sulfur metabolism, scientists engineered the bacterial genome to include or remove the gene cluster that controls the production of nitrogenase-like proteins.
Researchers were able to confirm the presence of the nitrogenase-like protein system and ethylene production pathway by feeding radioactive carbon-labeled compounds to the bacteria cells.
"When the proteins that make ethylene were present in the cell, the methylthio-ethanol was used and radioactive methionine was produced," North said. "But when we removed the proteins that make ethylene, methylthio-ethanol could not be used and no radioactive methionine was produced."
The novel pathway could be used to develop new ways to biomanufacture ethylene, but the research could also help waterlogged plants.
"For decades, scientists have observed that when fields flood and the soil becomes filled with water and depleted in oxygen, large amounts of ethylene are produced to levels that can be damaging to crops," North said.
Researchers have also known that bacteria and fungi that thrive in low-oxygen environs were likely responsible for the excess ethylene, but until now, the only known biological ethylene production pathways required oxygen. Now, scientists have a potential explanation for the paradox.
"While our work has been solely in the lab, we believe this provides an explanation for this soil ethylene paradox, who is making it, and how it is produced when soils become oxygen deprived," North said.
In followup studies, researchers plan to test the hypothesis in the field.
"If this proves true, the goal will be to develop treatments or practices that either inhibit these ethylene-forming bacteria from growing or from producing ethylene to minimize the negative impacts of elevated ethylene on crops," North said.