Bacteria found on common UK trees may act as sink for air pollution, research finds

Bacteria found on the leaves of common UK tree species may remove toxic carbon monoxide (CO) from the air, according to researchers from the University of Warwick.

Carbon monoxide is found in small amounts throughout the atmosphere, produced by incomplete burning of fossil fuels, as well as from natural processes. It is toxic to humans, and as an air pollutant it can lead to poor health outcomes, including higher rates of heart failure and lower average birth weights. “Elevated concentrations of carbon monoxide over a longer term, even if they’re relatively low, have an effect on health,” said Hendrik Schäfer, Professor of Microbiology at the University of Warwick, “Air pollution is known to be a really important factor in morbidity, making people ill and leading to premature deaths.”

Whilst scientists already know that there are bacteria in soil that can break down carbon monoxide, Professor Schäfer and his co-worker Jess Palmer wanted to explore whether the same was true for microbial communities living in the above-ground areas of trees, called the ‘phyllosphere’.

The researchers dislodged micro-organisms from leaves from holly and hawthorn trees and found that, when they were sealed inside an air-tight container with carbon monoxide, the toxic gas gradually disappeared suggesting that the micro-organisms were breaking down the gas.

Professor Schäfer’s team then looked into specific genes of the microbes in question, looking especially for a gene (called coxL) which holds instructions to make part of the enzyme responsible for breaking down carbon monoxide. They found that a wide range of phyllosphere bacteria encoded this enzyme. Then, using a public database containing known genomes of micro-organisms, the researchers estimated that around 25% of bacteria in the phyllosphere possess carbon monoxide-degradation genes. “We were quite shocked, to be honest, by the number,” said Professor Schäfer, “25%, that’s a lot.”

The research demonstrates the important role micro-organisms may potentially play in reducing air pollution, if they are acting as a sink for carbon monoxide in the biosphere. “[Microbes] probably contribute in different ways than we’ve previously realised to the degradation of carbon monoxide in cities,” Professor Schäfer explained.

“Trees have an impact on air quality, not only because they produce oxygen and they draw down carbon dioxide, but perhaps also because they are associated with micro-organisms that may have an impact on other trace gases,” he said, “We may find unexpected potential benefits of trees that are rendered through microbial organisms.”

Professor Schäfer will present these findings, which were published in 2021, at the Microbiology Society’s Focused Meeting, Microbial Cycling of Volatile Organic Compounds: Biogeochemistry to Biotechnology. His talk, titled ‘Are carbon monoxide-degrading bacteria in the phyllosphere a significant sink in the CO cycle?’, will take place at 11:15 BST on Thursday 26 May 2022.

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