By Hanna Abdallah
A bacterium that lives on grape plants can break down guaiacol, an unpleasant-tasting substance that ruins wines made from grapes exposed to wildfire smoke, according to new research. The study results were published in the journal PLOS One.
Wildfires are increasing in wine-producing regions of the U.S. West Coast. Wine grapes can absorb substances from wildfire smoke that ultimately make their way into the bottle, resulting in a smoky, ashy-tasting pour. Prior research has shown that one such substance, guaiacol, can be broken down by certain species of bacteria living in soil, raising the possibility that bacterial metabolic processes could be harnessed to help fix the taste of smoke-exposed wines.
However, few studies have explored whether the ability to degrade guaiacol is also possessed by bacteria found naturally on grapevines as part of the plants’ microbiome.
“One of the big takeaways is the extent to which smoke exposure affects the microbiome on the plant surface,” said study co-author Tom Collins, an associate professor in Washington State University’s Department of Viticulture and Enology. “More work has been done on reactivity of the soil microbiome to environmental impacts. This is one of the first studies to look at the microbiome on the plant.”
The researchers collected leaves from two varieties of grape plants, chardonnay and cabernet sauvignon, then tested them in a lab for the presence of guaiacol-eating bacteria.
They found that the leaves harbored two strains of the same bacterial species, Gordonia alkanivorans, that can break down guaiacol in the lab. Analysis of their genomes revealed specific genes involved in this metabolic process, including a gene called guaA. When this gene was experimentally deleted in G. alkanivorans cells, the bacterium was unable to break down guaiacol, confirming that guaA is required for guaiacol degradation.
“In this study, we identified two members of the grape microbiome capable of degrading guaiacol, a volatile phenol that contributes to smoke taint of wine,” said study author Claudia Castro of the USDA Agricultural Research Service. “We also identified changes in the grape microbiome caused by simulated wildfire smoke with the goal of providing genetic tools to help combat smoke taint.”
The researchers exposed living merlot plants to smoke produced by a culinary smoker located at WSU’s Irrigated Agriculture Research and Extension Center. The smoker simulates exposure to wildfires, helping the researchers test which bacterial species were present on the plants before and after exposure. They found that the microbiome on both leaves and grapes changed significantly in the days following smoke exposure, with a notable increase of bacteria in the Bacilli class, which are known to survive in extreme environments.
“This work suggests the potential for another route to lessen the impact of smoke exposure in the vineyard,” Collins said. “There is still work to be done to sort out how to use these organisms to the benefit of the vine, but there are already organisms in the plant microbiome that can metabolize smoke-related compounds.”
Next steps include finding other organisms that could metabolize guaiacol and other smoke-related compounds, as well as learning more about how these organisms degrade guaiacol and other smoke-related compounds, said Collins.
Read more in the full Public Library of Science release
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