SEATTLE, March 25, 2015 — It appears that the major factor of a wine’s terroir has more to do with the soil microbes found around the plant’s roots than with the actual soil characteristics. New research published in the mBio open-access Journal of the American Society for Microbiology could have a long-standing impact on how those in the wine business think about soil and its effects on terroir.
The findings have helped dissect how microbes affect a wine’s properties and could help advance biotech in producing hardier crops and find new bacterial ways to help wineries influence even more a wine’s final outcome.
Gilles Martin, one of the team’s researchers, looked at four related Merlot plants, growing in five different vineyards which spanned a stretch on the North Fork of Long Island. He and the team sampled the soil, leaves, flowers, grapes and roots at each of the four locations through an entire growing season. They then used shotgun metagenomics sequencing to characterize the bacterial species found on each part of the grapevines.
“Growers have been sub-selecting the best regions to grow grapes over thousands of years, but the science of that is poorly understood,” says Jack Gilbert, a microbial ecologist at the Argonne National Laboratory in Illinois. “Just the same as the human biome plays a role in health, bacteria have intricate associations with plants that affect disease resistance, stress tolerance and productivity.”
“Where you grow that particular grapevine is the most important characteristic shaping which bacteria will colonize the plant,” says Gilbert.
Most of the bacterial species found in the plants were also in the soils around each plant, although there were a few rare species of bacteria found in the soil that were enriched in the above-ground grapes and leaves. The indication here is that the soil acts as a holding-ground for the majority of the bacteria that are colonizing the plants’ structures.
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They then compared the New York grapes’ microbiome to those associated with Merlot grapes from Bordeaux as well as crushed Merlot grapes from California. What was interesting is that they found similar bacteria species in all three samples — “No matter where you are in the world, the types of bacteria growing on or in Merlot grapes are quite similar,” says Gilbert.
The research manager in biosciences at the Australian Wine Research Institute, Dr. Paul Chambers, said, “Microbiome is a word we will hear a great deal more about in the near future. The proposition that microbiome composition determines terroir deserves further research. If a viticulturist can shape the style of wine in a controlled manner by managing the microbiome of her or his vineyard in a targeted way, it opens the way for winemakers to more effectively shape their wines to meet market demands.”
There is also a great deal of commercial interest outside of wine grapes in finding specific bacteria to benefit other crops as well — drought and pest resistance would top that list. However, the bigger issue for the wine industry is that there may just be a way to massage a wine’s outcome, no matter where you’re planting.
“From the wine industry’s perspective, terroir comes from the plant’s physiology, the chemical nature of the grapes and the yeast that do the fermenting work,” says Gilbert. “We don’t have evidence that bacteria are specifically contributing to terroir, but our next step is to figure out how those bacteria are affecting the chemistry of the plant.”
Gilbert went on to make the case that the microbes present in the soil, rather than the plant’s physical characteristics, may end up playing a bigger role when it comes to influencing terroir.