Yeast wars: Wine grapes growing in a vineyard. Many species of yeast grow on the surface of grapes, but only one survives the fermentation process.
Credit: Wikimedia
BRISBANE: The yeast that ferments grapes into wine, first evolved the ability to make alcohol to engineer its environment and poison its competitors, says a new report.
The yeast Saccharomyces cerevisiae makes up only a small proportion of the yeast on grapes while growing in the vineyard, but it comes to dominate natural fermentation processes by producing alcohol and heat.
Together, these make the environment toxic to most other microorganisms, and while not ideal for S.cerevisiae either, the food freed up gave the species an evolutionary edge that more than compensated.
Niche construction
Environmental engineering, or niche construction, has been observed by experts before, but the study reported today in the journal Ecology is the first to quantify the benefits of the strategy.
"It shows how the here and now actions of organisms alter the selection pressures they are exposed to," said Matthew Goddard, author of the study and a wine scientist at the University of Auckland in New Zealand.
To make the discovery, Goddard sampled yeasts from grape juice at a winery, and identified them by DNA analysis. He tracked alcohol levels and temperatures in fermenting barrels, and also measured how fast each species could grow at different ethanol concentrations in the laboratory.
The results have revealed that during fermentation S.cerevisiae has a seven per cent advantage over its competitors.
About ten species of yeasts can be found on grapes, but only S. cerevisiae can complete the wine-making process, Goddard said. It ferments the grape juice to produce ethanol and heat even when it would be more efficient for it to respire and produce carbon dioxide and water.
"Improving flavour profiles"
In place of adapting to the environment around them, organisms can opt to modify their environment to adapt to them instead, said Goddard.
"This concept is not new – Darwin's final book describes how earthworms alter the soil around them," he said. "Humans might be the extreme example – think of how we have changed the planet."
Microbiologist Paul Henschke, of the Australian Wine Research Institute in Adelaide, said that the findings would be interesting for ecologists, and could also aid winemakers in improving the flavour profile of wine.
Keeping grape juice artificially cool in the early stages of fermentation could encourage flavour development by other yeasts, he said, and then allowing the temperature to rise would help S.cerevisiae beat its competitors and finish the process.
