The study, published in Nature, suggests that specific microbes in our digestive tract known as Bacteroides thetaiotomicron have evolved the ability to unravel difficult to break down complex carbohydrates that make up the yeast cell wall.
This evolution, thought to have taken place over the 7,000 years that we have been eating fermented food and drink, means that the common gut bacteria’s ability to degrade yeasts is almost exclusively found in the human gut, according to the new study.
Led by Professor Harry Gilbert of Newcastle University, UK, the team suggests the discovery of this process could accelerate the development of prebiotics that may help people suffering from bowel problems and autoimmune diseases.
"People are very interested in developing dietary regimes where good bacteria are of benefit," said Gilbert. "When you have certain bacteria dominant in the gut these microorganisms can produce molecules which have health-promoting effects.”
"The more you understand about how complex glycans are degraded the more you can think about developing sophisticated prebiotics that target the growth of specific beneficial bacteria," he added.
Involving an international team of scientists from the United Kingdom, Australia, Canada, United States and Belgium, the team began to unravel the mechanism by which B. thetaiotaomicron has learned to feast upon difficult to break down complex carbohydrates called yeast mannans.
"One of the big surprises in this study was that B. thetaiotaomicron is so specifically tuned to recognize the complex carbohydrates present in yeasts, such as those present in beer, wine and bread," commented study co-author Eric Martens from the University of Michigan.
The researchers believe this mechanism emanated from the ability of common gut bacteria to recycle chemically similar carbohydrates present on intestinal cells, which are constantly being shed and renewed to keep the intestinal lining healthy.
"However, these bacteria turned out to be smarter than we thought: they recognise and degrade both groups of carbohydrates, but have entirely separate strategies to do so despite the substantial chemical similarity between the host and yeast carbohydrates," said Martens.
"Even the relatively small amounts of yeast that we commonly consume in foods are enough to impact the physiology of our friendly gut bacteria."
The authors then tested this idea by feeding mice a diet consisting of 50% yeast leavened bread baked at Zingerman's Bakehouse in Ann Arbor, USA.
Bakehouse bread crumbs were used to create a customized mouse food. By working with an artisanal bakery, researchers were able to confirm the quantity of yeast consumed, they said.
It is hoped the research could aid a better understanding of how to provide nutrients to specific organisms in the microbiome.
Volume 517, Pages 165–169, doi: 10.1038/nature13995
“Human gut Bacteroidetes can utilize yeast mannan through a selfish mechanism”
Authors: Fiona Cuskin, et al