Beer, bread yeast-eating bacteria aid human health

Led by Newcastle University, UK, and the University of Michigan, the study shows how microbes in our digestive tract have learned to unravel the difficult to break down complex carbohydrates that make up the yeast cell wall.

Evolving over the 7,000 years humans have consumed fermented food and drink, the ability of strains of Bacteroides thetaiotomicron (Bt) ­­­to degrade yeasts is almost exclusively found in the human gut.

Publishing their findings in Nature, the international research team say the discovery of this process could accelerate the development of prebiotic medicines to help people suffering from bowel problems and autoimmune diseases.

The study, led by Professor Harry Gilbert at Newcastle University, Professor Eric Martens, of the University of Michigan, and Dr Wade Abbott of Agriculture and Agri-Food Canada, has identified the complex machinery that targets yeast carbohydrates.

This has provided a better understanding of how our unique intestinal soup of bacteria -- termed the microbiome -- has the capacity to obtain nutrients from our highly varied diet.

"People are very interested in developing dietary regimes where good bacteria are of benefit," explained Professor Gilbert.

"When you have certain bacteria dominant in the gut these microorganisms can produce molecules which have health promoting effects.

"There's a lot of interest in developing prebiotics. 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."

The research involving scientists from Newcastle, Australia, Canada, USA and Belgium has unraveled the mechanism by which Bt, a dominant member of the human microbiome, has learned to feast upon difficult to break down complex carbohydrates called yeast mannans.

Mannans, derived from the yeast cell wall, are a component in our diet from fermented foods including bread, beer, wine and soy sauce.

It is hoped the research could aid a better understanding of how to provide nutrients to specific organisms in the microbiome. Indeed, given that Bt has been granted Orphan Designation by the FDA for Paediatric Crohn's Disease (Thetanix^TM), yeast mannan may have health promoting effects on the microbiome by stimulating the growth of Bt.

Professor Gideon Davies, of York Structural Biology Laboratory at the University of York, who contributed to the work, said: "The ability of Bacteroides thetaiotaomicron to degrade yeast cell wall components may be of importance in fighting off yeast infections and in autoimmune diseases such as Crohn's disease."

Professor Spencer Williams, of the University of Melbourne, who also contributed to the research added: "Bacteroides thetaiotaomicron is an important part of our microbiota, the community of bacteria that live within us.

"By consuming carbohydrates that we can't, which they convert to short-chain fatty acids that they secrete into our distal gut, these bacteria establish a symbiosis that nourishes the cells that line our gut wall and provide important immune signals that establish a healthy immune response."