A sulfosugar from green vegetables promotes the growth of important intestinal bacteria

A team of scientists analyzed how gut microbes process sulfoquinovose, a plant-based sugar containing sulfur. Their study revealed that specialized bacteria cooperate in the use of sulfosugar, producing hydrogen sulfide. This gas has disparate effects on human health: at low concentrations, it has an anti-inflammatory effect, while increased amounts of hydrogen sulfide in the gut are associated with diseases such as cancer.

Diet and the gut microbiome

With the consumption of a single type of vegetable, such as spinach, hundreds of chemical compounds enter our digestive tract. They are then metabolized by the gut microbiome, a unique collection of hundreds of microbial species. The gut microbiome thus plays a major role in determining the impact of diet on our health. "Until now, however, the metabolic capabilities of many of these microbiome organisms are still unknown. This means we don't know what substances they feed on and how they process them," says Buck Hanson, lead author of the study and a microbiologist at the Center for Microbiology and Environmental Systems Science (CMESS) at the University of Vienna. "By exploring for the first time the microbial metabolism of sulfosugar sulfoquinovose in the gut, we have shed light on this black box," he adds. The study thus generates the knowledge needed to therapeutically target nutrition-microbiome interactions in the future.

Sulfosugars in green plants and algae

Sulfoquinovose is a sulfonic acid derivative of glucose and is found as a chemical building block primarily in green vegetables such as spinach and lettuce, as well as in algae. Previous studies by the research group led by microbiologist David Schleheck at the University of Konstanz have shown that other microorganisms can in principle use sulfosugar as a nutrient. In their current study, the researchers from the Universities of Konstanz and Vienna used analyses of stool samples to determine how these processes specifically take place in the human gut. "We have now been able to show that, unlike glucose, for example, which feeds a large number of microorganisms in the gut, sulfoquinovose stimulates the growth of very specific key organisms in the gut microbiome," explains David Schleheck. These key organisms include the Eubacterium rectale species of bacteria, which is one of the ten most common gut microbes in healthy people. "The E. rectale bacterium ferments sulfoquinovose through a metabolic pathway that we only recently deciphered, producing, among other things, a sulfur compound, dihydroxypropane sulfonate or DHPS, which in turn serves as an energy source for other gut bacteria such as Bilophila wadsworthia. Bilophila wadsworthia finally produces hydrogen sulfide from DHPS by a metabolic pathway that has also only recently been discovered," explains the microbiologist.

A matter of dose: hydrogen sulfide in the gut

Hydrogen sulfide is produced in the gut by our own body cells as well as by specialized microorganisms and has various effects on our body. "This gas is a Janus-faced metabolic product," explains Alexander Loy, head of the research group at the University of Vienna. "According to current knowledge, it can have a positive but also a negative effect on gut health." According to him, a decisive factor is the dose: in small amounts, hydrogen sulfide can have an anti-inflammatory effect on the intestinal mucosa, among other things. On the other hand, increased production of hydrogen sulfide by gut microbes is associated with chronic inflammatory diseases and cancer. Until now, it was known that sulfate and taurine, which are found in increased amounts in the gut following a diet high in meat or fat, were primarily sources of hydrogen sulfide for the microorganisms. So the discovery that sulfoquinovose from green foods such as spinach and seaweed also contributes to the production of this gas in the gut was a surprise.

"We have shown that we can use sulfoquinovose to promote the growth of very specific gut bacteria that are an important component of our gut microbiome. We now also know that these bacteria in turn produce the contradictory hydrogen sulfide from it," summarizes Loy. Further studies by the scientists in Konstanz and Vienna will determine whether and how the consumption of plant-based sulfosugar can have a beneficial effect on health. "It is also possible that sulfoquinovose can be used as a prebiotic," Schleheck adds. Prebiotics are ingredients or food additives that are metabolized by specific microorganisms and used to explicitly support the gut microbiome