Structure-function relationships of (prebiotic) carbohydrates and their selective consumption by probiotic bacteria

The human gut microbiota comprises a large diversity of microbial cells. It has been a major focus of medical research in the last decade which suggested a crucial role in human health and disease via several mechanisms (e.g. in obesity, metabolic disorders, development of the immune system, psychiatric diseases via the gut-brain axis). There are two established ways in order to improve human microbiota composition. Firstly, by giving probiotics which are living beneficial microorganism and secondly by prebiotics which are compounds such as complex carbohydrates that are selectively fermented by beneficial members of the human microbiota. Both routes, pro- and prebiotics, may also be applied together (synbiotics), but this is less well understood.In this work we used a combined set of structural analysis tools and (traditional) culturing techniques to investigate degradation of (prebiotic) carbohydrates by selected single strains of probiotic bacteria. What we found is that prebiotics often show a complex composition e.g. 40 to 60 individual compounds (e.g. in prebiotic galactooligosaccharides or inulin). In single culture experiments with probiotic strains, probiotics degraded prebiotics often to a limited extent and used specific compounds. Some strains however used the entire prebiotic employing extracellular enzymes. We characterized some of these extracellular enzymes by solving in case of one example (Bacteroides thetaiotaomicron) the three-dimensional structure. This provided detailed insights into how probiotics degrade prebiotic compounds on the molecular level and the obtained results can be used for novel applications of pre- and probiotic formulations