The human microbiome fulfills a variety of functions. Each function is ascribed a set of bacteria, and these all have various functions under different circumstances. A bacterial consortium needs to be versatile, balanced and cover all the essential functions.
The human microbiota is a dense ecosystem with an inter tangled cross-feeding network and complex nutritional requirements. Dietary fibers and carbohydrates that are not digested in the stomach are utilized by the gut bacteria, resulting in the production of various metabolites. These products can either be taken up by the human host or further metabolized to give rise to end-metabolites. The metabolic profile of a healthy gut is dominated by the short chain fatty acids (SCFAs) Acetate, Propionate and Butyrate at ratios of around 6:2:2. These SCFAs are important regulators of the human energy metabolism and health. Butyrate is the main energy source of the intestinal epithelium and therefore crucial for it’s integrity. Altered ratios of SCFAs or overproduction of intermediate metabolites is correlated with a broad range of metabolic diseases.
To guarantee the desired SCFA ratio and thereby the basis for a healthy host, all necessary functions need to be covered. To achieve this every function is encoded by a set of bacteria rather than one single bacterium. In addition, most intestinal strains are able to fulfill different functions depending on their environment. The resulting fragile network requires close interaction of bacteria and a balanced cross-feeding, only established by the presence of the whole ecosystem.
The disruption of this complex network during dysbiosis therefore represents a challenge that can only be addressed with function-based bacterial mixes that respect the nutritional and ecological conditions in the gut.