Fig. 1From: Studying microbial functionality within the gut ecosystem by systems biologyThe gut in the focus of meta-omics science. An overview of a main sampling sites and b microbial complexity is given, together with c an overview over the physiology. d The number of the studied hosts and e methods to improve gut health are indicated. All data was retrieved via PubMed searches for the corresponding terms. For the exact search terms, please see Additional file 1Back to article page