Microbial communities populate almost every part of the planet, ranging from hot springs to deep oceans, soil environments, and human bodies. Among various microbial habitats, our body is the site of an extraordinarily complex and dynamic ecosystem, often called the human microbiota or microbiome. Advances in technologies have revealed connections between the human microbiota and our health and disorders, such as obesity, diabetes, inflammatory bowel disease, allergy, cancer, and even neurological disorders.

In our body, the most densely populated is the large intestine, wherein microbes survive and grow by consuming diet- derived and host-derived chemical compounds as well as metabolic byproducts excreted by other microbes. Undigested dietary macromolecules (such as fibers) and host-derived substrates are broken down by microbial species, and then the solubilized molecules become available to other members of the community as public goods for uptake. Additionally, inherent microbial activities with importing metabolic resources and exporting metabolic byproducts give rise to competition for metabolic resources and cooperative relations such as cross-feeding of metabolic byproducts, among resident microbes in the gut environment. Furthermore, microbial metabolic byproducts have active roles in our normal human physiology, and sometimes can be toxic to our tissues by impairing their function.

These intricate microbe-microbe and human-microbe interconnections serve the formation of a complex ecological system in the human gut environment. Notwithstanding the importance of individual microbial species, the microbiota dynamics and consequent impact on our body would be largely attributed to the collective activities of numerous microbial species and chemical compounds, thoroughly interlinked by network relationships. This realization calls for a global map of such chemical cross-talk network of the gut microbiota, as an extensive data resource to help unravel the complexity of the gut microbiota and to facilitate a design of intervention strategies for our healthy gut environment.