Article in Nature Microbiology of 12 March 2018 describes:
The human body is increasingly seen as a complex ecosystem, home to thousands of microorganisms and their metabolites. The health of this ecosystem hinges on the relationship between the microbes and human cells and tissues, and metabolites are often the key to this relationship.
“Metabolites are vital, but it is often difficult to find out which ones are present at a specific site in the body. There are many different metabolites, and their concentrations can vary widely,” explains research leader Dr. Bas Dutilh from Utrecht University. “Since metabolites are so closely linked to the growth of bacteria, we thought that it might be possible to predict their composition based on the types of bacteria present. The only input we need for that is the abundances of the bacteria and their genes, and progress in the field of metagenomics has made it relatively easy to get those.”