When the host senses the microbiota's metabolism - the interplay between food and microbiota in C. elegans.

The microbiota plays a major role in metazoan physiology, particularly in the intestinal tract. Nonetheless, its extreme complexity hinders functional studies. Taking advantage of the Caenorhabditis elegans and Escherichia coli model systems, Feng et al. report the physiological effect of purine biosynthesis deficiencies in E. coli-the microbiota in this experimental system-on C. elegans. Mutant E. coli bacteria, particularly those harboring mutations in the purE gene, trigger a stress response in C. elegans. The E. coli purE mutant is defective for the enzyme N⁵-carboxyaminoimidazole ribonucleotide mutase (N⁵-CAIR), suggesting that this intermediate metabolite may play a central role in this microbiota-host interaction.