Probiotics are live microorganisms that have beneficial effects on host health, including extended lifespan, when they are administered or present in adequate quantities. However, the mechanisms by which probiotics stimulate host longevity remain unclear and very poorly understood. In a recent study (Nat. Commun. 8, 14332 (2017) doi: 10.1038/ncomms14332), we used the spore-forming pro biotic bacterium Bacillus subtilis and the model organism Caenorhabditis elegans to study the mechanism by which a probiotic bacterium affects host longevity. We found that biofilm-proficient B. subtilis colonized the C. elegans gut and extended the worm lifespan significantly longer than did biofilm-deficient isogenic strains. In addition to biofilm proficiency, the quorum-sensing pentapeptide CSF and nitric oxide (NO) represent the entire B. subtilis rep ertoire responsible for the extended longevity of C. ele gans. B. subtilis grown under biofilm-supporting condi tions synthesized higher levels of NO and CSF than under planktonic growth conditions, emphasizing the key role of the biofilm in slowing host aging. Significantly, the pro longevity effect of B. subtilis was primarily due to a downregulation of the insulin-like signaling system that precisely is a key partaker in the healthy longevity of hu man centenarians. These findings open the possibility to test if the regular consumption of B. subtilis incorporated in foods and beverages could significantly extend human life expectancy and contribute to stop the development of age-related diseases.