Bifidobacterium animalis was grown for 72 h on anoxic BSM broth at 37°C. Afterward, 150 uL of bacterial culture was spread onto medium-sized NGM plates (4 plates) and incubated for 24 h at 37°C in an anaerobic container (BD GasPak™ EZ container systems) prior to worm addition. E. coli OP50 was grown on NGM at normoxic conditions. C. elegans N2 population was synchronized as described above and approximately 150 worms were seeded on either B. animalis or OP50 plates. Plates were incubated for 24 h at 20°C in the anaerobic container. Developmental assay was carried out as previously described.122 (link) In brief, 30 worms per bacterium were put individually onto small UV-killed OP50 plates and incubated for 48 h at 20°C before developmental stage of each worm was visually assessed. Reproductive aging assay was carried out as described previously.123 (link) In brief, after incubation with B. animalis or OP50 the worms were washed with M9 and let to develop until L4 stage on UV-killed OP50 plates at 20°C, normoxia. At this moment 25 randomly picked worms (per condition) were transferred individually onto small-sized UV-killed OP50 plates. Every day the brood size of each worm was determined (sum of eggs and L1s) and parent worm was transferred to new plate until egg laying ceased. These experiments were performed 3 times.