BDNF and depressive disorder: Amuc_1100Δ80 can affect the level of 5-HT and the downstream 5-HTR1A-CREB-BDNF signaling pathway through its interaction with TLR2 and the modulation of the gut microbial composition, leading to a superior antidepressant effect compared to Amuc_1100 in ameliorating CUMS-induced depression in mice (Cheng et al., 2022).