BDNF and depressive disorder: Spearman’s correlation analysis showed that different microbial communities (Corynebacterium, Faecalibaculum, Enterorhabdus, Desulfovibrio) correlation with differential metabolites (Cholic acid, Deoxycholic acid, etc.)and depression-related biochemical indicators (5-HT, DA, BDNF, IL-6, and TNF-α).