Shotgun metagenomics reveals both taxonomic and tryptophan pathway differences of gut microbiota in major depressive disorder patients

Bacteroidetes abundance was strongly reduced and Actinobacteria was significantly increased in MDD patients compared to healthy controls.

• MDD patients showed increased levels of Bifidobacterium, a common probiotic.
• Four specific gene functions related to the microbial tryptophan biosynthesis pathway were significantly lower in the MDD group.
• A negative correlation was observed between one of the gene functions and depression severity as measured by HAMD scores.
• Classification based on gut microbiota at the genus level achieved a high accuracy, with an area under the receiver operating characteristic curve of 0.890.

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