There is increasing knowledge regarding the role of the microbiome in modulating brain and behaviour. Indeed, the actions of microbial metabolites are key for appropriate gut-brain communication in humans. Among these metabolites short-chain fatty acids, tryptophan, and bile acid metabolites/pathways show strong preclinical evidence for involvement in various aspects of brain function and behaviour. With the identification of neuroactive gut-brain modules, new predictive tools can potentially be applied to existing datasets. We identified 278 studies relating to the human microbiota-gut-brain axis which included sequencing data. This spanned across psychiatric and neurological disorders with a small number also focused on normal behavioural development. With a consistent bioinformatics pipeline, thirty-five of these datasets were reanalyzed from publicly available raw sequencing files and the remainder summarized and collated. Among the reanalyzed studies, we uncovered evidence of disease-related alterations in microbial metabolic pathways in Alzheimer’s Disease, schizophrenia, anxiety and depression. Amongst studies that could not be reanalyzed, many sequencing and technical limitations hindered the discovery of specific biomarkers of microbes or metabolites conserved across studies. Future studies are warranted to confirm our findings. We also propose guidelines for future human microbiome analysis to increase reproducibility and consistency within the field.
Copyright © 2021. Published by Elsevier Ltd.