Integrating multiomics datasets is critical for microbiome research; however, inferring interactions across omics datasets has multiple statistical challenges. We solve this problem by using neural networks (https://github.com/biocore/mmvec) to estimate the conditional probability that each molecule is present given the presence of a specific microorganism. We show with known environmental (desert soil biocrust wetting) and clinical (cystic fibrosis lung) examples, our ability to recover microbe–metabolite relationships, and demonstrate how the method can discover relationships between microbially produced metabolites and inflammatory bowel disease.
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The cystic fibrosis sequencing and metadata data can be found at https://qiita.microbio.me/ under study ID 10863. The corresponding GNPS analysis can be accessed at https://gnps.ucsd.edu/ProteoSAFe/status.jsp?task=34d825dbf4e9466e81d809faf814995b. The biocrust soil data were retrieved from the supplemental section in Swenson et al.30. The HFD murine model case study 16S rRNA data can be found at https://qiita.microbio.me/ under study ID 10856. The HFD murine model case study data are publicly available at https://massive.ucsd.edu/ under MassIVE ID MSV000080918. The GNPS analysis for this study can be accessed at https://gnps.ucsd.edu/ProteoSAFe/status.jsp?task=977d85bba47b4e96bf69872b961b8edd. The IBD data used can be found under https://ibdmdb.org/.
The software implementing the mmvec algorithm can be found under https://github.com/biocore/mmvec. Differential abundance analyses in the HFD study were performed using L2-regularized multinomial regression using software available at https://github.com/biocore/songbird. The software used to build the multiomics network can be found at https://github.com/mortonjt/multiomics_network. Biplots were generated using Emperor47.
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We would like to thank V. Pawlowsky, J. J. Egozcue and S. Holmes for their insights on the geometry of this neural network model. In addition, we would also like to thank N. Bokulich for feedback and contributions on the mmvec software package. T.L.S., M.W.V.G. and T.R.N. acknowledge funding from the Office of Science Early Career Research Program, Office of Biological and Environmental Research of the U.S. Department of Energy under contract number DE-AC02-05CH11231 to Lawrence Berkeley National Laboratory. This study was in part supported by grant P41GM103484 for the Center for Computational Mass Spectrometry and instrument support through National Institutes of Health grants S10RR029121 and R03 CA211211 on reuse of metabolomics data. Y.V.B. is funded by the Janssen Human Microbiome Institute through a collaboration with the Center for Microbiome Innovation. J.T.M. was funded by National Science Foundation grant GRFP DGE-1144086. R.K. and S.J.S. have been funded by Janssen under grant number 20175015 and the Alfred P. Sloan Foundation under grant number G-2017-9838.
Mingxun Wang is the founder of Ometa Labs LLC. The remaining authors declare no competing interests.
Peer review information Lei Tang was the primary editor on this article and managed its editorial process and peer review in collaboration with the rest of the editorial team.
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(a) An illustration of how false negatives can occur - in the absolute abundance data, there is a strong Pearson correlation between the microbes and the metabolites across (n=50 samples). These correlations disappear when considering the corresponding proportions. (b) An illustration of how false positives can occur - in the absolute abundance data, there is no correlation between the dark green molecule and the dark blue microbe (n=50 samples). However, the proportions of the same dataset show that there is a very strong correlation between the dark blue and the dark green molecule.
(a) Absolute abundances and relative abundances of microbes/metabolites observed in an environment over time, with each microbe/metabolite colored according to its rate of increase / decrease (n=30). (b) A scale-invariance comparison of statistical methodologies. Points are colored by the corresponding microbes in the interactions; triangle markers represent increasing metabolites and decreasing metabolites. Mmvec is the only method that remains consistent between the absolute and relative abundances.
(a) Estimates of P. aeruginosa associated molecules between Pearson and the conditional probabilities calculated from the mmvec applied to the cystic fibrosis study dataset. The annotations correspond to level 2 or 3 of the metabolomics standards initiative and may correspond to different isomeric species (n=462 molecules). (b) Ranks of Pearson coefficients and conditional probabilities from the mmvec for the Rhamnolipids (n=462 molecules). (c) Pyochelin proportions vs P. aeruginosa proportions.
Tensorboard visualization of training error and cross-validation error of mmvec on the IBG dataset. Five different runs with differing initialization conditions are shown.
An example of job on the GNPS website with the job description and the downloadable output files from mmvec.
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Morton, J.T., Aksenov, A.A., Nothias, L.F. et al. Learning representations of microbe–metabolite interactions. Nat Methods (2019) doi:10.1038/s41592-019-0616-3