Abstract
Despite the fundamental role of bacterial strain variation in gut microbiota function1,2,3,4,5,6, the number of unique strains of a species that can stably colonize the human intestine is still unknown for almost all species. Here we determine the strain richness (SR) of common gut species using thousands of sequenced bacterial isolates with paired metagenomes. We show that SR varies across species, is transferable by faecal microbiota transplantation, and is uniquely low in the gut compared with soil and lake environments. Active therapeutic administration of supraphysiologic numbers of strains per species increases recipient SR, which then converges back to the population average after dosing is ceased. Stratifying engraftment outcomes by high or low SR shows that SR predicts microbial addition or replacement in faecal transplants. Together, these results indicate that properties of the gut ecosystem govern the number of strains of each species colonizing the gut and thereby influence strain addition and replacement in faecal microbiota transplantation and defined live biotherapeutic products.
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Data availability
Sequence data files (FASTQ) for all cultured and whole-genome assembled sequences are stored in the SRA under project number PRJNA880610. Previously published whole-genome assembled sequenced can be found under project number PRJNA637878. Sequence data files (FASTQ) for all metagenomic sequencing samples from the US FMT study for rCDI patients can be found under project number PRJNA637878. Sequence data files (FASTQ) for all metagenomic sequencing samples from the Leiden FMT validation cohort for rCDI patients can be found under project number PRJEB44737. Sequence data files for metagenomic sequencing samples from the pooled donor FMT trial for UC patients can be found at PRJEB26357. B. fragilis isolate whole genomes7 that were used for validation can be accessed at project number PRJNA524913. Isolate whole genomes from ref. 46 can be accessed at project number PRJNA544527. Source data for Extended Data Fig. 1g,h are based on source data from Extended Data Fig. 1d–f. Source data for Fig. 2b and Extended Data Fig. 1a,b are available at Zenodo (https://doi.org/10.5281/zenodo.13942097)84. Source data are provided with this paper.
Code availability
The strain-tracking algorithm, Strainer, was published previously8. Code for Strainer can be accessed at https://bitbucket.org/faithj02/strainer-metagenomics/.
Change history
28 January 2025
A Correction to this paper has been published: https://doi.org/10.1038/s41586-024-08566-8
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Acknowledgements
We thank C. Fermin, E. Vazquez and G. N. Escano for gnotobiotic husbandry. This work was supported in part by the staff and resources of the Mount Sinai Gnotobiotic Facility and the Scientific Computing Division at the Icahn School of Medicine at Mount Sinai. This work was supported by the National Institutes of Health grants (nos. NIDDK DK112978, NIDDK DK124133, NIDDK DK123749), an NIH F30 to A.C.-L. (NIDDK DK131862), Crohn’s and Colitis Foundation awards (no. 650451 to V.A.; no. 651867 to J.J.F.; no. 988415 to N.O.K.) and Janssen Research & Development.
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A.C.-L. and J.J.F. wrote the manuscript. A.C.-L., I.M., Z.L. and J.E. performed the microbiology, mouse model and molecular biology experiments on human bacterial isolates. R.L.K., F.E.R., I.M., Z.L., A.C.-L. and J.J.F performed the microbiology and molecular biology experiments on environmental microbes. A.G., A.C.-L., J.J.F. and V.A. performed the US rCDI clinical study and analysis. E.M.T., J.J.K., B.O., J.M.N., R.M., A.R.W., E.C., A.C.-L. and J.J.F. performed the Netherlands rCDI clinical study, data generation and analysis. S.P., N.O.K., C.H., M.A.K., T.J.B., V.A., A.C.-L. and J.J.F. performed the UC FMT clinical study, data generation and analysis. M.C.D., D.H., J.F.C., A.H., J.W., E.S.N.L-S., J.J.F. and A.C.-L., performed the non-FMT human clinical collections, data generation and analysis. All authors read and provided critical feedback and approved the final manuscript.
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J.J.F. is a scientific advisory board member and consultant to Vedanta Biosciences, Inc. A.H., J.W., E.S.N.L.-S. are employees of Janssen Research & Development. B.O., J.M.N., R.M., A.R.W. and E.C. are employees of Vedanta Biosciences. J.K. and E.T. received research grants from Vedanta Biosciences. The remaining authors declare no competing interests.
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Extended data figures and tables
Extended Data Fig. 1 Determination of SRj strain threshold and validation of SRj with deeper sampling of a subset of cultured gut bacterial species.
A, K-mer overlap was calculated for all pairwise combinations of isolates from a species cultured from two unrelated individuals (purple) with no direct microbial transfer between them or an individual’s own microbes from a single timepoint (green). Dotted line shows the threshold of 0.96 k-mer similarity. B, fastANI versus pairwise k-mer overlap for isolates of the same species. Dotted line represents k-mer overlap threshold of 0.96 (k-mer distance of <0.04). C, Comparison of B. fragilis SRij for the individuals in this study and in the study by Zhao et al. D, Preliminary calculation of SRj using genomes isolated from the Broad pipeline (standard pipeline used to create libraries of cultured gut bacteria). For deeper sampling estimates of SRj, we isolated additional genomes from the same species from E, the original human stool sample and F, mouse stool samples from gnotobiotic mice colonized with the same human stool (N = 2-3 mice per microbiota/diet combination) and given unique diets for strain enrichment. Error bars in D–F represent SEM. Comparison of SRj calculated with genomes from the broad pipeline or the broad pipeline plus additional genomes from G, human stool samples or H, human and mouse stool samples. I–L, Rarefaction curves for validation species. Dotted line shows the mean isolates/species for each species (overall mean isolates/species across the dataset was 4.7 isolates as demonstrated in Fig. 1b). M,N, Rarefaction curves for a soil species (M) and lake species (N). **p < 0.01, paired Wilcoxon test, each point represents the average SRj measured from microbiomes of a healthy or disease state. ns: not significant by paired Wilcoxon test. Grey regions on rarefaction curves indicate 95% confidence intervals.
Extended Data Fig. 2 The influence of core genome size and disease state on strain richness.
A, Spearman rank correlation for SRj versus core genome fraction for several genera. B, SRj was compared for 59 species present in both healthy and CD microbiomes. C, SRj was compared for 51 species present in both healthy and UC microbiomes. Each point represents the average SRj of a species as calculated using isolates cultured from healthy microbiomes or isolates cultured from disease microbiomes. Lines in B,C connect the SRj for each shared species between a healthy subject and a subject with IBD. ns: not significant by paired Wilcoxon test.
Extended Data Fig. 3 Metagenomics-quantified SRj correlates with the cultured SRj measured across our cohort.
A, Spearman correlation between donor SRj as measured by metagenomics and SRj from our original cultured cohort (first panel) and differences in SRj between the two groups (second panel). B, Spearman correlation between recipient SRj as measured by metagenomics at week 8 post-FMT and SRj from our original cohort (first panel) and differences in SRj between the two groups (second panel). A,B, Each point represents the average SRj for species. C, Heatmap representing the remaining six donors who donated stool to six different recipients. D, Correlation of SRj across all recipients and all donors in an independent FMT validation cohort (Leiden).
Extended Data Fig. 4 An ecological framework for strain persistence, replacement, or addition based on strain richness.
A, Schematic for FMT experimental design with multi-donor stool batches administered to each recipient. B, Within a species, bacterial strains vary in their engraftment frequency when administered in the context of a multi-donor FMT product. C, Spearman rank correlation between the metagenomics SRj of the individual FOCUS donors with the overall cultured SRj measured across our cohort. D, Expected outcomes for donor strain engraftment based on species SRj.
Supplementary information
Supplementary Tables
Table 1. Characteristics of participants used in this study, including health status and recent antibiotic use. Table 2. Strain genomes, accessions, and donor health status. Table 3. Species frequency and SRj. Table S4 Enrichment of COG categories and COGs in genes associated with SR.
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Chen-Liaw, A., Aggarwala, V., Mogno, I. et al. Gut microbiota strain richness is species specific and affects engraftment. Nature 637, 422–429 (2025). https://doi.org/10.1038/s41586-024-08242-x
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