Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Escherichia coli limits Salmonella Typhimurium infections after diet shifts and fat-mediated microbiota perturbation in mice

Nature Microbiology volume 4, pages 2164–2174 (2019)Cite this article

Subjects

Abstract

The microbiota confers colonization resistance, which blocks Salmonella gut colonization1. As diet affects microbiota composition, we studied whether food composition shifts enhance susceptibility to infection. Shifting mice to diets with reduced fibre or elevated fat content for 24 h boosted Salmonella Typhimurium or Escherichia coli gut colonization and plasmid transfer. Here, we studied the effect of dietary fat. Colonization resistance was restored within 48 h of return to maintenance diet. Salmonella gut colonization was also boosted by two oral doses of oleic acid or bile salts. These pathogen blooms required Salmonella’s AcrAB/TolC-dependent bile resistance. Our data indicate that fat-elicited bile promoted Salmonella gut colonization. Both E. coli and Salmonella show much higher bile resistance than the microbiota. Correspondingly, competitive E. coli can be protective in the fat-challenged gut. Diet shifts and fat-elicited bile promote S. Typhimurium gut infections in mice lacking E. coli in their microbiota. This mouse model may be useful for studying pathogen–microbiota–host interactions, the protective effect of E. coli, to analyse the spread of resistance plasmids and assess the impact of food components on the infection process.

This is a preview of subscription content, access via your institution

Access options

Buy this article

  • Purchase on Springer Link
  • Instant access to full article PDF
Buy now

Prices may be subject to local taxes which are calculated during checkout

Fig. 1: A shift to WD and oleic acid gavage promote S.Tm blooms, enteropathy and plasmid transfer.
Fig. 2: Primary bile salts can explain S.Tm blooms.
Fig. 3: Modelling and experimental data validate that bile resistance promotes S.Tm growth in the fat-exposed gut.
Fig. 4: E. coli limits the S.Tm infection after WD-shift or oleic acid gavage.

Similar content being viewed by others

Data availability

16S rRNA raw reads have been deposited at the European Nucleotide Archive (ENA) with accession no. PRJEB33890. All other data needed to evaluate the conclusions in this Article are presented in the paper or the Supplementary Information. Any additional data can be requested from the corresponding author.

References

  1. Stecher, B., Berry, D. & Loy, A. Colonization resistance and microbial ecophysiology: using gnotobiotic mouse models and single-cell technology to explore the intestinal jungle. FEMS Microbiol. Rev. 37, 793–829 (2013).

    CAS  PubMed  Google Scholar 

  2. David, L. A. et al. Diet rapidly and reproducibly alters the human gut microbiome. Nature 505, 559–563 (2014).

    CAS  Google Scholar 

  3. Desai, M. S. et al. A dietary fiber-deprived gut microbiota degrades the colonic mucus barrier and enhances pathogen susceptibility. Cell 167, 1339–1353 (2016).

    CAS  PubMed  PubMed Central  Google Scholar 

  4. Barthel, M. et al. Pretreatment of mice with streptomycin provides a Salmonella enterica serovar Typhimurium colitis model that allows analysis of both pathogen and host. Infect. Immun. 71, 2839–2858 (2003).

    CAS  PubMed  PubMed Central  Google Scholar 

  5. Brugiroux, S. et al. Genome-guided design of a defined mouse microbiota that confers colonization resistance against Salmonella enterica serovar Typhimurium. Nat. Microbiol. 2, 16215 (2016).

    CAS  PubMed  Google Scholar 

  6. Stecher, B. et al. Gut inflammation can boost horizontal gene transfer between pathogenic and commensal Enterobacteriaceae. Proc. Natl Acad. Sci. USA 109, 1269–1274 (2012).

    CAS  PubMed  Google Scholar 

  7. Arkan, M. C. et al. IKK-β links inflammation to obesity-induced insulin resistance. Nat. Med. 11, 191–198 (2005).

    CAS  PubMed  Google Scholar 

  8. Kim, K. A., Gu, W., Lee, I. A., Joh, E. H. & Kim, D. H. High fat diet-induced gut microbiota exacerbates inflammation and obesity in mice via the TLR4 signaling pathway. PLoS ONE 7, e47713 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  9. Moya-Perez, A., Neef, A. & Sanz, Y. Bifidobacterium pseudocatenulatum CECT 7765 reduces obesity-associated inflammation by restoring the lymphocyte-macrophage balance and gut microbiota structure in high-fat diet-fed mice. PLoS ONE 10, e0126976 (2015).

    PubMed  PubMed Central  Google Scholar 

  10. Hwang, D. H., Kim, J. A. & Lee, J. Y. Mechanisms for the activation of Toll-like receptor 2/4 by saturated fatty acids and inhibition by docosahexaenoic acid. Eur. J. Pharm. 785, 24–35 (2016).

    CAS  Google Scholar 

  11. Stecher, B., Maier, L. & Hardt, W. D. ‘Blooming’ in the gut: how dysbiosis might contribute to pathogen evolution. Nat. Rev. Microbiol. 11, 277–284 (2013).

    CAS  PubMed  Google Scholar 

  12. Reddy, B. S., Mangat, S., Sheinfil, A., Weisburger, J. H. & Wynder, E. L. Effect of type and amount of dietary fat and 1,2-dimethylhydrazine on biliary bile acids, fecal bile acids and neutral sterols in rats. Cancer Res. 37, 2132–2137 (1977).

    CAS  PubMed  Google Scholar 

  13. Reddy, B. S. Diet and excretion of bile acids. Cancer Res. 41, 3766–3768 (1981).

    CAS  PubMed  Google Scholar 

  14. Cummings, J. H. et al. Influence of diets high and low in animal fat on bowel habit, gastrointestinal transit time, fecal microflora, bile acid and fat excretion. J. Clin. Invest. 61, 953–963 (1978).

    CAS  PubMed  PubMed Central  Google Scholar 

  15. Begley, M., Gahan, C. G. & Hill, C. The interaction between bacteria and bile. FEMS Microbiol. Rev. 29, 625–651 (2005).

    CAS  PubMed  Google Scholar 

  16. Islam, K. B. et al. Bile acid is a host factor that regulates the composition of the cecal microbiota in rats. Gastroenterology 141, 1773–1781 (2011).

    CAS  PubMed  Google Scholar 

  17. Urdaneta, V. & Casadesus, J. Interactions between bacteria and bile salts in the gastrointestinal and hepatobiliary tracts. Front. Med. 4, 163 (2017).

    Google Scholar 

  18. MacConkey, A. T. Bile salt media and their advantages in some bacteriological examinations. J. Hyg. 8, 322–334 (1908).

    CAS  PubMed  Google Scholar 

  19. Buckley, A. M. et al. The AcrAB-TolC efflux system of Salmonella enterica serovar Typhimurium plays a role in pathogenesis. Cell. Microbiol. 8, 847–856 (2006).

    CAS  PubMed  Google Scholar 

  20. Nishino, K., Latifi, T. & Groisman, E. A. Virulence and drug resistance roles of multidrug efflux systems of Salmonella enterica serovar Typhimurium. Mol. Microbiol. 59, 126–141 (2006).

    CAS  PubMed  Google Scholar 

  21. Devkota, S. et al. Dietary-fat-induced taurocholic acid promotes pathobiont expansion and colitis in Il10−/− mice. Nature 487, 104–108 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  22. Stecher, B. et al. Salmonella enterica serovar Typhimurium exploits inflammation to compete with the intestinal microbiota. PLoS Biol. 5, 2177–2189 (2007).

    CAS  PubMed  Google Scholar 

  23. Winter, S. E. et al. Gut inflammation provides a respiratory electron acceptor for Salmonella. Nature 467, 426–429 (2010).

    CAS  PubMed  PubMed Central  Google Scholar 

  24. Winter, S. E. et al. Host-derived nitrate boosts growth of E. coli in the inflamed gut. Science 339, 708–711 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  25. Raffatellu, M. et al. Lipocalin-2 resistance confers an advantage to Salmonella enterica serotype Typhimurium for growth and survival in the inflamed intestine. Cell Host Microbe 5, 476–486 (2009).

    CAS  PubMed  PubMed Central  Google Scholar 

  26. Litvak, Y., Byndloss, M. X. & Baumler, A. J. Colonocyte metabolism shapes the gut microbiota. Science 362, eaat9076 (2018).

    PubMed  PubMed Central  Google Scholar 

  27. Miki, T., Goto, R., Fujimoto, M., Okada, N. & Hardt, W. D. The bactericidal lectin RegIIIβ prolongs gut colonization and enteropathy in the streptomycin mouse model for Salmonella diarrhea. Cell Host Microbe 21, 195–207 (2017).

    CAS  PubMed  Google Scholar 

  28. Miki, T., Holst, O. & Hardt, W. D. The bactericidal activity of the C-type lectin RegIIIβ against Gram-negative bacteria involves binding to lipid A. J. Biol. Chem. 287, 34844–34855 (2012).

    CAS  PubMed  PubMed Central  Google Scholar 

  29. Mukherjee, S. et al. Antibacterial membrane attack by a pore-forming intestinal C-type lectin. Nature 505, 103–107 (2014).

    PubMed  Google Scholar 

  30. Lopez, C. A. et al. Phage-mediated acquisition of a type III secreted effector protein boosts growth of Salmonella by nitrate respiration. mBio 3, e00143-12 (2012).

    PubMed  PubMed Central  Google Scholar 

  31. Berg, R. D. The indigenous gastrointestinal microflora. Trends Microbiol. 4, 430–435 (1996).

    CAS  PubMed  Google Scholar 

  32. Piddock, L. J. Multidrug-resistance efflux pumps—not just for resistance. Nat. Rev. Microbiol. 4, 629–636 (2006).

    CAS  PubMed  Google Scholar 

  33. Wotzka, S. Y. et al. Microbiota stability in healthy individuals after single-dose lactulose challenge—a randomized controlled study. PLoS ONE 13, e0206214 (2018).

    PubMed  PubMed Central  Google Scholar 

  34. Litvak, Y. et al. Commensal Enterobacteriaceae protect against Salmonella colonization through oxygen competition. Cell Host Microbe 25, 128–139 (2019).

    CAS  PubMed  Google Scholar 

  35. Sana, T. G. et al. Salmonella Typhimurium utilizes a T6SS-mediated antibacterial weapon to establish in the host gut. Proc. Natl Acad. Sci. USA 113, E5044–E5051 (2016).

    CAS  PubMed  Google Scholar 

  36. Deriu, E. et al. Probiotic bacteria reduce Salmonella Typhimurium intestinal colonization by competing for iron. Cell Host Microbe 14, 26–37 (2013).

    CAS  PubMed  PubMed Central  Google Scholar 

  37. Nedialkova, L. P. et al. Temperate phages promote colicin-dependent fitness of Salmonella enterica serovar Typhimurium. Environ. Microbiol. 18, 1591–1603 (2016).

    CAS  PubMed  Google Scholar 

  38. Conway, T. & Cohen, P. S. Commensal and pathogenic Escherichia coli metabolism in the gut. Microbiol. Spectr. 3, MBP-0006-2014 (2015).

    Google Scholar 

  39. Baucheron, S. et al. AcrAB-TolC directs efflux-mediated multidrug resistance in Salmonella enterica serovar Typhimurium DT104. Antimicrob. Agents Chemother. 48, 3729–3735 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  40. Eaves, D. J., Ricci, V. & Piddock, L. J. Expression of acrB, acrF, acrD, marA and soxS in Salmonella enterica serovar Typhimurium: role in multiple antibiotic resistance. Antimicrob. Agents Chemother. 48, 1145–1150 (2004).

    CAS  PubMed  PubMed Central  Google Scholar 

  41. Urdaneta, V. & Casadesus, J. Adaptation of Salmonella enterica to bile: essential role of AcrAB-mediated efflux. Environ. Microbiol. 20, 1405–1418 (2018).

    CAS  PubMed  Google Scholar 

  42. Theriot, C. M. et al. Antibiotic-induced shifts in the mouse gut microbiome and metabolome increase susceptibility to Clostridium difficile infection. Nat. Commun. 5, 3114 (2014).

    PubMed  PubMed Central  Google Scholar 

  43. Rozwandowicz, M. et al. Plasmids carrying antimicrobial resistance genes in Enterobacteriaceae. J. Antimicrob. Chemother. 73, 1121–1137 (2018).

    CAS  PubMed  Google Scholar 

  44. Hoiseth, S. K. & Stocker, B. A. Aromatic-dependent Salmonella Typhimurium are non-virulent and effective as live vaccines. Nature 291, 238–239 (1981).

    CAS  PubMed  Google Scholar 

  45. Datsenko, K. A. & Wanner, B. L. One-step inactivation of chromosomal genes in Escherichia coli K-12 using PCR products. Proc. Natl Acad. Sci. USA 97, 6640–6645 (2000).

    CAS  Google Scholar 

  46. Grant, A. J. et al. Modelling within-host spatiotemporal dynamics of invasive bacterial disease. PLoS Biol. 6, e74 (2008).

    PubMed  PubMed Central  Google Scholar 

  47. Gil, D. & Bouche, J. P. ColE1-type vectors with fully repressible replication. Gene 105, 17–22 (1991).

    CAS  PubMed  Google Scholar 

  48. Kaiser, P. et al. Cecum lymph node dendritic cells harbor slow-growing bacteria phenotypically tolerant to antibiotic treatment. PLoS Biol. 12, e1001793 (2014).

    PubMed  PubMed Central  Google Scholar 

  49. Moor, K. et al. High-avidity IgA protects the intestine by enchaining growing bacteria. Nature 544, 498–502 (2017).

    CAS  PubMed  Google Scholar 

  50. Sturm, A. et al. The cost of virulence: retarded growth of Salmonella Typhimurium cells expressing type III secretion system 1. PLoS Pathog. 7, e1002143 (2011).

    CAS  PubMed  PubMed Central  Google Scholar 

  51. Li, H. et al. The outer mucus layer hosts a distinct intestinal microbial niche. Nat. Commun. 6, 8292 (2015).

    CAS  PubMed  PubMed Central  Google Scholar 

  52. Apprill, A., McNally, S., Parsons, R. & Weber, L. Minor revision to V4 region SSU rRNA 806R gene primer greatly increases detection of SAR11 bacterioplankton. Aquatic Microbial Ecol. 75, 129–137 (2015).

    Google Scholar 

  53. Parada, A. E., Needham, D. M. & Fuhrman, J. A. Every base matters: assessing small subunit rRNA primers for marine microbiomes with mock communities, time series and global field samples. Environ. Microbiol. 18, 1403–1414 (2016).

    CAS  PubMed  Google Scholar 

  54. Dey, N. et al. Regulators of gut motility revealed by a gnotobiotic model of diet–microbiome interactions related to travel. Cell 163, 95–107 (2015).

    CAS  PubMed  PubMed Central  Google Scholar 

  55. Fuhrer, T., Heer, D., Begemann, B. & Zamboni, N. High-throughput, accurate mass metabolome profiling of cellular extracts by flow injection-time-of-flight mass spectrometry. Anal. Chem. 83, 7074–7080 (2011).

    CAS  PubMed  Google Scholar 

  56. Kanehisa, M. & Goto, S. KEGG: Kyoto Encyclopedia of Genes and Genomes. Nucleic Acids Res. 28, 27–30 (2000).

    CAS  PubMed  PubMed Central  Google Scholar 

  57. Yin, S. et al. Factors affecting separation and detection of bile acids by liquid chromatography coupled with mass spectrometry in negative mode. Anal. Bioanal. Chem. 409, 5533–5545 (2017).

    CAS  PubMed  PubMed Central  Google Scholar 

  58. Wiegand, I., Hilpert, K. & Hancock, R. E. Agar and broth dilution methods to determine the minimal inhibitory concentration (MIC) of antimicrobial substances. Nat. Protoc. 3, 163–175 (2008).

    CAS  PubMed  Google Scholar 

  59. Lambert, R. J. & Pearson, J. Susceptibility testing: accurate and reproducible minimum inhibitory concentration (MIC) and non-inhibitory concentration (NIC) values. J. Appl. Microbiol. 88, 784–790 (2000).

    CAS  PubMed  Google Scholar 

  60. Cremer, J., Arnoldini, M. & Hwa, T. Effect of water flow and chemical environment on microbiota growth and composition in the human colon. Proc. Natl Acad. Sci. USA 114, 6438–6443 (2017).

    CAS  PubMed  Google Scholar 

  61. Vandeputte, D. et al. Quantitative microbiome profiling links gut community variation to microbial load. Nature 551, 507–511 (2017).

    CAS  PubMed  Google Scholar 

  62. Soetaert, K., Petzoldt, T. & Setzer, R. W. Solving differential equations in R: Package deSolve. J. Stat. Softw. 33, 1–25 (2010).

    Google Scholar 

  63. R Core Team R: A Language and Environment for Statistical Computing (R Foundation for Statistical Computing, 2014); https://www.R-project.org/

  64. Letunic, I. & Bork, P. Interactive tree of life (iTOL) v3: an online tool for the display and annotation of phylogenetic and other trees. Nucleic Acids Res. 44, W242–W245 (2016).

    CAS  PubMed  PubMed Central  Google Scholar 

Download references

Acknowledgements

We thank members of the Hardt laboratory and R. Stocker for helpful scientific discussions and the RCHCI staff (especially K. Holzinger, D. Mollenhauer and S. Nowok) for excellent support of our animal work. E.S. is supported by the Swiss National Science Foundation (SNF, Marie Heim-Vögtlin award PMPDP3_158364 and Ambizione award PZ00P3_136742) and the Gebert Rüf ‘Microbials’ programme (GRS-073/17). W.-D.H. is supported by the SNF (310030_153074 and 310030B_173338/1; Sinergia CRSII_154414/1; NRP 72 407240-167121), ETH Zurich (ETH-33 12-2), the Novartis Freenovation Programme and the Promedica Foundation. S.S. is supported by ETH Zurich and the Helmut Horten Foundation. E.B. is supported by a Boehringer Ingelheim Fonds PhD Stipend and E.G. by a grant from the Monique Dornonville de la Cour Foundation. B.S. is supported by the German Research Foundation (STE 1971/4-2 SPP 1656/2) and the German Center for Infection Research (DZIF).

Author information

Author notes

  1. These authors contributed equally: Sandra Y. Wotzka, Markus Kreuzer.

Authors and Affiliations

  1. Institute of Microbiology, D-BIOL, ETH Zürich, Zürich, Switzerland

    Sandra Y. Wotzka, Markus Kreuzer, Markus Arnoldini, Bidong D. Nguyen, Alexander O. Brachmann, Dorothée L. Berthold, Mirjam Zünd, Annika Hausmann, Erik Bakkeren, Daniel Hoces, Ersin Gül, Tamas Dolowschiak, Kathrin Moor, Jörn Piel, Médéric Diard, Shinichi Sunagawa, Emma Slack & Wolf-Dietrich Hardt

  2. European Molecular Biology Laboratory, Heidelberg, Heidelberg, Germany

    Lisa Maier & Athanasios Typas

  3. Max von Pettenkofer Institute, Faculty of Medicine, LMU Munich, Munich, Germany

    Markus Beutler & Bärbel Stecher

  4. Institute of Molecular Systems Biology, D-BIOL, ETH Zürich, Zürich, Switzerland

    Michael Zimmermann, Tobias Fuhrer & Uwe Sauer

  5. Maurice Müller Laboratories, University Clinic for Visceral Surgery and Medicine, University of Bern, Bern, Switzerland

    Andrew J. Macpherson

  6. German Center for Infection Research (DZIF), Munich, Germany

    Bärbel Stecher

Authors
  1. Sandra Y. Wotzka
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Markus Kreuzer
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Lisa Maier
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Markus Arnoldini
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Bidong D. Nguyen
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Alexander O. Brachmann
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Dorothée L. Berthold
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Mirjam Zünd
    View author publications

    You can also search for this author in PubMed Google Scholar

  9. Annika Hausmann
    View author publications

    You can also search for this author in PubMed Google Scholar

  10. Erik Bakkeren
    View author publications

    You can also search for this author in PubMed Google Scholar

  11. Daniel Hoces
    View author publications

    You can also search for this author in PubMed Google Scholar

  12. Ersin Gül
    View author publications

    You can also search for this author in PubMed Google Scholar

  13. Markus Beutler
    View author publications

    You can also search for this author in PubMed Google Scholar

  14. Tamas Dolowschiak
    View author publications

    You can also search for this author in PubMed Google Scholar

  15. Michael Zimmermann
    View author publications

    You can also search for this author in PubMed Google Scholar

  16. Tobias Fuhrer
    View author publications

    You can also search for this author in PubMed Google Scholar

  17. Kathrin Moor
    View author publications

    You can also search for this author in PubMed Google Scholar

  18. Uwe Sauer
    View author publications

    You can also search for this author in PubMed Google Scholar

  19. Athanasios Typas
    View author publications

    You can also search for this author in PubMed Google Scholar

  20. Jörn Piel
    View author publications

    You can also search for this author in PubMed Google Scholar

  21. Médéric Diard
    View author publications

    You can also search for this author in PubMed Google Scholar

  22. Andrew J. Macpherson
    View author publications

    You can also search for this author in PubMed Google Scholar

  23. Bärbel Stecher
    View author publications

    You can also search for this author in PubMed Google Scholar

  24. Shinichi Sunagawa
    View author publications

    You can also search for this author in PubMed Google Scholar

  25. Emma Slack
    View author publications

    You can also search for this author in PubMed Google Scholar

  26. Wolf-Dietrich Hardt
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

S.Y.W. contributed to Figs. 1–3 and Supplementary Figs. 2–5, 7, 8, 10, 11, 16, 18, 22 and 23, B.N. to Supplementary Fig. 24, L.M. and A.T. to Fig. 2e and Supplementary Fig. 12, A.O.B. and J.P. to Fig. 2a, M.A. to Fig. 3a,b and Supplementary Figs. 13–15, D.L.B. to Supplementary Figs. 19 and 21b and Supplementary Tables 4 and 5, M. Zünd and S.S. to Supplementary Figs. 7 and 26, A.H. to Supplementary Fig. 21, E.B. and M.D. to Fig. 1e and Supplementary Fig. 6, K.M. to Fig. 1b–d, M.K. to Fig. 4 and Supplementary Figs. 4, 17, 18g and 25, D.H. and E.S. to Fig. 2d and Supplementary Fig. 23, M.B. and B.S. to Supplementary Fig. 7b, T.D. to Supplementary Fig. 19, M. Zimmermann, T.F. and U.S. to Supplementary Figs. 9 and 18a–b,f and E.G. to Supplementary Fig. 20. A.J.M and B.S. (Oligo mice) performed the experiments and analysed the data. S.Y.W., M.K., B.N., L.M., D.H., E.S. and W.-D.H. designed the experiments. S.Y.W., M.K. and W.-D.H. wrote the manuscript.

Corresponding author

Correspondence to Wolf-Dietrich Hardt.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Methods, Supplementary Discussion, Supplementary Tables 1–6, Supplementary Figs. 1–26 and Supplementary References.

Reporting Summary

Supplementary Data 1

Mass spectrometry data for Supplementary Fig. 9.

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Wotzka, S.Y., Kreuzer, M., Maier, L. et al. Escherichia coli limits Salmonella Typhimurium infections after diet shifts and fat-mediated microbiota perturbation in mice. Nat Microbiol 4, 2164–2174 (2019). https://doi.org/10.1038/s41564-019-0568-5

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41564-019-0568-5

This article is cited by

Search

Advanced search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing