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:

A flavin-based extracellular electron transfer mechanism in diverse Gram-positive bacteria

Nature volume 562, pages 140–144 (2018)Cite this article

Subjects

Abstract

Extracellular electron transfer (EET) describes microbial bioelectrochemical processes in which electrons are transferred from the cytosol to the exterior of the cell1. Mineral-respiring bacteria use elaborate haem-based electron transfer mechanisms2,3,4 but the existence and mechanistic basis of other EETs remain largely unknown. Here we show that the food-borne pathogen Listeria monocytogenes uses a distinctive flavin-based EET mechanism to deliver electrons to iron or an electrode. By performing a forward genetic screen to identify L. monocytogenes mutants with diminished extracellular ferric iron reductase activity, we identified an eight-gene locus that is responsible for EET. This locus encodes a specialized NADH dehydrogenase that segregates EET from aerobic respiration by channelling electrons to a discrete membrane-localized quinone pool. Other proteins facilitate the assembly of an abundant extracellular flavoprotein that, in conjunction with free-molecule flavin shuttles, mediates electron transfer to extracellular acceptors. This system thus establishes a simple electron conduit that is compatible with the single-membrane structure of the Gram-positive cell. Activation of EET supports growth on non-fermentable carbon sources, and an EET mutant exhibited a competitive defect within the mouse gastrointestinal tract. Orthologues of the genes responsible for EET are present in hundreds of species across the Firmicutes phylum, including multiple pathogens and commensal members of the intestinal microbiota, and correlate with EET activity in assayed strains. These findings suggest a greater prevalence of EET-based growth capabilities and establish a previously underappreciated relevance for electrogenic bacteria across diverse environments, including host-associated microbial communities and infectious disease.

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

Access options

Buy this article

  • Purchase on SpringerLink
  • Instant access to full article PDF
Buy now

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

Fig. 1: An uncharacterized genetic locus associated with EET activity.
Fig. 2: A parallel electron transfer pathway segregates EET from aerobic respiration.
Fig. 3: A surface-associated flavoprotein establishes the extracellular component of the EET apparatus.
Fig. 4: EET supports anaerobic growth, confers a competitive advantage in the intestinal lumen, and is active in multiple Firmicutes.

Similar content being viewed by others

Data availability

The datasets generated during the current study are available from the corresponding author on reasonable request.

References

  1. Shi, L. et al. Extracellular electron transfer mechanisms between microorganisms and minerals. Nat. Rev. Microbiol. 14, 651–662 (2016).

    Article  CAS  Google Scholar 

  2. Myers, C. R. & Nealson, K. H. Bacterial manganese reduction and growth with manganese oxide as the sole electron acceptor. Science 240, 1319–1321 (1988).

    Article  ADS  CAS  Google Scholar 

  3. Lovley, D. R. & Phillips, E. J. Novel mode of microbial energy metabolism: organic carbon oxidation coupled to dissimilatory reduction of iron or manganese. Appl. Environ. Microbiol. 54, 1472–1480 (1988).

    CAS  PubMed  PubMed Central  Google Scholar 

  4. Carlson, H. K. et al. Surface multiheme c-type cytochromes from Thermincola potens and implications for respiratory metal reduction by Gram-positive bacteria. Proc. Natl Acad. Sci. USA 109, 1702–1707 (2012).

    Article  ADS  CAS  Google Scholar 

  5. Freitag, N. E., Port, G. C. & Miner, M. D. Listeria monocytogenes – from saprophyte to intracellular pathogen. Nat. Rev. Microbiol. 7, 623–628 (2009).

    Article  CAS  Google Scholar 

  6. Deneer, H. G. & Boychuk, I. Reduction of ferric iron by Listeria monocytogenes and other species of Listeria. Can. J. Microbiol. 39, 480–485 (1993).

    Article  CAS  Google Scholar 

  7. Kim, B. H., Kim, H. J., Hyun, M. S. & Park, D. H. Direct electrode reaction of Fe(III)-reducing bacterium, Shewanella putrefaciens. J. Microbiol. Biotechnol. 9, 127–131 (1999).

    Google Scholar 

  8. Marsili, E., Rollefson, J. B., Baron, D. B., Hozalski, R. M. & Bond, D. R. Microbial biofilm voltammetry: direct electrochemical characterization of catalytic electrode-attached biofilms. Appl. Environ. Microbiol. 74, 7329–7337 (2008).

    Article  CAS  Google Scholar 

  9. Xu, S. J. Y. & El-Naggar, M. Y. Disentangling the roles of free and cytochrome-bound flavins in extracellular electron transport from Shewanella oneidensis MR-1. Electrochim. Acta 198, 49–55 (2016).

    Article  CAS  Google Scholar 

  10. Karpowich, N. K., Song, J. M., Cocco, N. & Wang, D. N. ATP binding drives substrate capture in an ECF transporter by a release-and-catch mechanism. Nat. Struct. Mol. Biol. 22, 565–571 (2015).

    Article  CAS  Google Scholar 

  11. Kerscher, S., Dröse, S., Zickermann, V. & Brandt, U. The three families of respiratory NADH dehydrogenases. Results Probl. Cell Differ. 45, 185–222 (2008).

    Article  CAS  Google Scholar 

  12. Unden, G. & Bongaerts, J. Alternative respiratory pathways of Escherichia coli: energetics and transcriptional regulation in response to electron acceptors. Biochim. Biophys. Acta 1320, 217–234 (1997).

    Article  CAS  Google Scholar 

  13. Bertsova, Y. V. et al. Alternative pyrimidine biosynthesis protein ApbE is a flavin transferase catalyzing covalent attachment of FMN to a threonine residue in bacterial flavoproteins. J. Biol. Chem. 288, 14276–14286 (2013).

    Article  CAS  Google Scholar 

  14. Deka, R. K., Brautigam, C. A., Liu, W. Z., Tomchick, D. R. & Norgard, M. V. Evidence for posttranslational protein flavinylation in the syphilis spirochete Treponema pallidum: structural and biochemical insights from the catalytic core of a periplasmic flavin-trafficking protein. MBio 6, e00519-15 (2015).

    Article  Google Scholar 

  15. Zückert, W. R. Secretion of bacterial lipoproteins: through the cytoplasmic membrane, the periplasm and beyond. Biochim. Biophys. Acta 1843, 1509–1516 (2014).

    Article  Google Scholar 

  16. Glasser, N. R., Saunders, S. H. & Newman, D. K. The colorful world of extracellular electron shuttles. Annu. Rev. Microbiol. 71, 731–751 (2017).

    Article  CAS  Google Scholar 

  17. Brutinel, E. D. & Gralnick, J. A. Shuttling happens: soluble flavin mediators of extracellular electron transfer in Shewanella. Appl. Microbiol. Biotechnol. 93, 41–48 (2012).

    Article  Google Scholar 

  18. Marsili, E. et al. Shewanella secretes flavins that mediate extracellular electron transfer. Proc. Natl Acad. Sci. USA 105, 3968–3973 (2008).

    Article  ADS  CAS  Google Scholar 

  19. von Canstein, H., Ogawa, J., Shimizu, S. & Lloyd, J. R. Secretion of flavins by Shewanella species and their role in extracellular electron transfer. Appl. Environ. Microbiol. 74, 615–623 (2008).

    Article  Google Scholar 

  20. Kotloski, N. J. & Gralnick, J. A. Flavin electron shuttles dominate extracellular electron transfer by Shewanella oneidensis. MBio 4, e00553-12 (2013).

    Article  Google Scholar 

  21. Powers, H. J. Riboflavin (vitamin B-2) and health. Am. J. Clin. Nutr. 77, 1352–1360 (2003).

    Article  CAS  Google Scholar 

  22. Hühner, J., Ingles-Prieto, Á., Neusüß, C., Lämmerhofer, M. & Janovjak, H. Quantification of riboflavin, flavin mononucleotide, and flavin adenine dinucleotide in mammalian model cells by CE with LED-induced fluorescence detection. Electrophoresis 36, 518–525 (2015).

    Article  Google Scholar 

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

    Article  ADS  CAS  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).

    Article  ADS  CAS  Google Scholar 

  25. Slobodkin, A. I. et al. Dissimilatory reduction of Fe(III) by thermophilic bacteria and archaea in deep subsurface petroleum reservoirs of western Siberia. Curr. Microbiol. 39, 99–102 (1999).

    Article  CAS  Google Scholar 

  26. Roh, Y. et al. Isolation and characterization of metal-reducing thermoanaerobacter strains from deep subsurface environments of the Piceance Basin, Colorado. Appl. Environ. Microbiol. 68, 6013–6020 (2002).

    Article  CAS  Google Scholar 

  27. Ogg, C. D. & Patel, B. K. Fervidicola ferrireducens gen. nov., sp. nov., a thermophilic anaerobic bacterium from geothermal waters of the Great Artesian Basin, Australia. Int. J. Syst. Evol. Microbiol. 59, 1100–1107 (2009).

    Article  CAS  Google Scholar 

  28. Ogg, C. D. & Patel, B. K. Thermotalea metallivorans gen. nov., sp. nov., a thermophilic, anaerobic bacterium from the Great Artesian Basin of Australia aquifer. Int. J. Syst. Evol. Microbiol. 59, 964–971 (2009).

    Article  CAS  Google Scholar 

  29. Ogg, C. D., Greene, A. C. & Patel, B. K. Thermovenabulum gondwanense sp. nov., a thermophilic anaerobic Fe(III)-reducing bacterium isolated from microbial mats thriving in a Great Artesian Basin bore runoff channel. Int. J. Syst. Evol. Microbiol. 60, 1079–1084 (2010).

    Article  CAS  Google Scholar 

  30. Ogg, C. D. & Patel, B. K. Fervidicella metallireducens gen. nov., sp. nov., a thermophilic, anaerobic bacterium from geothermal waters. Int. J. Syst. Evol. Microbiol. 60, 1394–1400 (2010).

    Article  CAS  Google Scholar 

  31. Masuda, M., Freguia, S., Wang, Y. F., Tsujimura, S. & Kano, K. Flavins contained in yeast extract are exploited for anodic electron transfer by Lactococcus lactis. Bioelectrochemistry 78, 173–175 (2010).

    Article  CAS  Google Scholar 

  32. Zhang, E., Cai, Y., Luo, Y. & Piao, Z. Riboflavin-shuttled extracellular electron transfer from Enterococcus faecalis to electrodes in microbial fuel cells. Can. J. Microbiol. 60, 753–759 (2014).

    Article  CAS  Google Scholar 

  33. Dong, Y. et al. Orenia metallireducens sp. nov. strain Z6, a novel metal-reducing member of the phylum Firmicutes from the deep subsurface. Appl. Environ. Microbiol. 82, 6440–6453 (2016).

    Article  CAS  Google Scholar 

  34. Keogh, D. et al. Extracellular electron transfer powers Enterococcus faecalis biofilm metabolism. MBio 9, e00626-17 (2018).

    Article  Google Scholar 

  35. Pankratova, G., Leech, D., Gorton, L. & Hederstedt, L. Extracellular electron transfer by the Gram-positive bacterium Enterococcus faecalis. Biochemistry 57, 4597–4603 (2018).

    Article  CAS  Google Scholar 

  36. Pedersen, M. B., Gaudu, P., Lechardeur, D., Petit, M. A. & Gruss, A. Aerobic respiration metabolism in lactic acid bacteria and uses in biotechnology. Annu. Rev. Food Sci. Technol. 3, 37–58 (2012).

    Article  CAS  Google Scholar 

  37. Hodgson, D. A. Generalized transduction of serotype 1/2 and serotype 4b strains of Listeria monocytogenes. Mol. Microbiol. 35, 312–323 (2000).

    Article  CAS  Google Scholar 

  38. Zemansky, J. et al. Development of a mariner-based transposon and identification of Listeria monocytogenes determinants, including the peptidyl-prolyl isomerase PrsA2, that contribute to its hemolytic phenotype. J. Bacteriol. 191, 3950–3964 (2009).

    Article  CAS  Google Scholar 

  39. Whiteley, A. T., Pollock, A. J. & Portnoy, D. A. The PAMP c-di-AMP is essential for Listeria monocytogenes growth in rich but not minimal media due to a toxic increase in (p)ppGpp. Cell Host Microbe 17, 788–798 (2015).

    Article  CAS  Google Scholar 

  40. Xayarath, B., Alonzo, F. III & Freitag, N. E. Identification of a peptide-pheromone that enhances Listeria monocytogenes escape from host cell vacuoles. PLoS Pathog. 11, e1004707 (2015).

    Article  Google Scholar 

  41. Burke, T. P. et al. Listeria monocytogenes is resistant to lysozyme through the regulation, not the acquisition, of cell wall-modifying enzymes. J. Bacteriol. 196, 3756–3767 (2014).

    Article  Google Scholar 

  42. Lovley, D. R. & Phillips, E. J. Organic matter mineralization with reduction of ferric iron in anaerobic sediments. Appl. Environ. Microbiol. 51, 683–689 (1986).

    CAS  PubMed  PubMed Central  Google Scholar 

  43. Light, S. H., Cahoon, L. A., Halavaty, A. S., Freitag, N. E. & Anderson, W. F. Structure to function of an α-glucan metabolic pathway that promotes Listeria monocytogenes pathogenesis. Nat. Microbiol. 2, 16202 (2016).

    Article  CAS  Google Scholar 

  44. Portnoy, D. A., Jacks, P. S. & Hinrichs, D. J. Role of hemolysin for the intracellular growth of Listeria monocytogenes. J. Exp. Med. 167, 1459–1471 (1988).

    Article  CAS  Google Scholar 

  45. Bou Ghanem, E. N. et al. InlA promotes dissemination of Listeria monocytogenes to the mesenteric lymph nodes during food borne infection of mice. PLoS Pathog. 8, e1003015 (2012).

    Article  CAS  Google Scholar 

  46. Becattini, S. et al. Commensal microbes provide first line defense against Listeria monocytogenes infection. J. Exp. Med. 214, 1973–1989 (2017).

    Article  CAS  Google Scholar 

  47. Auerbuch, V., Lenz, L. L. & Portnoy, D. A. Development of a competitive index assay to evaluate the virulence of Listeria monocytogenes actA mutants during primary and secondary infection of mice. Infect. Immun. 69, 5953–5957 (2001).

    Article  CAS  Google Scholar 

  48. Neilson, K. A. et al. Less label, more free: approaches in label-free quantitative mass spectrometry. Proteomics 11, 535–553 (2011).

    Article  CAS  Google Scholar 

  49. Nahnsen, S., Bielow, C., Reinert, K. & Kohlbacher, O. Tools for label-free peptide quantification. Mol. Cell. Proteomics 12, 549–556 (2013).

    Article  CAS  Google Scholar 

  50. Plumb, R. S. et al. UPLC/MSE; a new approach for generating molecular fragment information for biomarker structure elucidation. Rapid Commun. Mass Spectrom. 20, 1989–1994 (2006).

    Article  ADS  CAS  Google Scholar 

  51. Shliaha, P. V., Bond, N. J., Gatto, L. & Lilley, K. S. Effects of traveling wave ion mobility separation on data independent acquisition in proteomics studies. J. Proteome Res. 12, 2323–2339 (2013).

    Article  CAS  Google Scholar 

  52. Altschul, S. F. et al. Gapped BLAST and PSI-BLAST: a new generation of protein database search programs. Nucleic Acids Res. 25, 3389–3402 (1997).

    Article  CAS  Google Scholar 

  53. Larkin, M. A. et al. Clustal W and Clustal X version 2.0. Bioinformatics 23, 2947–2948 (2007).

    Article  CAS  Google Scholar 

  54. Jones, D. T., Taylor, W. R. & Thornton, J. M. The rapid generation of mutation data matrices from protein sequences. Comput. Appl. Biosci. 8, 275–282 (1992).

    CAS  Google Scholar 

  55. Kumar, S., Stecher, G. & Tamura, K. MEGA7: molecular evolutionary genetics analysis version 7.0 for bigger datasets. Mol. Biol. Evol. 33, 1870–1874 (2016).

    Article  CAS  Google Scholar 

Download references

Acknowledgements

We thank G. Chen, J.-D. Sauer, E. Stevens, M. Marco and N. Freitag for providing bacterial strains; H. Carlson, A. Williamson and J. Coates for helpful feedback; and N. Garelis for experimental assistance. Research reported in this publication was supported by funding from the National Institute of Allergy and Infectious Diseases of the National Institutes of Health (F32AI136389 to S.H.L., 1P01 AI063302 to D.A.P., and 1R01 AI27655 to D.A.P.), the Office of Naval Research (N0001417WX01603 to C.M.A.-F.), and the China Scholarship Council (no. 201606090098 to L.S.). A mass spectrometer used in this study was purchased with NIH support (grant 1S10OD020062-01). Work at the Molecular Foundry was supported by the Office of Science, Office of Basic Energy Sciences, of the US Department of Energy under Contract No. DE-AC02-05CH11231.

Reviewer information

Nature thanks N. Freitag, J. Gralnick, K. Nealson and G. Reguera for their contribution to the peer review of this work.

Author information

Authors and Affiliations

  1. Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA, USA

    Samuel H. Light, Rafael Rivera-Lugo, Alexander Louie & Daniel A. Portnoy

  2. Molecular Foundry, Molecular Biophysics and Integrated Bioimaging, and Synthetic Biology Institute, Lawrence Berkeley National Laboratory, Berkeley, CA, USA

    Lin Su, Jose A. Cornejo & Caroline M. Ajo-Franklin

  3. State Key Laboratory of Bioelectronics, School of Biological Science and Medical Engineering, Southeast University, Nanjing, 210018, China

    Lin Su

  4. QB3/Chemistry Mass Spectrometry Facility, University of California, Berkeley, Berkeley, CA, USA

    Anthony T. Iavarone

  5. Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA, USA

    Daniel A. Portnoy

Authors
  1. Samuel H. Light
    View author publications

    You can also search for this author in PubMed Google Scholar

  2. Lin Su
    View author publications

    You can also search for this author in PubMed Google Scholar

  3. Rafael Rivera-Lugo
    View author publications

    You can also search for this author in PubMed Google Scholar

  4. Jose A. Cornejo
    View author publications

    You can also search for this author in PubMed Google Scholar

  5. Alexander Louie
    View author publications

    You can also search for this author in PubMed Google Scholar

  6. Anthony T. Iavarone
    View author publications

    You can also search for this author in PubMed Google Scholar

  7. Caroline M. Ajo-Franklin
    View author publications

    You can also search for this author in PubMed Google Scholar

  8. Daniel A. Portnoy
    View author publications

    You can also search for this author in PubMed Google Scholar

Contributions

S.H.L., A.T.I., C.M.A.-F. and D.A.P. designed the study. S.H.L, L.S. and J.A.C. performed electrochemical experiments. S.H.L. and A.T.I. performed mass spectrometric experiments. S.H.L., A.L. and R.R.-L. performed microbiological and biochemical experiments. S.H.L. and D.A.P. wrote the manuscript.

Corresponding author

Correspondence to Daniel A. Portnoy.

Ethics declarations

Competing interests

D.A.P. has a consulting relationship with and a financial interest in Aduro Biotech; both he and the company stand to benefit from the commercialization of this research.

Additional information

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

Extended data figures and tables

Extended Data Fig. 1 Electrochemical analyses of L. monocytogenes.

a, The double chamber cell used for electrochemical experiments. CE, counter electrode; CEM, cation exchange membrane; RE, reference electrode; WE, working electrode. Inlets and outlets for N2 gas are labelled. b, Cyclic voltammograms of wild-type and ndh2::tn strains of L. monocytogenes. ‘Abiotic’ refers to an uninoculated control. Arrows highlight the initiation of the catalytic wave. Results are representative of three independent experiments.

Source data

Extended Data Fig. 2 EET activity maintains cellular redox homeostasis.

Ratio of NAD+ to NADH in wild-type and ndh2::tn strains supplemented with ferric ammonium citrate under aerobic or microaerophilic conditions. Results from three independent experiments are expressed as mean ± s.e.m. A statistically significant difference between microaerophilic cells incubated with or without iron is indicated; *P = 0.0015, unpaired two-sided t-test.

Source data

Extended Data Fig. 3 Evidence that a distinct menaquinone derivative functions in aerobic respiration.

a, Ferric iron reductase activity of mutants described in Fig. 2 demonstrates that genes essential for growth on aerobic respiration medium are dispensable for EET. Results from three independent experiments are expressed as mean ± s.e.m. b, The L. monocytogenes hep operon. Notably, menG—which encodes demethylmenaquinone transferase (the enzyme that converts demethylmenaquinone to menaquione) (Fig. 2b)—neighbours the hepT and hepS genes, which function in quinone biosynthesis and are essential for aerobic respiration (Fig. 2c).

Source data

Extended Data Fig. 4 Recombinant FmnB FMNylates PplA at two discrete sites.

a, b, Deconvoluted mass spectra from a single experiment of recombinant PplA (a) and recombinant PplA incubated with FAD + FmnB (b). The observed molecular weight change (877 Da) is consistent with two post-translational FMNylations (2 × 438.3 Da) on PplA.

Source data

Extended Data Fig. 5 Proposed role of RibU and FmnA in FAD secretion.

a, Simplified adaptation of a previously proposed model of L. monocytogenes riboflavin uptake through the RibU, EcfT, EcfA and EcfA’ transporter10. According to this model, EcfT, EcfA and EcfA’ couple ATP hydrolysis with conformational changes that result in substrate bound to RibU being released into the cytosol. b, On the basis of protein homology (FmnA shares 50% sequence identity with EcfT) and the expectation that extracellular FAD is required for FmnB to catalyse FMNylation of PplA, we propose that the FmnA interacts with RibU to promote FAD secretion. c, Ferric iron reductase activity of strains incubated with 0.5 mM FAD for 1 h. The ability of exogenous FAD to specifically rescue ferric iron reductase activity in the fmnA::tn and ribU::tn strains is consistent with FmnA and RibU functioning in FAD secretion. Results from three independent experiments are expressed as mean ± s.e.m. Statistically significant differences between untreated and FAD-treated cells are indicated; *P = 0.038, **P < 0.0001, unpaired two-sided t-test.

Source data

Extended Data Fig. 6 Flavin shuttles promote EET activity.

a, Chronoamperometry results from L. monocytogenes-inoculated electrochemical reactors with 1 μM FMN injections at the indicated time points. Results are representative of three independent experiments. b, The effect of flavins on L. monocytogenes (Lm) ferric iron reductase activity with insoluble ferric (hydr)oxide (top) and soluble ferric ammonium citrate (bottom). With insoluble substrate the local iron concentration for most cells is low, whereas with soluble substrate the concentration of iron in the direct vicinity of cells is high (insets). Results from three independent experiments are expressed as mean ± s.e.m.

Source data

Extended Data Fig. 7 EET supports anaerobic growth on ferric iron.

a, Growth following incubation of L. monocytogenes strains on xylitol medium without (left) or with (right) ferric iron under aerobic (top) or anaerobic (bottom) conditions. Results are representative of three independent experiments. Strain labels are coloured based on attributed deficiencies (Fig. 2d) in aerobic respiration (blue) or EET (red). Ndh1 and Ndh2 are probably functionally redundant under aerobic conditions, as a growth phenotype is only observed in the double mutant. Note the visual evidence of ferrous iron production in the agar adjoining anaerobically growing cells. b, CFUs of L. monocytogenes strains anaerobically incubated in xylitol medium without (−) or with (+) ferric supplementation. Results for soluble ferric ammonium citrate (top) and insoluble ferric (hydr)oxide (bottom) are shown. Dashed lines denote the number of cells at the start of the experiment. Results from three independent experiments are expressed as mean ± s.e.m. Statistically significant differences in the ferric iron-supplemented condition are noted; ***P < 0.0001, unpaired two-sided t-test.

Source data

Extended Data Fig. 8 EET genes are dispensable for L. monocytogenes intracellular growth.

a, Mouse bone-marrow-derived macrophages were infected with L. monocytogenes, and CFUs were enumerated at the indicated times. Results from three independent experiments are expressed as mean ± s.e.m. b, L. monocytogenes burdens in mouse organs (n = 5) 48 h after intravenous infection. Representative results from two independent experiments are expressed as median and s.e.

Source data

Extended Data Fig. 9 Identified EET loci are widespread in the Firmicutes phylum.

a, Phylogenetic tree constructed from select Ndh2 homologue sequences. A more comprehensive list of organisms that possess an EET locus is provided in Supplementary Table 3. Labels on the branches refer to the percentage of replicate trees that gave the depicted branch topology in a bootstrap test of 1,000 replicates. b, Distinct EET loci from select genomes are shown. Although the arrangement of genes varies, a locus with genes associated with EET is present in many genomes. Some loci contain ECF transporter ATPase subunits (homologous to those depicted in Extended Data Fig. 5a) that probably function with RibU and FmnA subunits in flavin transport. The dmkA-like gene found in Caldanaerobius fijiensis (and other genomes) lacks homology to dmkA, but is annotated as catalysing the same reaction. The pplA variant in some genomes contains a single FMNylated domain (rather than two) and this property is indicated by a shorter arrow. A few bacteria (including Lactococcus spp.) lack a recognizable locus and distribute genes associated with EET throughout the genome.

Supplementary information

Supplementary Figures

This file contains Supplementary Figure 1: Uncropped gel from Fig. 3c.

Reporting Summary

Supplementary Tables 1-4

This file contains Supplementary Tables 1-4. Supplementary Table 1 provides proteomics evidence of the FMNylation of PplA. Supplementary Table 2 identifies surface-associated proteins in Listeria monocytogenes. Supplementary Table 3 identifies Firmicutes species with homologous EET genes. Supplementary Table 4 contains information about strains used in this study.

Source data

Rights and permissions

Reprints and permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Light, S.H., Su, L., Rivera-Lugo, R. et al. A flavin-based extracellular electron transfer mechanism in diverse Gram-positive bacteria. Nature 562, 140–144 (2018). https://doi.org/10.1038/s41586-018-0498-z

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI: https://doi.org/10.1038/s41586-018-0498-z

Keywords

This article is cited by

Search

Advanced search

Quick links

Nature Briefing Microbiology

Sign up for the Nature Briefing: Microbiology newsletter — what matters in microbiology research, free to your inbox weekly.

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