Letter | Published:

Conditional toxicity and synergy drive diversity among antibacterial effectors

Nature Microbiologyvolume 3pages440446 (2018) | Download Citation

Abstract

Bacteria in polymicrobial habitats contend with a persistent barrage of competitors, often under rapidly changing environmental conditions1. The direct antagonism of competitor cells is thus an important bacterial survival strategy2. Towards this end, many bacterial species employ an arsenal of antimicrobial effectors with multiple activities; however, the benefits conferred by the simultaneous deployment of diverse toxins are unknown. Here we show that the multiple effectors delivered to competitor bacteria by the type VI secretion system (T6SS) of Pseudomonas aeruginosa display conditional efficacy and act synergistically. One of these effectors, Tse4, is most active in high-salinity environments and synergizes with effectors that degrade the cell wall or inactivate intracellular electron carriers. We find Tse4 synergizes with these disparate mechanisms by forming pores that disrupt the ΔΨ component of the proton motive force. Our results provide evidence that the concomitant delivery of a cocktail of effectors serves as a bet-hedging strategy to promote bacterial competitiveness in the face of unpredictable and variable environmental conditions.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Additional information

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

References

  1. 1.

    Stubbendieck, R. M. & Straight, P. D. Multifaceted interfaces of bacterial competition. J. Bacteriol. 198, 2145–2155 (2016).

  2. 2.

    Hibbing, M. E., Fuqua, C., Parsek, M. R. & Peterson, S. B. Bacterial competition: surviving and thriving in the microbial jungle. Nat. Rev. Microbiol. 8, 15–25 (2010).

  3. 3.

    Hood, R. D., Peterson, S. B. & Mougous, J. D. From striking out to striking gold: discovering that type VI secretion targets bacteria. Cell Host Microbe 21, 286–289 (2017).

  4. 4.

    Hood, R. D. et al. A type VI secretion system of Pseudomonas aeruginosa targets a toxin to bacteria. Cell Host Microbe 7, 25–37 (2010).

  5. 5.

    Hachani, A., Wood, T. E. & Filloux, A. Type VI secretion and anti-host effectors. Curr. Opin. Microbiol. 29, 81–93 (2016).

  6. 6.

    Pukatzki, S., Ma, A. T., Revel, A. T., Sturtevant, D. & Mekalanos, J. J. Type VI secretion system translocates a phage tail spike-like protein into target cells where it cross-links actin. Proc. Natl Acad. Sci. USA 104, 15508–15513 (2007).

  7. 7.

    Alcoforado Diniz, J., Liu, Y. C. & Coulthurst, S. J. Molecular weaponry: diverse effectors delivered by the type VI secretion system. Cell. Microbiol. 17, 1742–1751 (2015).

  8. 8.

    Russell, A. B., Peterson, S. B. & Mougous, J. D. Type VI secretion system effectors: poisons with a purpose. Nat. Rev. Microbiol. 12, 137–148 (2014).

  9. 9.

    Russell, A. B. et al. Type VI secretion delivers bacteriolytic effectors to target cells. Nature 475, 343–347 (2011).

  10. 10.

    Russell, A. B. et al. Diverse type VI secretion phospholipases are functionally plastic antibacterial effectors. Nature 496, 508–512 (2013).

  11. 11.

    Whitney, J. C. et al. An interbacterial NAD(P)+ glycohydrolase toxin requires elongation factor Tu for delivery to target cells. Cell 163, 607–619 (2015).

  12. 12.

    Durand, E., Cambillau, C., Cascales, E. & Journet, L. VgrG, Tae, Tle, and beyond: the versatile arsenal of type VI secretion effectors. Trends Microbiol. 22, 498–507 (2014).

  13. 13.

    Fischbach, M. A. Combination therapies for combating antimicrobial resistance. Curr. Opin. Microbiol. 14, 519–523 (2011).

  14. 14.

    Goodman, A. L. et al. A signaling network reciprocally regulates genes associated with acute infection and chronic persistence in Pseudomonas aeruginosa. Dev. Cell 7, 745–754 (2004).

  15. 15.

    Leroux, M. et al. Quantitative single-cell characterization of bacterial interactions reveals type VI secretion is a double-edged sword. Proc. Natl Acad. Sci. USA 109, 19804–19809 (2012).

  16. 16.

    Whitney, J. C. et al. Genetically distinct pathways guide effector export through the type VI secretion system. Mol. Microbiol. 92, 529–542 (2014).

  17. 17.

    Casabona, M. G., Vandenbrouck, Y., Attree, I. & Coute, Y. Proteomic characterization of Pseudomonas aeruginosa PAO1 inner membrane. Proteomics 13, 2419–2423 (2013).

  18. 18.

    Kim, S. et al. Transmembrane glycine zippers: physiological and pathological roles in membrane proteins. Proc. Natl Acad. Sci. USA 102, 14278–14283 (2005).

  19. 19.

    Hoffman, J. F. & Laris, P. C. Determination of membrane potentials in human and Amphiuma red blood cells by means of fluorescent probe. J. Physiol. 239, 519–552 (1974).

  20. 20.

    Mahon, M. J. pHluorin2: an enhanced, ratiometric, pH-sensitive green florescent protein. Adv. Biosci. Biotechnol. 2, 132–137 (2011).

  21. 21.

    Rice, K. C. & Bayles, K. W. Death’s toolbox: examining the molecular components of bacterial programmed cell death. Mol. Microbiol 50, 729–738 (2003).

  22. 22.

    Baym, M., Stone, L. K. & Kishony, R. Multidrug evolutionary strategies to reverse antibiotic resistance. Science 351, aad3292 (2016).

  23. 23.

    Stover, C. K. et al. Complete genome sequence of Pseudomonas aeruginosa PA01, an opportunistic pathogen. Nature 406, 959–964 (2000).

  24. 24.

    Hoang, T. T., Kutchma, A. J., Becher, A. & Schweizer, H. P. Integration-proficient plasmids for Pseudomonas aeruginosa: site-specific integration and use for engineering of reporter and expression strains. Plasmid 43, 59–72 (2000).

  25. 25.

    Kulasekara, B. R. et al. c-di-GMP heterogeneity is generated by the chemotaxis machinery to regulate flagellar motility. eLife 2, e01402 (2013).

  26. 26.

    Ma, L. S., Hachani, A., Lin, J. S., Filloux, A. & Lai, E. M. Agrobacterium tumefaciens deploys a superfamily of type VI secretion DNase effectors as weapons for interbacterial competition in planta. Cell Host Microbe 16, 94–104 (2014).

  27. 27.

    Miyata, S. T., Unterweger, D., Rudko, S. P. & Pukatzki, S. Dual expression profile of type VI secretion system immunity genes protects pandemic Vibrio cholerae. PLoS Pathog. 9, e1003752 (2013).

  28. 28.

    Russell, A. B. et al. A widespread bacterial type VI secretion effector superfamily identified using a heuristic approach. Cell Host Microbe 11, 538–549 (2012).

  29. 29.

    Whitney, J. C. et al. Identification, structure, and function of a novel type VI secretion peptidoglycan glycoside hydrolase effector-immunity pair. J. Biol. Chem. 288, 26616–26624 (2013).

  30. 30.

    Rietsch, A., Vallet-Gely, I., Dove, S. L. & Mekalanos, J. J. ExsE, a secreted regulator of type III secretion genes in Pseudomonas aeruginosa. Proc. Natl Acad. Sci. USA 102, 8006–8011 (2005).

  31. 31.

    Silverman, J. M. et al. Separate inputs modulate phosphorylation-dependent and -independent type VI secretion activation. Mol. Microbiol. 82, 1277–1290 (2011).

  32. 32.

    Mougous, J. D. et al. A virulence locus of Pseudomonas aeruginosa encodes a protein secretion apparatus. Science 312, 1526–1530 (2006).

Download references

Acknowledgements

We thank D. Raible for providing pHluorin2 DNA, D. Walker for pyocin S5, the UW Cystic Fibrosis Research Development Program for sequencing, A. Roehrich for ICP-OES training, Tamir Gonen, B. Krantz, K. Ghosal and D. Das for assistance with Tse4 biochemical analysis, T. Kinkel and D. Prunkard for flow cytometry protocol development and analysis, R. Siehnel for assistance with barcode sequences, S. Dove for critical reading of the manuscript, and members of the Mougous laboratory for helpful discussions. This work was funded by the NIH (R01-AI080609 to JDM) and the Defense Threat Reduction Agency (HDTRA1-13-1-0014 to J.D.M.). K.D.L. was supported by the UW Cellular and Molecular Biology Training Grant (T32GM007270), and J.D.M. holds an Investigator in the Pathogenesis of Infectious Disease Award from the Burroughs Wellcome Fund and is an HHMI Investigator.

Author information

Affiliations

  1. Department of Microbiology, University of Washington, Seattle, WA, USA

    • Kaitlyn D. LaCourse
    • , S. Brook Peterson
    • , Hemantha D. Kulasekara
    • , Matthew C. Radey
    • , Jungyun Kim
    •  & Joseph D. Mougous
  2. Howard Hughes Medical Institute, University of Washington, Seattle, WA, USA

    • Joseph D. Mougous

Authors

  1. Search for Kaitlyn D. LaCourse in:

  2. Search for S. Brook Peterson in:

  3. Search for Hemantha D. Kulasekara in:

  4. Search for Matthew C. Radey in:

  5. Search for Jungyun Kim in:

  6. Search for Joseph D. Mougous in:

Contributions

K.D.L., S.B.P., H.D.K. and J.D.M. designed the study. K.D.L., S.B.P., H.D.K, M.C.R., R.K. and J.D.M. performed experiments, and K.D.L., S.B.P., H.D.K., M.C.R. and J.D.M analysed data. K.D.L., S.B.P., and J.D.M. wrote the manuscript.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Joseph D. Mougous.

Supplementary information

  1. Supplementary Information

    Supplementary Figures 1–5 and Supplementary Tables 1–4.

  2. Life Sciences Reporting Summary

  3. Supplementary Table 1

    Effector repertoires of T6SS-containing Proteobacteria.

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/s41564-018-0113-y

Further reading