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Conditional toxicity and synergy drive diversity among antibacterial effectors

Nature Microbiology volume 3, pages 440–446 (2018)Cite this article

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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.

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Fig. 1: Diverse species of Gram-negative bacteria encode multiple T6SS effectors with distinct biochemical activities.
Fig. 2: PAEE reveals that environmental conditions influence the potency of T6SS effectors.
Fig. 3: Environmental conditions and effector activities influence synergy between T6SS effectors.
Fig. 4: A synergistic T6SS effector of previously unknown function introduces ion permeability.

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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.

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Authors and 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

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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.

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Correspondence to Joseph D. Mougous.

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Supplementary Information

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

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Supplementary Table 1

Effector repertoires of T6SS-containing Proteobacteria.

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LaCourse, K.D., Peterson, S.B., Kulasekara, H.D. et al. Conditional toxicity and synergy drive diversity among antibacterial effectors. Nat Microbiol 3, 440–446 (2018). https://doi.org/10.1038/s41564-018-0113-y

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