A multicomponent toxin from Bacillus cereus incites inflammation and shapes host outcome via the NLRP3 inflammasome

Abstract

Host recognition of microbial components is essential in mediating an effective immune response. Cytosolic bacteria must secure entry into the host cytoplasm to facilitate replication and, in doing so, liberate microbial ligands that activate cytosolic innate immune sensors and the inflammasome. Here, we identified a multicomponent enterotoxin, haemolysin BL (HBL), that engages activation of the inflammasome. This toxin is highly conserved among the human pathogen Bacillus cereus. The three subunits of HBL bind to the cell membrane in a linear order, forming a lytic pore and inducing activation of the NLRP3 inflammasome, secretion of interleukin-1β and interleukin-18, and pyroptosis. Mechanistically, the HBL-induced pore results in the efflux of potassium and triggers the activation of the NLRP3 inflammasome. Furthermore, HBL-producing B. cereus induces rapid inflammasome-mediated mortality. Pharmacological inhibition of the NLRP3 inflammasome using MCC950 prevents B. cereus-induced lethality. Overall, our results reveal that cytosolic sensing of a toxin is central to the innate immune recognition of infection. Therapeutic modulation of this pathway enhances host protection against deadly bacterial infections.

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Fig. 1: A secreted factor of B. cereus activates the NLRP3 inflammasome.
Fig. 2: The inflammasome-activating factor is highly prevalent in B. cereus isolates and is associated with isolates expressing HBL.
Fig. 3: HBL triggers activation of the NLRP3 inflammasome.
Fig. 4: Recombinant HBL components assemble sequentially to induce activation of the NLRP3 inflammasome.
Fig. 5: HBL induces pores on the host cell membrane.
Fig. 6: The NLRP3 inflammasome mediates lethality induced by B. cereus infection in vivo.

Data availability

The data that support the findings of this study are included in this published article along with its Supplementary Information files, and are available from the corresponding author upon request.

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Acknowledgements

The authors would like to thank V. M. Dixit (Genentech, USA), K. Schroder (Institute of Molecular Bioscience, Australia), P. Broz (University of Lausanne, Switzerland), J. Ng (Westmead Hospital, Australia), A. Rice (The Canberra Hospital, Australia) and J. Bates (Department of Health Queensland, Australia) for reagents. They also thank B. Quah (ANU, Australia), C. Gillespie (ANU, Australia), I. Sastalla (National Institutes of Health, USA), M. Rug (Centre for Advanced Microscopy, ANU, Australia), J. Lee (Centre for Advanced Microscopy, ANU, Australia), C. O’Brien (The Canberra Hospital, Australia) and D. Gordon (ANU, Australia) for assistance. A.M. is supported by a John Curtin School of Medical Research International Ph.D. scholarship. S.H.L. is supported, in part, by the Intramural Program of the National Institute of Allergy and Infectious Diseases, NIH, USA. N.O.K. is supported by a Career Development Fellowship from the Cancer Institute NSW (15/CDF/1-11). S.M.M. is supported by the Australian National University, The Gretel and Gordon Bootes Medical Research Foundation, and the National Health and Medical Research Council of Australia (under Project Grants APP1141504 and APP1146864) and the R.G. Menzies Early Career Fellowship (APP1091544).

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A.M. and S.M.M. conceptualized the study. A.M., S.F., J.A.H., C.N., D.F., I.I.A., J.D.P. and N.O.K. performed the experiments. A.M., S.F., J.A.H., C.N., D.F. and N.O.K. conducted the analyses, and A.M. and S.M.M. wrote the manuscript. S.M.M. acquired the funding, and I.I.A., J.D.P., K.S., E.M., A.A.B.R., G.B., E.M.F. and S.H.L. provided resources and intellectual input. S.M.M. provided overall supervision, and all authors reviewed the manuscript.

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Correspondence to Si Ming Man.

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I.I.A. is Director of Lipotek, a niche biotech company with a focus on liposome technology. I.I.A. and J.D.P. are shareholders of Lipotek. A.A.B.R. is a named inventor on inflammasome inhibitor patents (WO2017140778 and WO2016131098). All other authors have no competing interests.

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Mathur, A., Feng, S., Hayward, J.A. et al. A multicomponent toxin from Bacillus cereus incites inflammation and shapes host outcome via the NLRP3 inflammasome. Nat Microbiol 4, 362–374 (2019). https://doi.org/10.1038/s41564-018-0318-0

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