Bacillus cereus cytotoxin K triggers gasdermin D-dependent pyroptosis

Bacillus cereus is well known as a causative agent of foodborne gastrointestinal diseases and systemic non-gastrointestinal diseases. We have recently identified a pathogenic B. cereus (named H2) from a deep-sea cold-seep. H2 possesses the pyroptosis-inducing capacity and contains a number of enterotoxins including cytotoxin K (CytK). In the present work, we examined the cytotoxicity of the CytK of H2 to human macrophages. CytK bound macrophages by interaction with the plasma membrane and caused cellular structure damage. CytK-cell interaction triggered rapid pyroptosis mediated by caspase 1-activated gasdermin D (GSDMD). CytK-induced pyroptosis required NLRP3 inflammasome activation, K⁺ efflux, and intracellular Ca²⁺ accumulation. CytK exhibited apparent binding to several cytomembrane lipids, in particular phosphatidic acid, which proved to be essential to CytK-elicited cell death. Together, these results add new insights into the cytotoxic mechanism of CytK.