The arms race among microorganisms is a key driver in the evolution of not only the weapons but also defence mechanisms. Many Gram-negative bacteria use the type six secretion system (T6SS) to deliver toxic effectors directly into neighbouring cells. Defence against effectors requires cognate immunity proteins ...
The arms race among microorganisms is a key driver in the evolution of not only the weapons but also defence mechanisms. Many Gram-negative bacteria use the type six secretion system (T6SS) to deliver toxic effectors directly into neighbouring cells. Defence against effectors requires cognate immunity proteins. However, here we show immunity-independent protection mediated by envelope stress responses in Escherichia coli and Vibrio cholerae against a V. cholerae T6SS effector, TseH. We demonstrate that TseH is a PAAR-dependent species-specific effector highly potent against Aeromonas species but not against its V. cholerae immunity mutant or E. coli. A structural analysis reveals TseH is probably a NlpC/P60-family cysteine endopeptidase. We determine that two envelope stress-response pathways, Rcs and BaeSR, protect E. coli from TseH toxicity by mechanisms including capsule synthesis. The two-component system WigKR (VxrAB) is critical for protecting V. cholerae from its own T6SS despite expressing immunity genes. WigR also regulates T6SS expression, suggesting a dual role in attack and defence. This deepens our understanding of how bacteria survive T6SS attacks and suggests that defence against the T6SS represents a major selective pressure driving the evolution of species-specific effectors and protective mechanisms mediated by envelope stress responses and capsule synthesis.
Organizational Affiliation:
State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic and Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, China. tdong@ucalgary.ca.
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