Iron regulates Bacillus thuringiensis haemolysin hlyII gene expression during insect infection

• B. thuringiensis haemolysin HlyII is a virulence factor responsible for insect death.
• We show that hlyII gene regulation depends on the regulator Fur, independently of HlyIIR.
• We show that hlyII is repressed by iron in vitro and during insect infection.
• HlyII may induce host cell death to allow bacteria to gain access to iron.

Bacillus thuringiensis (Bt) is a spore-forming entomopathogen broadly used in agriculture crop. The haemolysin HlyII is an important Bt virulence factor responsible for insect death. In this work, we focused on the regulation of the hlyII gene throughout the bacterial growth in vitro and in vivo during insect infection. We show that hlyII regulation depends on the global regulator Fur. This regulation occurs independently of HlyIIR, the other known regulator of hlyII gene expression. Moreover, we show that hlyII is highly expressed when iron is depleted in vivo. As HlyII induces haemocyte and macrophage death, which are involved in the sequestration of iron upon infection, HlyII may induce host cell death to allow bacteria to gain access to iron.

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