Stress-induced iron-sulfur cluster damage as a conserved trigger of the bacterial stringent response

Pathogenic bacteria rely on the stringent response to adapt to hostile environments encountered within the host. However, the mechanisms by which host-induced stress activates this response remain poorly understood. Here, we identify iron-sulfur (Fe-S) cluster damage as a conserved trigger of the stringent response in major Gram-negative pathogens, including Salmonella enterica, Enterobacter cloacae, and Klebsiella pneumoniae. We demonstrate that Fe-S cluster disruption-triggered by oxidative stress or metal imbalance-limits intracellular pools of sulfur-containing and branched-chain amino acids, thereby activating the (p)ppGpp synthetase RelA. We further show that during Fe-S cluster stress, (p)ppGpp plays a dual role: enhancing bacterial fitness and promoting virulence by upregulating the Salmonella SPI-2 type III secretion system. These findings reveal a conserved mechanism by which pathogenic bacteria integrate host-associated stresses into an adaptive transcriptional response that promotes fitness and virulence, highlighting Fe-S cluster integrity as a central hub for environmental sensing during infection.