The RNA chaperone Hfq is a novel regulator of catalase expression and hydrogen peroxide-induced oxidative stress response in Listeria monocytogenes EGD-e

The RNA chaperone Hfq plays a pivotal role in many bacteria, acting as a regulator of gene expression and promoting interaction between mRNA-sRNA pairs in Gram-negative bacteria. However, in Gram-positive bacteria this protein is expendable for riboregulation, and the main function of Hfq remains elusive. This work unveils a novel function for Hfq in the oxidative stress response of the human pathogen Listeria monocytogenes, a Gram-positive bacterium responsible for the infectious disease listeriosis. Disruption of hfq gene ( Delta hfq ) results in a hypersensitive phenotype towards hydrogen peroxide (H2O2), in which sub-inhibitory concentrations of this reactive oxygen species (ROS) severely impair growth and viability of L. monocytogenes EGD-e. A Delta hfq- com- plemented strain does not show this phenotype. This Hfq-dependent regulation of oxidative stress seems specific for H2O2, as exposure to superoxides caused no differences. We demonstrate that Hfq has a dual regulatory role in the expression of catalase (kat), the key enzyme involved in H2O2 detoxification. Hfq influences kat transcription under non-stress conditions by modulating the levels of the transcriptional repressor PerR, and also acts post-transcriptionally by stabilizing kat mRNA under H2O2-induced stress. Indeed, enzymatic assays revealed reduced catalase activity in Delta hfq cell extracts, a result unrelated to differences in cellular iron content. Bacterial infection triggers immune cells to produce massive amounts of ROS, like H2O2. We show that inactivation of Hfq increases susceptibility to macrophage killing, connecting Hfq with the stress resistance and virulence of L. monocytogenes EGD-e. Overall, these findings advance the understanding of Hfq function within Gram-positive bacteria, revealing for the first time that Hfq is a novel regulator of catalase expression. This paves the way for the study of yet unknown oxidative stress response pathways regulated by Hfq in other pathogens.