ABSTRACT
Phenotypic resistance describes a bacterial population that becomes transiently resistant to an antibiotic without requiring a genetic change. We here investigated the role of the small regulatory RNA (sRNA) RyhB, a key contributor to iron homeostasis, in the phenotypic resistance of Escherichia coli to various classes of antibiotics. We found that RyhB induces resistance to gentamicin, an aminoglycoside that targets the ribosome, when iron is scarce. RyhB induced resistance is due to the inhibition of respiratory complexes Nuo and Sdh activities. These complexes, which contain numerous Fe-S clusters, are crucial for generating a proton motive force (pmf) that allows gentamicin uptake. RyhB directly represses the expression of nuo and sdh operons by binding to their mRNAs, thereby inhibiting their translation. Indirectly, RyhB also inhibits the maturation of Nuo and Sdh by repressing synthesis of the Isc Fe-S biogenesis machinery. Notably, our study identifies nuo as a new direct RyhB target and shows that respiratory complexes activity levels are predictive of the bacterial sensitivity to gentamicin. Altogether, these results unveil a new role for RyhB in the adaptation to antibiotic stress, an unprecedented consequences of its role in iron starvation stress response.
AUTHOR’S SUMMARY Understanding the mechanisms at work behind bacterial antibiotic resistance has become a major health issue in the face of the antibiotics crisis. Here, we show that RyhB, a bacterial small regulatory RNA, induces resistance of Escherichia coli to the antibiotic gentamicin when iron is scarce, an environmental situation prevalent during host-pathogen interactions. This resistance is due to RyhB repression of the synthesis and post-translational maturation of the respiratory complexes Nuo and Sdh. These complexes are crucial in producing the proton motive force that allows uptake of the antibiotics in the cell. Altogether, these data point out to a major role for RyhB in escaping antibacterial action.
