H-NS controls the susceptibility of Escherichia coli to aminoglycosides by interfering its uptake and efflux

H-NS is a histone-like nucleoid-structuring protein that regulates gene expressions, particularly acquired foreign genes, however, little is known about whether H-NS can modulate bacterial susceptibility by regulating its intrinsic genes. The <i>hns</i>-deleted mutant EΔ<i>hns</i>, the <i>hns</i>-complemented strain EΔ<i>hns</i>/p<i>hns</i> and the <i>hns</i>-overexpressed strain E/p<i>hns</i> were derivatives of <i>Escherichia coli</i> ATCC 25922, the susceptibility of which were assessed by the broth microdilution method and time-kill curves assays. We found that the MICs for strain EΔ<i>hns</i> against gentamicin and amikacin were significantly decreased by 8-16 folds in contrast to <i>E. coli</i> ATCC 25922. Further studies displayed that the absence of <i>hns</i> caused damage to the bacterial outer membrane and increased the expression levels of porin-related genes, such as <i>ompC, ompF, ompG</i>, and <i>ompN</i>, thus obviously enhancing aminoglycosides uptake of strain EΔ<i>hns</i>. Meanwhile, <i>hns</i> deletion also led to remarkable inhibition of the efflux pumps activity and decreased expressions of efflux-related genes <i>clbM, acrA, acrB, acrD</i>, and <i>emrE</i>, which reduced the efflux of aminoglycosides. In addition, the activation of glycolysis and electron transport chain, as well as the reduction of Δψ dissipation, could lead to a remarkable increase in proton motive force (PMF), thus further inducing more aminoglycosides uptake by strain EΔ<i>hns</i>. Our findings reveal that H-NS regulates the resistance of <i>E. coli</i> to aminoglycosides by influencing its uptake and efflux, which will enrich our understanding of the mechanism by which H-NS modulates bacterial resistance.