Mutations in the Ferric Uptake Regulator Gene (fur) Suppress the Bacitracin Sensitivity of a Helicobacter pylori fapH Deletion Mutant

<i>Helicobacter pylori</i> uses a cluster of polar flagella for motility. <i>H. pylori</i> FapH forms a ring-like flagellar motor accessory associated with the outer membrane. A <i>H. pylori</i> Δ<i>fapH</i> mutant displays a motility-dependent sensitivity to bacitracin, an antibiotic that is normally excluded by the outer membrane, which suggests that FapH helps to maintain the integrity of the outer membrane during flagellar rotation. We report here that deletion of the ferric uptake regulator (<i>fur</i>) gene suppressed the bacitracin sensitivity of the <i>H. pylori</i> Δ<i>fapH</i> mutant. Depleting intracellular iron in the <i>H. pylori</i> Δ<i>fapH</i> mutant with the iron chelator 2,2'-dipyridyl similarly suppressed the bacitracin sensitivity of the strain. We postulate the altered expression of Fur-regulated genes as a result of deleting <i>fur</i> or that iron deprivation suppressed the bacitracin sensitivity of the Δ<i>fapH</i> mutant. We also isolated two bacitracin-resistant Δ<i>fapH</i> strains that had a nonsense mutation in <i>lpxF</i>, which encodes a lipid A 4'-phosphatase. Loss of LpxF alters the structure of the lipid A backbone in lipopolysaccharide that stabilizes the outer membrane, which we hypothesize compensated for the loss of FapH by minimizing damage to the membrane resulting from flagellar rotation.