DNA-binding protein from starvation cells traps intracellular free-divalent iron and plays an important role in oxidative stress resistance in Acetobacter pasteurianus NBRC 3283.

Acetobacter pasteurianus accumulates reactive oxygen species (ROS). ROS are produced by electron and oxygen coupling in the electron transport chain in the intracellular environment during the stationary and in the acetic acid over-oxidation phases in the presence of ethanol, thereby exposing cell to oxidative stress. In this study, to reveal the resistance mechanism to oxidative stress in A. pasteurianus, we focused on DNA-binding protein from starvation cells (Dps) and analyzed the function of Dps against oxidative stress. When Dps under the copresence of plasmid DNA was exposed to H2O2 and divalent iron, plasmid DNA fragmentation was suppressed under the presence of Dps; however, DNA binding was not observed, revealing a defensive activity for oxidative damage. In addition, this finding revealed that Dps incorporates a divalent iron intracellularly, forming a ferroxidase center. Moreover, levels of hydroxyl radicals produced by Fenton reaction under the presence of H2O2 and divalent iron were decreased by the addition of Dps, resulting in the suppression of the Fenton reaction. Through fluorescence microscopy using a divalent-iron-specific fluorescent probe, we found that, in dps gene disruptants, the accumulation of the divalent iron increased, and the dps gene disruptants showed higher sensitivity to H2O2 than the wild-type. These result strongly suggested that Dps traps intracellular free-divalent iron and plays an important role in the oxidative stress resistance of A. pasteurianus NBRC 3283 after the acetic acid fermentation phase.

Two-step modulation of ion recognition using a bis(saloph)-macrocyclic host having a 24-crown-8-like cavity.

Precise modulation of cation binding affinity was accomplished by the efficient two-step conversion of a newly synthesized macrocyclic ligand H4L2 having a 24-crown-8-like cavity and two saloph moieties. The conversion of H4L2 into L2Ni2 resulted in a 120-fold enhancement in the binding affinity towards Cs+. The electrochemical reduction of L2Ni2 further enhanced the recognition ability by 3 orders of magnitude.