Reduction of iron oxides by Klebsiella pneumoniae L17: Kinetics and surface properties

The kinetics of the reduction dissolution of iron oxides was studied by using Klebsiella pneumoniae L17 in a pH 7.0 bicarbonate buffer. The microbial reduction of various iron oxides was measured in the absence and presence of AQDS (9,10-anthraquinone-2,6-disulfonic acid), and the results of their rates vs. the surface areas of iron oxides suggested that the iron oxide reduction rate by L17 was obviously affected by the surface area but did not completely depend on it especially for hydrous ferric oxide. Increasing the crystalline degree of hematite decreased the rate of iron reduction, indicating that a higher crystalline degree inhibited microbial iron reduction. Increasing the AQDS concentration significantly increased the rate of HFO reduction, which suggested that the addition of AQDS significantly accelerated the microbial reduction of crystalline Fe(III) oxides. From the increased production of AH2DS (2,6-anthrahydroquinone disulfonate) and cell numbers, it can be concluded that the enhancement may be because of the growth in cells and abiotic Fe(III) reduction by AH2DS. X-ray diffraction, Fourier transform infrared spectra and scanning electron microscopy all indicated that secondary minerals (e.g., vivianite (Fe3(PO4)2) and siderite (FeCO3)) were the biogenic Fe(II) solids formed upon the bioreduction of iron oxides.