Iron (oxyhydr)oxides are widespread in natural and engineered systems, potent adsorbents of contaminants and a source of energy for iron-reducing bacteria. Microbial reduction of iron (oxyhydr)oxides results in the formation of Fe(II) which can induce the transformation of these iron minerals, typically from less crystalline to more crystalline forms, affecting the biogeochemical cycling of iron and the behavior of any species adsorbed to the iron (oxyhydr)oxides. Factors influencing the transformation rate of the poorly crystalline iron (oxyhydr)oxide, ferrihydrite, to more crystalline forms in the presence of the iron reducing bacterium Shewanella oneidensis MR-1 are investigated under controlled laboratory conditions in this work. In particular, the amount of Fe(II) produced increased the transformation rate while increasing concentrations of the electron donor, lactate, decreased the rate. Using kinetic parameters determined from abiotic controls, the results of transformation experiments in the presence of Shewanella oneidensis were modeled with this exercise revealing that less goethite and more lepidocrocite formed than expected. Conversely, studies using the Shewanella exudate only, containing biogenic Fe(II), displayed rates of transformation that were satisfactorily modeled using these abiotic control kinetic parameters. This result suggests that the physical presence of the microbes is pivotal to the reduction in ferrihydrite transformation rate observed in the biotic experiments relative to the analogous abiotic controls.

Nanohydroxyapatite (n-HA)/zinc oxide (ZnO) complex was synthesized by a direct precipitation method, and the antibacterial capability and antibacterial mechanism of this complex were investigated in this article. Transmission electron microscope (TEM), Fourier transform infrared, X-ray photoelectronic spectroscopy (XPS), and X-ray diffraction (XRD) were used to analyze the materials. In addition, the antibacterial capacity of n-HA/ZnO complex was examined by bacteriolytic plate, inhibition effect, and antibacterial rate assays under light or without light. Furthermore, agarose gel electrophoresis of plasmid DNA (pUC18) was used to study biocidal action of this complex. The results of TEM observation revealed that the complex's rods had a single crystalline obelisk-like hexagonal wurtzite structure and the crystal retained the nanometer size. XRD analysis indicated that the phase of ZnO appeared and the lattice parameters of n-HA and ZnO changed. XPS spectra showed that the bonding energy of Ca, P, and O atoms changed in the complex. The analyses also showed that the two phases of ZnO and n-HA combined closely. Further, the results of the antibacterial test revealed that this complex possessed strong antibacterial capability; the antibacterial rate was 99.45% to S. aureus and 95.65% to E. coli under light, respectively. The antibacterial activity of this complex under light was better than without light, which was attributed to the generation of .OH under light. From the agarose gel electrophoresis, the dissolving solution of this complex could catalyze the cleavage of pUC18.

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