The Mn 2؉ -oxidizing bacterium Pseudomonas fluorescens GB-1 deposits Mn oxide around the cell. During growth of a culture, the Mn 2؉ -oxidizing activity of the cells first appeared in the early stationary growth phase. It depended on the O 2 concentration in the culture during the late logarithmic growth phase. Maximal activity was observed at an oxygen concentration of 26% saturation. The activity could be recovered in cell extracts and was proportional to the protein concentration in the cell extracts. The specific activity was increased 125-fold by ammonium sulfate precipitation followed by reversed-phase and gel filtration column chromatographies. The activity of the partly purified Mn 2؉ -oxidizing preparation had a pH optimum of circa 7 and a temperature optimum of 35°C and was lost by heating. The Mn 2؉ -oxidizing activity was sensitive to NaN 3 and HgCl 2 . It was inhibited by KCN, EDTA, Tris, and o-phenanthroline. Although most data indicated the involvement of protein in Mn 2؉ oxidation, the activity was slightly stimulated by sodium dodecyl sulfate at a low concentration and by treatment with pronase and V8 protease. By polyacrylamide gel electrophoresis, two Mn 2؉ -oxidizing factors with estimated molecular weights of 180,000 and 250,000 were detected.

The structure of cobalt oxide (CoO) nanoparticles dispersed on rutile TiO (R-TiO) was characterized by X-ray diffraction, UV-vis-NIR diffuse reflectance spectroscopy, high-resolution transmission electron microscopy, X-ray absorption fine-structure spectroscopy, and X-ray photoelectron spectroscopy. The CoO nanoparticles were loaded onto R-TiO by an impregnation method from an aqueous solution containing Co(NO)·6HO followed by heating in air. Modification of the R-TiO with 2.0 wt % Co followed by heating at 423 K for 1 h resulted in the highest photocatalytic activity with good reproducibility. Structural analyses revealed that the activity of this photocatalyst depended strongly on the generation of CoO nanoclusters with an optimal distribution. These nanoclusters are thought to interact with the R-TiO surface, resulting in visible light absorption and active sites for water oxidation.

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