The effects of cyanide, azide, and 2-n-Heptyl-4-hydroxy-quinoline-N-oxide (HQNO) on the oxidation of ferrous ion or elemental sulfur with Acidithiobacillus ferrooxidans NASF-1 cells grown in iron-or sulfurmedium were examined. The iron oxidation of both iron-and sulfur-grown cells was strongly inhibited by cyanide and azide, but not by HQNO. Sulfur oxidation was relatively resistant to cyanide and azide, and inhibited by HQNO. Higher sulfide oxidation, ubiquinol dehydrogenase activity, and sulfide:quinone oxidoreductase (SQR) activity were observed in sulfur-grown cells more than in iron-grown cells. Sulfide oxidation in the presence of ubiquinone with the membrane fraction was inhibited by HQNO, but not by cyanide, azide, antimycin A, and myxothiazol. The transcription of three genes, encoding an aa 3 -type cytochrome c oxidase (coxB), a bd-type ubiquinol oxidase (cydA), and an sqr, were measured by real-time reverse transcription polymerase chain reaction. The transcriptional levels of coxB and cydA genes were similar in sulfur-and irongrown cells, but that of sqr was 3-fold higher in sulfurgrown cells than in iron-grown cells. A model is proposed for the oxidation of reduced inorganic sulfur compounds in A. ferrooxidans NASF-1 cells.

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bThiosulfate dehydrogenase is known to play a significant role in thiosulfate oxidation in the acidophilic, obligately chemolithoautotroph, Acidithiobacillus ferrooxidans. Enzyme activity measured using ferricyanide as the electron acceptor was detected in cell extracts of A. ferrooxidans ATCC 23270 grown on tetrathionate or sulfur, but no activity was detected in ferrous iron-grown cells. The enzyme was enriched 63-fold from cell extracts of tetrathionate-grown cells. Maximum enzyme activity (13.8 U mg ؊1 ) was observed at pH 2.5 and 70°C. The end product of the enzyme reaction was tetrathionate. The enzyme reduced neither ubiquinone nor horse heart cytochrome c, which serves as an electron acceptor. A major protein with a molecular mass of ϳ25 kDa was detected in the partially purified preparation. Heme was not detected in the preparation, according to the results of spectroscopic analysis and heme staining. The open reading frame of AFE_0042 was identified by BLAST by using the N-terminal amino acid sequence of the protein. The gene was found within a region that was previously noted for sulfur metabolismrelated gene clustering. The recombinant protein produced in Escherichia coli had a molecular mass of ϳ25 kDa and showed thiosulfate dehydrogenase activity, with maximum enzyme activity (6.5 U mg ؊1 ) observed at pH 2.5 and 50°C.

The CoAl 2 O 4 pigment commonly used for coloring ceramic products was synthesized by microwave hydrothermal processing (M-H), and ink-jet printing with this aqueous pigment ink was performed to decorate porcelain. First, a precursor was prepared by adjusting the solution to pH 12. Then, M-H reaction was applied to this precursor at 240°C for 2 h, yielding particles of CoAl 2 O 4 . In addition, the precursor concentration of the suspension was shown to greatly affect the color tone of the resulting particles. As the precursor concentration increased, the synthesized particles that were bluish-green at lower concentrations took on a darker blue color. The synthesized CoAl 2 O 4 particles were regular octahedrons measuring approximately 70 nm. The particles synthesized by M-H reaction were used to prepare an aqueous suspension, which was then used for printing on tiles by an ink-jet printing system. The synthesized particles were well dispersed in the prepared aqueous suspension, as little sediment was formed in this suspension left for 1 week. The printing system experienced no clogging and the printed image was of good quality.