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Journal Articles

Manganese and arsenic oxidation performance of Bacterium-Yunotaki 86 (BY86) from Hokkaido, Japan, and the bacterium's Phylogeny

Ozaki, Takuo*; Wang, X.*; Onuki, Toshihiko

Geomicrobiology Journal, 30(7), p.559 - 565, 2013/05

 Times Cited Count:4 Percentile:15.24(Environmental Sciences)

The bacterium collected at Yunotaki, Hokkaido, Japan did not oxidized As(III) to As(V) in the absence of Mn. In the presence of Mn, however, As(III) was rapidly oxidized to As(V) on the cell surfaces. A phylogenetical study disclosed that BY86 was most losely related to Bacillus cereus with an identity of 99.90%.

Journal Articles

Association of actinides with microorganisms and clay; Implications for radionuclide migration from waste-repository sites

Onuki, Toshihiko; Kozai, Naofumi; Sakamoto, Fuminori; Ozaki, Takuo; Nankawa, Takuya; Suzuki, Yoshinori; Francis, A. J.*

Geomicrobiology Journal, 27(3), p.225 - 230, 2010/04

 Times Cited Count:15 Percentile:21.04(Environmental Sciences)

The recent research results on the interation of heavy-elements and microorganisms are shown. (1) Adsorption of Pu(IV), Th(IV) and Eu(III)-DFO complexes on bacteria, (2) Biodegradation of Eu(III) in the presence of malic acids.

Journal Articles

Modeling of the interaction of Pu(VI) with the mixture of microorganism and clay

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Nankawa, Takuya; Suzuki, Yoshinori; Francis, A. J.*

Journal of Nuclear Science and Technology, 46(1), p.55 - 59, 2009/01

 Times Cited Count:8 Percentile:53.11(Nuclear Science & Technology)

Model analysis of the transformation of Pu(VI) in a mixture of a common soil bacterium, Bacillus subtilis, and kaolinite clay was carried out. When we assumed in the model analysis that reduction rate of Pu(V) to Pu(IV) was higher on B. subtilis than on kaolinite, the estimated fractions of Pu in the solution and in the mixture, oxidation states of Pu in the solution and in the mixture were in good agreement with the measured ones. On the contrary, assumption that reduction rate of Pu(V) to Pu(IV) was the same on kaolinite as on ${it B. subtilis}$ gave wrong prediction of Pu association with the mixture. These results strongly suggested the electron transfer from the bacteria to Pu(V) on the bacterial cell to be reduced to Pu(IV) during the accumulation of Pu(VI) to the mixture.

Journal Articles

Concurrent transformation of Ce(III) and formation of biogenic manganese oxides

Onuki, Toshihiko; Ozaki, Takuo; Kozai, Naofumi; Nankawa, Takuya; Sakamoto, Fuminori; Sakai, Takuro; Suzuki, Yoshinori; Francis, A. J.*

Chemical Geology, 253(1-2), p.23 - 29, 2008/07

 Times Cited Count:24 Percentile:54.78(Geochemistry & Geophysics)

We examined the changes in the chemical states of Ce(III) during the formation of manganese oxide occasioned by Mn(II)-oxidizing bacteria. The oxidation states of Ce and Mn then were measured by X-ray Absorption Near Edge Structure (XANES). We also determined the elemental distributions in the bacteria and precipitates by Scanning-Proton Induced X-ray Emission (S-PIXE). We found that the precipitation of Ce is preceded by its accumulation by the bacterium, followed by its oxidization to Ce(IV) by the Mn(III, IV)-containing precipitates that the bacteria generate.

Journal Articles

Sorption of U(VI) on the 4-mercaptopyridine self-assembled monolayer

Nankawa, Takuya; Suzuki, Yoshinori; Ozaki, Takuo; Francis, A. J.; Onuki, Toshihiko

Journal of Nuclear Science and Technology, 45(3), p.251 - 256, 2008/03

 Times Cited Count:3 Percentile:25.63(Nuclear Science & Technology)

Sorption of U(VI) on the 4-mercaptopyridine self-assembled-monolayer (4-PyS-SAM) on Au(111) was studied by cyclic voltammetry. Cyclic voltammograms (CV) of the 4-PyS-SAM working electrode was obtained by contact with 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ solution, 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and 50 mM acetic acid solution, or 1 mM UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and 50 mM oxalic acid solution for 6 h at pH 4. Reduction current of uranium(VI) to U(V) was detected in the CV. The CV of the U(VI) associated 4-PyS-SAM after transporting to U(VI) free 0.1 M NaClO4 solution showed that the reduction current was detected in the cases of UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and U(VI)-acetate, but not in the case of U(VI)-oxalate solutions, indicating that U(VI) was adsorbed on the 4-PyS-SAM from the UO$$_{2}$$(NO$$_{3}$$)$$_{2}$$ and U(VI)-acetate solutions, but not from U(VI)-oxalate solution. These results suggests that stability of U(VI)-4-PyS-SAM is not so high that U(VI)-4-PyS-SAM cannot be formed in the presence of 50 mM oxalate.

Journal Articles

Electrochemical studies on uranium in the presence of organic acids

Suzuki, Yoshinori; Nankawa, Takuya; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*; Enokida, Yoichi*; Yamamoto, Ichiro*

Journal of Nuclear Science and Technology, 44(9), p.1227 - 1232, 2007/09

 Times Cited Count:13 Percentile:69.08(Nuclear Science & Technology)

We examined electrochemical redox reactions of UO$$_{2}$$$$^{2+}$$ in organic acid (oxalic, malonic, succinic, adipic, L-malic, and L-tartaric acids) solutions using cyclic voltammetry. A redox reaction of UO$$_{2}$$$$^{2+}$$/UO$$_{2}$$$$^{+}$$ and an oxidation reaction of U(IV) were observed. The peak potentials of the UO$$_{2}$$$$^{2+}$$ reduction showed a good linear relationship with the log of the stability constants of 1:1 UO$$_{2}$$$$^{2+}$$-organic complexes. We also revealed the redox reactions of UO$$_{2}$$$$^{2+}$$ in the presence of malonic or oxalic acids between pH 1 and 6.

Journal Articles

Chemical speciation and association of plutonium with bacteria, kaolinite clay, and their mixture

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Nankawa, Takuya; Suzuki, Yoshinori*; Francis, A. J.

Environmental Science & Technology, 41(9), p.3134 - 3139, 2007/05

 Times Cited Count:28 Percentile:56.67(Engineering, Environmental)

We investigated the interactions of Pu(VI) with Bacillus subtilis, kaolinite clay, and a mixture of the two to determine and delineate the role of the microbes in regulating the environmental mobility of Pu. The amount of Pu sorbed by B. subtilis increased with time, but had not reached equilibrium in 48 h, whereas equilibrium was attained in kaolinite within 8 h. After 48 h, the oxidation state of Pu in the solutions exposed to B. subtilis and the mixture had changed to Pu(V), whereas the oxidation state of Pu associated with B. subtilis and the mixture was Pu(IV). In contrast, there was no change in the oxidation state of Pu in the solution or on kaolinite after exposure to Pu(VI). SEM-EDS analysis indicated that most of the Pu in the mixture was associated with B. subtilis. These results suggest that Pu(IV) is preferably sorbed to bacterial cells in the mixture, and that Pu(VI) is reduced to Pu(V) and Pu(IV).

Journal Articles

Effects of ionic strength on the coordination of Eu(III) and Cm(III) to a Gram-negative bacterium, Paracoccus denitrificans

Ozaki, Takuo; Kimura, Takaumi; Onuki, Toshihiko; Francis, A. J.

Radiochimica Acta, 94(9-11), p.715 - 721, 2006/11

 Times Cited Count:9 Percentile:56.05(Chemistry, Inorganic & Nuclear)

no abstracts in English

Journal Articles

Reduction behavior of uranium in the presence of citric acid

Suzuki, Yoshinori; Nankawa, Takuya; Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.; Tsushima, Satoru*; Enokida, Yoichi*; Yamamoto, Ichiro*

Radiochimica Acta, 94(9-11), p.579 - 583, 2006/11

 Times Cited Count:20 Percentile:81.23(Chemistry, Inorganic & Nuclear)

We examined the reduction behavior of UO$$_{2}$$$$^{2+}$$ in citrate media at pH 2.0-7.0 by column electrodes. At pH 2.0, UO$$_{2}$$$$^{2+}$$ was reduced to U(IV) through a one-step reduction process, while it was reduced to U(IV) through a two-step reduction process at pH 3.0-5.0. The reduction potential of UO$$_{2}$$$$^{2+}$$ shifted to lower values with an increase in pH from 2.0 to 7.0. At pH 6.0 and 7.0, UO$$_{2}$$$$^{2+}$$ was not reduced to U(IV) completely at the electrode potential above -0.8 V. Ultraviolet-visible spectroscopy and speciation calculation of UO$$_{2}$$$$^{2+}$$ in citrate media indicated that uranium existed as a mainly UO$$_{2}$$$$^{2+}$$ at pH 2-3, and a predominant species at pH 3-5 was [(UO$$_{2}$$)$$_{2}$$Cit$$_{2}$$]$$^{2-}$$. At pH 5-7, polymeric complexes were present. These findings suggest that the reduction of UO$$_{2}$$$$^{2+}$$ is more difficult by polymerization of UO$$_{2}$$$$^{2+}$$ with citric acid at higher pHs.

Journal Articles

Association of europium(III), americium(III), and curium(III) with cellulose, chitin, and chitosan

Ozaki, Takuo; Kimura, Takaumi; Onuki, Toshihiko; Kirishima, Akira*; Yoshida, Takahiro*; Isobe, Hiroshi*; Francis, A. J.

Environmental Toxicology and Chemistry, 25(8), p.2051 - 2058, 2006/08

 Times Cited Count:7 Percentile:16.79(Environmental Sciences)

no abstracts in English

Journal Articles

Degradation of Eu(III)-malic acid complexes by $$Pseudomonas fluorescens$$

Nankawa, Takuya; Suzuki, Yoshinori*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*

Journal of Alloys and Compounds, 408-412, p.1329 - 1333, 2006/02

 Times Cited Count:2 Percentile:23.4(Chemistry, Physical)

We studied the biodegradation of Eu(III)-malic acid complexes by $$Pseudomonas fluorescens$$. Ten milimolar Malic acid was degraded in the absence and in the presence of Eu(III) of 0.05, 0.1, and 0.2 mM. The degradation rate of malic acid increased with decreasing the ratios of Eu(III) to malic acid. These results suggest that the toxicity of Eu(III) can be masked through its complexation with malic acid. The degradation of malic acid was followed by the production of unidentified metabolites which were associated with Eu(III). One of the unidentified organic acids was analysed to be pyruvic acid. Our findings suggest that metabolites can influence the environmental behavior of Eu(III) by biologically transformed through subsequent complexation with Eu(III).

Journal Articles

Interactions of rare earth elements with bacteria and organic ligands

Ozaki, Takuo; Suzuki, Yoshinori*; Nankawa, Takuya; Yoshida, Takahiro; Onuki, Toshihiko; Kimura, Takaumi; Francis, A. J.*

Journal of Alloys and Compounds, 408-412, p.1334 - 1338, 2006/02

 Times Cited Count:41 Percentile:87.19(Chemistry, Physical)

We investigated the interactions of Eu(III) with the common soil bacterium Pseudomonas fluorescens and organic ligands, such as malic acid, citric acid, and a siderophore (DFO). Malic acid formed complexes with Eu(III), but degradation of malic acid was observed when the ratio of malic acid to Eu(III) was high. Citric acid formed a stoichiometric complex with Eu(III) that was not degraded by P. fluorescens. Adsorption of Eu(III) from the DFO complex occurred as a free ion dissociated from DFO and not as the Eu(III)-DFO complex. Time-resolved laser-induced fluorescence spectroscopy analysis showed that adsorption of Eu(III) on P. fluorescens was through a multidentate and predominantly inner-spherical coordination.

Journal Articles

Mechanisms of uranium mineralization by the yeast ${it saccharomyces cerevisiae}$

Onuki, Toshihiko; Ozaki, Takuo; Yoshida, Takahiro*; Sakamoto, Fuminori; Kozai, Naofumi; Wakai, Eiichi; Francis, A. J.; Iefuji, Haruyuki*

Geochimica et Cosmochimica Acta, 69(22), p.5307 - 5316, 2005/11

 Times Cited Count:45 Percentile:68.99(Geochemistry & Geophysics)

no abstracts in English

Journal Articles

Interactions of uranium with bacteria and kaolinite clay

Onuki, Toshihiko; Yoshida, Takahiro*; Ozaki, Takuo; Samadfam, M.*; Kozai, Naofumi; Yubuta, Kunio*; Mitsugashira, Toshiaki*; Kasama, Takeshi*; Francis, A. J.*

Chemical Geology, 220(3-4), p.237 - 243, 2005/08

 Times Cited Count:46 Percentile:70.65(Geochemistry & Geophysics)

no abstracts in English

Journal Articles

A Continuous flow system for in-situ XANES measurements of change in oxidation state of Ce(III) to Ce(IV)

Onuki, Toshihiko; Yoshida, Takahiro*; Nankawa, Takuya; Ozaki, Takuo; Kozai, Naofumi; Sakamoto, Fuminori; Suzuki, Yoshinori*; Francis, A. J.*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.65 - 67, 2005/07

no abstracts in English

Journal Articles

Associations of Eu(III) with Gram-Negative Bacteria, $$Alcaligenes faecalis$$, $$Shewanella putrefaciens$$, and $$Paracoccus denitrificans$$

Ozaki, Takuo; Kimura, Takaumi; Onuki, Toshihiko; Francis, A. J.*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.73 - 76, 2005/07

no abstracts in English

Journal Articles

Effect of Eu(III) on the degradation of malic acid by ${it Pseudomonas fluorescens}$ and the subsequent production of pyruvic acid

Nankawa, Takuya; Suzuki, Yoshinori*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.95 - 98, 2005/07

We studied the biodegradation of Eu(III)-malic acid complexes by ${it Pseudomonas fluorescens}$. L-malic acid can be found in the environment and is one of the microbial metabolites which are formed in the TCA cycle. Malic acid was degraded in the absence and in the presence of Eu(III) of 0.05, 0.1, and 0.2 mM. The degradation rate of malic acid increased with decreasing the ratios of Eu(III) to malic acid. These results suggest that the toxicity of Eu(III) can be masked through its complexation with malic acid. The degradation of malic acid was followed by the production of unidentified organic acids which showed higher affinities with Eu(III) than malic acid. Our findings suggest that organic acid with a low chelating ability can influence the environmental behavior of Eu(III) by biologically transformed into the one with a higher chelatingability and through subsequent complexation with Eu(III).

Journal Articles

Adsorption of Th(IV) and Pu(IV) on the surface of ${it Pseudomonas fluorescens}$ and ${it Bacillus subtilis}$ in the presence of desferrioxamine siderophore

Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Francis, A. J.

Journal of Nuclear and Radiochemical Sciences, 6(1), p.77 - 80, 2005/07

Thorium(IV) adsorption on bacterial cells in the presence of DFO was larger than that of Pu(IV) because of the smaller stability of the Th(IV)-DFO complex than that of the Pu(IV)-DFO complex. On the other hand, adsorption of Pu(IV) was larger than that of Fe(III), where in the stability of the Pu(IV)- and Fe(III)-DFO complex is comparable. P. fluorescens showed a higher affinity for Th(IV) and Pu(IV) than B. subtilis, though potentiometric titration of bacterial cells indicated that surfaces of P. fluorescens and B. subtilis cells showed similar proton binding properties.

Journal Articles

Cs accumulation behavior by ${it Pseudomonas fluorescens}$

Nakao, Atsushi*; Yoshida, Takahiro*; Ozaki, Takuo; Onuki, Toshihiko; Funakawa, Shinya*; Kozaki, Takashi*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.107 - 110, 2005/07

Cs accumulation by Pseudomonas fluorescens was examined under conditions of growth and resting to elucidate the interaction between Cs and bacteria. In the growth condition, P. fluorescens did not accumulate Cs irrespective of the presence of K. In the resting condition, the cells quickly adsorbed approximately 5 $$mu$$mol Cs/gcell dry-weight and subsequently released approximately 90 % of the adsorbed Cs with 1 M CH$$_{3}$$COONH$$_{4}$$. The amount of Cs adsorption by cells of P. fluorescens varied with changing pH and ionic strength of the solution. These results indicate that Cs accumulation by P. fluorescens occurs mainly by reversible adsorption on the cell walls, but not by intracellular accumulation under nutrient conditions.

Journal Articles

Accumulation of Cu and its oxidation state in ${it Tremolecia atrata}$ (rusty-rock lichen) mycobiont

Fujii, Hiromitsu*; Hara, Kojiro*; Komine, Masashi*; Ozaki, Takuo; Onuki, Toshihiko; Yamamoto, Yoshikazu*

Journal of Nuclear and Radiochemical Sciences, 6(1), p.115 - 118, 2005/07

We studied the association of a Cu tolerant mycobiont, Tremolecia atrata (rusty-rock lichen) with Cu. T. atrata mycobiont cell aggregates, which grew into a sperical shape, rapidly absorbed Cu into their inner and outer parts. The EDS/SEM study showed that Cu was more highly accumulated in the inner part than the outer part of the aggregates. The XANES study revealed that the Cu absorbed by the T. atrata mycobiont was both monovalent and divalent. These results suggested that the T. atrata mycobiont's high tolerance to Cu is attributable to its ability to store Cu(I) inside the cytoplasm and to adsorb Cu(II) on the cell wall.

53 (Records 1-20 displayed on this page)