Kazuhito Itoh

Shimane University, Matsu, Shimane Prefecture, Japan

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Publications (24)37.95 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Background and aims Bradyrhizobium japonicum and Bradyrhizobium elkanii dominated soybean nodules in temperate and subtropical regions in Nepal, respectively, in our previous study. The aims of this study were to reveal the effects of temperature on the nodulation dominancy of B. japonicum and B. elkanii and to clarify the relationship between the effects of temperature and the climate-dependent distribution of Bradyrhizobium species. Methods A laboratory competition experiment was conducted between B. japonicum and B. elkanii strains isolated from the same temperate location in Nepal. A mixture of each strain was inoculated into sterilized vermiculite with or without soybean seeds, and inoculated samples were incubated at 33/27 (day/night) and 23/17 °C. Relative populations in the non-rhizosphere, rhizosphere, and nodules were determined by competitive PCR using specific primers for each strain at 0, 1, 2, and 4 weeks after inoculation. Results Both separately inoculated B. japonicum and B. elkanii strains formed nodules at both temperatures. Under competitive conditions, B. japonicum strains dominated at low temperature; however, at high temperature, both strains achieved co-nodulation in 1 week, with B. elkanii dominating after 2 weeks. The relative populations of both strains were similar in the non-rhizosphere and rhizosphere at low temperature, but B. elkanii strains dominated in these regions at high temperature. Conclusions The domination of B. japonicum strains in nodules at the low temperature appeared to be due to preferential infection, while the domination of B. elkanii strains at high temperature appeared to be due to the higher population of B. elkanii in the non-rhizosphere and rhizosphere, in addition to its domination in nodules after co-nodulation. The effects of temperature on the competition between B. japonicum and B. elkanii strains were remarkable and corresponded with the distribution of bradyrhizobial species in Nepal.
    Plant and Soil 01/2014; · 3.24 Impact Factor
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    ABSTRACT: Background and Aims This study was conducted to reveal the genetic diversity of common bean (Phaseolus vulgaris L.) nodulating rhizobia in various agroecological regions in Nepal. Method A total of 63 strains were isolated from common bean grown in the soils collected from seven bean fields in Nepal and characterized based on the partial sequences of 16S–23S internal transcribed spacer (ITS) regions, 16S rDNA, nodC, and nifH. Symbiotic properties of some representative strains with host plants were examined to elucidate their characteristics in relation to genotype and their origin. Results The isolated strains belonged to Rhizobium leguminosarum, Rhizobium etli, Rhizobium phaseoli, and one unknown Rhizobium lineage, all belonging to a common symbiovar (sv.) phaseoli. Nine ITS genotypes were detected mainly corresponding to a single site, including a dominant group at three sites harboring highly diverse multiple ITS sequences. Three symbiotic genotypes corresponded to a geographical region, not to the ribosomal DNA group, suggesting horizontal transfer of symbiotic genes separately in each region. Great differences in nitrogenase activity and nodule forming ability among the strains irrespective of their species and origin were observed. Conclusions Nepalese Himalaya harbor phylogenetically highly diverse and site-specific strains of common bean rhizobia, some of which could have high potential of symbiotic nitrogen fixation.
    Plant and Soil 01/2013; 368(1-2). · 3.24 Impact Factor
  • Shohei Hayashi, Kazuhito Itoh, Kousuke Suyama
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    ABSTRACT: The cyanobacterium Synechococcus leopoliensis CCAP1405/1 does not grow on common solid media made of agar, agarose HT, noble agar, gelrite and gelatin, although it grows in liquid media with the same components. The inoculation of S. leopoliensis CCAP1405/1 at a high initial cell density allowed it to grow on the agar media, and co-inoculation with one of the heterotrophic bacterial strains belonging to a wide range of phylogeny, showed the same effects even at a low initial cell density of S. leopoliensis CCAP1405/1. The addition of thiosulfate and high concentrations of vitamin B(12), biotin and thiamine also supported growth on solid media, but catalase had no effect. On inorganic solid media, the autotrophic cyanobacterial strain supported the growth of heterotrophic bacteria, suggesting mutual interaction.
    Microbes and Environments 06/2011; 26(2):120-7. · 2.44 Impact Factor
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    Munir Mohammad, Kazuhito Itoh
    01/2011; , ISBN: 978-953-307-476-4
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    ABSTRACT: Due to the high importance of biofilms on river ecosystems, assessment of pesticides' adverse effects is necessary but is impaired by high variability and poor reproducibility of both natural biofilms and those developed in the laboratory. We constructed a model biofilm to evaluate the effects of pesticides, consisting in cultured microbial strains, Pedobacter sp. 7-11, Aquaspirillum sp. T-5, Stenotrophomonas sp. 3-7, Achnanthes minutissima N71, Nitzschia palea N489, and/or Cyclotella meneghiniana N803. Microbial cell numbers, esterase activity, chlorophyll-a content, and the community structure of the model biofilm were examined and found to be useful as biological factors for evaluating the pesticide effects. The model biofilm was formed through the cooperative interaction of bacteria and diatoms, and a preliminary experiment using the herbicide atrazine, which inhibits diatom growth, indicated that the adverse effect on diatoms inhibited indirectly the bacterial growth and activity and, thus, the formation of the model biofilm. Toxicological tests using model biofilms could be useful for evaluating the pesticide effects and complementary to studies on actual river biofilms.
    Archives of Environmental Contamination and Toxicology 01/2011; 60(1):44-56. · 2.01 Impact Factor
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    ABSTRACT: Dechlorination of all mono- and dichlorophenol isomers in anaerobic sediment samples of estuarine Lake Shinji and Lake Nakaumi was examined to characterize the chlorophenol-dechlorinating microbial communities in the environments with different salinity levels. Dechlorination was observed only in 2-chlorophenol (2-CP), 3-chlorophenol (3-CP) and 2,6-dichlorophenol (2,6-DCP), and in 2-CP and 2,6-DCP in the Lake Shinji and Nakaumi sediment, respectively. In the sediment of Lake Shinji, the highest activity was observed without adding sodium chloride and sulfate, whereas in the Lake Nakaumi sediment, the highest activity was at 0.7 % of sodium chloride and 6.0 mM of sodium sulfate. The chlorophenols were degraded to benzoate via phenol in both sediments under methanogenic conditions. Benzoate then disappeared from the cultures. All microbial consortia enriched with each monochlorophenol dechlorinated 2-CP, but showed different substrate specificities for dichlorophenols as follows: 2-CP-enriched consortium dechlorinated 2,3-dichlorophenol and 2,6-DCP, 3-CP-enriched consortium dechlorinated all dichlorophenol isomers, and 4-chlorophenol-enriched consortium dechlorinated 2,4-dichlorophenol and 2,6-DCP. Maintenance of the population by halorespiration was suggested in the dechlorination of 2-CP.
    Journal of Environmental Science and Health Part B Pesticides Food Contaminants and Agricultural Wastes 07/2010; 45(5):399-407. · 1.10 Impact Factor
  • Nguyen L Huong, Kazuhito Itoh, Kousuke Suyama
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    ABSTRACT: Changes in the bacterial community in soil-water suspensions during the enrichment period of 2,4-D and 2,4,5-T degraders were examined using denaturing gradient gel electrophoresis (DGGE) analysis of the 16S rRNA gene. The nucleotide sequences of almost all major bands at the degradation of 2,4-D and 2,4,5-T corresponded to those of 2,4-D- and 2,4,5-T-degrading isolates, and successions of diverse 2,4-D- and 2,4,5-T-degrading bacterial communities were demonstrated in the DGGE profile. These results suggested that 2,4-D- and 2,4,5-T-degrading isolates were responsible for the degradation of 2,4-D and 2,4,5-T in soil-water suspensions; however, one major band of a non-degrader was found in some cases. Therefore, to elucidate the relationship between the structures and functions of bacterial communities, the importance of a combined approach using both culture-dependent and -independent methods was demonstrated.
    Microbes and Environments 01/2008; 23(2):142-8. · 2.44 Impact Factor
  • Journal of Pesticide Science - J PESTIC SCI. 01/2008; 33(1):51-57.
  • Munir Mohammad, Kazuhito Itoh, Kousuke Suyama
    Journal of Pesticide Science - J PESTIC SCI. 01/2008; 33(2):171-174.
  • Sonny Conde, Kousuke Suyama, Kazuhito Itoh
    Journal of Pesticide Science - J PESTIC SCI. 01/2008; 33(1):73-75.
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    ABSTRACT: The tfdB gene encoding chlorophenol hydroxylase and its homolog were found in 2,4-dichlorophenoxyacetic acid (2,4-D)-degrading strain RD5-C2, which belongs to Bradyrhizobium sp. of alpha-Proteobacteria. The nucleotide and deduced amino acid sequence identities of the two genes, designated tfdBa and tfdBb, were 60% and 57% respectively. Their nucleotide sequences most closely matched those of previously reported tfdB, which consisted of those from 2,4-D-degrading beta- and gamma-Proteobacteria and Sphingomonas sp. in alpha-Proteobacteria, with 61-67% identity. The TfdBa expressed in Escherichia coli showed the highest activity for 2,4-dichlorophenol but a narrower range of activity for the other chlorophenols than previously reported TfdBs. In the case of TfdBb, however, no observable activity for any chlorophenols or phenol was detected, although production of a protein with an appropriate molecular size was observed. Based on codon usage patterns and the GC content of the genes, it probable that the tfdBa genes in the 2,4-D-degrading Bradyrhizobium sp. were obtained through horizontal gene transfer.
    Bioscience Biotechnology and Biochemistry 08/2007; 71(7):1691-6. · 1.27 Impact Factor
  • Microbes and Environments 01/2007; 22(3):243-256. · 2.44 Impact Factor
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    ABSTRACT: The distribution of tfdAalpha and cadA, genes encoding 2,4-dichlorophenoxyacetate (2,4-D)-degrading proteins which are characteristic of the 2,4-D-degrading Bradyrhizobium sp. isolated from pristine environments, was examined by PCR and Southern hybridization in several Bradyrhizobium strains including type strains of Bradyrhizobium japonicum USDA110 and Bradyrhizobium elkanii USDA94, in phylogenetically closely related Agromonas oligotrophica and Rhodopseudomonas palustris, and in 2,4-D-degrading Sphingomonas strains. All strains showed positive signals for tfdAalpha, and its phylogenetic tree was congruent with that of 16S rRNA genes in alpha-Proteobacteria, indicating evolution of tfdAalpha without horizontal gene transfer. The nucleotide sequence identities between tfdAalpha and canonical tfdA in beta- and gamma-Proteobacteria were 46 to 57%, and the deduced amino acid sequence of TfdAalpha revealed conserved residues characteristic of the active site of alpha-ketoglutarate-dependent dioxygenases. On the other hand, cadA showed limited distribution in 2,4-D-degrading Bradyrhizobium sp. and Sphingomonas sp. and some strains of non-2,4-D-degrading B. elkanii. The cadA genes were phylogenetically separated between 2,4-D-degrading and nondegrading strains, and the cadA genes of 2,4-D degrading strains were further separated between Bradyrhizobium sp. and Sphingomonas sp., indicating the incongruency of cadA with 16S rRNA genes. The nucleotide sequence identities between cadA and tftA of 2,4,5-trichlorophenoxyacetate-degrading Burkholderia cepacia AC1100 were 46 to 53%. Although all root nodule Bradyrhizobium strains were unable to degrade 2,4-D, three strains carrying cadA homologs degraded 4-chlorophenoxyacetate with the accumulation of 4-chlorophenol as an intermediate, suggesting the involvement of cadA homologs in the cleavage of the aryl ether linkage. Based on codon usage patterns and GC content, it was suggested that the cadA genes of 2,4-D-degrading and nondegrading Bradyrhizobium spp. have different origins and that the genes would be obtained in the former through horizontal gene transfer.
    Applied and Environmental Microbiology 05/2004; 70(4):2110-8. · 3.95 Impact Factor
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    ABSTRACT: The distribution of tfdAα and cadA, genes encoding 2,4-dichlorophenoxyacetate (2,4-D)-degrading proteins which are characteristic of the 2,4-D-degrading Bradyrhizobium sp. isolated from pristine environments, was examined by PCR and Southern hybridization in several Bradyrhizobium strains including type strains of Bradyrhizobium japonicum USDA110 and Bradyrhizobium elkanii USDA94, in phylogenetically closely related Agromonas oligotrophica and Rhodopseudomonas palustris, and in 2,4-D-degrading Sphingomonas strains. All strains showed positive signals for tfdAα, and its phylogenetic tree was congruent with that of 16S rRNA genes in α-Proteobacteria, indicating evolution of tfdAα without horizontal gene transfer. The nucleotide sequence identities between tfdAα and canonical tfdA in β- and γ-Proteobacteria were 46 to 57%, and the deduced amino acid sequence of TfdAα revealed conserved residues characteristic of the active site of α-ketoglutarate-dependent dioxygenases. On the other hand, cadA showed limited distribution in 2,4-D-degrading Bradyrhizobium sp. and Sphingomonas sp. and some strains of non-2,4-D-degrading B. elkanii. The cadA genes were phylogenetically separated between 2,4-D-degrading and nondegrading strains, and the cadA genes of 2,4-D degrading strains were further separated between Bradyrhizobium sp. and Sphingomonas sp., indicating the incongruency of cadA with 16S rRNA genes. The nucleotide sequence identities between cadA and tftA of 2,4,5-trichlorophenoxyacetate-degrading Burkholderia cepacia AC1100 were 46 to 53%. Although all root nodule Bradyrhizobium strains were unable to degrade 2,4-D, three strains carrying cadA homologs degraded 4-chlorophenoxyacetate with the accumulation of 4-chlorophenol as an intermediate, suggesting the involvement of cadA homologs in the cleavage of the aryl ether linkage. Based on codon usage patterns and GC content, it was suggested that the cadA genes of 2,4-D-degrading and nondegrading Bradyrhizobium spp. have different origins and that the genes would be obtained in the former through horizontal gene transfer.
    Applied and Environmental Microbiology. 04/2004; 70(4).
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    ABSTRACT: Arsenic extractability with various solutions from peat samples collected in Deuli Village, Bangladesh, was investigated to reveal the leaching mechanisms of arsenic in sediments to groundwater. Peat layer was distributed at the depth of 7–8 m in the sediments, and the peat samples collected and used in this experiment contained 137 mg kg arsenic. A wide range of pH values and concentrations of phosphoric acid and trisodium citrate was used for the extracting solutions. Arsenic extractability with Hel (25–1,000 mM) or NaOH (20–500 mM) at different pH values ranged for 30 to 60% in strong acid or alkali, while was less than 0.1% in the neutral pH range against the total content. Extraction of arsenic with 100 mM phosphoric acid and 100 mM trisodium citrate was about 20% even at a neutral pH, while the extractability with these solutions at concentrations below 1 mM was similar to that with distilled water. These results suggest that competitive exchange and / or chelating action are / is the prior possible mechanism for arsenic leaching from peat. However, the experimental conditions such as pH value or phosphate anion concentration differed from those in the study area where the pH of groundwater was almost neutral and the phosphate anion concentration was only 0.01 mM. Moreover, since the experiment was conducted using a batch system under oxidative conditions and not using a continuous flow system, the importance of the oxidation-reduction potential in the sediments and organic matter content in the groundwater should be investigated.
    Soil Science and Plant Nutrition 12/2003; 49(6):859-865. · 0.89 Impact Factor
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    ABSTRACT: Major and trace elements, including total arsenic (T-As), 1 M HCl-extractable arsenic (Ex-As), total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS), in sediment columns collected in 2000 through 5 boring operations to a depth of 15 m in Deuli Village, Bangladesh were analyzed to reveal the source of arsenic contamination in groundwater. This area mainly consists of sandy, clayey, and peaty layers, and the chemical composition changes considerably with the sediment properties. The concentrations of T-As (20 to 111 mg kg) in the samples of peat and peaty clay sediments from a depth of 7 to 10 m were significantly higher than the concentrations in the samples of clayey sediments (4 to 18 mg kg) or sandy sediments (3 to 7 mg kg), and the concentrations of the other elements were also high in the samples of peaty sediments. T-As concentration shows a significant correlation with the contents of both TS and TOC (p < 0.05). These results suggest that arsenic is retained in the sediments in the form of sulfide or is combined with organic matter. On the other hand, the extraction rate (Ex-As / T-As) changed depending on the Toe content in the sediments, in spite of the high correlation between the concentrations of T-As and Ex-As. This indicates that arsenic speciation was different in the samples of peaty sediments from the sandy and clayey sediments with a relatively low TOC content. The peat layer, in which arsenic is concentrated as a pool, may be the key layer to elucidate the mechanism of solubilization of arsenic in the sediments by groundwater.
    Soil Science and Plant Nutrition. 08/2003; 49(4):567-574.
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    Journal of Pesticide Science - J PESTIC SCI. 01/2003; 28(1):51-54.
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    ABSTRACT: The 2,4-dichlorophenoxyacetate (2,4-D)/alpha-ketoglutarate dioxygenase gene (tfdA) homolog designated tfdAalpha was cloned and characterized from 2,4-D-degrading bacterial strain RD5-C2. This Japanese upland soil isolate belongs to the Bradyrhizobium-Agromonas-Nitrobacter-Afipia cluster in the alpha subdivision of the class Proteobacteria on the basis of its 16S ribosomal DNA sequence. Sequence analysis showed 56 to 60% identity of tfdAalpha to representative tfdA genes. A MalE-TfdAalpha fusion protein expressed in Escherichia coli exhibited about 10 times greater activity for phenoxyacetate than 2,4-D in an alpha-ketoglutarate- and Fe(II)-dependent reaction. The deduced amino acid sequence of TfdAalpha revealed a conserved His-X-Asp-X(146)-His-X(14)-Arg motif characteristic of the active site of group II alpha-ketoglutarate-dependent dioxygenases. The tfdAalpha genes were also detected in 2,4-D-degrading alpha-Proteobacteria previously isolated from pristine environments in Hawaii and in Saskatchewan, Canada (Y. Kamagata, R. R. Fulthorpe, K. Tamura, H. Takami, L. J. Forney, and J. M. Tiedje, Appl. Environ. Microbiol. 63:2266-2272, 1997). These findings indicate that the tfdA genes in beta- and gamma-Proteobacteria and the tfdAalpha genes in alpha-Proteobacteria arose by divergent evolution from a common ancestor.
    Applied and Environmental Microbiology 08/2002; 68(7):3449-54. · 3.95 Impact Factor
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    ABSTRACT: Different microbial communities characterized by the Biolog pattern were developed in the rhizosphere of radish grown on a rockwool hydroponic system treated with chloropicrinfumigated and non-fumigated soil suspensions although no differences were observed in their viable counts. Different microbial communities also were developed in the rhizosphere and non-rhizosphere. After the development of microbial communities in the rhizosphere, bud cells of Fusarium oxysporum that causes vascular wilt of radish plants were inoculated, and disease symptoms were examined. Treatment with the non-fumigated soil suspension was much more effective than that with the fumigated one in controlling the disease, indicating that the Biolog method might be applicable to characterize microbial communities that control the disease caused by F. oxysporum.
    Soil Science and Plant Nutrition 06/2002; 48(3):333-339. · 0.89 Impact Factor
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    ABSTRACT: Degradation of an acylated starch-plastic mulch film was evaluated in two soil types, a gray lowland soil (A) and a volcanic andosol (V). Weight loss, tensile strength (TS) loss and loss of percentage elongation (%E) were measured under laboratory conditions (black and white mulch films), and in the field (black films). Changes in the counts of total bacteria, total fungi, gram-negative bacteria, total Fusarium, ATP (adenosine triphosphate) content, % nitrification, pH (H2O), and total C and total N contents were determined at 4,8, 12, and 20 months in the field test soils where the mulch was repeatedly applied, and compared with controls. Film weight loss was greater in soil V than in soil A in both the laboratory and the field, and the losses were greater in the laboratory than in the field in both soils A and V. Significant TS losses and considerable %E losses were observed. Values were similar in the laboratory and in the field. No significant changes in the counts of bacteria, fungi, gram-negative bacteria, and Fusarium were observed. The ATP content of the test soils increased slightly compared with the initial values. The ATP content in the control soils initially fell, and then increased in response to weeding. Nitrification remained almost unchanged in the test soils, but fell in the control soils until the last sampling. However, the mulch film underwent a definite process of degradation in the soils, with great loss of physical properties and lesser weight loss. This degradation had no adverse impact on the soil microflora.
    Soil Science and Plant Nutrition - SOIL SCI PLANT NUTR. 01/2002; 48(5):701-709.

Publication Stats

178 Citations
37.95 Total Impact Points

Institutions

  • 2000–2014
    • Shimane University
      • • Faculty of Life and Environmental Science
      • • Department of Regional Environmental Sciences
      Matsu, Shimane Prefecture, Japan
  • 2004
    • National Institute of Advanced Industrial Science and Technology
      Tsukuba, Ibaraki, Japan