The 16s rRNA sequences of seven representative Agrobacterium strains, eight representative Rhizobium strains, and the type strains of Azorhizobium caulinodans and Bradyrhizobium japonicum were determined. These strains included the type strains of Agrobacterium tumefaciens, Agrobacterium rhizogenes, Agrobacterium radiobacter, Agrobacterium vitis, Agrobacterium rubi, Rhizobium fredii, Rhizobium galegae, Rhizobium huukuii, Rhizobium leguminosarum, Rhizobium loti, Rhizobium meliloti, and Rhizobium tropici. A phylogenetic analysis showed that the 15 strains of Agrobacterium and Rhizobium species formed a compact phylogenetic cluster clearly separated from the other members of the alpha subclass of the Proteobacteria. However, Agrobacterium species and Rhizobium species are phylogenetically entwined with one another, and the two genera cannot be separated. In the Agrobacterium species, the strains of biovar 1, biovar 2, Agrobacterium rubi, and Agrobacterium vitis were clearly separated. The two biovars exhibited homogeneity in their phenotypic, chemotaxonomic, and phylogenetic characteristics, and two species should be established for the two biovars. We considered the nomenclature of the two biovars, and revised descriptions of Agrobacterium radwbacter (for the biovar 1 strains) and Agrobacterium rhizogenes (for the biovar 2 strains) are proposed. The name Agrobacterium tumefaciens is rejected because the type strain of this species was assigned to Agrobacterium radiobacter, and consequently the description of the genus Agrobacterium is revised.The genus Agrobactenum was established by Conn (4) in 1942. This genus has been a member of the family Rhizobiaceae since it was first established. The members of the family Rhizobiaceae have a unique ability to induce cortical hypertrophies on plants (26). The genera Rhizobium and Bradyrhizobium are well-known nitrogen-fixing noduleforming bacteria associated with legumes. The members of genus Phyllobactenum induce the formation of nodules on the leaves of certain plant species.All of the members of the genus Agrobactenum except Agrobacterium radiobacter induce cortical hypertrophy of the upper parts of roots (Agrobacterium tumefaciens and Agrobacterium rubi) or abnormal root growth Cllgrobacterium rhizogenes) on many kinds of plants. Many non-tumorforming strains closely related to the tumor formers which have been found in soil or in the rhizospheres of plants (3,4) and in clinical specimens (13) have been identified as Agrobacterium radiobacter strains (4, 26). Later, molecular biological studies have revealed that the tumor-or hairy-rootforming ability is due to the presence of large indigenous plasmids (22, 23, 30,33,46,49,52), and the inclusion of the organisms that do not form tumors in the genus Agrobacterium has been confirmed. Also, recent rRNA-DNA homology studies (9, 19) have revealed the close relationship between the non-tumor-forming strains and the tumor formers.The separation of the genus Agrobacterium from allied genera and also the separation of species in...

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We investigated the spatial variation in the stress fields of Kyushu Island, southwestern Japan. Kyushu Island is characterized by active volcanoes (Aso, Unzen, Kirishima, and Sakurajima) and a shear zone (western extension of the median tectonic line). Shallow earthquakes frequently occur not only along active faults but also in the central region of the island, which is characterized by active volcanoes. We evaluated the focal mechanisms of the shallow earthquakes on Kyushu Island to determine the relative deviatoric stress field. Generally, the stress field was estimated by using the method proposed by Hardebeck and Michael (2006) for the strike-slip regime in this area. The minimum principal compression stress (σ3), with its near north-south trend, is dominant throughout the entire region. However, the σ 3 axes around the shear zone are rotated normal to the zone. This result is indicative of shear stress reduction at the zone and is consistent with the right-lateral fault behavior along the zone detected by a strain-rate field analysis with global positioning system data. Conversely, the stress field of the normal fault is dominant in the Beppu-Shimabara area, which is located in the central part of the island. This result and the direction of σ3 are consistent with the formation of a graben structure in the area.

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Distinct S waves reflected from a midcrustal seismic velocity discontinuity are detected beneath Nikko‐Shirane volcano in the southernmost part of the northeastern Japan arc. A detailed travel time analysis of the reflected S waves by using data acquired through a dense seismic network temporarily set up in this region shows that this unusual S wave reflector is distributed over an area of 15 × 15 km2 at depths ranging from 8 to 15 km. The reflector has a conical shape becoming shallow toward the summit of Nikko‐Shirane volcano. Observed amplitude spectral ratios of reflected S waves to direct S waves show that the reflector body has a strong velocity contrast to the surrounding medium and its thickness is of the order of 100 m at most. The reflector body is approximated by two thin layers probably filled with partially molten materials. Cutoff depth for shallow seismicity in this area is 3–5 km above the reflector and becomes shallow toward Nikko‐Shirane volcano, nearly parallel to the reflector. The depth to brittle‐ductile transition zone seems to be prescribed by the existence of the reflector body, which is perhaps a thin magma body.