Eleven isolates of slow-growing oligotrophic bacteria from grassland soil were found to be closely related by partial 16S rRNA sequence similarity and many common taxonomic traits. Analysis of full 16S rRNA gene sequences of four representative isolates and Agromonas oligotrophica S58 indicated that they were more closely related to Bradyrhizobium japonicum, a symbiotic nitrogen-fixing bacterium, (similarity values: 98.1^98.8%) than other strains such as Bradyrhizobium elkanii, Nitrobacter spp., Rhodopseudomonas palustris, and Afipia spp. This result was supported by analysis of phenotypic traits and DNA-DNA hybridization analysis. No strain showed hybridization to nodD I YABC of B. japonicum, and only strain G14130 exhibited hybridization to nifDK-and hupSL-specific DNA. These latter genotypes are involved in the phenotypes of nodulation and nitrogen fixation under microaerobic conditions. These results suggest that the isolates possess a unique phylogenetic position since they are closely related to B. japonicum though they do not have characteristics of symbiotic nitrogen fixation.
We present the first direct measurement of dynamic behavior of ions in an aqueous solution at high temperatures and pressure using Raman spectroscopy. We have studied the N−O symmetric stretching mode at high temperatures up to 340 °C and at a high pressure of 30 MPa. The Raman spectra of 1.3 M aqueous zinc nitrate solution have been analyzed by curve fitting. The zinc ion forms two species. In one species Zn2+ is bound more strongly to the NO3 -, and in the other Zn2+ is bound more strongly to H2O. The ratio of the former to the latter remains unaltered with temperatures below 300 °C, but above 300 °C the ratio increases significantly. The average number of water molecules bound to Zn2+ (n H 2 O) is estimated using the intensity of peak frequency of the symmetric stretching mode of the haxaaquazinc(II) cation. As the temperature increases, the n H 2 O gradually decreases, but above 300 °C it shows a large decrease, suggesting the displacement of water molecules from the first solvation shell around Zn2+ and the concomitant entry of NO3 - into the shell. The perpendicular orientational relaxation time (τ⊥) decreases significantly with temperature; the values of τ⊥ were 1.86 and 0.25 ps, respectively, at 20 and 340 °C. The Arrhenius plot gives two activation energies, 2.1 kcal mol-1 below 300 °C and 6.4 kcal mol-1 above 300 °C. The activation energy for the orientational motion, 6.4 kcal mol-1, is larger than that for orientational motion of water, 4−5 kcal mol-1, and we assume that orientational motion of the anion above 300 °C requires the breaking of water−water hydrogen bonds. Furthermore, the experimental values of the perpendicular diffusion constant (D ⊥) at higher temperatures than 300 °C are in agreement with those of D i calculated from the slightly damped free-rotor (SDFR) model, and the rotation around the C 3 axis of the anion is confirmed to proceed rapidly and approach that in the free dilute gas phase.
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