We investigated the relationship between the genetic diversity of indigenous soybean-nodulating bradyrhizobia and their geographical distribution in the United States using nine soil isolates from eight states. The bradyrhizobia were inoculated on three soybean Rj genotypes (non-Rj, Rj 2 Rj 3 , and Rj 4 ). We analyzed their genetic diversity and community structure by means of restriction fragment length polymorphisms of PCR amplicons to target the 16S-23S rRNA gene internal transcribed spacer region, using 11 USDA Bradyrhizobium strains as reference strains. We also performed diversity analysis, multidimensional scaling analysis based on the Bray-Curtis index, and polar ordination analysis to describe the structure and geographical distribution of the soybean-nodulating bradyrhizobial community. The major clusters were Bradyrhizobium japonicum Bj123, in the northern United States, and Bradyrhizobium elkanii, in the middle to southern regions. Dominance of bradyrhizobia in a community was generally larger for the cluster belonging to B. elkanii than for the cluster belonging to B. japonicum. The indigenous American soybean-nodulating bradyrhizobial community structure was strongly correlated with latitude. Our results suggest that this community varies geographically.

No abstract

No abstract

No abstract

In most of the bubble column design, it is assumed that liquid phase is well mixed and spatial distributions of molar concentrations for all components are uniform. However, there is liquid mixing in actual bubble column reactors. The performance of a bubble column strongly depends on the liquid mixing induced by bubbles in the column. Those assumptions therefore cause some errors in column optimum design. Only a few quantitative investigations have been carried out on two-phase turbulence and liquid mixing. In this study, numerical simulations for liquid mixing in a bubble column have been carried out and compared with experiments. The transient behavior of tracer concentration was measured for test columns of 0.3 m in diameter. The height of the columns was 1 m. Bubbles were supplied by using two types of spargers: ring spargers and a perforated plate. A hybrid method, NP2-3D, which is based on the combination of multi-fluid and interface tracking methods, was used to simulate the flow. In a two-phase turbulence model, linear superposition of bubble-induced turbulence and shear-induced turbulence was assumed. Numerical prediction could qualitatively describe the effects of column diameter and gas inlet on the liquid mixing in a column.