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Title: Changes in Population Occupancy of Bradyrhizobia under Diffrent Temperature Regimes

Author
item SAEKI, Y - University Of Miyazaki
item OZUMI, S - University Of Miyazaki
item YAMAMOTO, A - University Of Miyazaki
item YAMAKAWA, T - Kyushu University
item Sigua, Gilbert

Submitted to: Microbes and Environments
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/27/2010
Publication Date: 11/2/2010
Citation: Saeki, Y., Ozumi, S., Yamamoto, A., Yamakawa, T., Sigua, G.C. 2010. Changes in Population Occupancy of Bradyrhizobia under Diffrent Temperature Regimes. Microbes and Environments. 25(4):309-312.

Interpretive Summary: The ecology and distribution of soybean-nodulating bacteria that may vary over wide regions of the world because of geographical and climatic differences are not well understood, thus needing additional studies. In this study, we examined the different response attributes and changes in occupancy of some bradyrhizobial strains in liquid and soil cultures under different temperature regimes and incubation periods. Cultivation of different strains (Bradyrhizobium japonicum strains: USDA 6T, 38, and 123; Bradyrhizobium elkanii strain: USDA76T) using liquid and soil media were conducted to estimate the strain population occupancy of bradyrhizobial organisms at three different temperature conditions, low temperature (0-4-15-4°C cycle), middle temperature (4-15-25-15°C cycle), and high temperature (15-25-35-25°C cycle). Results demonstrated that population occupancies of Bradyrhizobium elkanii USDA 76T and Bradyrhizobium japonicum USDA 123 in soils may change depending on incubation temperatures. The changes that were observed in our study were similar with the results from analyses of indigenous soybean-nodulating bradyrhizobia. These results confirmed that temperature could be one of the major environmental factors affecting the ecology and population occupancies of bradyrhizobia in soils. Results could have some promising impact on soybean-nodulation potentials and improving nitrogen fixation efficiency at subtropical and tropical regions.

Technical Abstract: Cultivation of Bradyrhizobium japonicum strains (USDA 6T, 38, and 123) and Bradyrhizobium elkanii strain (USDA 76T) were conducted to compare their respective proliferation traits under different cultivation temperature conditions with yeast-extract mannitol broth medium and to estimate the strain population occupancy of bradyrhizobial organisms in soil. The soil samples were incubated at three different temperature conditions, low temperature (0-4-15-4°C cycle), middle temperature (4-15-25-15°C cycle), and high temperature (15-25-35-25°C cycle). These temperature cycles were assumed to represent the four seasons at northern, central and southern regions in Japan, respectively. Results demonstrated that population occupancies of USDA 76T and USDA 123 in soils after longer incubation may change depending on incubation temperatures. The changes that were observed in our study were similar with the results from analyses of indigenous soybean-nodulating bradyrhizobia. These results confirmed that temperature could be one of the major environmental factors affecting the ecology and occupancies of bradyrhizobia in soils. Results could have some promising impact on soybean-nodulation potentials at tropical and subtropical regions.