359-K230JP. Symbiotic Nitrogen-Fixing Soil Bacterium Has an Ability of Methanol Utilization Depending on Rare Earth Elements

Bradyrhizobium genus is one of bacterial soil fertilizers in agricultural system. In this study, we showed that the most popular soil fertilizer, B. japonicum strain USDA110, has an ability to utilize methanol depending on Ce3+, which is one of the rare earth elements. In strain USDA110, methanol dehydrogenase (MDH) activity was induced by presence of Ce3+, although it was reported that the strain did not show enough MDH activity depending on Ca2+. Moreover, we purified MDH from the strain grown on methanol/Ce3+ medium. Purified MDH showed single band on SDS-PAGE, and its specific activity was 2.69 U/mg. Its optimum pH and temperature were 9.0 and 35oC, respectively, and the Km value with methanol was calculated to be 0.423 mM. From these results, it is suggested that rare earth elements, especially Ce3+, is one of the important factors for the methanol utilization of B. japonicum strain USDA110, and Ce3+ functions as inducer/cofactor for MDH encoded by xoxF gene.