1Tohoku univ. life.
Because nitrous oxide (N2O) is a greenhouse gas with a global warming potential approximately 300 times that of CO2, the anthropogenic N2O emission should be reduced. To reduce N2O into harmless N2 by bacterial denitrification process, the presence of nosZ gene encoding a N2O reductase is important. Aeschynomene indica is an annual aquatic legume plant, which often grows wild on footpath between paddy fields. A. indica generally forms nitrogen-fixing root/stem nodules by infection of photosynthetic bradyrhizobia strains, such as Bradyrhizobium sp. ORS278 and BTAi1. Bradyrhizobium oligotrophicum S58, which was isolated from paddy field soil, also shows nodulation and symbiotic nitrogen fixation on A. indica (Okubo et al. Appl. Environ. Microbiol. 2013. 79:2542-51). However, there is no report on N2O reductase by these A. indica bradyrhizobia. In this study, we investigated the distribution of N2O reductase gene in A. indica bradyrhizobia, and their N2O reductase activities under culture condition. BLAST search showed that nosZ gene was identified from the genomes of S58 and BTAi1 with high homology to that of USDA110, whereas not identified in ORS278 genome. To examine whether these strains show N2O reductase activity according to their genotype, we tested N2O uptake under culture conditions. N2O uptake by strain S58 was detected, whereas it was not observed in ORS278 culture. In addition, the decrease of N2O concentration in the gas-phase of S58 culture depended on the starting bacterial density. These results indicate that A. indica bradyrhizobia have a potential of N2O reduction as well as soybean bradyrhizobia, which depend on the existence of nosZ in the genome. In this presentation, we will report N2O reduction activity of strain S58 in symbiotic state on root/stem nodules.