Infection mechanism of nitrogen-fixing bacteria to nonlegume and its application to construction of agriculture independent on chemical nitrogenous fertilizers

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Due to the increasing cost of chemical nitrogenous fertilizer and concerns about contamination of soil and water, there is a need to reduce usage of chemical fertilizer. Plant-associated microorganisms containing nitrogenases have attracted attention as alternative biofertilizers, since nitrogenase catalyzes a reaction referred to as biological nitrogen fixation. Among endophytic nitrogen-fixing bacteria, we selected Gluconacetobacter diazotrophicus(Gdi) and analyzed the function as the biofertilizer. We found that, depending on the phosphate concentration in the medium, this bacterium produces copious amount of polyssacharide levan, a D-fructofuranosyl polymer, as an exopolysaccharide essential in the infection of the bacterium to the plants and in the protection of invasion of other bacteria in the environment.