Some characteristics of nitrogen-fixing bacteria isolated from cultivated and uncultivated sites

Nitrogen-fixing bacteria grown in semisolid malate agar were isolated from the soils and various plant roots of cultivated and noncultivated sites in and near Tokyo University Forest in Aichi, and characteristics of the isolates were compared. Nitrogen-fixing bacteria were present in all of the root and soil samples from the cultivated site, and most of them were Azospirillum brasilense-like. All of these isolates reduced nitrate and a large portion of them formed gas in anaerobic culture. The incidence of nitrogen-fixing bacteria from the forest site was much lower and their presence was demonstrated in about 40% of the forest samples. The characteristics of the forest isolates were generally different from those of A. brasilense, as they required yeast extract for nitrogen-fixing growth. More than half of the forest isolates failed to reduce nitrate and none of them produced gas from nitrate. Since the characteristics of both types of bacteria in the cultivated and the forest sites were observed when the bacteria were collected in an area along a path in the garden of the University Forest, the floral characteristics of the nitrogen-fixing bacteria in this site seemed to be intermediate between those of the two sites.