A vigorously nitrogen-fixing bacterium was isolated from a West Bengal soil. Cells from young cultures on nitrogen-deficient agar medium appear as rods measuring approx. 3–6x1.0–1.2 μ., with rounded ends and homogeneous cytoplasm. Older cells contain big refractile bodies representing vacuoles and fat deposits and show a wide variation in shape. Short motile cells with a single polar flagellum arise in liquid medium with combined (ammonia) nitrogen. The Gram reation is negative and endospores are not formed.
The organism is aerobic but catalase-negative. It grows rather feebly in sugar-free protein media, but in nitrogen-deficient media it produces ah heavy and extremely tenacious growth, of a characteristic uneven appearance on agar and changing from white to dark red-brown. Glucose, fructose, ethanol, glycerol, mannitol and sorbitol are the best sources of carbon. Acid but no gas is formed from several carbohydrates. Nitrogen fixation is slow but may amount to 20–25 mg. per gram glucose or mannitol supplied. Molybdenum stimulates nitrogen fixation strongly and cannot be replaced by vanadium.
Various forms of combined nitrogen, especially glutamic acid, are assimilated more readily than free nitrogen. Growth can be initiated within aPh-interval from approx. 5 to 9; growing cultures may be acidified to Ph 4.5 or less.
The organism is morphologically, culturally and serologically different from Azotobacter and Beijerinckia and is regarded as representing a new genus.
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Jensen, H.L., Petersen, E.J., De, P.K. et al. A new nitrogen-fixing bacterium: Derxia gummosa nov. gen. nov. spec.. Archiv. Mikrobiol. 36, 182–195 (1960). https://doi.org/10.1007/BF00412286
- Nitrogen Fixation