Add 2% mannitol to Azotobacter Basal Medium (see below); and adjust pH to 6.0 Azotobacter Basal Medium: K₂HPO₄, 1.0 g, MgSO₄ . 7H₂O, 0.2 g, NaCl, 0.2 g, FeSO₄, 5.0 mg, Soil Extract (see below); 100.0 ml, Agar, 15.0 g. Tap water, 900.0 ml. Soil Extract: African violet soil, 77.0 g, Na₂CO₃, 0.2 g, Distilled water, 200.0 ml. Autoclave for one hour. Filter through paper before using in media.