Studies on the aerobic non-symbiotic nitrogen-fixing bacteria, other than Azotobacter, in Egyptian soils.

Twenty isolates of micro-organisms capable of growing on nitrogen-deficient medium and found as contaminants in Azotobacter cultures were isolated from Egyptian soils and studied for their morphological, cultural, and physiological properties. These micro-organisms s are members of Rhizobiaceae, Pseudomonadaceae, Achromobacteriaceae, Enterobacteriaceae, Micrococcaceae, Bacillaceae, and Streptomycetaceae as well as some yeasts. In nitrogen-free medium the micro-organism fixed only small amounts of atmospheric nitrogen, hardly exceeding 3 ppm and because of their low sugar consumption rates, efficiences of N2-fixation sometimes reaching 18 mg nitrogen fixed/g carbon oxidized were recorded. Addition of 15 ppm combined nitrogen to the medium increased the amounts of nitrogen fixed to 3--9 ppm.