Ammonium‐nitrogen metabolism and nitrogen fixation in azotobacter vinelandii

Abstract The probable effect of increasing levels of ammonium nitrogen on the growth, efficiency of nitrogen fixation, and main cellular constituents of Azotobacter vinelandii was studied under shaking and static culture conditions. The presence of NH4+‐N up to 50 mgl‐1 level has no harmful effect on the multiplication as well as the yield efficiency ratio of the tested organism. A. vinelandii was able to fix dinitrogen in the presence of NH4+‐N when both nitrogen sources were available in the culturing medium. The efficiency of nitrogen fixation was affected by the initial presence of NH4+‐N in the medium, it was quite low at the highest level. The crude protein efficiency ratio was correlated inversely with the initial NH4+‐N concentration, whereas the total carbohydrate efficiency ratio as well as the total lipid efficiency ratio were positively correlated with the NH4+‐N concentration. The presence of NH4+‐N in the culturing medium has no essential influence on the qualitative composition of the amino acids in the Azotobacter cells.