Factors Influencing Growth (Count and Yield) and Nitrogen Fixation by Azotobacters: I. Properties of Particular Strains

Abstract

Summary The effect of strain specificity on the growth and efficiency of nitrogen fixation by Azotobacter chroococcum and Azotobacter vinelandii , grown in nitrogen-free liquid medium under shaking and static culture conditions, was investigated. The properties of the particular strain markedly affected the proliferation of Azotobacter in either culture condition. In A. chroococcum (strains 1 and 2) and A. vinelandii (strains A and B) multiplication rates were much higher, the counts reaching 21 – 36 × 10 9 and 18–32 × 10 9 cells/ml after 10 days, associated with high yields, ranging from 264 – 420 and from 220 – 260 mg dry wt. organisms/100 ml, while in A. chroococcum (strains 3 and 4) and A. vinelandii (strains C and D) the counts were 6–11 × 10 9 and 5 – 9 × 10 9 cells/ml after the same period, associated with low yields, ranging from 135 – 172 and from 120 – 165 mg dry wt. organisms/100 ml. There is a considerable variation in the amount of nitrogen gains and the oxidation of carbonaceous material between the different strains under either condition of cultivation, which is directly reflected on the efficiency of nitrogen fixation. The studied strains comprised two groups with a high and a low rate of fixation, the former of these fixed 14 – 20 mg N/g glucose consumed and the latter 10 – 14 mg N/g glucose consumed.