Growth and dinitrogen fixation by azospirillum, species grown under various growth conditions

The effect of strain specificity, various culturing conditions, and incubation periods on the growth and efficiency of dinitrogen fixation by A. lipoferum and A. brasilense, grown in semisolid N2 malate medium was investigated. The properties of the particular strain markedly affected the proliferation as well as the nitrogen gains of Azospirillum in either growth condition. In A. lipoferum strain 1244 and A. brasilense strrain 1771 the multiplication rates were much higher, the counts reaching 7 × 106 and 9 × 106 cells/ml after 15 days in case of 50/300 ml growth condition, associated with high nitrogen gains reaching 99.8 and 114.3 mgl−1, while in A. lipoferum strain 8670 and A. brasilense strain 5677 the counts were 6 × 105 and 2 × 106 cells/ml after both the same period and growth condition, associated with low nitrogen gains, reaching 62.5 and 69.6 mgl−1, i. e., the amounts of nitrogen fixed is usually linked to cell proliferation. The microbial activity in both nitrogen fixation and oxidation of carbonaceous material is directly reflected on the efficiency of dinitrogen fixation. In all treatments the efficiency of N2-fixation generally increased markedly with time. In A. lipoferum strains 1244 and 8670 the efficiency of N2-fixation was 118.5 and 107.4 in case of 50/100 ml growth condition after 20 days, while in A. brasilense strains 1771 and 5677 the corresponding figures were 126.5 and 115.4. The response of the available oxygen was linked to the growth conditions, accordingly, the efficiency of N2-fixation increased by 4.4% & 8.8% in case of A. lipoferum strains 1244 and 8670, and 11.0% & 9.8% in case of A. brasilense strains 1771 and 5677 as a result of increasing the surface area: depth ratio by altering the volume of medium in the experimental flasks.