Physiological properties of Azotobacter paspali in culture and the rhizosphere

Changes in cell morphology of Azotobacler paspali were dependent on culture growth conditions. They were influenced by the C-source, sucrose content of the medium, presence or absence of N, PO 2 and the shaking rate. The bacteria produced different cell forms, including rods, filaments, pairs of cocci and cysts. The proportions between the morphological types changed according to the culture composition. Aggregation of cells in the culture increased under high C-to-N ratio and with culture age. The optimal PO 2 for nitrogenase activity by batch cultures of 10 8 colony forming units (cfu) ml −1 was 0.025–0.05 atm. A. paspali colonized the roots of several plants. Bacterial numbers counted on wheat and sunflower root surface, following inoculation with 5 × 10 7cfu ml −1 were between 10 5 and 10 6 cfu g −1 root dry weight after 1 week, 10 −4−l0 −5 after 2 weeks and 10 3cfu ml −1 after 3 weeks. Bacterial numbers in the soil in the first week after inoculation were about l0 5cfu g −1 soil and 10 3 after 3 weeks. Inoculation with A. paspali, 5 × 10 8 cfu ml −1 under gnotobiotic conditions in Petri dishes increased root hair formation in canola roots 24 h after inoculation.