PHYSIOLOGICAL-PROPERTIES OF AZOTOBACTER-PASPALI IN CULTURE AND THE RHIZOSPHERE

Changes in cell morphology of Azotobacter paspali were dependent on cu lture growth conditions. They were influenced by the C-source, sucrose content of the medium, presence or absence of N, PO2 and the shaking rate. The bacteria produced different cell forms, including rods, fila ments, pairs of cocci and cysts. The proportions between the morpholog ical types changed according to the culture composition. Aggregation o f cells in the culture increased under high C-to-N ratio and with cult ure age. The optimal PO2 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 wh eat and sunflower root surface, following inoculation with 5 x 10(7) c fu ml-1 were between 10(5) and 10(6) cfu g-1 root dry weight after 1 w eek, 10(-4)-10(-5) after 2 weeks and 10(3) cfu ml-1 after 3 weeks. Bac terial numbers in the soil in the first week after inoculation were ab out 10(5) cfu g-1 soil and 10(3) after 3 weeks. Inoculation with A. pa spali, 5 x 10(8) cfu ml-1 under gnotobiotic conditions in Petri dishes increased root hair formation in canola roots 24 h after inoculation.