Tactic responses of azospirillumbrasilense towards oxygen and organic compounds

Azospirillum brasilense responded towards self-created oxygen gradients by forming aerotactic bands in capillary tubes and by actively moving towards a limited oxygen zone, optimal for their motility. Increasing oxygen concentration in capillaries containing phosphate buffer increased the number of bacteria attracted and decreased band velocity. High oxygen concentrations and H₂o₂ caused a temporary repulsion of the bacteria from the capillary mouth and formation of a highly motile bacterial arc around it. Exogenous sources of energy were not necessary for aerotaxis in Azospirillum. The aerotactic response of Azospirillum was not affected by the removal of the combined nitrogen from the growth medium. Substrates added to capillaries containing phosphate buffer increased the number of bacteria attracted only 1.2-3 fold. Chemotaxis in Azospirillum could not be measured using the capillary assay, but was examined using the agar plate method in which the aerotactic response was prevented.