BEHAVIOR OF RHIZOBIUM-MELILOTI IN OXYGEN GRADIENTS

Rhizobium meliloti cells responded to an abrupt change in oxygen conce ntration by changing the cell speed (chemokinesis), but they did not a lter the frequency at which swimming cells stopped briefly (aerotaxis) . Changes in cell speed upon stimulation with oxygen coincided with ch anges in membrane potential, The cells did not form an aerotactic band in a spatial gradient of oxygen as do the cells of other bacterial sp ecies. The fixL; and fixJ genes which encode a heme-containing protein kinase that senses oxygen and a response regulator, respectively, wer e not involved in the behavior of R. meliloti in oxygen gradients.