Phototaxis and membrane potential in the photosynthetic bacterium Rhodospirillum rubrum

Abstract

Cells of the photosynthetic bacterium R. rubrum, cultivated anaerobically in light, show phototaxis. The behavior of individual cells in response to the phenomenon is reversal(s) of the swimming direction when the intensity of the light available to them abruptly decreases. The tactic response was inhibited by antimycin, an inhibitor of the photosynthetic electron transfer system. The inhibitory effect of antimycin was overcome by phenazine methosulfate. Motility of the cells was not impaired by antimycin under aerobic conditions. Valinomycin plus K also inhibited their phototactic response, but valinomycin or K alone had no effect. A change in membrane potential of the cells was measured as an absorbance change of carotenoid. Changes in the membrane potential caused by on-off light were prevented by antimycin and by valinomycin plus K, but not by antimycin plus phenazine methosulfate nor valinomycin or K alone. The phototactic response of R. rubrum is apparently mediated by a sudden change in electron flow in the photosynthetic electron transfer system. The membrane potential apparently plays an important role in manifestation of the response.