ROLE OF PROTON MOTIVE FORCE IN PHOTOTACTIC AND AEROTACTIC RESPONSES OF RHODOPSEUDOMONAS-SPHAEROIDES

R. sphaeroides grown under nonrigorous anaerobic conditions in the light developed components of a branched respiratory electron transfer chain and a photosynthetic electron transfer chain. Both respiratory pathways were sensitive to rotenone and high concentrations of cyanide, but O2 uptake was only partially inhibited by the addition of low concentrations of cyanide or antimycin A. When incubated anaerobically in the dark, R. sphaeroides responded positively to an O2 gradient in the absence of rotenone. In the presence of rotenone, aerotaxis only occurred when the antimycin A-sensitive branch of the pathway was functioning, although both branches still reduced O2. Although there was electron movement along the respiratory chain, aerotaxis only occurred in response to a change in proton motive force. When incubated anaerobically in the light, the movement of R. sphaeroides up a light gradient depended on photosynthetic electron transport. When incubated aerobically, high-intensity actinic illumination inhibited O2 uptake and aerotaxis. In a low-intensity light gradient the phototactic response was inhibited by O2. These results are discussed in relation to the interaction of the electron transfer chains and their roles in controlling tactic responses in R. sphaeroides.