SWIMMING SPEED AND CHEMOKINETIC RESPONSE OF RHODOBACTER-SPHAEROIDES INVESTIGATED BY NATURAL MANIPULATION OF THE MEMBRANE-POTENTIAL

The Delta psi of R. sphaeroides, grown under high light to reduce the levels of light-harvesting bacteriochlorophyll, was naturally manipula ted using light intensity. The relationship between Delta psi and the swimming speed of free swimming populations of cells was investigated. After de-energisation by incubation in the dark there was an apparent threshold of about -13 mV which had to be overcome before functional motor rotation could resume and at -45 mV the motor saturated. Further increases in Delta psi over -45 mV did not increase the free swimming velocity. However, when a chemokinetic effector was added there was a n increase in swimming speed, even though the Delta psi was well above saturation, indicating that the chemokinetic response is independent of normal relationship between motor rotation and Delta psi.