Potassium chemotaxis in Rhodobacter sphaeroides

The addition of potassium to Rhodobacter sphaeroides in the absence of magnesium increased the membrane potential, as measured by the carotenoid bandshift. In the presence of magnesium, potassium decreased the membrane potential. Potassium stimulated the mean population swimming speed by 33% and 48% in the presence or absence of magnesium, respectively. Chemotactic responses of R. sphaeroides to potassium were also unaffected by the presence or absence of magnesium. These results suggest that the membrane potential and by inference the ΔpH and Δμ H + are not involved in chemotactic signalling towards potassium.