Chemotactic response of wild-type and aggregation-defective mutants of Polysphondylium violaceum

Abstract

The aggregation-specific chemoattractant for Polysphondylium violaceum is N-propionyl-γ-L-glutamyl-L-ornithine-δ-lactam ethyl ester, or glorin. Wild-type amoebae allowed to develop in liquid culture acquire increased ability to respond to glorin shortly after starvation, i.e., just prior to the time they become aggregation competent. Similarly, as development proceeds, the amoebae show decreased sensitivity to folic acid, but they show almost no response to cyclic AMP at any time during their development in liquid culture. The optimum concentrations for the chemotactic response are 10 -8 M for glorin and 10 -5–10 -6 M for folic acid. A class of aggregation-defective mutants, aggA, will not aggregate in the absence of an excreted pheromone, D factor. During development in liquid culture in the presence or absence of D factor, these aggA mutants show a chemotactic response similar to that of wild-type amoebae to folic acid and glorin. However, D factor does enhance the chemotactic response of aggA mutants to glorin. In the absence of D factor, mutant amoebae will form fruiting bodies if exposed to a chemotactic gradient of either folic acid or glorin. Under these conditions, the mutant amoebae circumvent the requirement for D factor in order to develop.