Mechanism of action of Pseudomonas syringae phytotoxin, syringomycin. Interaction with the plasma membrane of wild-type and respiratory-deficient strains of Saccharomyces cerevisiae.

The effects of the phytotoxin, syringomycin, produced by Pseudomonas syringae pv. syringae, were examined on cells of a wild-type and a respiratory-deficient (rho0) mutant of Saccharomyces cerevisiae. The growth of both strains in liquid culture was inhibited by 0.5 micrograms syringomycin per ml and higher. Uptake rates of tetraphenylphosphonium and dimethyloxazolidine ions in cell suspensions of both strains increased when 1.5 micrograms per ml syringomycin was added. These responses were kinetically and quantitatively similar in the two strains and indicated increases in electrical potential (cell interior negative) and pH differences (cell interior alkaline) across the plasma membrane. Glucose (0.1 M) enhanced the effect on the electrical potential, was required for the pH changes, and increased the cellular ATP levels. These results show that the effects of syringomycin are energy-dependent and are due to alterations of plasma membrane and not to mitochondrial function.