Regulation of syringomycin synthesis in Pseudomonas syringae pv. syringae and defined conditions for its production.

Production of the phytotoxin, syringomycin (SR), by Pseudomonas syringae pv. syringae strain B301D was regulated by both iron and inorganic phosphate similar to that of many bacterial secondary metabolites. Iron concentrations of 2 mumol/l or more in deferrated potato-dextrose broth (PDB) resulted in the production of 1024 SR units/ml, a yield comparable to that produced in non-deferrated PDB. Moreover, production of one SR unit required approximately 0.4 ng of available FeCl3. No SR was produced by strain B301D in deferrated PDB despite growth nearly identical with that of B301D in deferrated PDB supplemented with 10 mumol/l FeCl3. Furthermore, a phosphate concentration of 1 mmol/l or more was suppressive to SR production. Of the amino acids tested, L-histidine at a concentration of ca 20 mmol/l was the most effective nitrogen source for SR synthesis under defined conditions. Based on these observations, a synthetic medium, SR minimal, was formulated for SR or syringotoxin production by representative strains of Ps. syringae pv. syringae. The regulation of phytotoxin production is discussed in relation to pathogen survival and virulence.