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

Abstract

Production of the phytotoxin, syringomycin (SR) by Pseudomonas syringae pv. [pathovar] syringae strain B301D was regulated by Fe and P similiar to that of many bacterial secondary metabolites. Fe concentrations of .gtoreq. 2 .mu.mol/l in deferrated potato-dextrose broth (PDB) resulted in the production of 1024 SR U/ml, a yield comparable to that produced in non-deferrated PDB. Production of one SR unit required .apprx. 0.4 ng of available FeCl3. No SR was produced by strain B301D in deferred PDB despite growth nearly identical with that of B301D in deferrated PDB supplemented with 10 .mu.mol/l FeCl3. A phosphate concentration of .gtoreq. 1 mmol/l was suppressive to SR production. Of the amino acids tested, L-histidine at a concentration of .apprx. 20 mmol/l was the most effective N 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 P. syringae pv. syringae. The regulation of phytotoxin production is discussed in relation of pathogen survival and virulence.