BIOLOGICAL PROPERTIES AND SPECTRUM OF ACTIVITY OF PSEUDOMONAS-SYRINGAE PV SYRINGAE TOXINS

Syringomycin E (SR-E), syringotoxin (ST) and two forms (SP22-A and SP2 5-A) of syringopeptin (SP), the main lipodepsipeptides produced by str ains of Pseudomonas syringae pv. syringae, were investigated for their biological activities. All toxins caused lysis of sheep erythrocytes, but SPs were more active than SR-E and ST. The lytic concentrations w ere 0.8 and 0.6 mu m for SP22-A and SP25-A and 1.4 and 5.9 mu M for SR -E and ST, respectively. The effect of toxins on the electrolyte leaka ge from carrot tissues and on the viability of potato tuber tissues co nfirmed the higher phytotoxicity of SPs in comparison to the SR-E or S T. A relevant effect on electrolyte leakage was induced by 0.4 mu M SP 22-A and 10 mu M ST, respectively. The spectrum of antimicrobial activ ity indicated that 50 mu M toxin solutions did not inhibit the growth of Gram-negative bacteria. Grampositive bacteria were sensitive to SPs but in contrast, SR-E and ST had no relevant effect on the growth of these bacteria. In particular, the growth of Bacillus megaterium was i nhibited by 1.56 mu M SP22-A and 3.12 mu M SP25-A, but was unaffected by 50 mu M SR-E or ST. The effects of toxins on fungi were variable. F or example, 6.25 mu M SR-E or ST, 12.5 mu M SP22-A and 37.5 mu M SP25- A inhibited the growth of the yeast Rhodotorula pilimanae. The mycelia l growth of the plant pathogenic fungus Botrytis cinerea was inhibited by 1.6 mu M SP25-A, 12.5 mu M SP22-A, 18.7 mu M SR-E and 25 mu M ST. Furthermore, SR-E was the most active toxin in inhibiting conidial ger mination and germ tube elongation of this fungus. (C) 1997 Academic Pr ess Limited.