Biological properties and spectrum of activity ofPseudomonas syringaepv.syringaetoxins

Abstract

Syringomycin E (SR-E), syringotoxin (ST) and two forms (SP22-A and SP25-A) of syringopeptin (SP), the main lipodepsipeptides produced by strains ofPseudomonas syringaepv.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 were 0.8 and 0.6 μMfor SP22-A and SP25-A and 1.4 and 5.9 μMfor SR-E and ST, respectively. The effect of toxins on the electrolyte leakage from carrot tissues and on the viability of potato tuber tissues confirmed the higher phytotoxicity of SPs in comparison to the SR-E or ST. A relevant effect on electrolyte leakage was induced by 0.4 μMSP22-A and 10 μMST, respectively. The spectrum of antimicrobial activity indicated that 50 μMtoxin solutions did not inhibit the growth of Gram-negative bacteria. Gram-positive 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 ofBacillus megateriumwas inhibited by 1.56 μMSP22-A and 3.12 μMSP25-A, but was unaffected by 50 μMSR-E or ST. The effects of toxins on fungi were variable. For example, 6.25 μMSR-E or ST, 12.5 μMSP22-A and 37.5 μMSP25-A inhibited the growth of the yeastRhodotorula pilimanae. The mycelial growth of the plant pathogenic fungusBotrytis cinereawas inhibited by 1.6 μMSP25-A, 12.5 μMSP22-A, 18.7 μMSR-E and 25 μMST. Furthermore, SR-E was the most active toxin in inhibiting conidial germination and germ tube elongation of this fungus.