Antimicrobial activity on plant-pathogenic microorganisms and phytogrowth-inhibitory activity of streptothricin antibiotics, racemomycin-A and -C.

Abstract

Streptothricin antibiotics, racemomycin-A and -C(RM-A and -C), which contain one and two β-lysine moieties in the molecule, were found to show antimicrobial activity on plant-pathogenic microorganisms and phytogrowth-inhibitory activity.RN-A and -C showed antimicrobial activities against all the plant-pathogenic microorganisms tested. In particular, RM-C showed strong antifungal activity on Fusarium oxysporum f. sp. lycopersici IFO-6531 (minimal inhibitory concentration (MIC) : 3.0 μg/ml). Both antibiotics storongly inhibited the growth of the root of Brassica rapa L. even at the low concentration of 50 ppm. These activities of RM-C were slightly stronger than those of RM-A. This would indicated that the β-lysine moiety in the molecule plays some role in the activity of streptothricin antibiotics.On the other hand, racemomycinic-A-acid (RM-A-acid), produced by opening the lactam ring of the streptolidine moiety of RM-A, did not show any of the above-mentioned activities. This would suggest a close relationship betweem the streptolidine moiety in the molecule of streptothricin antibiotics and the activities.