Oligomycins and Pamamycin Homologs Impair Motility and Induce Lysis of Zoospores of the Grapevine Downy Mildew Pathogen, Plasmopara Viticola

Four antibiotics (pamamycin, oligomycin A, oligomycin B and echinosporin) were isolated and characterized from the fermentation broth of the marine Streptomyces strains B8496 and B8739. Bioassays revealed that each of these compounds impaired motility and caused subsequent lysis of P. viticola zoospores in a dose- and time-dependent manner. Pamamycin displayed the strongest motility inhibitory and lytic activities (IC50 0.1 μg mL(-1)) followed by oligomycin B (IC50 0.15 and 0.2 μg mL(-1)) and oligomycin F (IC50 0.3 and 0.5 μg mL(-1)). Oligomycin A and echinosporin also showed motility inhibitory activities against the zoospores with IC50 values of 3.0 and 10.0 μg mL(-1), respectively. This is the first report of motility inhibitory and lytic activities of these antibiotics against zoospores of a phytopathogenic peronosporomycete. Structures of all the isolated compounds were determined based on detailed spectroscopic analysis.