Gageopeptins A and B, new inhibitors of zoospore motility of the phytopathogen Phytophthora capsici from a marine-derived bacterium Bacillus sp. 109GGC020

Abstract

The motility of zoospores is critical in the disease cycles of the peronosporomycetes that cause devastating diseases in plants, fishes, vertebrates, and microbes. In the course of screening for secondary metabolites regulating the motility of zoospores of Phytophthora capsici, we discovered two new inhibitors from the ethyl acetate extract of the fermentation broth of a marine-derived strain Bacillus sp. 109GGC020. The structures of these novel metabolites were elucidated as new cyclic lipopeptides and named gageopeptins A (1) and B (2) by spectroscopic analyses including high resolution MS and extensive 1D and 2D NMR. The stereoconfigurations of 1 and 2 were assigned based on the chemical derivatization studies and reviews of the literature data. Although compounds 1 and 2 impaired the motility of zoospores of P. capsici in dose- and time-dependent manners, compound 1 (IC50 = 1 μg/ml) was an approximately 400-fold stronger motility inhibitor than 2 (IC50 = 400 μg/ml). Interestingly, the zoospores halted by compound 1 were subsequently lysed at higher concentrations (IC50 = 50 μg/ml). Compounds 1 and 2 were also tested against some bacteria and fungi by broth dilution assay, and exhibited moderate antibacterial and good antifungal activities.

Keywords: Lytic acitivity; Marine bacteria; Phytopathogens; Phytophthora capsici; Zoospore motility inhibitors.