Viscosinamide, a new cyclic depsipeptide with surfactant and antifungal properties produced by Pseudomonas fluorescens DR54

Pseudomonas fluorescens DR54 showed antagonistic properties against plant p athogenic Pythium ultimum and Rhizoctonia solani both in vitro and in plant a. Antifungal activity was extractable from spent growth media, and fractio nation by semi-preparative HPLC resulted in isolation of an active compound , which was identified as a new bacterial cyclic lipodepsipeptide, viscosin amide, using 1D and 2D H-1-, C-13-NMR and mass spectrometry. The new antibi otic has biosurfactant properties but differs from the known biosurfactant, viscosin, by containing glutamine rather than glutamate at the amino acid position 2 (AA2). No viscosin production was observed, however, when Ps. fl uorescens DR54 was cultured in media enriched with glutamate, In vitro test s showed that purified viscosinamide also reduced fungal growth and aerial mycelium development of both P. ultimum and R. solani. Viscosinamide produc tion by Ps. fluorescens DR54 was tightly coupled to cell proliferation in t he batch cultures, as the viscosinamide produced per cell mass unit approac hed a constant value. In batch cultures with variable initial C, N or P nut rient levels, there were no indications of elevated viscosinamide productio n during starvation or maintenance of the cultures in stationary phase. Ana lysis of cellular fractions and spent growth media showed that a major frac tion of the viscosinamide produced remained bound to the cell membrane of P a. fluorescens DR54. The isolation, determination of structure and producti on characteristics of the new compound with both biosurfactant and antibiot ic properties have promising perspectives for the application of Ps. fluore scens DR54 in biological control.