Evaluation of the antibiotic activity of extracellular compounds produced by the Pseudomonas strain against the Xanthomonas citri pv. citri 306 strain

In this work, we evaluated the antibiotic activity of metabolites produced by the Pseudomonas sp. LV strain and their effects on the cell morphology of the Xanthomonas citri pv. citri 306 strain (Xcc 306), which causes citrus canker lesions. The LV strain was cultivated, centrifuged, a cell-free supernatant was treated with dichloromethane and then concentrated, frozen in liquid nitrogen and lyophilized. The dichloromethane phase (DP) was fractionated by vacuum liquid chromatography (VLC) using six organic solvents with a crescent polarity. The antibiotic activity of the DP and all the fractions from VLC were tested against Xcc 306 and only the F3 fraction showed antimicrobial activity. The antibiotic activity of F3 was determined by minimum inhibitory concentration and the action on the cell morphology of Xcc 306 carried out in glass tubes with cell suspensions plus F3 solution sampled at three different times (one, three and six hours). The effects were analyzed by electron microscopy. Both the DP and F3 showed antibiotic activity against Xcc 306 in in vitro experiments. Electron microscopy showed that the F3 fraction completely disrupted the cell integrity after six hours. In a greenhouse experiment, the DP and F3 fraction (highly effective in in vitro experiments), reduced the formation of lesions by approximately 80% and 94%, respectively.