Bacterial leaf blight caused by Xanthomonas axonopodis is a major problem in the production of eucalyptus seedlings. The pathogen causes leaf lesions that reduce the photosynthetic area and limit plant growth. The objective of this study was to evaluate the antibiotic activity of secondary metabolic compounds of a Pseudomonas sp. against X. axonopodis, following extraction with dichloromethane and fractionation by vacuum liquid chromatography. The antibiotic activity of an ethyl acetate phase (F3 fraction) was determined by agar diffusion tests and bioautography. The minimum inhibitory concentration of F3 fraction and the action of F3 on the cell morphology of X. axonopodis was determined by scanning electron microscopy. Electron microscopy revealed changes in exopolysaccharides and morphology of treated cells. When eucalyptus seedlings were sprayed with the F3 fraction before or after inoculation with X. axonopodis in a greenhouse experiment the number of leaf lesions was respectively 93.9% and 89.7% lower than in untreated control plants. High antibiotic activity of the F3 fraction against X. axonopodis and leaf blight suggests that it has potential to control the disease in eucalyptus seedlings.
This work evaluated the effect of secondary bacterial metabolites produced by Pseudomonas sp LV strain in control of Lactobacillus sp. population in the microcosm of the vat during ethanol fermentation. The fraction F4 produced by Pseudomonas aeruginosa was extracted with dichloromethane and fractionating by vacuum liquid chromatography obtained in a methanol phase. The evaluation of antibiotic activity of F4 fraction mixed or not with sulphuric acid and Kamoram ® . The antibiotic activity of F4 fraction was determined as well as the fermentation efficiency. Also was determined yeast cell viability, budding formation, the viability of budding cells, and number of populations of Saccharomyces cerevisiae and Lactobacillus sp. The results showed that the F4 fraction had high selective antibiotic activity against Lactobacillus sp. but not for S. cerevisae, and no inhibitory effect was observed in the fermentation process by yeast. Also F4 fraction decreased flocculation and foam formation. The F4 has an antibiotic activity against Lactobacillus sp. and should be used as an alternative to control bacteria contamination and foam and flocculation formation in the fuel ethanol fermentation process. The F4 fraction could reduce the use of antibiotics in the control of Lactobacillus sp. population during the fuel ethanol production.
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