Xanthomonas campestris biocontrol agent: Selection, medium formulation and bioprocess kinetic analysis

Black rot, caused by Xanthomonas campestris pv. campestris, is one of the most important diseases of cruciferous crops which causes significant yield losses. Biological control of black rot by microbial biocontrol agents represents a promising alternative to chemical treatments and good agricultural practices which show only limited success. This study was carried out to assess a potential of different antagonists, including Bacillus, Pseudomonas, Lactobacillus, Streptomyces, Saccharomyces and Trichoderma genera, for biological control of black rot. Cultivation broth samples and their filtrates were examined against seven X. campestris strains, isolated from diseased cruciferous plants, using the diffusion-disc method. Bacillus velezensis has showed the highest inhibition zone diameter of 35.62?3.76 mm. Afterwards, different combinations of carbon and nitrogen sources were used in the cultivation medium to maximize antagonistic activity of B. velezensis. The best combinations were glycerol and yeast extract, lactose and peptone, as well as sucrose and yeast extract, suggesting the potential of biodiesel, dairy and sugar industry effluents in the production of bioactive compounds effective against the black rot pathogen. The validation experiment was performed in a laboratory-scale bioreactor, in order to investigate bioprocess kinetics of biomass growth and carbon source consumption, using the cultivation medium containing the optimal carbon and nitrogen source.