Unsteady flow in a supercritical supersonic diffuser

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77051/1/AIAA-10045-786.pd

Extracellular enzyme systems of antagonistic Bacillus strains isolated from tomato rhizosphere

Chitinolytic, proteolytic and lipolytic enzymes could be important in the biological control of soil borne plant-pathogenic microorganisms by antagonistic microbes and in this way besides antibiotic production, the secretion of certain extracellular enzymes also could have great importance in the effectiveness of biocontrol bacilli. Some of these enzymes could directly promote the inhibition processes, while others could help the competition of the bacilli against other rhizosphere microbes. In case of five Bacillus strains, which showed excellent antagonistic effects against phytopathogenic fungi and bacteria, the secretion of some components of the protease, chitinase, cellulase, lipase and β-1,3-glucanase enzyme systems were investigated under inductive and non-inductive circumstances. Enzyme activities were measured both with classical methods and with other experimental approaches based on chromogenic enzyme substrates. The best biocontrol strains constitutively secreted chymotrypsin-like proteases and/or trypsin-like proteases, and lipases. On the contrary, the chitinase components were only secreted in chitin containing media. Cellulases and β-1,3- glucanases were produced only at very low level either in inductive media

Influence of culture conditions on the antibiotic production of antagonistic Bacillus strains isolated from tomato rhizosphere

Many phytopathogenic bacteria and fungi attack tomato plants both in seedling (e.g. Rhizoctonia solani, Pythium debaryanum) and in developed foliar state (e.g. Phytophthora infestans, Botrytis cinerea, Alternaria solani, Xanthomonas vesicatoria, Pseudomonas syringae pv. tomato, Clavibacter michiganensis). It would be desirable to find an efficient biocontrol approach for preventing the destructive effect of these pathogens. In the frame of this study, more than 250 bacteria with antagonistic properties were isolated and characterized. Results of the preliminary antagonism tests revealed that the strains belonging into the genus Bacillus were the most efficient agents against the tomato pathogenic bacteria and fungi. The Bacillus strains with the best antagonistic traits were investigated in detail. The antibiotics present in the cell-free ferment broths were detected and analysed by thin layer chromatography. Specific PCR-based approach was developed and used for the detection of the distinct antibiotic-synthesis gene clusters (iturin, surfactin, fengycin, bacillomycin and mycosubtilin) in the genomes of the strains. Our investigation revealed that the best antagonistic strains produced high amount of surfactin and/or fengycin antibiotics. On the basis of these experiments two strains were selected for further investigations. The influence of the Cu2+ and Fe2+ ions and the quality of carbon and nitrogen sources were tested in liquid culture for the antibiotic production levels by the strains. Both copper and iron highly elevated the production rate at least of the tyrosine containing antibiotics. The applied carbon and nitrogen sources highly influenced both the quantity and quality of the antibiotic mixture secreted by the strain B23 of Bacillus subtilis