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dc.contributor.advisorBrzezinski, Ryszardfr
dc.contributor.advisorBeaulieu, Carolefr
dc.contributor.authorLi, Tongfr
dc.date.accessioned2014-05-16T15:26:29Z
dc.date.available2014-05-16T15:26:29Z
dc.date.created1993fr
dc.date.issued1993fr
dc.identifier.urihttp://savoirs.usherbrooke.ca/handle/11143/4322
dc.description.abstractElicitors are molecules which can trigger phytoalexin and pathogenesis-related proteins biosynthesis in plants. Chitosan as an elicitor has important roles in the interaction between pathogenic fungi and plants. Chitosan can inhibit fungal DNA transcription into mRNA, and it can also trigger the specific defensive genes which encode for at least 20 kinds of proteins related to resistant mechanism in plants. Elicitors are molecules which can trigger phytoalexin and pathogenesis-related proteins biosynthesis in plants. Chitosan as an elicitor has important roles in the interaction between pathogenic fungi and plants. Chitosan can inhibit fungal DNA transcription into mRNA, and it can also trigger the specific defensive genes which encode for at least 20 kinds of proteins related to resistant mechanism in plants. Chitosanase is an endoglycosidase that can hydrolyze chitosan into oligosaccharide fragments. Chitosan heptamer-more fractions showed maximal activity in both antifungal properties and induction of plant resistance. In this work, recombinant strains of Streptomyces lividans were used for production of chitosanase, then we used this enzyme to prepare the active chitosan oligomers and to test their antifungal properties and their ability to induce defensive responses in plants. In order to produce large amounts of chitosanase, the chitosanase gene from Streptomyces N174 was cloned in the high copy-number vector pFD666 and transformed into protoplasts of S. lividans TK24 and 10-164. These recombinant strains could produce chitosanase efficiently. The chitosanase activity could reach up to 95 units per millilitre of fermentation liquid on natural substrate (mycelium of Mucor rouxii. When DNA sequences were deleted in upstream or downstream of the chitosanase gene, chitosanase production became lower. Maybe, these sequences have some functions for the chitosanase gene expression and stability. In the chitosan medium, the chitosanase activity of the recombinant strains S. lividans TK24 decreased quickly after 3 days. We have shown that it related to the production of a specific proteolytic enzyme for chitosanase. On the contrary, the chitosanase activity could maintain high level after 3 days in M. rouxii mycelium as fermentation substrate. If S. lividans 10-164 was used as host for carrying the chitosanase gene, chitosanase activity reached high level after 2 days and the same level was maintained for a few days in D-glucosamine medium. The enzyme was recovered by polyacrylic acid precipitation. The enzyme prepared with this method has stable activity for long time. Using chitosanase hydrolysis, the heptamer-more fractions were prepared. These chitosan oligomers could inhibit fungal growth and could induce the production of pathogenesis-related proteins such as [beta]-1,3-glucanase, chitinase and chitosanase by plants.fr
dc.language.isoengfr
dc.publisherUniversité de Sherbrookefr
dc.rights© Tong Lifr
dc.titleProduction of chitosanase by recombinant Streptomyces Lividans and enzymatic preparation of chitosan oligomersfr
dc.typeMémoirefr
tme.degree.disciplineBiologiefr
tme.degree.grantorFaculté des sciencesfr
tme.degree.levelMaîtrisefr
tme.degree.nameM. Sc.fr


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