Mechanisms involved during the ultrasonically induced depolymerization of chitosan: characterization and control.
ABSTRACT The existence of two mechanisms involved in the ultrasonically induced depolymerization of chitosan is evidenced. The first leads to a rapid scission of polymer chains and a lowering of the polydispersity, and the second is responsible for obtaining short polymer chains and oligomers with a polydispersity increase. A systematic experimental study allowed us to identify and quantify the main parameters influencing the chain scission kinetics. Consequently, using a "master curve" approach, a general law of variation of the molecular weight during the depolymerization is proposed. This law can be used in various experimental conditions to easily control the production of chitosan chains of precise length and low polydispersity or a collection of chito-oligosaccharides (COS). Characterization of the latter by (1)H NMR and MALDI-TOF mass spectrometry shows their high purity and an unchanged primary structure.
Article: Modification of genetic regulation of a heterologous chitosanase gene in Streptomyces lividans TK24 leads to chitosanase production in the absence of chitosan.[show abstract] [hide abstract]
ABSTRACT: Chitosanases are enzymes hydrolysing chitosan, a β-1,4 linked D-glucosamine bio-polymer. Chitosan oligosaccharides have numerous emerging applications and chitosanases can be used for industrial enzymatic hydrolysis of chitosan. These extracellular enzymes, produced by many organisms including fungi and bacteria, are well studied at the biochemical and enzymatic level but very few works were dedicated to the regulation of their gene expression. This is the first study on the genetic regulation of a heterologous chitosanase gene (csnN106) in Streptomyces lividans. Two S. lividans strains were used for induction experiments: the wild type strain and its mutant (ΔcsnR), harbouring an in-frame deletion of the csnR gene, encoding a negative transcriptional regulator. Comparison of chitosanase levels in various media indicated that CsnR regulates negatively the expression of the heterologous chitosanase gene csnN106. Using the ΔcsnR host and a mutated csnN106 gene with a modified transcription operator, substantial levels of chitosanase could be produced in the absence of chitosan, using inexpensive medium components. Furthermore, chitosanase production was of higher quality as lower levels of extracellular protease and protein contaminants were observed. This new chitosanase production system is of interest for biotechnology as only common media components are used and enzyme of high degree of purity is obtained directly in the culture supernatant.Microbial Cell Factories 02/2011; 10:7. · 3.55 Impact Factor